Disorders• 4 SECTIONVision Retrochiasmal

Homonymous Hemianopia

Key Facts

•Temporal field defect in one eye and nasal field defect in the other eye, with defect borders aligned to vertical meridian

•Lesion usually lies in visual cortex but could be in optic tract or optic radiations

•Common causes:

•infarction • closed head injury • lobar hemorrhage • tumor • reversible posterior leukoencephalopathy syndrome (RPLS)

•If defects are large, patients are not permitted to drive a passenger car in most locales

•No solid evidence that visual training or optical devices afford benefit

Clinical Findings

•Vision loss in one or both hemifields, difficulty reading, sometimes with visual hallucinations and perceptual distortions

•Visual field defects may be

• unilateral or bilateral • complete or incomplete • quadrantic • paracentral

• sparing the central 10º (macular sparing) • crescentic (limited to unpaired temporal crescent beyond 30º of fixation) • sparing the temporal crescent (temporal crescent sparing)

•Visual acuity is spared unless defects are bilateral and involve the paracentral region on both sides

•Pupil reactions and optic discs are normal

Ancillary Testing

•Acute infarcts: CT may be normal within first 48 h, but MRI diffusion-weighted studies are always abnormal from the outset, showing areas of restricted diffusion in occipital lobe (cytotoxic edema)

•Tumors or hemorrhages: CT and MRI always show abnormalities from outset

•RPLS: MRI shows high signal on FLAIR and T2 MRI in posterior cerebral white matter but no restricted diffusion (vasogenic edema)

Differential Diagnosis

•Common causes:

•ischemic stroke • occipital hemorrhage • RPLS • occipital tumor

•Uncommon causes:

•adrenoleukodystrophy • mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) • acute disseminated encephalomyelitis • multiple sclerosis • toxic leukoencephalopathy (methanol, cyclosporine, intrathecal methotrexate, brain irradiation) • progressive multifocal leukoencephalopathy • Alzheimer disease • Creutzfeldt–Jakob disease

• sagittal sinus thrombosis • hypoxic encephalopathy • head trauma

•Do not forget psychogenic visual loss

Treatment

• No solid evidence that visual training or optical devices afford benefit

Prognosis

•Patients compensate with adaptive eye movements, but if defects are large they are not permitted to drive a passenger car in most locales

Fig. 4.1 Automated (Humphrey perimeter) visual fields show a dense right homonymous hemianopia.

Fig. 4.2 Homonymous hemianopia caused by left optic radiations and visual cortex infarction. Axial FLAIR MRI shows a left occipital lobe signal abnormality in the distribution of the left posterior cerebral artery (arrow), consistent with infarction.

Hemianopia Homonymous

A B C

Fig. 4.3 Consecutive bilateral posterior cerebral infarctions. (A) Axial FLAIR MRI shows high signal in the distribution of the right calcarine artery (arrow) and very low signal in the distribution of the left parieto-occipital artery. (B) Diffusionweighted MRI shows high signal in the right occipital region. (C) Apparent diffusion MRI shows a low signal in that region, confirming that the right occipital infarction is recent. The left parieto-occipital infarction is old and has caused destruction of tissue (encephalomalacia).

Fig. 4.4 Progressive multifocal leukoencephalopathy causing cerebral blindness. Axial FLAIR MRI shows ex vacuo dilatation of occipital horns and high signal in the remaining occipital white matter.

Blindness Cortical) (Retrogeniculate, Cerebral

A B C

Fig. 4.5 Reversible posterior leukoencephalopathy syndrome in a patient with hypertension of pregnancy and subacute bilateral blindness. (A) Axial FLAIR MRI performed at time of blindness shows high signal in the occipital and temporal lobes. (B) Diffusion-weighted MRI shows no restricted diffusion, indicating that the high FLAIR signal represents vasogenic edema rather than cytotoxic edema of recent stroke. (C) Axial FLAIR MRI performed 2 weeks after induced delivery of the baby, correction of hypertension, and gradual full recovery of vision. It shows no abnormalities.

Fig. 4.6 Hypoxic–ischemic encephalopathy in a 10 monthold victim of strangulation. Axial CT performed 1 month after the event shows signs of infarction, especially in occipital lobes. Dark areas (arrowheads) represent ischemic edema and bright strips (arrows) represent laminar dystrophic calcification.

(continued) Blindness Cortical) (Retrogeniculate, Cerebral