Endoscopic Endonasal Approaches to the Optic Apparatus: Technique and Pathology

Pituitary Adenoma

Pituitary adenomas represent the most frequent type of sellar mass with a prevalence of 77 to 100 cases per 100,000 population. These tumors can be classified into nonfunctional or functional (hormone-secreting) subtypes.

Among the pituitary tumors that are associated with visual dysfunction, nonfunctioning adenomas are the most common (58%). Superior extension of tumors may compress the optic chiasm and lead to visual field deficits, most commonly bitemporal hemianopia. Other visual symptoms may include loss of visual acuity and diplopia. The progression of visual loss is typically slow (50%); however, rapid (27%) and intermittent progression (12.5%) have also been reported. Importantly, although 75% of patients with pituitary adenomas have visual field defects, fewer than half report these visual changes subjectively. This underscores the importance of obligatory visual field testing in all patients with pituitary adenomas irrespective of whether they report visual impairment.

Treatment of pituitary tumors is individualized and is based on tumor type, size, anatomic location relative to surrounding critical structures (optic apparatus, carotid arteries, third ventricle) and the degree of visual and/or hormonal impairment. Surgical resection is first-line treatment for most tumors except prolactinomas, which typically respond well to medical management with a dopamine agonist. Today at most academic medical centers, the overwhelming majority of surgical resections are performed through an endoscopic transsphenoidal approach.

Meningioma

Meningiomas arising from the optic nerve sheath or in proximity to the optic chiasm in the suprasellar region may affect the optic apparatus. Optic nerve sheath meningiomas, which arise from cap cells of the arachnoid surrounding the optic nerve and spread through subarachnoid spaces, are the most common optic nerve sheath tumors and account for one-third of intrinsic optic nerve tumors. Involvement of the extraorbital portion of the optic nerve without (49%) or with involvement of optic chiasm (40%) is common. These tumors usually present with unilateral symptoms and are frequently seen in middle-aged women. Prognosis depends largely on the size and extent of the tumor and less so on histopathologic features.

Suprasellar meningiomas may arise from the tuberculum sellae (TS), diaphragma sellae (DS), or planum sphenoidale (PS). The majority (50%) arise from the TS ¹⁹ and are most commonly seen in women in their fifth decade. Identification of the anatomic subtype is important in selecting the type of surgical approach for resection, which is often challenging. The relative displacement of the optic apparatus, however, can help in distinguishing one subtype from another. For example, TS meningiomas lead to posterior or superoposterior displacement of the optic chiasm, whereas DS meningiomas lead to superior displacement, and PS meningiomas lead to posterior and inferior displacement. The nuances of surgical approach can then be based on these anatomic distinctions. Although TS meningiomas can be resected using a purely supradiaphragmatic approach, a combined supradiaphragmatic and infradiaphragmatic approach is necessary for DS meningiomas.

GTR of tumor (at least Simpson grade I/II) with improvement or stabilization of visual function are the goals of surgical treatment. Surgical treatment is also a viable option for radiation-resistant meningiomas.

Craniopharyngioma

Craniopharyngiomas are the most common suprasellar tumor found in children, accounting for 50% of masses in this region. These tumors arise from remnants of the Rathke pouch and demonstrate a bimodal age distribution, most commonly affecting children 5 to 14 years and adults 65 to 74 years.

Although a benign tumor, craniopharyngiomas are associated with significant mortality among all sellar and suprasellar tumors, with a standardized overall mortality rate ranging from 2.88% to 9.28%. In pediatric patients, symptoms of elevated intracranial pressure (ICP) are commonly seen, whereas in adults, visual disturbance and hypopituitarism are also noted. Hypothalamic involvement is frequently seen in pediatric patients. Gross total resection (GTR) of the tumor with maintenance of hypothalamic functionality should be the goal of treatment; however, in patients in whom maintaining hypothalamic functionality is challenging owing to unfavorable tumor localization, subtotal resection followed by adjuvant radiotherapy should be performed. Additionally, adjuvant radiotherapy improves local control and helps prevent permanent endocrine and neurocognitive sequelae, as well as injury to critical neurovascular structures in difficult tumors. If GTR is not possible, our preference is to preserve the pituitary stalk. In addition to visual dysfunction, long-term morbidity associated with craniopharyngiomas includes hypopituitarism, hypothalamic injury, detrimental cardiovascular effects, reduced bone health, neurologic deficits, lower cognitive function, and poorer quality of life.

Rare Pathologies Affecting Optic Apparatus

Other, less common lesions affecting the optic apparatus are listed in Table 36.1 .

Preoperative Planning

Preoperative assessment using magnetic resonance imaging and computed tomography is recommended. Anatomic ease of access (deviated nasal septum, concha bullosa, sphenoid sinus pneumatization, intrasphenoid and intersphenoid septae, and so on), tumor characteristics (consistency, extension, and so on), and surrounding critical structures (prefixed and postfixed chiasma, bony dehiscence, carotid artery position and encasement, location of the pituitary gland and its stalk, apoplexy, and so on) should be noted. Patient selection is of paramount importance for success of the procedure and hence should be done based on the surgeon’s expertise.