Atypical intraosseous meningioma of the calvarium

43-year-old female presented with headache with progressive swelling in the scalp preceded by the history of trauma.

Plain CT head showed an extra-axial homogenous hyperattenuated lytic lesion centered in the left parietal bone. The lesion was noted to extend through the skull defect both intra- and extracranially causing mass effect on the underlying parietal brain parenchyma.

MRI- Brain(P+C) showed a calvarial mass in left parietal region that was isointense on T1-weighted and hyperintense on T2-weighted images. The lesion demonstrated avid homogenous enhancement with multiple intralesional flow voids and peripheral feeding vessels. The intracranial and extracranial extent of the lesion was clearly visible on MR imaging. There was also associated thickening, and enhancement of the adjacent dura noted.

The most frequent non-glial tumour of the central nervous system is meningioma (CNS) [1]. The reported incidence of extracranial meningiomas is between 1% and 2% of all meningiomas, making them uncommon [2, 3]. About two-thirds of extradural meningiomas are primary intraosseous meningiomas, a subtype of primary extradural meningiomas [4].

A subtype of extradural meningiomas that develop in bone is referred to as primary intraosseous meningioma. These meningiomas have a different clinical presentation and radiological differential diagnosis than intradural meningiomas because they develop within the skull's bones [4, 5].

In our case, the left parietal lesion appeared hyperdense and showed vivid enhancement with presence of multiple intralesional and peripheral feeding vessels, thus keeping intraosseous meningioma as the first differential diagnosis. However, in absence of hyperostosis of bone, which is a typical associated finding in meningioma, other close differential diagnoses were considered, like hemangiopericytoma, metastasis from an unknown primary.

The patient underwent tumor excision. Further follow-up CT brain imaging showed no residual lesion.

Histopathological analysis post tumor excision showed features consistent with atypical meningioma, clear cell ( WHO type 2) with foci of rhabdoid cell-like morphology.