Solitary fibrous tumor (hemangiopericytoma)

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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