Hemangiopericytomas

Hemangiopericytoma is a rare vascular neoplasm arising from pericytes around capillaries. Historically described as a distinct tumor, it is now regarded as part of the solitary fibrous tumor (SFT) spectrum, and occurring variants are often described as HPC-like patterns within SFT. It can arise in soft tissues, skin, or visceral sites, with intracranial meningeal involvement being a well-recognized presentation.

Epidemiology and presentation are usually in adults, often in middle age. Patients may present with a slow-growing, painless mass or symptoms related to mass effect, depending on location (for example, neurological deficits with intracranial disease or limb swelling with extremity lesions). Imaging typically reveals a well-defined, lobulated, highly vascular lesion with prominent arterial feeders. On MRI, the tumor often shows strong enhancement and variable signal intensity; CT may show intense vascularity and possible bone involvement in skull lesions.

Pathology features include a cellular spindle-cell proliferation with a prominent vascular network of thin-walled, branching “staghorn” vessels and perivascular hyalinization. Mitotic activity helps distinguish benign from malignant forms, with higher rates suggesting a more aggressive lesion. Immunohistochemistry places HPC on the SFT spectrum; STAT6 nuclear positivity supports SFT diagnosis due to NAB2-STAT6 fusion, while CD34 expression can be variable. Other markers such as vimentin are typically positive, and cytokeratins are usually negative.

Management centers on surgical excision with the aim of negative margins. Adjuvant radiotherapy is commonly used, especially for malignant or incompletely resected tumors. Chemotherapy has limited, nonuniform efficacy. Prognosis varies; there is a risk of local recurrence and, less frequently, distant metastasis, necessitating long-term follow-up. See also solitary fibrous tumor.