Intraosseous atypical meningioma

Case contributed by Dr Louise Hartley


Forehead swelling. Trauma at site 6 months ago.

Patient Data

Age: 60 years
Gender: Female

Ultrasound demonstrates an oval hypoechoic soft tissue mass involving the midline frontal skull vault with internal vascularity (2.3 x 1.5 x 2.0 cm). 


Unenhanced CT head demonstrates a 2.3 cm solitary osteolytic midline frontal skull vault lesion with scalloped smooth lateral margins.  The lesion erodes through the inner table and there is soft tissue extension to the overlying subcutaneous tissues.  No hyperostosis or periosteal reaction.  

Additional small focus of high attenuation in the inferior left frontal lobe.

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 hemosiderin draining into a surface vein in keeping with a small cavernous malformation and developmental venous anomaly.

Case Discussion

Differential diagnosis:

The differential diagnosis of this solitary expansile destructive lytic skull vault lesion with avid enhancement and meningeal thickening in a patient of this age includes metastatic disease, intraosseous meningioma, intraosseous hemangioma, hemangiopericytoma or plasmacytoma.

The lesion was resected and pathology confirmed the tumor to be an atypical intraosseous meningioma (WHO Grade II).



A  piece of bone that measures 59 x 54 x10 mm with a grey/red/cream firm lesion measuring 50 x 30 x 23 mm on surface.


Microscopy shows a tumor composed of spindled cells arranged in fascicles and sheets.  Mitotic figures are observed - more than 4 per 10 high power fields in some of the more active areas. The Ki67 proliferative activity is above 12% in these fragments.  The tumor cells are EMA positive and also label for CD34, but STAT6 nuclear staining is negative.


The appearances are of an atypical intraosseous meningioma, WHO Grade II.

Intraosseous meningiomas:

Extradural meningiomas account for 1-2% of all meningiomas.  Intraosseous meningiomas arise in bone and represent two-thirds of all extradural meningiomas.  They are thought to originate 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 (1).

59% of intraosseous meningiomas are osteosclerotic, 32% osteolytic and 6% mixed features of both osteolysis and hyperostosis (2).  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 tumors do not usually exhibit the 'dural tail' of intradural meningiomas although enhancement of the underlying dura can be seen (3).

As in this case, osteolytic intraosseous meningiomas have a greater risk of atypical or malignant features compared to osteosclerotic lesions (4).

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