To describe a rare case of optic chiasm involvement of posterior reversible encephalopathy syndrome (PRES).

PRES is a cerebral syndrome characterized by cerebrovascular dysregulation and endothelial dysfunction. It is associated with severe hypertension, renal failure, and use of toxic drugs or agents, including chemotherapeutic and immune-modifying drugs. It can present with coma, seizures, headache, vision abnormalities, and other focal neurologic deficits. PRES is typically characterized by bilateral, occipital, and white matter lesions on neuroimaging although unilateral, gray matter, and other patterns have been reported.

A 43 year-old female patient with a past medical history of acute myeloid leukemia who was admitted for allogeneic stem cell transplant was noted to develop a seizure while speaking to family members. 24-hour vital signs demonstrated a BP range of 136-175 systolic and 75-122 diastolic. A STAT Brain CT demonstrated hypodensities in bilateral occipital lobes and Brain MRI subsequently demonstrated T2 hyperintensities in bilateral occipital lobes and the optic chiasm, suggestive of a diagnosis of PRES. She was subsequently started on Keppra for seizure prevention. She was also on immunosuppressive therapy with cyclosporine which was discontinued.  Three months later she reported that she had an inability to see and repeat Brain MRI at that time demonstrated persistent T2 hyperintensities in the optic chiasm, although no evidence of chiasmopathy was noted on her ophthalmological exam. Serum AQP-4 antibody was negative, excluding an optic chiasm involvement due to neuromyelitis optica.

Although PRES is typically characterized by parieto-occipital involvement on neuroimaging, this case illustrates an atypical case with optic chiasm involvement. To the best of our knowledge, this is the third case of PRES with optic chiasm involvement and sixth with optic pathway involvement reported. Clinicians should be able to recognize PRES with optic pathway involvement to ensure prompt diagnosis and management.