A Colloid Cyst Masquerading As Idiopathic Intracranial Hypertension in a Young Woman: A Diagnostic Pitfall

Colloid cysts of the third ventricle are rare, benign intracranial lesions that can produce a broad spectrum of symptoms that depend on both the degree and rate of cerebrospinal fluid (CSF) obstruction. When the presentation is insidious, these lesions may at first mimic idiopathic intracranial hypertension (IIH), particularly in young women who may first develop headaches and papilledema without any focal neurological deficits on exam. We describe the case of a 24-year-old woman with several months of non-positional headaches accompanied by intermittent nausea, photophobia, and brief episodes of visual obscuration. Initially, she was evaluated by an optometrist, who identified bilateral papilledema and further recommended Diamox (acetazolamide) and brain imaging. Upon presentation to the emergency department, her neurological examination was normal, but the bedside ocular ultrasound (US) demonstrated optic nerve sheath enlargement and optic disc elevation that is consistent with papilledema. The non-contrast computed tomography (CT) of the head then revealed a 1.3 x 1.4 x 1.8 cm hyperdense lesion at the foramen of Monro, causing obstructive hydrocephalus, consistent with a colloid cyst. As such, the patient was admitted to the neuro-intensive care unit for monitoring and underwent endoscopic resection of the cyst. Her postoperative recovery was relatively uncomplicated. Furthermore, her headaches and visual symptoms were resolved completely. This case illustrates how a slowly progressive colloid cyst can masquerade as IIH and highlights the importance of obtaining neuroimaging prior to lumbar puncture in any patient presenting with papilledema. Maintaining a broad differential that recognizes secondary causes of elevated intracranial pressure early is essential to prevent vision loss and ensure timely neurosurgical management.