Intracranial Pseudotumors: Making Sense Of The Maddening Mystery

The definition of a pseudotumor is something that looks like a neoplasm—but isn’t.  “Intracranial inflammatory pseudotumor” (IIPT) is an umbrella term that encompasses a spectrum of nonneoplastic infectious, reactive and/or reparative processes that are characterized histopathologically by mass-like cellular aggregates consisting of polyclonal mononuclear infiltrates in a prominent fibrocollagenous stroma.  Some IIPTs are idiopathic but a growing number have recognized causes such as IgG4-related disease.  In this presentation we delineated 5 major anatomic patterns of IIPTs, each with its distinctive imaging findings and associated pathologies.  We emphasize the falcotentorial/posterior fossa pattern and the “Eiffel by night” sign on coronal contrast-enhanced T1-weighted MR.  At least half of these cases are associated with chronic dural sinus thrombosis. In the anterior pattern (orbital apex, superior orbital fissue/cavernous sinus ± dura), orbital pseudotumor, IgG4-RD and inflammatory myofibroblastic tumors predominate. Focal rather than diffuse dura-arachnoid thickening is seen with intracranial inflammatory myofibroblastic tumors, a recently-recognized entity that can be associated with invasion of the underlying brain.