December 2015
An 83-year-old woman with a rapidly growing mass in the occipital region
(No history of pain or bleeding)
Scalp Hemangiopericytoma (HPC) - WHO grade II
- Background:
- Rare neoplasm that is thought to arise from Zimmermann pericytes, but the cell of origin is still controversial.
- May appear anywhere in the body and can be either benign or malignant.
- Distinction between low-grade and high-grade lesions is difficult on the basis of histologic parameters (nuclear expression of STAT-6 is useful).
- Clinical Presentation:
- Hemangiopericytomas usually occur in middle-aged adults, average age at presentation of 38–42 years.
- The typical presentation is a slowly enlarging painless soft tissue mass. In threequarters of the cases, the tumor is well circumscribed or encapsulated.
- The tumor is firm on examination and may grow as large as 10 centimeters in diameter.
- They may be locally infiltrative, and they are occasionally associated with systemic symptoms such as hypoglycemia (because of overproduction of an insulinlike growth factor), arthralgia, and osteoarthropathy, as well as digital clubbing.
- There is no significant difference in age at time of diagnosis between head and neck HPC and other HPC.
- Head and neck HPC was most commonly located in the connective and soft tissue (18.4%), followed by the nasal cavity and paranasal sinuses (8.5%)
- Key Diagnostic Features:
- Plain film: Findings are nonspecific. Calcification within the tumour is infrequent.
- CT: Heterogeneous soft tissue mass density and intense enhancement after contrast administration. Can produce lytic calvarian lesions.
- MRI: Appear as well-circumscribed, solid masses with low-to-intermediate signal intensity on T1WI and heterogeneously high signal intensity on T2WI
- T2WI may also show a low-signal-intensity rim representing a pseudocapsule around the lesion.
- T1+Gadolinium: Variable enhancement, but enhancement is often intense because of HPCs' high vascularity, which also is shown as flow void areas in the T2WI and susceptibility secuences.
- Differential Diagnosis:
- Hemangiopericytoma (like an angiosarcoma or hemangioendothelioma) is a tumour that arises from vascular structures. They are typically difficult to distinguish from one another on imaging alone. Hemangioendothelioma typically occurs in young patients. Angiosarcoma, the most aggressive of the three, frequently has metastases at time of diagnosis and often recurs locally.
- Synovial sarcoma: Head and neck < 5% of cases, occurs mostly in young patients 15–40 years old, particularly if calcification is present
- Solitary fibrous tumor: Usually in the 6th to 7th decades, rarely presents secretion of insulin-like growth factor-2 (IGF-2). Only distinguished by histology.
- Treatment:
- Surgical excision is the treatment of choice. Up to half of the patients exhibit local recurrence. These tumors are not responsive to radiation or chemotherapy.
