Endoscopic Approach to Orbital Tumors
In many cases, particularly with optic nerve involvement, attempts at complete resection of orbital tumors via traditional methods may result in vascular or direct damage to the critical structures within the orbit such as the optic nerves and/or chiasm. At the Skull Base Institute endoscopic techniques have evolved dramatically and are routinely utilized to improve visualization and approach areas where surgical access is limited with minimal manipulation of tissues. These techniques allow adequate exposure of the operative site, yet avoid undue pressure on the globe and unnecessary compromise of its neurovascular supply. Orbital endoscopy is useful in managing various types of orbital tumors. With such endoscopic approaches complex lesions of the orbit are treated with low morbidity and treatment of tumors involving the optic nerves and chiasm can be successful in sparing vision. Either a supraorbital endoscopic approach, a transnasal endoscopic approach or a combination of both with removal of the medial orbital wall, the orbital roof, the lateral orbital wall or the orbital floor may be performed depending on the exact location, size or extent of the specific tumor.
Overview
The orbit is the cone-shaped bony socket that contains the eyeball; the orbital contents include the extraocular muscles that move the eye, the optic nerve, the nerves and blood vessels supplying these structures and the fat inbetween. Tumors that develop in any of the tissues that surround the eyeball are referred to as orbital tumors The periosteum lining the orbital walls, is continuous with the dura mater surrounding the brain at the optic foramen and superior orbital fissure.
Any of the orbital structures may give rise to a tumor; in addition, tumors originating from the surrounding paranasal sinuses, the brain and the nasal cavity may grow through the bone and invade the orbital confines. A wide variety of tumors may grow in the orbit. Tumors found in this region include optic nerve gliomas, orbital meningiomas, dermoids, hemangiomas, lymphangiomas, neurofibromas, sarcomas and metastatic lesions.
Orbital tumors may affect both adults and children. Fortunately, in both age groups most orbital tumors are benign. The most common benign orbital tumors in children are dermoids and vascular lesions such as capillary hemangiomas, lymphangiomas and cavernous hemangiomas. In adults, the most common benign tumors are also blood vessel tumors such as hemangiomas, lymphangiomas and arteriovenous malformations. Tumors of the nerves (schwannomas), fat (lipoma), as well as those that evolve from the surrounding sinuses (mucocele) occur less commonly.
Orbital malignancies in childhood are unusual, the most common are rhabdomyosarcomas, other malignant lesions that may affect the orbit include Burkitt's lymphoma and granulocytic sarcoma. Neuroblastoma, Ewing sarcoma, Wilm's tumor, and leukemias are the more common metastatic orbital lesions afflicting children.
The most common malignant orbital tumors in adults are lymphomas. Often they are initially confined to the orbit without any systemic manifestations. Direct invasion of the orbit from the surrounding skin and sinus cavities can occur from squamous and basal cell cancers. Other malignancies that arise from tissues within the orbit are less common (hemangiopericytoma, chondrosarcoma, malignant neurofibroma). Metastatic orbital tumors most frequently arise from the breast and the prostate.
Causes
The cause of primary orbital tumors is unknown. In children most orbital tumors result from developmental abnormalities.
When visual loss or deterioration occurs with an orbital tumor, it may result from either mass effect, compromise of the vasculature to the optic apparatus as a result of the tumor, or invasion of the optic nerve by the tumor.
Symptoms
Orbital tumors typically present with early unilateral proptosis of the globe and may adversely affect visual and extraocular muscle function.
Other symptoms include double vision (diplopia), and pupillary abnormalities. The associated lid dysfunction and incomplete lid closure (lagophthalmos) or lacrimal gland dysfunction can result in exposure keratopathy, keratitis, and ocular pain.
Diagnosis
Evaluation of a patient with a presumed orbital mass begins with a thorough ophthalmic and medical history including history of allergies, sinus infections, recent trauma to rule out all non-neoplastic sinonasal etiologies for the disease process.It is also important to ask about other medical conditions that may be associated with proptosis or other ocular manifestations, such as thyroid disorders, granulomatous diseases, and autoimmune disorders. In patients with the disease neurofibromatosis type I, orbital tumors are usually optic nerve gliomas. Laboratory evaluation with a complete blood count, sedimentation rate and thyroid function tests should be obtained to exclude infection, inflammation or thyroid disease as these conditions may cause ocular proptosis mimicking that caused by an orbital tumor.
Imaging techniques are used to define the extent and localization of orbital tumors. Ultrasonography is a relatively simple test for evaluating the orbit; however, its use has been largely supplanted by the more accurate computerized tomography (CT) and magnetic resonance imaging (MRI). CT scanning is useful in the detection and localization of orbital tumors and in defining their extent and relationship to the optic nerve, extraocular muscles, blood vessels, globe, sinuses and brain. MRI may provide excellent soft-tissue resolution, but CT scan is superior for gleaning details about orbital bony structures. Arteriography is useful for differentiating hemangiopericytoma from cavernous hemangioma (encapsulated venous malformations) and when preoperative embolization of vascular tumors is planned.
Once discovered and imaged with MRI/ CT, the next step in the management of orbital tumors is diagnosis of the type of tumor either with an open biopsy or a fine needle aspiration biopsy (FNAB). An open biopsy may be necessary if FNAB is not able to obtain adequate tissue for pathological assessment.
Opthalmological tests, including testing for visual acuity, visual fields, pupillary responses, ocular motility and inspection of the external surface of the globes, eyelids and surrounding structures is of paramount importance. Intraocular pressure may be elevated, and slit lamp examination may be necessary. Dilated funduscopic examination may reveal optic disc edema or pallor, retinal detachment, choroidal folds, vascular engorgement or shunt vessels, or indentation of the posterior pole.
Treatment
If the tumor is small and not symptomatic, it may be followed safely with serial MRI scans. When ocular symptoms such as visual loss or disfiguring proptosis are associated with mass effect from the orbital tumor, surgical removal is usually the best option.
The location of the lesion directs the surgeon toward selecting the most appropriate type and location of the orbitotomy. Many cutaneous and bony approaches to the orbit have been described. In general, when orbital tumors are situated lateral to the optic nerve, a lateral orbitotomy is performed. Tumors superior to the optic nerve or those with intracranial extension are usually approached via an orbitofrontal craniotomy. Tumors below the optic nerve can be approached via a medial orbitotomy, a transethmoid or a transmaxillary approach.
When an orbital meningioma or fibrous dysplasia is accompanied by hyperostosis of the optic canal, craniotomy is usually accompanied by bony decompression using a high-speed diamond drill. When the tumor is not completely removed surgically, this subtotal resection may be followed by some form of orbital irradiation.
Prognosis
Surgical removal is curative for many orbital tumors and the cosmetic results can be excellent. The outcome and prognosis ultimately depends on the pathological diagnosis. Some orbital tumors may require additional therapy rather than biopsy or removal this may include conventional "external beam" or Gamma Knife Radiotherapy. Occasionally adjuvant chemotherapy may also be necessary.
