This case demonstrates an extra-axial mass that expands and infiltrates the torcula, venous sinuses, leptomeningeal space and erodes the adjacent bone.

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

After surgery, histology confirmed the diagnosis of a solitary fibrous tumor of the dura (hemangiopericytoma). 

It is hard if not impossible to distinguish hemangiopericytoma from meningiomas on imaging. Meningiomas tend not to infiltrate leptomeningeal space and tend to thicken the adjacent bone.

Although invasion of the sinuses by a tumor, especially by a meningioma, can occur, mass lesions residing exclusively within the venous sinuses are rare. 

I would like to thank Dr. Hector Lambre, Jorge Chudyk, Pedro Lylyk, Ana Lia Taratuto and all Residents and Radiology Department staff of Clínica La Sagrada Familia.

Note: at the time of diagnosis this tumor was known as a hemangiopericytoma. Under the 5th Edition (2021) of the WHO classification of CNS tumors, it is now considered a solitary fibrous tumor of the dura.