Endoscopic Retrosigmoid Surgery: Chapter 9


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Endoscopic Skull Base Surgery - Chap 9, The Fully Endoscopic Retrosigmoid Approach
By Hrayr K. Shahinian, M.D., FACS

Abstract

This chapter discusses the application of the fully endoscopic retrosigmoid approach to access the cerebellopontine angle (CPA), petroclival, and foramen magnum regions for surgical management of tumors such as schwannomas or meningiomas and neurovascular conflicts involving cranial nerves V through XII that occur in this region of the skull base. The limitations to viewing angles imposed on the surgeon by the operating microscope contrasts with the ability for broad panoramic surveys and different angles of view when endoscopes are used. In our experience, the improved exposure of the entire tumor with virtually no cerebellar retraction has reduced the risk of injury to the brainstem and the surrounding cranial nerves, resulted in a more complete tumor removal, decreased the time required to access the CPA, allowed rapid recovery of the patients, and resulted in minimal postoperative discomfort. The chapter provides a thorough description of the fully endoscopic retrosigmoid approach, including indications, operating room setup, patient positioning, operative technique, state-of-the-art illustrative cases, potential complications, and ways to avoid these complications (in the author's experience).

1. Introduction

The neurovascular anatomy of the posterior cranial fossa is quite intricate. The limitations to viewing angles imposed on the surgeon by the operating microscope contrasts with the ability for broad panoramic surveys and different angles of view when endoscopes are used. The endoscope is particularly well suited to application at the cerebellopontine angle (CPA), where neurovascular structures are often obscured by the protrusion of the petrous portion of the temporal bone, and where mass lesions, including meningiomas and vestibular schwannomas (VS) that include portions within the internal auditory canal (IAC), are not always completely exposed microscopically. The endoscopic approach to the CPA, especially when angled endoscopes are used, allows the surgeon to visualize areas that were often hidden from the direct line of view of the operating microscope. Moreover, endoscopic procedures pose no additional risk to the patient and add no additional time to the total duration of surgery.

We have routinely used the endoscopic retrosigmoid approach for cranial nerve microvascular decompressions for trigeminal neuralgia, glossopharyngeal neuralgia, and hemifacial spasm, as well as for resection of CPA tumors, such as vestibular schwannomas, meningiomas, and others. The improved exposure of the entire tumor with virtually no cerebellar retraction has reduced the risk of injury to the brainstem and the surrounding cranial nerves, resulted in a more complete tumor removal, decreased the time required to access the CPA, allowed rapid recovery of the patients, and resulted in minimal postoperative discomfort.

2. Indications

The fully endoscopic retrosigmoid approach provides minimally invasive access to the CPA, petroclival, and foramen magnum regions for surgical management of tumors such as schwannomas or meningiomas and neurovascular conflicts involving cranial nerves V through XII that occur in this region of the skull base.

3. Instrumentation

The instrumentation needed to successfully execute this technique include an endoscopic tower, a high-definition digital camera, a xenon or halogen light source, 0- and 30-degree rigid endoscopes, an endoscope irrigation sheath, two endoscope holding arms, and precision microinstruments.

4. Operating Room Setup (Figure 1)

Once the patient is anesthetized, the operating room table is turned 180 degrees and corrugated extension tubing is used to lengthen the airway circuit. The patient is put in the lateral oblique (park bench) position and the surgeon stands on the side to be operated upon. Next, the endoscopic tower is placed directly opposite the surgeon. Two separate pneumatically-powered holding arms are affixed to the table, one on each side of the patient, and wrapped in sterile drapes. One holding arm is dedicated to holding the endoscope and the second is used to hold other microinstruments in place. A second monitor placed behind the surgeon allows the scrub technician or assistant, who stands facing the surgeon, to monitor the operation.

5. Patient Positioning (Figure 2)

A three-pin Mayfield clamp is applied to the patient's head and the patient is rolled into the lateral oblique position while the surgeon is controlling the patient's head. A beanbag is placed under the patient to conform to the patient's body. The Mayfield head clamp is positioned so that the side with two pins is supporting the dependent side of the head. With the head of the bed raised 30 degrees to facilitate venous drainage, the neck is flexed, rotated away from the surgeon, and fixed in position. The hip and knee joints are flexed and a pillow is placed between both knees. The patient's body is then secured to the table with adhesive tape, and an axillary roll is placed beneath the axilla of the dependent arm to protect the brachial plexus. The ipsilateral arm is retracted caudad and tucked under the bed sheet.

6. Operative Technique

Following the administration of general anesthesia (without paralysis), a color marker is used to draw the landmarks of the skin incision, and the retroauricular area is prepared with an antibacterial surgical scrub (Figures 3 (A) and (B)). Intraoperative cranial nerve and brainstem monitoring is performed in all cases. A longitudinal 3 cm retroauricular skin incision is performed and small hooks are used to retract the skin and soft tissues. Dissection is then carried out down to the cranium in a subperiosteal plane (Figures 4 (A), (B), and (C)). Using a microdrill, and the asterion as a bony anatomical landmark, a 1.5 cm keyhole craniotomy is made at the confluence of the transverse and sigmoid sinuses; the bone flap is removed in one piece to be returned in place during cranioplasty at the end of the operation (Figures 5 (A) and (B)). Bone wax is used to fill any mastoid air cells entered during the bone drilling.

The dura is then incised in a curvilinear fashion and reflected laterally (Figure 6). Cerebrospinal fluid (CSF) is then slowly drained from the paracerebellar cisterns. The combination of positioning, mild hyperventilation, and intravenous administration of mannitol allows the cerebellum to spontaneously retract, opening a narrow path between the posterior aspect of the petrous bone and the cerebellum through which a 2.7 or 4.0 mm 0-degree endoscope is introduced and then advanced slowly to the CPA (Figures 7 (A), (B), and (C)). Upon entering the CPA, the surgeon conducts a preliminary survey of the surrounding structures, including tentorial and emissary veins, the petrous temporal bone, the lower cranial nerves and jugular foramen, the acousticofacial bundle and the internal auditory meatus, the trigeminal nerve and Meckel's cave, the trochlear nerve along the tentorium, as well as the regional vascular anatomy (Figures 8 (A) - (E)). The irrigation sheath clears blood and debris from the lens of the endoscope, eliminating the time-consuming and dangerous practice of removing and reinserting the endoscope. The holding arm secures the endoscope in place, allowing bimanual surgical dexterity.

From this point, the procedure will vary according to the pathological condition being addressed (i.e., microvascular decompression vs. tumor extirpation). Once the intracranial portion of the procedure is completed and hemostasis is obtained, the dura is then closed in a watertight fashion and covered with a collagen dural substitute membrane followed by a dural sealant to prevent any CSF leak (Figures 9 (A), (B), and (C)). The bone plug is then replaced and secured in place by resorbable microplates and screws, and an injectable hydroxyapatite bone substitute is applied to fill the bone defect (Figures 10 (A) and (B)). The incision is then closed in anatomical layers without the use of any subcutaneous drains and an adhesive bandage dressing is applied to the suture line (Figures 11 (A) and (B)). Following extubation, the patient is typically transferred to either a step-down unit or the intensive care unit (ICU) for overnight monitoring. The vast majority of patients are discharged 48 hours after the operation.

7. Illustrative Cases

7.1. Trigeminal Neuralgia

7.1.1. Background (Figure 12)

Trigeminal neuralgia is a disease characterized by severe and often debilitating facial pain that occurs along the distribution of any of the three branches of the trigeminal nerve. As classically defined, attacks are intermittent and the quality of the pain is sharp or stabbing or mimics an electric shock. The mainstay of treatment for patients with trigeminal neuralgia prior to the modern surgical era was confined to either medical treatment of episodic symptoms, ablative procedures, or sectioning of the trigeminal nerve. According to our current understanding of the pathogenesis of trigeminal neuralgia, the most common cause is compression and distortion of the root entry zone (REZ) of the trigeminal nerve by aberrant arterial or venous structures (often the superior cerebellar artery), and thus removal of these traumatic insults results in alleviation of the neuropathic pain experienced by patients. Microvascular decompression (the Janetta procedure) rarely results in the numbness commonly associated with other destructive and ablative procedures.

Although trigeminal neuralgia is clinically diagnosed without the need for any additional investigations in the majority of cases, all suspected patients should have an MRI/MRA scan of the brain. These are reviewed by the surgeon and an experienced neuroradiologist to look for vessels abutting the trigeminal nerve, especially areas suspicious for compression of the trigeminal nerve at the REZ. In some cases, no discrete offending vessel is identified, but the suggestion of abnormal vascular anatomy within the prepontine and CPA cisterns coupled with the patient's clinical presentation is enough to merit surgical exploration. The MRI/MRA is also pertinent in ruling out other pathologies, such as tumors or aneurysms.

7.1.2. Approach

Following the initial exposure and once the cerebellum has fallen away from the petrous portion of the temporal bone, a 0-degree rigid endoscope is inserted through the craniotomy and a panoramic inspection of the CPA region is conducted. The trigeminal nerve is identified and contiguous vessels are viewed. Particular attention is given to the parts of the nerve that are more obscure, including the medial and inferior aspects of the nerve at the REZ, the superior, inferior, and medial aspects of the cisternal portion of the nerve, and the site of entry of the nerve into Meckel's cave. The offending vascular structures are identified and mapped proximally and distally. A site of compression is defined as an area of contact between the nerve and a vessel that results in a grossly appreciable change in the appearance of the nerve including indentation, discoloration, or other evidence of trauma to the nerve.

Once a thorough examination of the nerve is completed and the conflict(s) is satisfactorily identified, the 0-degree endoscope is replaced with the 30-degree endoscope and the examination is repeated. This secondary survey is critical in confirming that all neurovascular conflicts are identified because sites of compression can be multiple and complex. Dissecting instruments are then used to gently liberate the nerve from the compressing vessel(s). Teflon pads are interposed between the nerve and vessel(s) to maintain the separation and to "cushion" the nerve. A final survey, utilizing the 30-degree endoscope, is then conducted and further decompression is carried out if necessary. The entire area is then copiously irrigated and bathed with fibrin-based tissue glue to secure the Teflon pledgets in place; the dura is closed, followed by cranioplasty and layered closure of the soft tissues and skin.

7.1.3. Cases

7.1.3.1 Trigeminal neuralgia (left sided): Figures 13 (A) - (F)

7.1.3.2. Trigeminal neuralgia (left sided): Figures 14 (A) - (I)

7.1.3.3. Trigeminal neuralgia (right sided): Figures 15 (A) - (I)

7.1.3.4. Trigeminal neuralgia (right sided, post Gamma KnifeX2): Figures 16 (A) - (K)

7.2. Hemifacial Spasm and Glossopharyngeal Neuralgia

7.2.1. Background (Figure 17)

Hemifacial spasm is an uncommon disorder manifesting as a unilateral, involuntary, sporadic contraction of the musculature innervated by the facial nerve. The disorder almost always presents unilaterally, although bilateral involvement may occur rarely. In essentially all cases, primary hemifacial spasm is caused by an ectatic blood vessel (often the anterior inferior cerebellar artery) that irritates, compresses, or forms a loop around the facial nerve as it exits the brainstem.

The complex anatomy of the posterior cranial fossa, as well as the limited size of the craniotomy, makes adequate visualization of the facial nerve using an operating microscope difficult. Use of an operating microscope has several limitations. The facial nerve may not be clearly visualized medially because of an offending arterial loop, the flocculonodular lobe of the cerebellum or the choroid plexus of the lateral recess being in the way. Because the surgeon can only visualize objects directly ahead and is unable to see around objects or down narrow tortuous pathways, access to the site of disease may require wide exposure and retraction of adjacent structures. Retraction injury of the cerebellum or brainstem during decompressive surgery for hemifacial spasm can be a considerable source of morbidity. In contrast, the unimpeded view of the endoscope provides excellent panoramic views of the posterior fossa, CPA, as well as the root exit zone of the facial nerve, and allows for identification of the nerve-vessel conflicts in all cases without the need for brain retraction. The improved visualization enhances the surgeon's ability to perform the surgical dissection and assess the adequacy of the decompression, both of which are often difficult to appreciate using the operating microscope.

Glossopharyngeal neuralgia is a rare clinical entity; it is characterized by severe paroxysmal attacks of sharp, lancinating pain affecting the sensory distribution of the glossopharyngeal nerve, including the base of the tongue, soft palate, tonsils, pharyngeal pillars, posterior pharyngeal wall, and the inner ear. Attacks may be associated with vagally-mediated cardiovascular and hemodynamic compromise, such as bradycardia, hypotension, cardiac syncope, and even rarely, asystole may occur with episodes of neuralgia. Microvascular decompression of the glossopharyngeal nerve is an effective treatment for patients with glossopharyngeal neuralgia in whom compression of the nerve by a blood vessel is implicated in the pathogenesis of the disease.

In the surgical management of glossopharyngeal neuralgia, as for trigeminal neuralgia and hemifacial spasm, the use of endoscopes of varying angles is ideal because all neurovascular conflicts can be identified, and decompression of the nerve can be successfully performed with minimal disturbance to the surrounding structures.

7.2.2. Approach

Following entry into the CPA, the acousticofacial bundle is visualized and the facial nerve is stimulated and positively identified. Once identified, the surrounding vascular structures are surveyed to identify the nerve-vessel conflict(s) compressing the facial nerve. The 0-degree endoscope is replaced with the 30-degree endoscope and, as in cases of trigeminal neuralgia, a secondary survey is conducted to confirm that all neurovascular conflicts are identified. Using microdissection and gentle manipulation, vascular compressions of the facial nerve are dissected free. Teflon pledgets are then placed between the nerve and compressing vessels to provide complete decompression; they are secured in place with fibrin glue. The dura is then reapproximated, providing a watertight closure, and layered suturing of the wound is carried out.

The surgical approach to the lower cranial nerves, as in glossopharyngeal neuralgia, is essentially identical to that described above. Once the endoscope is passed into the CPA cistern, cranial nerves IX to XI are located caudally in the surgical field. They are identified by their "guitar-string" appearance and are seen passing into the jugular foramen. Closure is performed in similar fashion. Care must be taken while manipulating the endoscope and dissecting instruments so as not to damage the neurovascular structures that are located immediately cranially but out of view of the lens.

7.2.3. Cases

7.2.3.1. Hemifacial spasm (left sided): Figures 18 (A) - (H)

7.2.3.2. Hemifacial spasm (right sided): Figures 19 (A) - (G)

7.2.3.3. Hemifacial spasm (right sided): Figures 20 (A) - (J)

7.2.3.4. Hemifacial spasm (leftsided): Figures 21 (A) - (H)

7.2.3.5. Glossopharyngeal neuralgia (left sided): Figures 22(A) - (D)

7.3. Vestibular (Acoustic) Schwannoma and Posterior Fossa Meningioma

7.3.1. Background (Figure 23)

Vestibular schwannoma, also known as acoustic neuroma or neurinoma, is a benign overproliferation of the Schwann cells of the eighth cranial nerve sheath. Magnetic resonance imaging (MRI) is the gold standard in assessing patients with this tumor. Acoustic neuromas are typically described as small (less than 1.5 cm), medium (1.5 cm to 2.5 cm), or large (greater than 2.5 cm). A small acoustic neuroma is also referred to as "intracanalicular" because it is confined within the bony IAC. A medium-sized acoustic neuroma has extended from the bony canal into the brain cavity without producing pressure on the brain tissue itself. Large acoustic neuromas usually produce pressure manifestations.

Traditionally, either the translabyrinthine or the open suboccipital approach have been used to access and remove CPA tumors such as vestibular schwannomas. The traditional suboccipital approach suffers from the disadvantages of the operating microscope with its direct forward view, including the inability to completely visualize the lateral extent of the tumor within the IAC. Using the operating microscope, it is virtually impossible to "look around the corner" due to the oblique angle of the canal in relation to the trajectory of the dissection, as well as incomplete visualization of exposed air cells, which may lead to CSF rhinorrhea or otorrhea. The translabyrinthine approach allows wide exposure of the IAC and early identification of the facial nerve, which assists its preservation. However, this approach requires a wide disfiguring skin incision along with excessive drilling through the mastoid bone and inner ear; unfortunately, resulting in complete hearing loss in all cases, as well as a significantly higher incidence of postoperative CSF leakage.

The endoscope, with its superior visualization and imaging, provides improved recognition of exposed air cells and allows for more complete tumor removal by direct visualization of the IAC with direct view and angled endoscopes to remove any residual tumor that is out of the view of the operating microscope. In addition to the higher possibility of hearing preservation, and avoidance of blind dissection behind the facial nerve, the endoscope provides improved visualization of the skull base-where narrow recesses and angled trajectories impair the direct forward view of the operating microscope-without the need for cerebellar retraction. Endoscopic surgery allows for smaller craniotomies, less dissection, and virtually no cerebellar retraction, without compromising the goals of the operation.

7.3.2. Approach (Figure 24)

Upon entering the CPA, the surgeon conducts a preliminary survey of the surrounding structures, including the trigeminal and lower cranial nerves, as well as the regional vascular anatomy. The topography of the tumor and its relation to the surrounding structures is appreciated. The facial nerve is located and stimulated, and its response is measured with the facial nerve monitor. Once these relationships are identified, the tumor is gradually cored from its center using a combination of the microCUSA, bipolar electrocoagulation, suction-irrigation, and microinstruments. The capsule of the tumor is then gently dissected off of the facial nerve. Attention is then directed to the IAC. A diamond burr is used to remove the posterior wall of the canal, and the dura overlying the IAC is cauterized and incised. IAC dissection proceeds until the lateral extent of the tumor is visualized and normal nerve is identified. In cases of smaller tumors in patients with "serviceable" hearing, this portion of the dissection is performed with hearing preservation in mind and extreme caution not to injure the cochlear nerve. Further tumor dissection within the IAC is guided by the 30-degree endoscope, allowing complete visualization of the lateral extent of the tumor as it is separated from the facial nerve. Once tumor resection is complete, the facial nerve is once again stimulated to confirm its function. Complete hemostasis is then confirmed followed by closure of the dura, cranioplasty, and layered suturing of the soft tissue and skin.

The dissection of CPA or cerebellar convexity meningiomas is essentially the same as for vestibular schwannomas. The tumor is often more dense and the dissection can be more difficult, but extension into the IAC is rare. Because of the potentially adherent nature of the disease to nearby vessels and nerves in such a limited space, the chance of damage to surrounding critical structures is real; therefore, great care must be taken to identify and preserve these structures during tumor removal.

7.3.3. Cases

7.3.3.1. Large acoustic neuroma (right sided): Figures 25 (A) - (J)

7.3.3.2. Large acoustic neuroma (right sided): Figures 26 (A) - (R)

7.3.3.3. Large acoustic neuroma (leftsided): Figures 27 (A) - (P)

7.3.3.4. Large acoustic neuroma (right sided): Figures 28 (A) - (V)

7.3.3.5. Medium acoustic neuroma (right sided): Figures 29 (A) - (N)

7.3.3.6. Medium acoustic neuroma (left sided): Figures 30 (A) - (T)

7.3.3.7. Medium acoustic neuroma (left sided): Figures 31 (A) - (O)

7.3.3.8. Small, purely intracanalicular acoustic neuroma (left sided): Figures 32 (A) - (L)

7.3.3.9. Small, purely intracanalicular acoustic neuroma (right sided): Figures 33 (A) - (I)

7.3.3.10. Small, intracanalicular acoustic neuroma (right sided): Figures 34 (A) - (S)

7.3.3.11. Superior cerebellar convexity meningioma extending to CPA (left sided): Figures 35 (A) - (L)

7.3.3.12. Lateral CPA meningioma (left sided): Figures 29 (A) - (L)

7.3.3.13. Medial CPA meningioma (left sided): Figures 29 (A) - (T)

8. Potential Complications

Potential complications of the fully endoscopic retrosigmoid approach include the following:

Brain stem and cerebellar injuries, quadriparesis, hemiparesis, infection, bacterial or aseptic meningitis, hemorrhage (subdural/epidural/intraaxial), and death (these are also potential complications associated with open approaches with more extensive dissection)
Direct injuries include cerebellar injuries (cerebellar edema, hematoma, or infarction and direct injury to the cerebellar hemisphere), vascular injuries (to the anterior inferior cerebellar artery [AICA] or its branches, e.g., labyrinthine artery, or less commonly to the posterior inferior cerebellar artery [PICA]), and venous injuries (sigmoid sinus, petrosal vein, or vein of Labbé)
Early or delayed CSF leakage from the wound, ear (otorrhea), or nose (rhinorrhea)
Facial weakness or paralysis; this may be transient or permanent or may partially improve with some residual facial weakness
Eye complications such as dryness or redness secondary to facial paralysis
Hearing loss and/or tinnitus (VIII)
Other cranial nerve deficits (V, VI, IX, X, XI, XII)
Dizziness, balance, or coordination (ataxia) disturbances
Severe postoperative headaches
Mild or significant hydrocephalus

9. Avoiding Complications in Author's Experience

Major complications such as death, brainstem injury, quadriparesis, and hemiparesis are mostly avoided because dissection with the endoscopic approach is limited and cerebellar retraction is not used. Bacterial or aseptic meningitis also occurs less frequently than with traditional surgery because the operative field is reduced, along with the duration of the surgery. In general, the two major and most feared complications are CSF leakage and cranial nerve injuries. Hearing loss and facial paresis or paralysis depend on the size of the tumor resected. In general, the smaller the tumor the greater the chance for hearing preservation; with increasing size of the tumor within the CPA, the incidence of complications increases.

Acoustic tumors are typically in intimate contact with the facial nerve, which may be compressed, distorted, or, rarely, completely engulfed by the tumor; therefore, postoperative facial paralysis may result from nerve swelling or nerve damage. Despite the fact that facial nerve monitoring has greatly aided separation of the facial nerve from the tumor, anatomical and functional preservation of the facial nerve with complete tumor removal, especially in patients with large tumors, is still a challenge. Postoperative facial nerve paralysis is sometimes unavoidable. Fortunately, even when as little as 10% of the functioning facial motor neurons are left intact, normal facial nerve function can be preserved.

A high rate of functional cochlear nerve (hearing) preservation has been encountered in our vestibular schwannoma patient series, which reflects the improved outcome associated with the better visualization of the 0-degree and angled endoscopes. Resection of a macroscopically intact cochlear nerve in an attempt to seek complete tumor removal is not recommended; that nerve is almost never involved with tumor and can function well for decades. In these cases, total tumor removal should not result in unnecessary hearing loss.

Although vestibular nerve preservation is virtually impossible in the majority of cases, as most vestibular schwannomas arise from the vestibular nerve, this may not constitute a problem. The vestibular function is usually considerably reduced or even totally lost before vestibular schwannoma surgery, and immediate postoperative vertigo is usually minimal and transient and seldom causes any disability. Postoperative vertigo, dizziness, balance, or coordination problems may result from vestibular or cerebellar dysfunction and may be severe for days or weeks following surgery before completely resolving; these complications tend to persist longer in older patients. In many cases, tinnitus remains the same as before surgery, but it may be more or less noticeable in the early postoperative period. Direct injuries of cranial nerves V or, rarely, VI or the lower cranial nerves, vascular injuries to the AICA/PICA or their branches, and venous injuries are extremely rare complications.

Traditional open approaches require a certain degree of cerebellar retraction; therefore, cerebellar edema or hematoma can occur. This does not occur with the endoscopic approach because it does not require the use of any retractors. Hemorrhage into the posterior fossa or subdural or extradural hemorrhage in the immediate postoperative period can produce brainstem compression and rapid death. The prevention of secondary bleeding relies on strict hemostasis, and it is essential to coagulate both ends of any minor surface vessels during tumor resection.

Early or delayed CSF leakage from the wound, rhinorrhea, or otorrhea (either directly through the wound or via the eustachian tube and middle ear) can occur even if all the precautions have been taken to avoid them. In some cases, the leakage may be iatrogenic; this emphasizes the importance of watertight dural closure. The path of CSF egress is most commonly through mastoid air cells that were opened during the craniotomy.

The keyhole craniotomy, even though limited, can still result in some postoperative headaches, but these resolve spontaneously in the majority of cases. Taking great care to avoid contaminating CSF with bone dust and replacement of the keyhole bone flap have significantly reduced the incidence of this complication in our experience. Mild transient postoperative hydrocephalus rarely occurs in the early postoperative period; even when present, it generally resolves without difficulty in the first few postoperative weeks, and CSF shunting is rarely, if ever, required.

Legends: Figure1: Operating Room Setup Figure 2: Patient Positioning Figures 3 (A) and (B): Marking and Draping Figures 4 (A), (B), and (C): Skin Incision Figures 5 (A) and (B): Keyhole Craniotomy Figure 6: Dural Opening Figures 7 (A), (B), and (C): Endoscope Advancement to the Cerebellopontine Angle (CPA) Lower Case Figure 7 (A): a. Lateral Aspect of Cerebellar Hemisphere (left side) b. Petrous Temporal Bone c. Endoscope Trajectory Lower Case Figure 7 (C): a. Lateral Aspect of Cerebellar Hemisphere b. Petrous Temporal Bone c. Tentorium Figures 8 (A) - (E): Endoscopic Anatomy of the Cerebellopontine Angle (CPA) Lower Case Figure 8 (A): a. Ipsilateral Trigeminal Nerve (V) b. Meckel's Cave c. Tentorium d. Brainstem Lower Case Figure 8 (B): a. Ipsilateral Trigeminal Nerve (V) b. Ipsilateral Acousticofacial Nerve Bundle (VII,VIII) c. Internal Auditory Meatus (IAM) Lower Case Figure 8 (D): a. Ipsilateral Lower Cranial Nerves (IX,X and XI) Lower Case Figure 8 (E): a. Ipsilateral Lower Cranial Nerves (IX,X and XI) b. Brainstem c. Inferior Lateral Aspect of Cerebellum Figures 9 (A), (B), and (C): Closure of Dura Lower Case Figure 9 (B): a. Collagen Dural Substitute (Onlay Graft) Lower Case Figure 9 (C): a. Dural Sealant Figures 10 (A) and (B): Cranioplasty Lower Case Figure 10 (A): a. Absorbable Microplate and Screws Lower Case Figure 10 (B): a. Hydroxyapatite Bone Substitute Figures 11 (A) and (B): Skin Closure and Dressing Figure 12: No Legend Figures 13: (A) Intraoperative endoscopic close-up view showing initial exposure of trigeminal nerve and the related offending artery Lower Case Figure 13 (A): a. Trigemianl Nerve (V) b. Petrous Apex c. Tentorium d. Brainstem e. Trochlear Nerve (IV) f. Offending Artery g. Superior Aspect of Cerebellum (B) - (D) Intraoperative endoscopic view showing dissection of offending artery from the trigeminal nerve Lower Case Figure 13 (B): a. Arachnoid Lower Case Figure 13 (C): a. Main Offending Artery Identified (Loop of Superior Cerebellar Artery (SCA)) Lower Case Figure 13 (D): a. Lifting of offending artery away from the Trigeminal Nerve REZ (E) and (F) Intraoperative endoscopic view showing Teflon placement Lower Case Figure 13 (E): a. Offending Artery Seperated from the Trigeminal Nerve b. Teflon Lower Case Figure 13 (F): a. Offending Artery Following Complete Decompression b. Teflon c. Trigeminal Nerve (V) d. Meckel's Cave e. REZ f. Brainstem g. Acousticofacial Nerve Bundle h. Internal Auditory Meatus (IAM) i. Tentorium j. Tentorial Incisura k. Trochlear Nerve (IV) Figures 14: (A) and (B) Intraoperative endoscopic close-up view showing the trigeminal nerve and related offending artery Lower Case Figure 14 (A): a. Trigeminal Nerve (V) b. Offending Artery c. Brainstem d. Petrous Apex e. Tentorium f. Tentorial Incisura g. Trochlear Nerve (IV) Lower Case Figure 14 (B): a. Close up View of Trigeminal Nerve (V) b. Offending Artery (C) - (E) Intraoperative endoscopic view showing dissection of offending artery from trigeminal nerve Lower Case Figure 14 (C): a. Lifting of Offending Artery Away from Trigeminal Nerve Lower Case Figure 14 (D): a. Decompression of the Trigeminal Nerve Lower Case Figure 14 (E): a. Offending Artery Completely Separated from Trigeminal Nerve (F) - (H) Intraoperative endoscopic view showing Teflon placement Lower Case Figure 14 (F): a. Trigeminal Nerve (V) b. Offending Artery Separated from Trigeminal Nerve c. Teflon d. Trochlear Nerve (IV) Lower Case Figure 14 (G): a. Trigeminal Nerve b. Offending Artery Separated from Trigeminal Nerve c. Teflon Lower Case Figure 14 (H): a. Trigeminal Nerve (V) b. Offending Artery Following Complete Decompression c. Teflon d. Petrous Apex e. Tentorium f. Trochlear Nerve (IV) g. Superior Aspect of Cerebellum (I) Intraoperative endoscopic view showing the entire area bathed in fibrin glue Lower Case Figure 14 (I): a. Fibrin Glue Figures 15: (A) Intraoperative endoscopic close-up view showing the trigeminal nerve and related offending vessels Lower Case Figure 15 (A): a. Trigeminal Nerve (V) b. Offending Artery c. Meckel's Cave d. Brain Stem e. Tentorium f. Petrous Apex g. Cross-compressing Offending Veins h. (B) - (E) Intraoperative endoscopic view showing dissection of offending vessels from the trigeminal nerve Lower Case Figure 15 (B): a. Cross Compressing Veins are Electrocoagulated and Divided Lower Case Figure 15 (D): a. Close up View of Offending Artery after Separation from Trigeminal Nerve b. Trigeminal Nerve (V) c. Trochlear Nerve (IV) (F) - (H) Intraoperative endoscopic view showing Teflon Placement Lower Case Figure 15 (F): a. Trigeminal Nerve (V) b. Offending Artery Separated from the Trigeminal Nerve c. Teflon Lower Case Figure 15 (G): a. Close up View of the Trigeminal Nerve Lower Case Figure 15 (H): a. Trigeminal Nerve (V) b. Teflon pieces Completely Padding the Trigemianl Nerve c. Superior Aspect of Cerebellum d. Acousticofacial Nerve Bundle (VII, VIII) e. Tentorium f. Petrous Temporal Bone (I) Intraoperative endoscopic view showing the entire area bathed in fibrin glue Lower Case Figure 15 (I): a. Fibrin Glue Figures 16: (A) Intraoperative endoscopic close-up view showing the trigeminal nerve and the related neurovascular anatomy Lower Case Figure 16 (A): a. Trigeminal Nerve (V) b. Superior Aspect of Cerebellum c. Petrosal Veins d. Petrous Apex e. Dense Arachnoid Adhesions (Post Gamma KnifeX2) f. Trochlear Nerve (IV) g. Brainstem h. Tentorium i. Tentorial Incisura (B) - (F) Intraoperative endoscopic view showing dissection of offending artery from trigeminal nerve Lower Case Figure 16 (B): a. Trigeminal Nerve (V) b. Meckel's Cave c. Offending Artery (Superior Cerebellar Artery (SCA)) d. Petrosal Veins Electrocoagulated and Divided e. REZ f. Arachnoid Adhesions g. Acousticofacial Nerve Bundle (VII, VIII) Lower Case Figure 16 (C): a. Close up View of Offending Artery b. Trigeminal Nerve c. Meckel's Cave d. Trochlear Nerve (IV) e. Contralateral Trigeminal Nerve (V) Lower Case Figure 16 (D): a. Close up View of the Trigeminal Nerve b. Offending Artery c. An Elevator is introduced to separate the Offending Artery from the Nerve Lower Case Figure 16 (E): a. Elevation of Offending Artery away from Trigeminal Nerve b. Trigeminal Nerve (V) Lower Case Figure 16 (F): a. Close up View Showing Elevation of Offending Artery b. Trigeminal Nerve (V) (G) - (J) Intraoperative endoscopic view showing the Teflon placement Lower Case Figure 16 (G): a. Teflon b. Trigeminal Nerve (V) c. Offending Artery Lower Case Figure 16 (H): a. Teflon Lower Case Figure 16 (I) a. Trigeminal Nerve b. Offending Artery Completely Separated from Trigeminal Nerve c. Teflon Lower Case Figure 16 (J): a. Trigeminal Nerve b. Abducent Nerve c. Clivus d. Lateral Aspect of Cerebellum e. Brainstem f. Teflon g. Offending Artery h. Tentorium i. Meckel's Cave j. Petrous Apex k. Internal Auditory Meatus (IAM) (K) Intraoperative endoscopic view showing the entire area bathed in fibrin glue Lower Case Figure 16 (K): a. Fibrin Glue Figure 17: No Legend Figures 18: (A) Intraoperative endoscopic close-up view showing acousticofacial nerve bundle and related offending artery Lower Case Figure 18 (A): a. Acousticofacial Nerve Bundle b. Offending Artery Covered with Arachnoid Layer (Anterior Inferior Cerebellar Artery (AICA)) c. Lateral Aspect of Cerebellum d. Lower Cranial Nerves e. Jugular Foramen f. Petrous Temporal Bone (B) - (E) Intraoperative endoscopic view showing dissection of offending artery from the facial nerve Lower Case Figure 18 (B): a. Acousticofacial Nerve Bundle (VII, VIII) b. Offending Artery c. Brainstem d. Trigeminal Nerve (V) e. Lateral Aspect of Cerebellum Lower Case Figure 18 (C): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Offending Artery d. Brainstem Lower Case Figure 18 (E): a. Close up view of Facial Nerve (VII) b. Site of Contact between Facial Nerve and offending Artery (F) and (G) Intraoperative endoscopic view showing the Teflon pads separating the vessel from the facial nerve Lower Case Figure 18 (F): a. Facial Nerve (VII) b. Teflon c. Offending Artery Lower Case Figure 18 (G): a. Facial Nerve (VII) b. Vestibulocochlear Nerve (VIII) c. Teflon d. Offending Artery e. Lower Cranial Nerves f. Jugular Foramen g. Petrous Temporal Bone (H) Intraoperative endoscopic view showing entire area bathed in fibrin glue Lower Case Figure 18 (H): a. Fibrin Glue Figures 19: (A) and (B) Intraoperative endoscopic view showing acousticofacial nerve bundle and offending arteries Lower Case Figure 19 (A): a. Acousticofacial Nerve Bundle b. Internal Auditory Meatus (IAM) c. Brainstem d. Trigeminal Nerve (V) e. Meckel's Cave f. Tentorium g. Abducent Nerve h. Clivus i. Trochlear Nerve (IV) j. Lateral Aspect of Cerebellum k. Petrous Temporal Bone l. Offending Artery (Anterior Inferior Cerebellar Artery (AICA)) Lower Case Figure 19 (B): a. Close up View of the Acouticofacial Nerve Bundle and the Regional Anatomy (C) and (D) Intraoperative endoscopic view showing offending artery Lower Case Figure 19 (C): a. Facial Nerve Stimulator Lower Case Figure 19 (D): a. Facial Nerve (VII) b. Vestibulocochlear Nerve (VII, VIII) c. Main Offending Artery (Vertebral Artery) d. Abducent Nerve (VI) passing thru Dorello's Canal (E) - (G) Intraoperative endoscopic view showing Teflon placement Lower Case Figure 19 (E): a. Teflon Lower Case Figure 19 (G): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Teflon d. Internal Auditory Meatus (IAM) Figures 20: (A) Intraoperative endoscopic close-up view showing acousticofacial bundle and offending arteries Lower Case Figure 20 (A): a. Acousticofacial Nerve Bundle (VII, VIII) b. Offending Artery c. Brainstem d. Lateral Aspect of Cerebellum e. Lower Cranial Nerves f. Jugular Foramen g. Petrous Temporal Bone (B) - (J) Intraoperative endoscopic view showing dissection of offending arteries from facial nerve and Teflon placement Lower Case Figure 20 (B): a. Acousticofacial Nerve Bundle (VII, VIII) b. Offending Artery Lower Case Figure 20 (C): a. Facial Nerve (VII) b. Vestibulocochlear Nerve (VIII) c. Teflon d. Lower Cranial Nerves (IX, X, XI) e. Jugular Foramen Lower Case Figure 20 (G): a. Facial Nerve (VII) b. Vestibulocochlear Nerve (VIII) c. Offending Artery d. Teflon Lower Case Figure 20 (H): Facial Nerve b. Vestibular (Acoustic) Nerve c. Offending Artery d. Teflon Lower Case Figure 20 (I): a. Facial Nerve (VII) b. Vestibulocochlear Nerve (VIII) c. Offending Artery d. Teflon e. Brainstem f. Petrous Temporal Bone g. Lower Cranial Nerves Lower Case Figure 20 (J): a. Fibrin Glue Figures 21: (A) Intraoperative endoscopic close-up view showing initial exposure of acousticofacial nerve bundle Lower Case Figure 21 (A): a.Facial Nerve (VII) b. Vestibulocochlear Nerve (VIII) c. Superior Aspect of Cerebellum d. Trigeminal Nerve (V) Sensory Root e. Trigeminal Nerve (V) Motor Root f. Superior Cerebellar Artery (SCA) g. Trochlear Nerve (IV) h. Tentorium i. Petrous Apex j. Internal Auditory Meatus (IAM) Lower Case Figure 21 (B): a. Close up View of Facial Nerve (VII) and regional anatomy (C) - (H) Intraoperative endoscopic view showing dissection of offending artery from facial nerve and Teflon placement Lower Case Figure 21 (C): a. Facial Nerve (VII) b. Vestibulocochlear Nerve (VIII) c. Offending Artery Loop (Anterior Inferior Cerebellar Artery (AICA)) d. Abducent Nerve (VI) Lower Case Figure 21 (D): a. Close up view of Offending artery loop and Regional Anatomy Lower Case Figure 21 (E): a. Elevation of Offending Arterial Loop away from Facial Nerve b. Acousticofacial Nerve Bundle (VII, VIII) c. Lower Cranial Nerves (IX, X, XI) Lower Case Figure 21 (F): a. Close up view using 30-Degree Endoscope Showing Offending Arterial Loop completely separated from Facial Nerve b. Acousticofacial Nerve Bundle (VII, VIII) Lower Case Figure 21 (G): a. Teflon Lower Case Figure 21 (H): a. Facial Nerve (VII) b. Vestibular Nerve (VIII) c. Teflon d. Lateral Aspect of Cerebellum e. Brainstem f. Abducent Nerve (VI) g. Clivus h. Trigeminal Nerve (V) Sensory Root i. Trigeminal Nerve (V) Motor Root j. Superior Cerebellar Artery (SCA) k. Trochlear Nerve (IV) l. Tentorium m. Internal Auditory Meatus (IAM) n. Petrous Temporal Bone Figures 22: (A) and (B) Intraoperative endoscopic view showing lower Cranial Nerves (IX, X, XI) and Offending Artery Lower Case Figure 22 (A): a. Offending Artery (Vertebral Artery) b. Lower Cranial Nerves c. Petroous Temporal Bone d. Lower Lateral Aspect of Cerebellum Lower Case Figure 22 (B): a. Close up View of the Offending Artery and regional Anatomy (C) and (D) Intraoperative endoscopic view showing separation of offending artery from lower cranial nerves by Teflon pads Lower Case Figure 22 (C): a. Teflon Lower Case Figure 22 (D): a. Fibrin Glue Figure 23: No legend Figure 24: No legend Figures 25: (A) T1-weighted, contrast-enhanced axial MRI showing a large acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing a large acoustic neuroma (C) Intraoperative endoscopic view showing the initial exposure of a large acoustic neuroma (C) - (H) Intraoperative endoscopic view showing gradual resection of large acoustic neuroma Lower Case Figure 25 (C): a. Acoustic Neuroma b. Expanded Internal Auditory Canal (IAC) c. Petrous Temporal Bone d. Lateral Aspect of Cerebellum Lower Case Figure 25 (D): a. Acoustic Neuroma Partly Decompressed Lower Case Figure 25 (D): a. Acoustic Neuroma Capsule b. Abducent Nerve (VI) c. Trigeminal Nerve (V) Lower Case Figure 25 (G): a. Final Remnants of Acoustic Neuroma Capsule Overlying the Acouticofacial Nerve Bundle (VII, VIII) b. Trigeminal Nerve (V) Lower Case Figure 25 (G): a. Acousticofacial bundle (VII, VIII) after Complete Tumor Removal b. Brainstem c. Trigeminal Nerve (V) d. Drilled Posterior Wall of Internal Auditory Canal (IAC) e. Trochlear Nerve (IV) (I) Postoperative T1-weighted, contrast-enhanced axial MRI (J) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 26: (A) T1-weighted, contrast-enhanced axial MRI showing large acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing large acoustic neuroma (C) and (D) Intraoperative endoscopic view showing the initial exposure of large acoustic neuroma Lower Case Figure 26 (C): a. Acoustic Neuroma b. Lateral Aspect of Cerebellum c. Lower Cranial Nerves (IX, X, XI) d. Expanded Internal Auditory Meatus (IAM) e. Tentorium Lower Case Figure 26 (D): a. Close up View of Acoustic Neuroma and Regional Anatomy (E) - (N) Intraoperative endoscopic view showing gradual resection of large acoustic neuroma Lower Case Figure 26 (E): a. Acoustic Neuroma b. Cauterized Dura Lower Case Figure 26 (F): a. Acoustic Neuroma b. Cauterized Dura c. Bipolar Diathermy Tip Lower Case Figure 26 (G): a. Acoustic Neuroma b. Straight Microscissors Lower Case Figure 26 (I): a. Acoustic Neuroma Partly Debulked b. MicroCUSA Tip Lower Case Figure 26 (L): a. Final Remnants of Acoustic Neuroma Capsule b. Drilled Posterior Wall of Internal Auditory Canal (IAC) Lower Case Figure 26 (M): a. Final Portion of Acoustic Neuroma Capsule being Dissected b. Upward Angled MicroHook c. Atraumatic Suction Lower Case Figure 26 (N): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Final Portion of Acoustic Neuroma Capsule being Dissected d. Drilled Posterior Wall of Internal Auditory Canal (IAC) e. Upward Angled MicroHook f. Atraumatic Suction (O) and (P) Intraoperative endoscopic view following complete resection of large acoustic neuroma Lower Case Figure 26 (O): a. Vestibulocochlear Nerve following Complete Tumor Resection (VIII) b. Facial Nerve (VII) c. Trigeminal Nerve (V) d. Anterior Wall of Internal Auditory Canal (IAC) e. Posterior Wall of Internal Auditory Canal (IAC) f. Petrous Temporal Bone g. Lower Cranial Nerves (IX, X, XI) h. Lateral Aspect of Cerebellum i. Brainstem j. Trochlear Nerve (IV) k. Tentorium l. Tentorial Incisura Lower Case Figure 26 (P): a. Close Up View of Vestibulocochlear Nerve (VIII) b. Close Up View of Facial Nerve (VII) c. . Internal Auditory Canal (IAC) d. Trigeminal Nerve (V) e. Meckel's Cave f. Trochlear Nerve (IV) g. Tentorium h. Brainstem (Q) Postoperative T1-weighted, contrast-enhanced axial MRI (R) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 27: (A) T1-weighted, contrast-enhanced axial MRIs showing large acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRIs showing large acoustic neuroma (C) Intraoperative endoscopic view showing the initial exposure of large acoustic neuroma Lower Case Figure 27 (C): a. Acoustic Neuroma b. Expanded Internal Auditory Meatus (IAM) c. Lateral Aspect of Cerebellum d. Tentorium e. Petrous Temporal Bone (D) - (O) Intraoperative endoscopic view showing gradual resection of large acoustic neuroma Lower Case Figure 27 (F): a. Acoustic Neuroma Debulked b. Lower Cranial Nerves (IX, X, XI) Lower Case Figure 27 (G): a. Anterior Capsule of Acoustic Neuroma b. Trigeminal Nerve (V) c. Drilled Posterior Wall of Internal Auditory Canal (IAC) Lower Case Figure 27 (G): a. Anterior Capsule of Acoustic Neuroma b. Abducent Nerve (VI) Lower Case Figure 27 (I): a. Close up view of Intracanalicular Portion of Acoustic Neuroma Lower Case Figure 27 (J): a. Intracanalicular Portion of Acoustic Neuroma being Removed b. Angled Extended Ring Curette Lower Case Figure 27 (K): a. Close up view showing the removal of Intracanalicular Portion of Acoustic Neuroma Lower Case Figure 27 (L): a. Close up view showing clean Internal Auditory canal after removal of Intracanalicular Portion of Acoustic Neuroma b. Trigeminal Nerve (V) c. AcousticoFacial Nerve Bundle (VII, VIII) (M) and (N) Intraoperative endoscopic view after complete resection of large acoustic neuroma Lower Case Figure 27 (M): a. Acousticofacial Nerve Bundle (VII, VIII) after Complete Tumor Removal Lower Case Figure 27 (N): a. Acousticofacial Nerve Bundle (VII, VIII) b. Trigeminal Nerve (V) c. Brainstem d. Anterior Wall of Internal Auditory Canal (IAC) e. Posterior Wall of Internal Auditory Canal (IAC) f. Lower Cranial Nerves (IX, X, XI) g. Lateral Aspect of Cerebellum h Tentorium (O) Postoperative T1-weighted, contrast-enhanced axial MRIs (P) Postoperative T1-weighted, contrast-enhanced coronal MRIs Figures 28: (A) T1-weighted, contrast-enhanced axial and saggital MRIs showing large acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing large acoustic neuroma (C) and (D) Intraoperative endoscopic view showing the initial exposure of large acoustic neuroma Lower Case Figure 28 (D): a. Acoustic Neuroma b. Expanded Internal Auditory Meatus (IAM) c. Lateral Aspect of Cerebellum d. Tentorium e. Petrous Temporal Bone (E) - (T) Intraoperative endoscopic view showing gradual resection of large acoustic neuroma Lower Case Figure 28 (E): a. Acoustic Neuroma b. Bipolar Diathermy Tip c. Atraumatic Suction Lower Case Figure 28 (I): a. Acoustic Neuroma Partly Debulked b. MicroCUSA Tip Lower Case Figure 28(L): a. Anterior Capsule of Acoustic Neuroma b. Trigeminal Nerve (V) Lower Case Figure 28 (M): a. Anterior Capsule of Acoustic Neuroma b. Drilled Posterior Wall of Internal Auditory Canal (IAC) Lower Case Figure 28 (N): a. Anterior Capsule of Acoustic Neuroma b. Abducent Nerve (VI) Lower Case Figure 28 (P): a. Anterior Capsule of Acoustic Neuroma b. MicroCUSA Tip Lower Case Figure 28 (S): a. Final Portion of Anterior Capsule of Acoustic Neuroma b. Acousticofacial Nerve Bundle (VII, VIII) c. Brainstem d. Trigeminal Nerve (V) e. Abducent Nerve (VI) Lower Case Figure 28 (T): a. Acousticofacial Nerve Bundle (VII, VIII) after Complete Tumor Removal b. Brainstem c. Lateral Aspect of Cerebellum d. Trigeminal Nerve (V) (U) Postoperative T1-weighted, contrast-enhanced axial and saggital MRIs (V) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 29: (A) T1-weighted, contrast-enhanced axial MRI showing medium sized acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing medium sized acoustic neuroma (C) Intraoperative endoscopic view showing initial exposure of medium sized acoustic neuroma Lower Case Figure 29 (C): a. Acoustic Neuroma b. Acousticofacial Nerve Bundle (VII, VIII) c. Expanded Internal Canal (IAC) d. Petrous Temporal Bone e. Lateral Aspect of Cerebellum f. Tentorium (D) - (L) Intraoperative endoscopic view showing gradual resection of medium sized acoustic neuroma Lower Case Figure 29 (F): a. Acoustic Neuroma b. Acousticofacial Nerve Bundle (VII, VIII) c. Trigeminal Nerve (V) Lower Case Figure 29 (H): a. Drilled Posteior Wall of Internal Auditory Canal (IAC) b. Acoustic Neuroma c. Acousticofacial Nerve Bundle (VII, VIII) d. Trigeminal Nerve (V) Lower Case Figure 29 (I): a. Acoustic Neuroma Lower Case Figure 29 (J): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Acoustic Neuroma Lower Case Figure 29 (L): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Anterior Wall of Internal Auditory Canal (IAC) d. Drilled Posterior Wall of Internal Auditory Canal (IAC) e. Trigeminal Nerve (V) (M) Postoperative T1-weighted, contrast-enhanced axial MRI (N) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 30: (A) T1-weighted, contrast-enhanced axial MRI showing medium sized acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing medium sized acoustic neuroma (C) and (D) Intraoperative endoscopic view showing initial exposure of medium sized acoustic neuroma Lower Case Figure 30 (C): a. Acoustic Neuroma b. Acousticofacial Nerve Bundle (VII, VIII) c. Lateral Aspect of Cerebellum Tentorium d. Trigeminal Nerve (V) e. Brainstem f. Tentorium g. Petrous Temporal Bone h. Expanded Internal Meatus (IAM) (E) - (N) Intraoperative endoscopic view showing gradual resection of medium sized acoustic neuroma Lower Case Figure 30 (D): a. Close Up View of Acoustic Neuroma and Regional Anatomy Lower Case Figure 30 (E): a. Drilled Posteior Wall of Internal Auditory Canal (IAC) b. Acoustic Neuroma Lower Case Figure 30 (F): a. Intracanalicular Portion of Acoustic Neuroma Lower Case Figure 30 (G): a. Acoustic Neuroma b. Ring Curette Lower Case Figure 30 (L): a. Acoustic Neuroma b. MicroCUSA Tip Lower Case Figure 30 (M): a. Final Portions Acoustic Neuroma b. Vestibulocochlear Nerve (VIII) c. Facial Nerve (VII) Lower Case Figure 30 (N): a. Acoustic Neuroma b. Angled Extended Ring Curette (O) - (R) Intraoperative endoscopic view after complete resection of medium sized acoustic neuroma Lower Case Figure 30 (O): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Lateral Limit of Drilled Posterior Wall of Internal Auditory Canal (IAC) Lower Case Figure 30 (P): a. Measurement (1 mm Intervals) Lower Case Figure 30 (Q): a. Vestibulocochlear Nerve (VIII) (View using 30-Degree Endoscope) b. Facial Nerve (VII) (View using 30-Degree Endoscope) c. Trigeminal (V) Nerve Lower Case Figure 30 (R): a. Vestibulocochlear Nerve (VIII) (Close up View using 30-Degree Endoscope) b. Facial Nerve (VII) (Close up View using 30-Degree Endoscope) (S) Postoperative T1-weighted, contrast-enhanced axial MRI (T) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 31: (A) T1-weighted, contrast-enhanced axial MRI showing medium sized acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing medium sized acoustic neuroma (C) and (D) Intraoperative endoscopic view showing initial exposure of medium sized acoustic neuroma Lower Case Figure 31 (C): a. Acoustic Neuroma b. Superior Aspect of Cerebellum Acousticofacial Nerve Bundle (VII, VIII) c. Expanded Internal Meatus (IAM) d. Tentorium e. Trigeminal Nerve (V) f. Brainstem Lower Case Figure 31 (D): a. Acoustic Neuroma b. Acousticofacial Nerve Bundle (VII, VIII) Lower Case Figure 31 (D): a. Acoustic Neuroma b. Left Curved MicroScissors (E) - (K) Intraoperative endoscopic view showing gradual resection of medium sized acoustic neuroma Lower Case Figure 31 (H): a. Drilled Posterior Wall of Internal Auditory Canal (IAC) b. Acoustic Neuroma c. Acousticofacial Nerve Bundle (VII, VIII) d. Trigeminal Nerve (V) Lower Case Figure 31 (I): a. Close Up View of Final Portions of Acoustic Neuroma (L) and (M) Intraoperative endoscopic view after complete resection of medium sized acoustic neuroma Lower Case Figure 31 (L): a. Close Up View of Vestibulocochlear Nerve (VII, VIII) b. Close Up View of Facial Nerve (VII) c. Lateral Limit of Drilled Posteior Wall of Internal Auditory Canal (IAC) Lower Case Figure 31 (M): a. Vestibulocochlear Nerve (VIII) (Close up View using 30-Degree Endoscope) b. Facial Nerve (VII) (Close up View using 30-Degree Endoscope) (N) Postoperative T1-weighted, contrast-enhanced axial MRI (O) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 32: (A) T1-weighted, contrast-enhanced axial MRI showing a purely intracanalicular acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing a purely intracanalicular acoustic neuroma (C) - (J) Intraoperative endoscopic view showing exposure and resection of a purely intracanalicular acoustic neuroma Lower Case Figure 32 (C): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Lateral Aspect of Cerebellum d. Expanded Internal Meatus (IAM) e. Petrous Temporal Bone Lower Case Figure 32 (D): a. Close up view of Vestibulocochlear Nerve (VIII) and Regional Anatomy b. Facial Nerve (VII) Acousticofacial Nerve Bundle (VII, VIII) Lower Case Figure 32 (E): a. Drilling of Posterior Wall of Internal Auditory Canal (IAC) Lower Case Figure 32 (H): a. Acoustic Neuroma Lower Case Figure 32 (J): a. Intracanlicular Vestibulocochlear Nerve (VIII) after Complete Tumor Resection b. Facial Nerve (VII) c. Lateral Limit of Drilled Internal Auditory Canal (IAC) d. Brainstem (K) Postoperative T1-weighted, contrast-enhanced axial MRI (L) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 33: (A) T1-weighted, contrast-enhanced axial MRI showing a purely intracanalicular acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing a purely intracanalicular acoustic neuroma (C) - (G) Intraoperative endoscopic view showing exposure and resection of a purely intracanalicular acoustic neuroma Lower Case Figure 33(C): a. Vestibulocochlear Nerve (VIII) b. Drilling of Posterior Wall of Internal Auditory Canal (IAC) Lower Case Figure 33 (E): a. Acoustic Neuroma b. Vestibulocochlear Nerve (VIII) Lower Case Figure 33 (F): a. Acoustic Neuroma b. Right Curved Micro Cupped Forceps Tip c. Atraumatic Suction Lower Case Figure 33 (G): b. Acoustic Neuroma Cavity after Complete Tumor Resection (H) Postoperative T1-weighted, contrast-enhanced axial MRI (I) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 34: (A) T1-weighted, contrast-enhanced axial MRI showing intracanalicular acoustic neuroma (B) T1-weighted, contrast-enhanced coronal MRI showing intracanalicular acoustic neuroma (C) - (N) Intraoperative endoscopic view showing exposure and resection of intracanalicular acoustic neuroma Lower Case Figure 34 (C): a. Acoustic Neuroma b. Expanded Internal Meatus (IAM) c. Petrous Temporal Bone d. Tentorium e. Lateral Aspect of Cerebellum Lower Case Figure 34 (D): a. Acoustic Neuroma b. Vestibulocochlear Nerve (VIII) c. Drilling of Posterior Wall of Internal Auditory Canal (IAC) d. Trigeminal Nerve (V) Lower Case Figure 34 (F): a. Acoustic Neuroma b. Straight MicroScissors Lower Case Figure 34 (I): a. Acoustic Neuroma b. Upward Angled MicroHook c. Atraumatic Suction Lower Case Figure 34 (L): a. Final Portions of Acoustic Neuroma b.Vestibulocochlear Nerve (VIII) Lower Case Figure 34 (M): a. Final Portions of Acoustic Neuroma Being Removed b. Extended Angled Ring Curette (O) - (Q) Intraoperative endoscopic view after complete resection of intracanalicular acoustic neuroma Lower Case Figure 34 (O): a. Vestibulocochlear Nerve (VIII) b. Facial Nerve (VII) c. Lateral Limit of Drilled Posterior Wall of Internal Audiotory Canal (IAC) d. Lateral Aspect of Cerebellum Lower Case Figure 34 (P): a. Close up view of Vestibulocochlear Nerve (VIII) and Regional Anatomy Lower Case Figure 34 (Q): a. Close up view of Vestibulocochlear Nerve (VIII) and Regional Anatomy using 30-Degree Endoscope (R) Postoperative T1-weighted, contrast-enhanced axial MRI (S) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 35: (A) T1-weighted, contrast-enhanced axial MRI showing a superior cerebellar convexity meningioma extending to Cerebellopontine Angle (CPA) (B) T1-weighted, contrast-enhanced coronal MRI showing a superior cerebellar convexity meningioma extending to Cerebellopontine Angle (CPA) (C) Intraoperative endoscopic view showing initial exposure of a superior cerebellar convexity meningioma extending to Cerebellopontine Angle (CPA) Lower Case Figure 35 (C) a. Meningioma b. Superolateral Aspect of Cerebellum c. Atraumatic Suction (D) - (J) Intraoperative endoscopic view showing gradual Resection of a superior cerebellar convexity meningioma extending to Cerebellopontine Angle (CPA) Lower Case Figure 35 (C) a. Meningioma b. Superolateral Aspect of Cerebellum c. Atraumatic Suction Lower Case Figure 35 (C) a. Meningioma b. Straight MicroScissors c. Atraumatic Suction Lower Case Figure 35 (F) a. Meningioma Biopsied Lower Case Figure 35 (G) a. Meningioma Partly Debulked b. MicroCUSA Tip Lower Case Figure 35 (I) a. Meningioma Attachment Being Cauterized and Resected b. Facial Nerve (VII) c. Superior Aspect of Cerebellum Lower Case Figure 35 (J) a. Meningioma Attachement after complete Tumor Resection b. Tentorium c. Trochlear Nerve (IV) d. Trigeminal Nerve (V) e. Acousticofacial Nerve Bundle (VII, VIII) f. Superior Aspect of Cerebellum (K) Postoperative T1-weighted, contrast-enhanced axial MRI (L) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 36: (A) T1-weighted, contrast-enhanced axial MRI showing a lateral cerebellopontine angle (CPA) meningioma (B) T1-weighted, contrast-enhanced coronal MRI showing a lateral cerebellopontine angle (CPA) meningioma (C) Intraoperative endoscopic view showing initial exposure of a lateral cerebellopontine angle (CPA) meningioma Lower Case Figure 36 (C) a. Meningioma b. Lateral Aspect of Cerebellum c. Tentorium (D) - (N) Intraoperative endoscopic view showing gradual Resection of a Lateral cerebellopontine angle (CPA) meningioma Lower Case Figure 36 (E) a. Meningioma b. AcousticoFacial Nerve Bundle (VII, VIII) Stretched by Tumor Lower Case Figure 36 (F) a. Meningioma Capsule b. AcousticoFacial Nerve Bundle (VII, VIII) c. Trigeminal Nerve (V) d. Brainstem Lower Case Figure 36 (G) a. Meningioma Lower Case Figure 36 (H) a. Close up View of final portion of Meningioma attached to Petrous Temporal Bone Lower Case Figure 36 (I) a. Final portion of Meningioma attached to Petrous Temporal Bone b. Acousticofacial Nerve Bundle (VII, VIII) c. Trigeminal Nerve (V) d. Trochlear Nerve (IV) e. Brainstem f. Lateral Aspect of Cerebellum g. Clivus Lower Case Figure 36 (I) a. Clean Petrous Bone after complete Meningioma Resection b. Acousticofacial Nerve Bundle (VII, VIII) c. Trigeminal Nerve (V) d. Tentorium e. Brainstem f. Lateral Aspect of Cerebellum (K) Postoperative T1-weighted, contrast-enhanced axial MRI (L) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 37: (A) T1-weighted, contrast-enhanced axial MRI showing a medial Cerebellopontine Angle (CPA) meningioma (B) T1-weighted, contrast-enhanced coronal MRI showing a Medial Cerebellopontine Angle (CPA) meningioma (C) Intraoperative endoscopic view showing initial exposure of a Medial Cerebellopontine Angle (CPA) meningioma Lower Case Figure 37 (C) a. Meningioma b. Facial Nerve (VII) c. Vestibulocochlear Nerve (VIII) d. Petous Apex e. Tentorium f. Lateral Aspect of Cerebellum (D) - (R) Intraoperative endoscopic view showing gradual Resection of a Medial Cerebellopontine Angle (CPA) meningioma Lower Case Figure 37 (F) a. Meningioma Capsule b. Acousticofacial Nerve Bundle (VII, VIII) c. Bipolar Diathermy Tip d. Atraumatic Suction e. Trigeminal Nerve (V) f. Trochlear Nerve (IV) Lower Case Figure 37 (I) a. Meningioma b. Facial Nerve (VII) c. Vestibulocochlear Nerve (VIII) d. Internal Auditory Meatus (IAM) e. MicroCusa Tip f. Atraumatic Suction g. Trochlear Nerve (IV) Lower Case Figure 37 (J) a. Meningioma Capsule Lower Case Figure 37 (H) a. Close up View of final portion of Meningioma attached to Petrous Temporal Bone Lower Case Figure 37 (I) a. Final portion of Meningioma attached to Petrous Temporal Bone b. Acousticofacial Nerve Bundle (VII, VIII) c. Trigeminal Nerve (V) d. Trochlear Nerve (IV) e. Brainstem f. Lateral Aspect of Cerebellum g. Clivus Lower Case Figure 37 (I) a. Clean Petrous Bone after complete Meningioma Resection b. Acousticofacial Nerve Bundle (VII, VIII) c. Trigeminal Nerve (V) d. Tentorium e. Brainstem f. Lateral Aspect of Cerebellum (K) Postoperative T1-weighted, contrast-enhanced axial MRI (L) Postoperative T1-weighted, contrast-enhanced coronal MRI