What is your differential diagnosis of this lytic expansile enhancing skull vault lesion?
The main differential diagnosis includes metastatic disease, intraosseous meningioma, intraosseous haemangioma, haemangiopericytoma or plasmacytoma. In younger patients, eosinophilic granuloma should be considered.
Pathology confirmed the diagnosis of intraosseous meningioma. What are the typical imaging findings?
59% of intraosseous meningiomas are osteosclerotic, 32% osteolytic and 6% mixed features of both osteolysis and hyperostosis. Unlike the thickened sclerotic intraosseous meningiomas, the lytic subtype cause thinning, expansion, and interruption of the inner and outer cortical layers of the skull. Both are typically hyperdense on CT with dense contrast enhancement. MRI appearances include isointense T1/T2 signal with avid homogenous enhancement. These tumours do not usually exhibit the 'dural tail' of intradural meningiomas although enhancement of the underlying dura can be seen.
Why do meningiomas arise in bone?
Intraosseous meningiomas are thought to arise from trapped arachnoid cells in the cranial sutures or ectopic meningocytes. Misplacement of meningothelial cells into suture or fracture lines post-trauma has also been speculated.
Which type of meningiomas have the greatest malignant potential?
Extradural meningiomas are known to have the highest risk of atypical or malignant features, in particular osteolytic intraosseous meningiomas.
MRI head demonstrates a low T1/isointense T2 expansile intraosseous lesion in the midline anterior frontal bone with elevation of the adjacent subcutaneous tissues. The lesion enhances heterogeneously with meningeal thickening. No definite intradural extension.
Mixed vascular malformation in the subcortical white matter of the anteroinferior left frontal lobe; peripheral rim of haemosiderin draining into a surface vein in keeping with a small cavernous malformation and developmental venous anomaly.