The patient developed acute neurological deterioration on the ward before his surgery with a rapid decline in GCS, dilated unreactive right pupil and respiratory arrest. An urgent CTB was performed which demonstrated peritumoural bleeding with severe associated midline shift. The patient was transferred to the operating theater for an emergency craniotomy and excision of the left-sided lesion.

Histology

MICROSCOPIC DESCRIPTION: Sections show pieces of a densely cellular tumor. The tumor has a patternless architecture. The tumor cells are crowded and demonstrate prominent nuclear overlapping. The nuclei themselves are round-to-oval, with vesicular chromatin and a prominent nucleolus. They have small amounts of pale eosinophilic cytoplasm. Mitotic figures are difficult to identify. Thin walled wide caliber blood vessels are seen traversing the tumor. There is no necrosis. 

• Positive
  • STAT6
  • CD99
  • CD34
  • BC12
• Negative
  • AE1/AE3
  • CAM5.2
  • GFAP
  • OLIG2
  • SSTR2A
  • EMA
  • PR

FINAL DIAGNOSIS: Hemangiopericytoma (WHO grade II).

Meningeal hemangiopericytoma is a rare intracranial neoplasm accounting for less than one percent of all neoplasms of the central nervous system ^1,2,3. It is widely believed to arise from the pericytes of the capillaries and post-capillary venules of the microcirculation ^2,3. 

On MRI, hemangiopericytoma is an extra-axial dural-based lesion with predominant isointense appearance on both T1- and T2-weighted sequences. Prominent flow voids within the lesion, peritumoural edema and dural tail are common findings ^2,3. There is heterogenous vivid enhancement on post-contrast imaging. Unlike meningioma, it is not associated with intramural calcification or hyperostosis but it may result in the erosion of overlying bone ^3,4,5. 

Angiogram may demonstrate a hypervascular lesion with dual blood supply received from the external carotid artery as well as either the internal carotid artery or vertebral artery ². 

Histologically, it is a highly cellular vascular lesion characterized by crowded and irregular configuration of cells intersected by wide caliber vessels ⁶. 

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.