Weight loss and a shunt on "off": an odd case of overshunting in an idiopathic intracranial hypertension patient. Illustrative case.

backgroundCSF diversion with ventriculoperitoneal (VP) shunts is a common treatment for idiopathic intracranial hypertension (IIH). Rarely, overshunting can occur. Diagnosing and managing overshunting in an IIH patient with a shunt can be challenging. The authors present a unique etiology of overshunting successfully treated with shunt ligation. OBSERVATIONS: A 48-year-old female with IIH who had undergone VP shunt placement with a programmable Certas valve presented with symptoms concerning for low-pressure headaches following a 25-kg weight loss. Intracranial pressure (ICP) monitoring along with an inpatient headache diary facilitated the diagnosis of intracranial hypotension secondary to CSF overdrainage through the shunt. Following shunt ligation, the patient experienced significant and durable symptom improvement. LESSONS: In the setting of low-pressure headaches in an IIH patient with a functioning shunt, reductions in intra-abdominal pressure from weight loss can increase anterograde flow through the shunt. Additionally, the Certas programmable valve at its highest setting remains patent, but with a high opening pressure, potentially allowing for overdrainage due to the siphoning effect. Finally, ICP monitoring and headache diaries can significantly aid in the characterization of low-pressure headaches, and shunt ligation can be a curative solution. https://thejns.org/doi/10.3171/CASE25106.