Over time, Hemangiopericytomas have been found to have a general growth pattern that is shared by a variety of unrelated benign and malignant lesions over time. HPC was better considered as a diagnosis of exclusion. 
It appears mostly in tissues with increased vascularity and is mostly occurs in the lower extremities, pelvic cavity, and retroperitoneum.
Fifteen to sixteen percent of all are found in the head and neck region with a tendency to grow in the nasal cavity and paranasal sinuses. Sinonasal hemangiopericytoma (SNHPC) involves mostly The ethmoid and sphenoid sinuses. [4, 7]
These tumors can occur at any age, however, the peak incidence is usually between the 5th to 7th decades of life. An equal to slight female predominance was noted [8, 9].in our case, the two patients were women.
The etiology remains unknown; however, predisposing factors such as past trauma, hypertension, pregnancy, and the use of corticosteroids are considered[8–10].we didn’t identify any risk factors in our patients.
Clinical presentation is usually unilateral nasal obstruction, recurrent epistaxis, or both. Difficulty in breathing, visual disturbance, pain, and headache are less frequent symptoms [4, 8]. In our study, nasal obstruction was the main symptom followed by the epistaxis, then headache was present in the second patient and revealed a locally advanced stage tumor
On examination, SNHPC is usually unilateral, appears as a red to pink polypoid mass without surface ulceration. It measures on average 3 cm. Only histochemical examination can distinguish it from tumors that show similaritie, such as lobular capillary hemangiomas, solitary fibrous tumors, and glomus tumors. . In our cases, we highlight on the clinical exam a non-specific polypoid mass without any cervical lymphadenopathy.
CT scan findings are non-specific. On MRI, literature shows typically hyperintense signal on T2WI (T2 weighted image) with vascular signal voids, a high mean ADC (apparent diffusion coeficient) value, and a wash-in and washout pattern on DCE-MR imaging dynamic contrast-enhanced MRI. MR imaging findings, including the ADC value and DCE-MR imaging pattern, can help differentiate hemangiopericytoma from other hypervascular tumors in the head and neck, especially in the sinonasal cavity. In our two cases, CT scan and MRI describes the extension tumor without giving any specific signs related to hemangiopericytoma.
Histological analysis shows that the neoplasm consisted of uniform, monotonous cells, exhibiting minimal pleomorphism. A few mitotic figures can be seen without significant apoptosis or necrosis associated with the lesion. The cells appear to focally palisade around the vessels. Immunohistochemistry can show strong expression of vimentin and focal expression of smooth-muscle actin (SMA).  in the first case we reported, the histological exam confirmed the diagnosis, but in the second one, the diagnosis of hemangiopericytoma was missed then revised owing to the fact of unusual tumor progression.
Concerning treatment, surgery is still the gold standard.The high degree of vascularization makes the removal of these tumors usually challenging. A lateral rhinotomy is traditionally performed. Endoscopic approaches are, however, being increasingly used in managing sinonasal and skull tumors. 
Traditionally, SNHPCs are treated by wide surgical excision through an open craniofacial approach. Recently, endonasal removal has become popular with no significant statistical difference in the rate of recurrence reported in the literature between the two approaches . Regarding our first case, she was successfully treated by external approach surgery.
Radiotherapy is used for nonradical surgical resection, inoperable tumors, or metastases cases. The prognosis is usually favorable and depends on the mitotic activity in the tumor. such situation was the case of our second patient, in a way that extension tumor causes her death.
Preoperative angiography in the management of SNHPC is still controversial. To facilitate preoperative planning and to enable embolization, many authors indicate angiography in large tumors . It has been noted a significant reduction in the risk of intraoperative hemorrhage after angiography. In our patients, the tumoral resection of the first case was obtained by solely surgery ; there were no need to a preoperative embolization.
The prognosis of hemangiopericytoma is usually favorable and depends on the mitotic activity in the tumor . Indeed, in a study of 104 patients with sinonasal HPC, Thompson and al reported a disease-free survival rate of 74.2% at 5 years and 64.4% at 10 years. Overall, the prognosis for patients with the sinonasal type of HPC is favorable, as the raw 5-year survival rate in the study by Thompson et al was as high as 88% .