1084: Opioid-Induced Neurotoxicity in a Child: A Case Bridging Pounce and Chanter Syndromes

Introduction: Opioid-related neurotoxicity in children is rare but increasingly recognized, with potentially devastating consequences. POUNCE (Pediatric Opioid-Associated Unresponsive Cerebellar Edema) and CHANTER (Cerebellar Hippocampal and Basal Nuclei Toxicity in the Setting of Evolving Recreational Drug Use) are emerging syndromes characterized by distinct radiologic patterns linked to opioid toxicity. We describe a case in which image findings straddle both syndromes, underscoring evolving insights into pediatric opioid-induced encephalopathy. Description: A healthy 3-year-old girl presented with altered mental status; initial GCS was 4, and pupils were pinpointed. Vital signs were stable except for tachycardia. Naloxone administration had no effect. Laboratory evaluation revealed mixed acidosis, elevated lactate, and inflammatory markers. Head CT demonstrated diffuse cerebellar edema and tonsillar herniation, prompting emergent posterior fossa decompression and external ventricular drain placement. MRI showed restricted diffusion and increased T2/FLAIR signal throughout the cerebellar folia. Empiric antimicrobials, steroids, and IVIG were initiated, but later discontinued after broad infectious and autoimmune testing were unrevealing. Neurological status remained poor (GCS 5T), though brainstem reflexes were preserved. Initial urine drug screening that excluded synthetic opioids was negative, but expanded toxicology resulted on day 5 detecting Fentanyl. Multidisciplinary evaluation confirmed opioid-related cerebellar toxicity. Discussion: Due to unique neurodevelopmental receptor profiles, younger children are especially susceptible to central nervous system injury and cytotoxic edema. Imaging in this case revealed symmetric cerebellar swelling, bilateral hippocampal involvement, and scattered supratentorial white matter changes, with relative sparing of basal ganglia and thalami—placing it between classic POUNCE and the broader CHANTER spectrum. This highlights that opioid neurotoxicity in children may present along a continuum, blurring syndromic boundaries. Early neuroimaging and comprehensive toxicology are critical. In fulminant cases, urgent decompressive surgery can be lifesaving. Clinicians should consider opioid related toxicity in children with unexplained cerebellar findings.