Answer: Meningioma involving bone

Histology: The specimen consists of bone and soft tissue. Present within the bone is a spindled and swirled cellular proliferation associated with numerous psammoma bodies. The cells have bland appearing nuclei without significant cytologic atypia or mitoses.

Discussion: The tumor proliferation within bone primarily raises the differential between a metastatic epithelial tumor such as a carcinoma or direct extension of a tumor into the bone. In this case, the lesion is characteristic of a meningioma. The cellular proliferation plus the numerous calcified psammoma bodies are characteristic of meningiomas. The interesting feature of this case is the finding of meningioma in bone. Meningiomas can permeate the neighboring skull and on occasion, meningiomas may actually come to attention based on the finding of a visible skull mass. The finding of meningioma involving bone is in itself not an indication that the meningioma is a malignant meningioma. The recognition of a meningioma as malignant tumor is based on the given tumor’s histologic appearance and/or invasion into the brain. In this case, the tumor lacks the cytologic features associated with malignancy, such as increased mitotic activity, necrosis, or cytologic atypia.