Endoscopic Skull Base Surgery Chapter 1: Introduction to Endoscopic Skull Base Surgery


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Endoscopic Skull Base Surgery
Chapter 1: Introduction to Endoscopic Skull Base Surgery
By Hrayr K. Shahinian, M.D., FACS

Abstract

This chapter discusses the evolution from traditional surgical approaches to the anterior, middle, and posterior skull base to fully endoscopic skull base surgery. From its original reliance on microsurgical techniques, the field of skull base surgery is currently being transformed into an endoscopy-based specialty that is distinguished by excellent outcomes, shorter operating times, faster recoveries, fewer complications, and overall decreased patient morbidity. The chapter provides insight into the practice of fully endoscopic skull base surgery at the Skull Base Institute in Los Angeles, California. These techniques are routinely used in the surgical management of anterior, middle, and posterior skull base tumors, both primary and recurrent, as well as for various neurovascular compression syndromes, such as trigeminal neuralgia, hemifacial spasm, and others. In our experience, these endoscopic techniques have provided superior access and resulted in better surgical results and an unsurpassed intraoperative definition of neurovascular conflicts and tumor morphologies. More than 90% of all patients undergoing endoscopic skull base surgery are discharged from the hospital within 48 hours of their operation.

1. The Evolution from the Open Craniotomy to Fully Endoscopic Skull Base Surgery

For decades, surgeons interested in the field of skull base surgery have debated which techniques provide the best access to the skull base with the least amount of associated risk. Traditional approaches to the anterior, middle, and posterior skull base have included complex transcranial or transfacial operations. These procedures, facilitated by progress in the designs of surgical instruments and advances in perioperative intensive care, have afforded excellent exposure, allowing for complete removal of massive tumors. However, these open procedures have also been associated with significant morbidity and long-term convalescence: the burden on the patient has been great. As a result, the evolution of skull base surgery over the past decade has been characterized by an emphasis on the development of minimally invasive techniques that do not compromise surgical outcomes but do significantly diminish the perioperative burden on the patient.

Figure 1 (A): Traditional Bifrontal

Innovations in medical technology have again provided the raw materials needed for this progress. Advances in fiberoptic technology, including improved design of endoscopes, light sources, video cameras, and special microinstruments, have culminated in the development of safe and effective alternatives to traditional neurosurgical, neuro-otologic and craniofacial techniques. From its original reliance on microsurgical techniques, the field of skull base surgery is currently being transformed into an endoscopy-based specialty that is distinguished by excellent outcomes, shorter operating times, faster recoveries, fewer complications, and overall decreased patient morbidity (Figures 1 (A) and (B)).

Figure 1 (B): Endoscopic Endonasal

Progress is continuing, changing many scenarios in daily clinical life. The expectation of achieving the greatest therapeutic effect with the least iatrogenic injury is higher now than ever. Additionally, because of excellent diagnostic modalities such as computed tomography and magnetic resonance imaging, smaller lesions are being encountered, resulting in the increased use of early surgery. The best way to preserve collateral structures is not to touch them and, even better, not to expose them. Wide exposure of the brain, skull, and soft tissues under nonphysiological circumstances for several hours is certainly undesirable.

Figure 2 (A): Traditional Pterional

The main purpose of the keyhole approach is to use a more targeted approach that eliminates many of the steps that are necessary with conventional approaches. Although the radical cranial base approaches are well established and their features are widely recognized, it is not always necessary to resect or expose wide extracranial or intracranial compartments. The more the cranial base techniques become established, the more they can be refined and limited to the essential compartment. As this process is accelerated, lesions will be diagnosed when they are smaller in size, and the extent of the craniotomy will be reduced as a result (Figures 2 (A) and (B)).

Figure 2 (B): Endoscopic Supraorbital

Selecting short, direct, and precise routes to lesions without manipulating and exposing unaffected areas is essential for keyhole surgery. Because the surgeon does not have the flexibility to correct the angle of approach during the procedure, he or she must be familiar with the anatomic features of keyhole craniotomy to determine the adequate location and size of the craniotomy in each case. Precise knowledge about three-dimensional space characteristics of the target region with its corresponding windows is indispensable. Furthermore, affected structures are commonly displaced, so the individual anatomy and concomitantly the individual approach needs to be evaluated in detail for each patient preoperatively.

Figure 3 (A): Traditional Translabyrinthine

The concomitant use of rigid lens scopes during open microsurgical procedures offers an enormously increased panoramic overview with excellent visual quality in deep and narrow fields. Furthermore, this not only helps to inspect vessels and nerves around corners but can also assist in manipulating and resecting residual lesions beyond the direct view of the microscope, as described for Patient 36. With the endoscope attached to the holding arm, two-hand manipulation with regular microsurgical instruments beside the endoscope is feasible. This endoscope-assisted microsurgical technique is an important transitional step between traditional open techniques and fully endoscopic techniques and may provide the surgeon a gradual learning opportunity (Figures 3 (A) and (B)).

2. Endoscopic Skull Base Surgery in Practice

Figure 3 (B): Endoscopic Retrosigmoid

For the past decade at the Skull Base Institute in Los Angeles, California, we have been performing endoscope-assisted and fully endoscopic surgery of the anterior, middle, and posterior skull base. Applications of endoscopy at our institution have included treatment of primary and recurrent pituitary tumors (both with and without suprasellar extension), treatment of the various neurovascular compression syndromes (trigeminal neuralgia, hemifacial spasm, glossopharyngeal neuralgia, spasmodic torticollis) at the cerebellopontine angle (CPA), removal of vestibular schwannomas and other CPA tumors, as well as resection of various other skull base lesions, both malignant and benign. More than 90% of all patients undergoing endoscopic procedures of the skull base are discharged from the hospital within 48 hours.

For many indications, we now use only fully endoscopic techniques via "keyhole" craniotomy access points; the need for extensive craniotomies for intracranial exposure and retraction has been all but obviated. Visualization of the relevant anatomy has proven to be improved over microscopic imaging. Endonasal, supraorbital, transglabellar, retrosigmoid, subtemporal, and other tailored keyhole approaches have made virtually all skull base tumors amenable to endoscopic resection. Rigid endoscopes of varying lengths and angles of view have broadened the available surgical exposure without the need for of additional dissection or retraction; the resulting panoramic perspectives of the surgical field have allowed for thorough evaluations of the extent of intracranial disease. The maneuverability of the endoscope has allowed the surgeon to position it directly at the level of dissection, effectively reducing the viewing and operating distances.

In pituitary surgery, this has meant abandoning the transseptal-transsphenoidal microscopic technique in favor of a completely endoscopic endonasal approach. For larger tumors with significant suprasellar extension, endoscopic transcranial approaches-whether transglabellar or supraorbital-in conjunction with the endoscopic endonasal approach have been effective adjuncts that provide significantly less invasive alternatives to traditional transcranial approaches to the floor of the anterior fossa. Surgical outcomes and complication rates of endoscopic pituitary surgery have compared favorably to those that have been reported in large series of patients who have undergone microscopic transseptal pituitary surgery. At the CPA, the use of endoscopy-particularly implementing rigid endoscopes of varying angles of view-has vastly improved visualization around the contour of the petrous portion of the temporal bone, one of the most significant impediments to exposure using traditional microscopic techniques. In our experience this superior access has resulted in better surgical results due to better intraoperative definition of neurovascular conflicts and tumor morphology.

We offer this atlas as a resource for current practitioners of skull base surgery as well as students of the discipline. It contains detailed intraoperative photos demonstrating the endoscopic surgical anatomy encountered in a variety of approaches to the skull base, as well as rendered schematic images that assist in presurgical planning. It is our hope that this work will contribute to the ongoing evolution of minimally invasive skull base surgery.

Legends
Figures 1:

Traditional Bifrontal
Endoscopic Endonasal

Figures 2:

Traditional Pterional
Endoscopic Supraorbital

Figures 3:

Traditional Translabyrinthine
Endoscopic Retrosigmoid