We report a case of epidermoid cyst arising in the floor of the mouth, which developed gradually over the course of 7 years and caused delirium, dyspnea, oral disorder, dysphagia, and insomnia. A 63-year-old woman had noticed swelling in the submental region 7 years ago, but did not seek treatment. She visited the Department of Neurosurgery of our hospital with her family because of unstable behavior. Computed tomographic examination showed no evidence of neurosurgical disease, and she was referred to our department because of an enlarged tongue. At presentation, a large, elastic soft tumor mass was found in the floor of the mouth. The covering mucosa was normal, but the tongue was pushed posterosuperiorly and could not be observed directly.
A elastic soft tumor mass covered by normal skin was noted in the submental region. Magnetic resonance imaging showed a poorly demarcated, cyst-like structure from the subglossal space to the submental region. T2-weighted imaging revealed a 115 × 75 × 55 mm cystic lesion containing homogenous high signal intensity. A diagnostic puncture was carried out, and 200 mL of brownish-yellow muddy fluid was collected. Thereafter, the volume of the cyst decreased, and dyspnea was alleviated. The clinical diagnosis was an epidermoid cyst. The cyst was intraorally resected with the patient under general anesthesia. The pathological diagnosis was an epidermoid cyst. At present, functional impairment has improved, and the patient is under observation.