Fulminant Idiopathic Intracranial Hypertension Presenting With Bitemporal Hemianopia Mimicking Chiasmal Pathology in Early Pregnancy: A Case Report.

Idiopathic intracranial hypertension (IIH) is characterized by elevated intracranial pressure without an identifiable cause and typically presents with headache, papilledema, and transient visual obscurations (TVOs). Fulminant IIH is a rare, rapidly progressive subtype that can lead to permanent visual loss. Although visual field defects are common in IIH, bitemporal hemianopia is an uncommon and diagnostically challenging presentation that may initially suggest chiasmal compression. A 29-year-old woman with no significant medical history presented with two weeks of progressive peripheral visual loss, headache, dizziness, and gait imbalance. Examination revealed bitemporal hemianopia and severe papilledema. She was subsequently found to be in the very early stages of pregnancy. Urgent neuroimaging revealed radiological signs of increased intracranial pressure, without evidence of a chiasmal or sellar mass. Lumbar puncture confirmed markedly elevated opening pressure (>40 cmH₂O) with normal cerebrospinal fluid (CSF) composition. She underwent serial CSF drainage, received acetazolamide, and subsequently required ventriculoperitoneal shunt insertion, resulting in significant improvement in visual and gait symptoms. This case demonstrates an atypical presentation of fulminant IIH, where bitemporal hemianopia, which is typically associated with chiasmal lesions, occurred secondary to severe papilledema rather than structural compression. Although rare in IIH, such visual field patterns necessitate prompt differentiation from chiasmal pathology. Rapid diagnosis and early intervention are crucial for preventing irreversible visual loss in fulminant IIH. The patient's pregnancy raises the possibility that it may have precipitated the development of fulminant IIH.