Fulminant idiopathic intracranial hypertension mimicking Chiari I malformation in a pediatric patient: diagnostic value of MRI and promising outcomes with venous sinus stenting.

Idiopathic intracranial hypertension (IIH) is a rare but potentially serious condition in children, with the risk of permanent vision loss in rapidly progressing or treatment-resistant cases. One diagnostic challenge is that cerebellar tonsillar descent-a feature sometimes seen in IIH-can mimic Chiari I malformation, potentially leading to misdiagnosis and unnecessary, risky surgery. We report the case of a 13-year-old boy with fulminant idiopathic intracranial hypertension (IIH), who presented with rapidly worsening visual symptoms and severe papilledema over the course of a few days. Initial brain MRI excluded other causes of increased intracranial pressure, raising suspicion for IIH. The imaging also revealed cerebellar tonsillar descent, initially suggesting a possible Chiari I malformation. However, additional MRI findings were more consistent with IIH than Chiari I, including an arachnoidocele of the sella, flattening of the posterior sclera, and bilateral transverse sinus stenosis. A cerebral venography confirmed significant venous outflow obstruction, with a high-pressure gradient across the stenotic transverse sinuses. Based on these findings, venous sinus stenting was performed as a first-line treatment. This resulted in rapid symptom improvement, with complete resolution of headache and papilledema on follow-up. MRI plays a critical role in diagnosis-not only in excluding other conditions but also in positively identifying IIH, especially in atypical and fulminant presentations. When medical treatment fails, surgical options include CSF shunting or increasingly, venous sinus stenting, particularly when venous sinus stenosis is present. Though commonly used in adults, this approach is showing promise in pediatric patients as well, despite some specific challenges. Early diagnosis, appropriate imaging, and a multidisciplinary approach are essential to prevent vision loss and ensure the best possible outcomes in these complex pediatric cases.