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Microcystic meningioma

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

Microcystic architecture is a rare meningioma variant which leads to atypical imaging appearances and thus can pose a diagnostic challenge.

These tumours do not appear to differ epidemiologically or clinically from the more common subtypes. As such for a general discussion please refer to the meningioma article.

Pathology

Microcystic meningiomas account for only 1.6% of intracranial meningiomas¹. The microcysts represent extracellular spaces, scattered throughout the meningioma substrate. These tumours usually also show abundant vascularity.

Radiographic features

On both CT and MRI the imaging appearances are dominated by the high water content of these tumours.

CT

Typically these lesions have low density but usually still have strong homogeneous enhancement. Hyperostotic changes in the adjacent skull is seen in approximately half of cases ².

MRI

T1
- low intensity (similar to fluid)
- often have some solid components which are of more intermediate signal intensity
T2
- very high signal
- associated oedema in the adjacent brain is common²
T1 C+ (Gd)
- variable ^1-2
- usually intense homogeneous enhancement
- some tumours enhance only partially or very little
DWI / ADC: reduced restriction

DSA

The degree of angiographic vascularity can usually be predicted based on the degree of enhancement, with strong and uniform contrast enhancement demonstrating prominent supply from both meningeal (external carotid artery / vertebral artery) and pial vessels (internal carotid artery / vertebral artery).

Differential diagnosis

In cases where enhancement is prominent, there is usually little differential, although it is probably worth considering exophytic / cortical tumour (e.g. pleomorphic xanthoastrocyoma (PXA)).

In tumours where enhancement is very limited, few other lesions should be considered, although the signal characteristics on other sequences will usually aid in distinguishing a microcytic meningioma from other entities.