Bilateral intradiploic dermoid cysts with unilateral rupture causing hearing loss: illustrative case.

backgroundDermoid cysts are congenital lesions that typically occur along the midline. They usually remain asymptomatic unless ruptured, causing meningitis, hydrocephalus, or cranial nerve deficits. This case presents an exceptionally rare scenario of bilateral, symmetric intradiploic dermoid cysts of the occipital bone, which initially manifested as sensorineural hearing loss (an unusual symptom). OBSERVATIONS: A 21-year-old woman presented with right-sided hearing loss. Imaging showed bilateral, symmetric intradiploic cystic lesions within the occipital bone. The right-sided lesion had ruptured into the posterior fossa, releasing lipid-rich contents over the cerebellum. A T1-hyperintense signal along the right vestibular aqueduct suggested the migration of debris into the inner ear. Both lesions were resected with maximal safe resection, targeting the ruptured component and preventing future complications. Histopathological analysis confirmed that both lesions were dermoid cysts. LESSONS: Although typically associated with chemical meningitis, dermoid cyst rupture may rarely present solely with sensorineural hearing loss when fatty debris migrates into the vestibular aqueduct. Bilateral, symmetric intradiploic occipital lesions are rare and may reflect developmental anomalies at paired ossification centers. Surgical removal of the antigenic source, even without acute complications, may prevent delayed sequelae. A tailored resection approach that preserves vital structures, including the transverse sinus, is safe and effective. https://thejns.org/doi/10.3171/CASE2691.