A case of calvarial eosinophilic granuloma with rapid expansion and wide skull invasion: Immunohistochemical analysis of Ki-67

A 15-year-old male visited our neurological service with progressive occipitalgia. Computed tomography showed an osteolytic lesion at the occipital cranium, which grew rapidly during a month. Magnetic resonance imaging showed the lesion as low intensity on T1- and high intensity on T2-weighted images. The mass was soft and successfully removed with surrounding cranium. Histological examination revealed an eosinophilic granuloma with wide skull invasion. Immunohistochemical analysis on the specimen disclosed Ki-67 expression with labeling index of 6.2%. Relatively high proliferative activity in the present case indicates that the local replication of Langerhans' cells as well as inflammatory response contributes to the expansion of calvarial eosinophilic granuloma. This is the first report demonstrating the result of Ki-67 expression on calvarial eosinophilic granuloma.