DIAGNOSIS
Myopericytoma
DISCUSSION
Myopericytoma is a distinctive benign, soft tissue neoplasm most often affecting the extremities with only a few cases described in intracranial sites (5). Histologically, myopericytoma consists of oval-to-spindle shaped myoid-appearing cells with smooth muscle differentiation (actin expression) arranged in a concentric, perivascular pattern. It has been hypothesized that the neoplastic cells are derived from pluripotent periendothelial cells capable of differentiating along smooth muscle, pericytic and glomus cell lineages (4). Although myopericytoma is considered a generally benign tumor, rare malignant examples have been reported (3). To the best of our knowledge, only six cases of intracranial myopericytoma have been reported so far, which are summarized in Table 1. As in our case, most lesions were solitary (5, 6). Of note, two EBV-associated tumors in HIV positive patients were multifocal and associated with additional extracranial lesions (1, 2). The histological differential diagnosis primarily encompasses lesions characterized by whorl formation and hemangiopericytoma-like vasculature. Some variants of perineuriomas, which demonstrate whorls of uniform tumor cells embedded in a collagenized stroma, may resemble myopericytoma. However, the immunohistochemical detection of epithelial membrane antigen and the lack of SMA immunolabeling allows its distinction. Although meningiomas may initially be confused with myopericytoma, they lack HPC-like vessels and the tumor cells show EMA positivity without SMA expression. Solitary fibrous tumor shows a more patternless growth and diffuse CD34 expression; however, distinct nuclear STAT6 expression is characteristic of this neoplasm.
Similar to our example, most intracranial cases described in the literature resembled the radiographic and intraoperative appearance of a meningioma. Interestingly, our patient had two additional extra-axial lesions, including a foramen magnum lesion, a histologically confirmed meningioma, and another lesion over the right Sylvian fissure that was embolized, but has not been operated so far. Multifocal myopericytoma, mostly involving a particular anatomical region is known in the literature (1). Although exceedingly rare, myopericytoma should be included in the differential diagnosis of extra-axial lesions that mimic the appearance of meningioma.
REFERENCES
Contributed by Marian C Neidert, Henning Leske, Karl Frontzek, Beata Bode, David Capper, Luca Regli, Elisabeth J Rushing
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