Incorrect

Incorrect

Correct! Although this seems a relatively evasive answer, it is correct. You are looking at a complete homonymous hemianopia identified on confrontation and formal visual field testing. When a homonymous hemianopia is COMPLETE, you can localize it to the retrochiasmal visual pathway, but not to a specific region within that pathway! As the MRI is certifiably normal, you will wonder if the defect is of psychogenic origin. That presumption is difficult to disprove clinically. Some clinicians have developed maneuvers, such as having patients rapidly switch fixation back and forth between single targets displayed in opposite hemifields, but I have had a hard time convincing myself that I can exclude psychogenic “homonymous hemianopia.” Be careful here, as there are several retrochiasmal lesions that are either invisible on MRI or so subtle that they may be overlooked. Among those lesions are: 1) Recent hypoxic-ischemic injury owing to sudden systemic hypotension (MRI visual cortex volume loss may develop months later); 2) Creutzfeldt-Jakob disease, a prion protein disorder that may show subtle relevant MRI abnormalities only months later (positron emission tomography would earlier show a metabolically low visual cortex region); 3) focal encephalitis, also called “cerebritis” (small areas of high T2/FLAIR or cortical enhancement may be overlooked or dismissed); 4) Alzheimer disease with predominant volume loss in posterior cerebral hemisphere (relatively more MRI volume loss on the side opposite to the hemianopia may be overlooked); 5) focal metabolic encephalopathy in nonketotic hyperglycemia or mitochondrial cytopathy (which can be evanescent); and 6) optic tract lesion (because it is a narrow structure wedged between midbrain and temporal lobe, lesions here are often overlooked). This patient had signal abnormalities in the right optic tract

and in the cervical spinal cord consistent with multiple sclerosis.