Meningioma (dual component)
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A very large lobulated extra-axial mass centred in the left middle cranial fossa has a broad dural base of attachment from the greater wing of sphenoid, floor of middle cranial fossa, and the orbital plate of the left frontal bone, with prominent hyperostosis particularly at the level of the greater wing of sphenoid. At its most medial aspect the mass abuts the anterior clinoid process in close proximity to the optic nerve. No cavernous sinus invasion or involvement of the orbital apex. The mass has components of different signal characteristics. The central portion of the tumour is T2 bright and low T1 signal with vivid and homogeneous enhancement. More peripherally there are loculated components that are T2 isointense to cortex, mildly T1 hyperintense and demonstrate diffusion restriction in addition to vivid contrast enhancement. Associated left frontotemporal vasogenic oedema is noted.
Severe mass effect grossly indents the frontal and temporal lobes with 12 mm of rightward shift measured at foramina of Munro. There is left uncal herniation and prominent mid brain distortion. Cerebellar tonsils are normally positioned.
A second separate lesion bulges right and left from the mid-portion of the falx. This measures 2.6 x 1.8 x 1.5 cm and indents the paramedian frontal lobes bilaterally. There is enhancing dural thickening extending anteriorly and posteriorly from the main lesion along the falx.
Mildly dilated right lateral ventricle.
The large left sided mass arising from greater wing of sphenoid, orbital roof and squamous temporal bone and a smaller parafalcine mass have morphological characteristics consistent with meningioma.
There is severe mass effect with midline shift, uncal herniation, and suprasellar cistern effacement.
The patient went on to have a resection.
The sections show a moderately cellular meningioma with focal infiltration into the adjacent dura. The tumour forms sheets and whorls. The tumour cells have ovoid nuclei with mild nuclear pleomorphism and focal conspicuous nucleoli. The background is focally myxomatous with embedded cords of tumour, giving a chordoid-like appearance. This pattern is present in less than 50% of the tumour. There are up to 4 mitoses per 10 high power fields. No necrosis is found. No brain parenchyma is seen. No evidence of malignant change is identified. The features are those of atypical meningioma. The tumour cells are diffusely progesterone receptor positive. The Ki-67 index is about 8%.
DIAGNOSIS: Atypical meningioma (WHO Grade II) with bone invasion by tumour identified.
This case is a fantastic example of how just looking at a DWI isotropic image is not sufficient to estimate degree of restricted diffusion. In this example the anterior component is low on T2 and has significant restricted diffusion (~700 x 10-6 mm2/s) whereas the posterior component has high T2 signal and facilitated diffusion (1200-1500 x 10-6 mm2/s), and yet both components appear similar of DWI due to variable T2 shine through.