Pediatric Opioid‑Use‑Associated Neurotoxicity with Cerebellar Edema: A Case of POUNCE Syndrome Following Vein of Galen Aneurysm Treatment.

We report the case of a 4‑year‑old child who experienced rapid neurological decline following opioid administration during anesthesia for an interventional procedure to treat a vein of Galen aneurysm. Cerebral magnetic resonance imaging (MRI) revealed marked cytotoxic edema in both cerebellar hemispheres and the brainstem, indicative of opioid‑induced neurotoxicity. A follow‑up MRI, performed 2 weeks later, showed profound cerebellar and brainstem atrophy and showed reduction in mass effect due to cytotoxic edema. Pediatric opioid‑use‑associated neurotoxicity with cerebellar edema (POUNCE) syndrome is a rare condition, characterized by cerebellar edema as a hallmark feature, which can be identified on MRI in pediatric patients following opioid use.