Hemangiopericytoma/Solitary Fibrous Tumor of the Parietal Bone: A Case Report

Abstract

Hemangiopericytoma/solitary fibrous tumor (HPC/STF) is a rare tumor arising from Zimmerman's pericytes and it is characterized by an aggressive malignancy, with a high tendency for local and distant recurrence. The authors report the case of a middle-aged woman with HPC/SFT of the right parietal bone, which is an extremely rare primary location of involvement. The patient presented with a painful deformity of insidious growth at the right parietal region. Assessment with cranial computed tomography scan and magnetic resonance imaging revealed an expansive lesion at the right parietal bone, with exocranial extension and 27 mm of maximal diameter. Craniotomy with gross tumor removal, duraplasty, and cranioplasty was performed, and the diagnosis of HPC/SFT, WHO grade III, was established by pathological and immunohistochemical analysis. The patient was then evaluated for adjuvant radiation therapy and received a dose of 60 Gy (2 Gy/fraction) with 3D conformal radiotherapy to the surgical bed. The adjuvant treatment was uneventful and, after 8 months of follow-up, there was no suspected local or distant recurrence. The rarity of this diagnosis, its aggressive behavior, and the lack of published data posed several challenges for the treatment management.

Keywords: Adjuvant radiotherapy; Bone neoplasms; Hemangiopericytoma; Parietal bone; Solitary fibrous tumor.

Fig. 1

a Preoperative cranial MRI (T1 sequence) revealing a well-defined, isointense lesion at the right parietal bone with endo and exocranial extension. b Preoperative cranial CT scan (bone window) showing a lytic lesion at the right parietal bone with erosion of both cortical layers.

Fig. 2

Pathological and immunohistochemical analysis. a Patternless architecture with hypercellular and hypocellular areas and “stag-horn” vessels (hematoxylin and eosin; original magnification, ×50). b Bland, ovoid to spindle nuclei cells with hyaline collagen deposition (hematoxylin and eosin; original magnification, ×400). c Diffuse nuclear STAT6 expression (original magnification, ×400). d Positive immunostaining for CD34 (original magnification, ×400). e Gordon and Sweet's silver impregnation showing demonstration of reticulin fibers (original magnification, ×100). f Negative immunostaining for EMA (original magnification, ×400). g Negative immunostaining for somatostatin 2A receptors (original magnification, ×400).

Fig. 3

Treatment volumes contoured for adjuvant RT; tumor bed is represented in green, CTV in red, and PTV in blue. Dose distribution is displayed in color wash.