The lesion consists of dilated, endothelial-lined, blood-filled vascular spaces surrounded by concentric, loosely organized fibromuscular tissue. Stroma between vascular spaces is thick, of low cellularity, and cells are mostly thin spindle cells with small bland elongate nuclei and no evidence of anaplasia or mitoses. Movat stain shows no elastin within the lesion and Masson trichrome stain shows a significant amount of stromal collagen. Thin elongate cells in the stroma are strongly immunoreactive for smooth muscle actin (SMA) and the stroma is completely negative for CD-34 (endothelial cells lining the vascular spaces are CD-34 reactive). Cells are arranged in a general concentric perivascular pattern and separated by non-SMA reactive strands, consistent with collagen. The tumor is also completely non-reactive for epithelial membrane antigen (EMA). Only a very few nuclei (of both stromal and endothelial cells) show reactivity to Ki-67 (much less than 1%). The composition of benign smooth muscle cells, absence of elastin, and organization of stroma in irregular thick walls around vascular spaces rule out the major subtypes of vascular malformation (cavernous and arteriovenous). The absence of EMA reactivity and presence of smooth muscle rules out angiomatous meningioma. This pattern is diagnostic of benign angiomyoma, also known as angioleiomyoma.