Cancers metastatic to the skull or dura may cause subdural hematoma (SDH). However, the frequency is low, and the presence of underlying cancers has almost always been known in such situations. We report a case of skull angiosarcoma manifesting as SDH, posing a diagnostic challenge to physicians. A 75-year-old man visited our clinic with sensorimotor disturbance of gradual onset approximately 1 month after a minor head trauma. He was diagnosed with SDH after imaging studies, and underwent surgery to evacuate the hematoma. Because the hematoma was organized, surgery was switched from burr-hole drainage to craniotomy. The bone flap as well as the dura over the hematoma had grossly normal appearance, and only the hematoma itself was submitted for histological examination. Although postoperative recovery was uneventful, the patient experienced recurrence of the SDH 2 months after surgery. At the second surgery, the bone flap and dura were intermingled with tumor tissue, and histological examination revealed that an epithelioid angiosarcoma originating from the skull was responsible for the SDH. Timely diagnosis of angiosarcoma manifesting as SDH is difficult because of its rarity. In retrospect, however, the diagnosis might have been established earlier if the bone flap and/or the dura had been biopsied at the time of the first surgery. The present case gives us a lesson that SDH may be an unusual manifestation of malignant tumors of skull or dural origin, and histological examination of not only hematoma capsule but also of the surrounding tissues may provide important diagnostic clues.
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