[Case of enlargement of an intradiploic epidermoid cyst by a head contusion].

We report a case of enlargement of a intradiploic epidermoid cyst following head trauma in a 19-year-old man. The patient had a swelling on the right side of his forehead from the time of his birth. He sustained a bruise in this region when he was 15 years old, following which the swelling gradually enlarged. When the diameter of the mass increased to 5 cm, he visited our hospital. Computed tomography (CT) scan of the head showed a subcutaneous mass of low density extending from the diploe to the outer tables of the skull. Magnetic resonance imaging (MRI) showed a hyperintense mass in both T1- and T2-weighted images. During the operation, we found a tumor that was intradiploic and had a thin capsule. The effusion from the tumor resembled an old hematoma, and the tumor did not involve the paranasal sinuses. We concluded the operation by performing cranioplasty using artificial bone. Histological examination revealed that the thin capsule consisted of stratified squamous epithelium and ciliated epithelium. Needle-like cholesterol crystals and hemosiderosis were seen shown in the granulation-like tissue. On the basis of these findings, we diagnosed the mass to bean intradiploic epidermoid cyst and thought that it might have grown following head trauma associated with chronic hemorrhage. This paper reviews the differential diagnosis and pathologic findings of the intradiploic epidermoid cyst along with some previously published cases.