• Tomoki Kaneko, Yasunari Fujinaga, Fumihito Ichinohe, Toshihiro Ogiwara, and Tetsuyoshi Horiuchi.
• Department of Radiology, Shinshu University School of Medicine, Matsumoto, Japan. Electronic address: tk55@shinshu-u.ac.jp.
• World Neurosurg. 2020 Dec 1; 144: 238-243.

BackgroundGenerally, asymptomatic epidermoid cysts (ECs) or ECs with minor symptoms controlled by medication are not treated further. Although epidermoid carcinomas are only sporadically reported, the possibility of malignant transformation of ECs is of concern.Case DescriptionA 77-year-old man under observation for a left cerebellopontine angle tumor presented with no symptoms, including headache, dizziness, or other cranial nerve abnormalities typical of cerebellopontine angle tumors. The tumor manifested as an extra-axial mass in the left cerebellopontine angle and measured 24 × 16 mm (length × width) on magnetic resonance imaging (MRI). As he was asymptomatic, his primary physician did not pursue invasive treatment but ordered follow-up MRI every 2 years. The tumor decreased in size 2 years after the initial MRI, and no tumor fragmentation was observed on the patient's spinal MRI. Ultimately, the tumor shrank to 19 × 11 mm over 22 years.ConclusionsThe reduction of an EC is extremely rare. We report a case of spontaneous regression of an EC and consider similar previous cases.Copyright © 2020 Elsevier Inc. All rights reserved.

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