Repeated Short-Term Recurrence of Chronic Subdural Hematoma Associated with Metastasis to Hematoma Capsule Originating from Extracranial Malignant Tumor.

Background: The recurrence rate of chronic subdural hematoma (CSDH) after trepanation is relatively high and involves various factors. We encountered an extremely rare case in which metastasis of an extracranial malignant tumor to the hematoma capsule was thought to be causing short-term repeated recurrences of CSDH.
Case Description: The patient was a 74-year-old man who had undergone bur hole evacuation of left CSDH 7 months earlier and had been receiving chemotherapy for stage IV gastric cancer for the preceding 6 months. He presented with symptoms of right hemiparesis and was diagnosed with left CSDH. Bur hole evacuation was performed twice, but the hematoma enlarged again both times within a short period. A third bur hole evacuation was performed after middle meningeal artery embolization, but the hematoma again enlarged shortly thereafter. Hematoma enlargement was finally suppressed by extracting the hematoma capsule under craniotomy. In histopathologic examinations, hematoxylin-eosin staining showed poorly differentiated adenocarcinoma primarily along the luminal side of the hematoma capsule and immunohistochemical staining showed results identical to findings from the existing gastric cancer. Pathologic results confirmed metastasis of the gastric cancer to the hematoma capsule, and this was considered to be the cause of short-term repeated recurrence of CSDH.
Conclusions: To the best of our knowledge, this is the first report of metastasis to a hematoma capsule originating from an extracranial malignant tumor. The clinical course in the present case suggests metastasis of extracranial malignant tumor to the CSDH capsule as an extremely rare cause of recurrence.
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