Pituitary adenomas frequently manifest with neuro-ophthalmic symptoms and signs. The location of the pituitary gland makes involvement of both the visual pathways and the ocular motor cranial nerves likely when there is adenomatous expansion. A sudden expression of visual loss or diplopia commonly accompanies pituitary apoplexy. Several preoperative neuro-ophthalmic indicators help predict posttreatment outcomes and help determine the best intervention. Treatments themselves may also cause neuro-ophthalmic complications. The current literature and avenues of future research are reviewed.
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Patients with pituitary adenomas extending above the diaphragm sella should be assessed for visual acuity abnormalities, visual field defects, and ocular motility disturbances.
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Pituitary apoplexy must be considered in the setting of acute vision loss or ocular motor disturbance, especially if associated with headache, even if there is no previously known pituitary tumor or precipitating factor.
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Studies differ regarding the prognostic factors for visual recovery after apoplexy, but early diagnosis and treatment within 1 week will minimize visual morbidity.
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Not all studies are in agreement as to which factors predict a better visual outcome postoperatively; however, the presence of optic disk pallor with associated loss of the retinal nerve fiber layer (as measured by optical coherence tomography) indicates long-standing damage to the optic pathways, which is less likely to recover.
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The overall rate of visual field improvement with transsphenoidal excision of pituitary adenomas is 80%.
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After pituitary surgery, there may be immediate visual improvement secondary to decompression, then early recovery from restoration of axoplasmic flow, and less dramatic delayed recovery over 1 to 4 months because of remyelination and remodeling.
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Neuro-ophthalmic follow-up is required to monitor for recurrence and for complications of therapy, including chiasmal prolapse and radiation optic neuropathy.
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Patients with poor postoperative visual outcome or diplopia should be referred to appropriate low-vision and ophthalmic services for driving assessment and management.
Neuro-ophthalmic anatomy of the pituitary region
In 1704, in an attempt to explain the phenomenon of perceived singularity of vision derived from the two eyes, it was hypothesized that the optic chiasm was derived from a merger of both optic nerves with partial cross-over of nerve fibers. Today, an understanding of the visual pathways and the normal variants, from optic nerve to the chiasm and optic tracts, is fundamental in understanding the neuro-ophthalmic manifestations of pituitary tumors.
Afferent Visual Pathways
Optic nerves
The optic canal, located superomedially in the sphenoid bone, transmits the optic nerve from the orbit to the intracranial space. The optic canals are separated from the sphenoid sinus by a bony wall, which is only 0.5 mm thick or less in some patients. Therefore, injury to the lateral wall of the sphenoid sinus, such as during forced opening of a transsphenoidal speculum, can result in vision loss ( Fig. 1 ).
The falciform process, a reflected leaf of dura mater, covers the optic nerves as they emerge from the optic canals. The length of nerve covered only by dura can vary from 1 mm to 15 mm. Therefore, during any surgical approach, it should not be assumed that bone separates the dura from the proximal portion of the optic nerve.
When there is extensive anterior growth of the pituitary tumor or if the chiasm is postfixed, optic nerve involvement occurs. The junctional scotoma is classically seen when a lesion compresses the junction of the posterior optic nerve and chiasm, where the crossed ventral fibers loop anteriorly (Wilbrand knee). The resultant visual field defect is one of a hemianopic or central scotoma in the ipsilateral eye and a superior temporal defect in the contralateral eye ( Fig. 2 ). Damage to the anastomotic blood supply to the posterior portion of the nerve can also occur.
Chiasm
The chiasm is usually situated over the diaphragm sella, at the junction of the anterior wall and floor of the third ventricle. The chiasm may, however, be prefixed and overlie the tuberculum sella or postfixed and overlie the dorsum sella ( Fig. 3 ). A review of 225 autopsy cases found a normal chiasm in 80%, a prefixed chiasm in 9%, and a postfixed chiasm in 11%. These relationships have a direct bearing on the visual field defect resulting from an enlarging pituitary mass.
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