Benign hemangiopericytoma: Clinical features, Differential diagnosis,Investigation,Treatment
The separation between the hemangiopericytoma and the solitary fibrous tumor has become less and less distinct, and the validity of the hemangiopericytoma as a separate entity has been put in doubt because so many of its features are shared by other tumors. If we consider these two tumors to be part of a spectrum, the hemangiopericytoma is at the cellular end and the solitary fibrous tumor is at the hyalinized end. Because of this lack of distinction, these tumors are often classified as hemangiopericytoma/solitary fibrous tumor. The hemangiopericytoma is of uncertain histogenesis but is likely of fibroblastic origin. An exception is the sinonasal hemangiopericytoma, which does not appear to be of true pericytic origin.
- Hemangiopericytomas are part of a spectrum of tumors that range from benign to intermediate types to overtly malignant. Those of the intermediate type have features of both the benign and malignant forms and probably represent a low-grade malignancy. However, the overtly benign form is the most common.
- Men and women are affected equally.
- The peak incidence is between the ages of 30 and 50 years.
- The tumor grows very slowly and will often have a reported duration of several years.
- It will present as a deep-seated mass within muscle or within deeper fascial spaces. It tends not to occur at superficial levels such as the subcutaneous level or submucosa.
- The tumor mass is painless but often contains pulsations or audible bruits. This is due to the development of functional vascular spaces and prominent feeding vessels with arteriovenous shunting.
- The oral and maxillofacial area is an uncommon location for hemangiopericytomas, accounting for only 16% of cases. Most of these occur within the orbit.
- The deep-seated location of the mass is strongly suggestive of mesenchymal tumors such as
– nodular fasciitis
– aggressive fibromatosis
– fibrosarcomas and
– malignant fibrous histiocytomas
- If pulsations are noted, it may suggest an arteriovenous hemangioma or, if the nasal cavity or medial orbit is involved, a nasopharyngeal angiofibroma.
Despite its implied vascular nature, the tumor can undergo an incisional biopsy with normal hemostatic controls. The incisional biopsy should be of sufficient size for adequate histopathologic assessment. Determining the cellularity and number of mitotic figures on the basis of examination of 10 to 20 HPFs is critical in determining whether the tumor is benign or malignant. Moreover, immunostaining also may be required. Because of its deep location, a CT or MRI scan is recommended to determine its size and anatomical relationships. A Doppler examination is also suggested. If the tumor displays audible bruits with the Doppler, an angiogram should follow.
The tumors that may still be considered to belong under this designation are usually well circumscribed. They will resemble the cellular component of the solitary fibrous tumor but have very consistent thin-walled branching vessels with the typical staghorn appearance. The cells are round to spindled and closely packed with small vesicular nuclei. These tumors have a more uniform appearance than those designated as solitary fibrous tumors and lack the hyalinization. They are CD34 and CD99 positive. Features of potential malignancy include nuclear pleomorphism, necrosis, and a size greater than 5 cm, but the most reliable indicator is the presence of more than 4 mitoses per 10 HPFs.
If histopathology confirms a benign hemangiopericytoma, treatment is local excision with margins of 0.5 to 1.0 cm. Because many hemangiopericytomas have feeder vessels and the lesion itself is vascular, ligation of all feeding vessels in the immediate area is advised.
The prognosis of this tumor is excellent; no recurrences are expected when it is excised with clear margins.