Malignant hemangiopericytoma: Clinical features, Differential diagnosis, Investigation, Treatment
- Most hemangiopericytomas are obviously benign, a few are obviously malignant.
- The oral and maxillofacial area is an uncommon site, accounting for only 16% of all types of hemangiopericytomas.
- Males and females are affected equally.
- Malignant hemangiopericytomas are diagnosed and graded by their cellular nature and mitotic figures per HPF.
- The most common malignant hemangiopericytoma presents as a painless, deep-seated mass arising in the nasal cavity.
- The lesions are richly vascular with functional vessels that may produce a pulsatile thrill or an audible bruit.
- The incidence increases with advancing age up to a peak in the 30- to 50-year age range. However, a rare, separate infantile form occurs more commonly in the superficial subcutaneous fat rather than deep within muscle as does the adult type, and it grows in a rapid infiltrative pattern, forming satellite lesions. By contrast, the adult type is slower growing and develops into a lobulated mass, sometimes reaching large sizes. Most adult types are present for several months or even years before the individual seeks medical attention.
Because of its rarity, a malignant hemangiopericytoma is usually not an initial consideration. Deep-seated tissue masses in the nasal cavity in mid-adult life may suggest several salivary gland neoplasms, particularly the more common ones such as the pleomorphic adenoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma. The deep location and large size are also consistent with benign and malignant fibrous histiocytomas. If pulsations are present or a bleeding history is elicited, an arteriovenous hemangioma is appropriate, or a nasopharyngeal angiofibroma should be considered.
The tumor’s deep location requires a CT or MRI scan to delineate its true size and anatomical relationships. It is also recommended that angiography be performed because many tumors have a rapid circulation pattern with feeders and considerable arteriovenous shunting. The diagnosis requires an incisional biopsy of sufficient size to take several sections for histopathology. Because the differentiation between benign and malignant (and thus the treatment approach) is based on the mitotic figures and the cellular pattern, the biopsy is exceedingly important.
These circumscribed tumors consist of closely packed cells arranged around ramifying, thin-walled, endothelially lined vascular channels of greatly varying size. Small vessels may be obscured by tumor cell proliferation and compression. The cells have round to oval nuclei and may sometimes be spindled. They can resemble endothelial cells, fibroblasts, and histiocytes. The vessels often have a “staghorn” configuration. Because it acts as an arteriovenous shunt, the periphery of the tumor tends to be under increased venous pressure with resultant vascular dilation, so there is the potential for considerable hemorrhage during surgical removal.
The behavior of the malignant hemangiopericytoma can be difficult to predict, but it is most closely associated with mitotic activity. Fewer than 2 mitoses per 10 HPFs indicates a favorable prognosis, whereas 4 or more per 10 HPFs correlates with recurrent disease and metastasis. Greater aggression also may be seen with tumors that show increased cellularity, pleomorphism, and/or necrosis and hemorrhage. Malignant hemangiopericytomas occurring in the upper aerodigestive tract typically lack these aggressive histologic features and metastatic potential.
The diagnosis depends on the architecture of the lesion. Immunocytochemistry is nonspecific.
Truly malignant hemangiopericytomas are usually treated with preoperative embolization and surgical excision followed by postoperative radiotherapy in doses between 3,500 cGy and 5,500 cGy. Even with preoperative embolization, it is wise to approach the lesion with identification and ligation of the known feeding vessels as identified by the angiogram.
The prognosis of malignant hemangiopericytomas depends on the size of the tumor and the number of mitotic figures per HPF. Metastasis, usually to lung or bone, can occur as much as 10 years after initial therapy. Metastasis incidence is difficult to ascertain because of the rarity of this tumor, but it ranges from 20% to 50%.