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J Neurosurg Case Lessons | Vol 11 | Issue 22 | June 1, 2026 | 1JOURNAL OF NEUROSURGERY:Case Lessons© 2026 The authors, CC BY-NC-ND 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)ABBREVIATIONS EVD = external ventricular drain; ICP = intracranial pressure; LP = lumbar puncture; VP = ventriculoperitoneal.INCLUDE WHEN CITING Published June 1, 2026; DOI: 10.3171/ CASE2654.SUBMITTED January 18, 2026. ACCEPTED April 10, 2026. Lumbar puncture–induced negative-pressure hydrocephalus in a child with a ventriculoperitoneal shunt and ventricular obstruction: illustrative caseBryn L. Hoffman, MD, 1 Arjun Suresh Chandran, MD, 3 Suzanne Laughlin, MD, 2 and George M. Ibrahim, MD, PhD 31 Division of Neurosurgery, University of Toronto, Ontario; 2 Department of Radiology, The Hospital for Sick Children, Toronto, Ontario; and 3 Division of Neurosurgery, The Hospital for Sick Children, Toronto, Ontario, CanadaBACKGROUND Negative-pressure hydrocephalus is a rare form of symptomatic ventriculomegaly characterized by subatmospheric intracranial pressure (ICP). It can occur following lumbar puncture (LP) in patients with impaired CSF dynamics and is frequently mistaken for ventriculoperitoneal (VP) shunt malfunction.OBSERVATIONS The authors describe the case of a 9-year-old boy with prior medulloblastoma and a VP shunt who presented with neurological decline following LP. Symptoms transiently improved following a large-volume shunt tap, but ventriculomegaly persisted despite shunt revision. ICP monitoring conf i rmed negative pressure, consistent with post-LP negative-pressure hydrocephalus. Management with an epidural blood patch, neck wrapping, and shunt valve adjustment resulted in clinical and radiographic improvement, notably without the need for prolonged subatmospheric external ventricular drainage.LESSONS Negative-pressure hydrocephalus should be suspected in patients with a shunt who present with ventriculomegaly, a plausible CSF leak, low-pressure CSF, and poor response to shunt revision. The presence of fourth ventricular obstruction should further heighten suspicion. Effective management involves recognizing altered CSF pressure gradients that mimic high-pressure hydrocephalus, considering epidural blood patch placement to repair CSF leakage, using neck wrapping to augment venous pressure and raise intraventricular pressure to the valve’s opening threshold, and avoiding unnecessary shunt revisions or repeat LPs in susceptible patients.https://thejns.org/doi/abs/10.3171/CASE2654KEYWORDS negative-pressure hydrocephalus; lumbar puncture; medulloblastoma; ventriculoperitoneal shunt; pediatric neurosurgeryNegative-pressure hydrocephalus, a severe form of low-pressure hydrocephalus, represents a rare but clinically important syndrome characterized by ventriculomegaly with paradoxically low or negative intracranial pressure (ICP). First characterized by Pang and Altschuler in 1994, 1 the condition has since been described in both children and adults, often in the context of prior shunt placement, posterior fossa tumors, cranial base surgery, or craniospinal irradiation. 2–5 Negative-pressure hydrocephalus poses a diagnostic challenge, as the radio-graphic appearance of enlarged ventricles is often attributed to shunt malfunction, leading to repeated and often unsuccessful revisions. Lumbar puncture (LP) or lumbar drain insertion has been identif i ed as a precipitating factor in patients with a shunt, particularly those with posterior fossa pathology, where altered viscoelastic properties of the brain and impaired CSF compliance create vulnerability to abrupt pressure shifts. 3,6–8 Here, we present the case of a 9-year-old boy with treated medulloblastoma who developed post-LP negative-pressure hydrocephalus.Illustrative CaseThis is the case of a 9-year-old boy with a history of WHO grade 4 medulloblastoma who underwent posterior fossa craniotomy for tumor resection followed by ventriculoperitoneal (VP) shunt placement. His initial postoperative course was complicated by shunt infection requir-ing shunt externalization, 6 weeks of intravenous antibiotics, and even-tual reinsertion of a medium-pressure shunt valve. He subsequently underwent craniospinal irradiation followed by 9 cycles of multiagent chemotherapy.He presented to care at our institution 4 years following the initial resection and underwent LP for disease monitoring. Three days later, he presented to the emergency department with severe headache, vomiting, and somnolence. CT of the head demonstrated marked ventriculomegaly (Fig. 1). Shunt tap yielded 20 mL of low-pressure CSF with transient clinical improvement. He was taken to the operating room for shunt exploration. CSF fl ow from the burr hole reservoir was J Neurosurg Case Lessons 11(22): CASE2654, 2026DOI: 10.3171/CASE2654Unauthenticated | Downloaded 07/07/26 01:15 AM UTC