Unilateral Hearing Loss as the Sole Presentation of Extensive Intracranial Epidermoid Cyst: A Case Report.

Epidermoid cysts are rare congenital tumors of the central nervous system. These histologically benign, slow-growing lesions form when ectodermal cells become trapped during the closure of the neural tube. Histologically, they consist of a core composed of keratin, desquamated epithelial cells, and cholesterol, surrounded by a layer of stratified squamous epithelium. Clinical features depend on the lesion's location. In the cerebellopontine angle (CPA), they typically present with tinnitus, vertigo, hearing loss, and facial weakness, with or without cerebellar signs and symptoms. Unilateral hearing loss as the sole presenting symptom is uncommon in the setting of a large, extensive cyst and may delay diagnosis. A 35-year-old male presented with progressive left-sided hearing loss for one year, without vertigo, tinnitus, or other neurological symptoms. Audiological testing revealed severe-to-profound sensorineural hearing loss in the left ear. Temporal bone computed tomography and brain magnetic resonance imaging showed a large, extra-axial cystic lesion in the left CPA with characteristic diffusion-weighted imaging restriction, consistent with an epidermoid cyst. The lesion caused significant mass effect, including compression of the brainstem, cranial nerves, basilar artery, left vertebral artery, and left posterior cerebral artery. The patient underwent successful surgical excision via a retrosigmoid suboccipital craniotomy. Histopathological examination confirmed the diagnosis of an epidermoid cyst. This case report highlights an unusual presentation of an extensive epidermoid cyst in the left CPA that manifested solely as unilateral hearing loss, underscoring the diagnostic challenges posed by this rare lesion. The findings emphasize the importance of considering atypical presentations of intracranial tumors in the differential diagnosis of patients with unexplained hearing loss.