Pathology report:

Gross description: The received specimen is composed of hemorrhagic soft tissue fragments and bone measuring up to ~ 1×1 cm in the aggregates.

Histologic study: The tumor is highly vascularized and shows atypical spindle cell proliferation with irregular vascular formation involving soft tissue and bone. The tumor shows reactive lymphocytic infiltrate with areas of hypercellularity, mitotic activity and focal necrosis 

IHC study:

• CD31 marker is positive for the tumor cells which determine the endothelial cell origin
• KI67 marker is generally ~20% with few hot spots with high mitotic activity up to 80%

Conclusion: Scalp, mastoid and soft tissue mass extending the posterior fossa; resection. Low to intermediate-grade blood vascular neoplasm in keeping with hemangioendothelioma (a borderline vascular neoplasm)/low-grade angiosarcoma.