Shunt overdrainage represents a nebulous condition of variable clinical and imaging presentations, where the diagnosis is primarily clinical. The condition presents a diagnostic challenge particularly in patients with cognitive impairment and developmental delays. Here we present a 3-year-old boy with drug-resistant focal onset seizures due to hemimegalencephaly who previously underwent functional hemispherotomy followed by ventriculoperitoneal shunt placement for postoperative hydrocephalus. The subsequent clinical course was complicated by delayed diagnosis of shunt overdrainage in the absence of significant image findings. Maintaining a high index of suspicion for the possibility of shunt overdrainage is critical even in the face of unremarkable imaging findings.