When imaging fails: surgical discovery of an occult ovarian teratoma in severe refractory anti-NMDA receptor encephalitis

Anti-N-methyl-D-aspartate (NMDA) encephalitis is marked by rapidly evolving and severe neuropsychiatric symptoms that can affect any age. This case illustrates a woman in her early 40s who was admitted with refractory headache, hallucinations and progressive encephalopathy. After imaging failed to detect a neoplasm, a left salpingo-oophorectomy was performed due to high clinical suspicion, which revealed a mature teratoma. Surgery and immunotherapy led to gradual recovery in physical function and improvement in consciousness. This case highlights the importance of aggressive multimodal therapy, thorough tumour evaluation and consideration of surgical exploration in imaging-negative, refractory anti-NMDA receptor encephalitis.