Meningiomas are commonly identified on imaging, however intraventricular meningiomas are a rare subtype of the more classical extra-axial meningioma. They represent between 0.5-2% of all meningiomas and as in this case have a strong prelidiction for the trigone of the lateral ventricles, with 80% occuring at this site.  This is one type of several intraventricular lesions.

A common pathology at an uncommon site may catch the unwary and is exactly why this kind of case is popular in fellowship exams such as the FRCR 2B.  It is used to assess the generic approach of the candidate.