To develop a list of possible causes of hemianopsia, trace the fibers of the optic nerve through the optic chiasma, optic tract, optic radiation, and optic cortex and apply a mnemonic such as VINDICATE to prompt the recall of the conditions affecting each level.
· Optic chiasma. Vascular— aneurysm; inflammatory— syphilis, arachnoiditis; neoplasm— pituitary adenoma, suprasellar cysts, meningiomas; congenital— hydrocephalus; autoimmune— multiple sclerosis; trauma— gunshot wound; endocrine— pituitary tumors, pseudotumor cerebri.
· Optic tract. Aneurysm, arachnoiditis, brainstem tumors, gunshot wounds, and multiple sclerosis.
· Optic radiations. Hemorrhage or infarct of the internal capsule (as occurs in the thalamic syndrome), parietal and temporal lobe tumors, lupus erythematosus, and multiple sclerosis.
· Optic cortex. Posterior cerebral artery embolism or thrombosis, occipital lobe tumors, abscess, or hematoma.
Approach to the Diagnosis
A careful outline of the field defect by a tangent screen or perimetry is essential. An ophthalmologist should be consulted to do this. A bitemporal hemianopsia suggests a pituitary tumor warranting a CT scan or MRI. The finding of hair loss, weight loss, and/or loss of secondary sexual characteristics points to a pituitary tumor as the cause. It is wise to order a 24-hour urine gonadotropins and other tests of pituitary function.
Long tract signs suggest a vascular, neoplastic, or demyelinating lesion in the brainstem or cerebral cortex. A neurologist should be consulted before ordering expensive diagnostic tests.
Other Useful Tests
1. VDRL (syphilis)
2. Visual evoked potentials (VEPs) (multiple sclerosis)
3. Spinal tap (syphilis, multiple sclerosis, pseudotumor cerebri)
4. ANA (collagen disease)
5. Four-vessel cerebral angiography (posterior cerebral artery thrombosis).