Solitary fibrous tumor (hemangiopericytoma)

Case contributed by Dr Bruno Di Muzio

Presentation

Sudden right-sided weakness.

Patient Data

Age: 60 years
Gender: Male

CT Brain demonstrates a soft tissue mass expanding and eroding the left parietal bone and extending intracranially compressing the adjacent left temporal and parietal lobes. There is an expressive mass effect characterized by vasogenic edema, compression of the left lateral ventricle and midline shift to the right. The mass vividly enhances after contrast administration. The remainder brain is unremarkable. Further assessment with MRI is advised.

MRI Brain

MRI

The large and bilobed extra-axial mass is again demonstrated extending into destroying left parietal bone and with an intra dural component that severely indents the left frontoparietal lobe.  At the deep margin where brain parenchyma is indented, there are 2 cystic components. There is marked left frontoparietal vasogenic edema which extends inferiorly along internal and external capsules. The lesion has heterogeneous low and intermediate T2 signal and demonstrates a diffuse vivid enhancement. No internal diffusion restriction. A few foci of susceptibility artefact reflect calcification or blood product. There is linear dural enhancement extending along the displaced and distorted dura. There is 12 mm of midline shift toward the right at the level of the foramen of Monro and uncal herniation with the distorted region of the midbrain. No tonsillar herniation. Dilated entrapped left temporal horn. No distant areas of pathological enhancement. A few small T2 hyperintense white matter foci are compatible with expected age-related changes of chronic small vessel ischemia.

Conclusion: Severe mass effect due to a large left extra-axial mass with intraosseous and intradural components. The main differential diagnosis is between metastasis, meningioma, and hemangiopericytoma.

Histology

Pathology

MICROSCOPIC DESCRIPTION: The sections show a variably hypercellular spindle and epithelioid cell tumor with a broad dural attachment. The tumor is intensely vascular and, in many areas, vessels have "staghorn" profiles. Tumor cells show moderate nuclear pleomorphism and are dispersed in a fibrous stroma. Occasional mitotic figures are identified (3/30HPF). No areas of necrosis are identified. Infiltration into bone is seen in specimen 2. There is no evidence of brain invasion.

Inmmunohistochemistry shows strong staining in tumor cells for bcl-2 and MIC2 (CD99) and moderate staining for CD34. Immunostaining for epithelial membrane antigen (EMA) and progesterone receptor (PgR) is negative.

The features are of solitary fibrous tumor/hemangiopericytoma spectrum tumor (WHO Grade II). The topoisomerase labeling index is approximately 1%.

DIAGNOSIS: Bone/skull/brain tumor: Solitary fibrous tumor/hemangiopericytoma spectrum tumor (WHO Grade II).

SUPPLEMENTARY REPORT: Sections of decalcified tissue show permeation of bone by tumor extending to but not breaching the outer table.

Case Discussion

This case demonstrates an extra-axial mass that expands and partially destroys the left parietal bone and causes an expressive mass effect over the adjacent brain. 

The main radiological differentials to be considered are meningioma, hemangiopericytoma and a lytic skull metastasis. The latter less likely due the homogeneous signal and enhancement in a big soft tissue mass. 

After surgery, histology study confirmed the diagnosis of solitary fibrous tumor (previously hemangiopericytoma). 

It is hard if not impossible to distinguish hemangiopericytoma from meningiomas on imaging. Meningiomas are less likely to erode adjacent bone though. 

Note: Due to molecular/genetic similarities hemangiopericytomas are no longer recognized as distinct entities. Instead, they represent cellular higher-grade solitary fibrous tumors. In the 2016 revised 4th Edition of the WHO classification of CNS tumors, they were grouped together under one diagnosis (solitary fibrous tumor/hemangiopericytoma), and in the 2021 5th edition the term hemangiopericytoma was dropped entirely. 

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