Atypical intracranial meningioma

Clinical History

The patient had a generalized tonic-clonic seizure.

Imaging Findings

A 54-year-old woman, with no history of neurological or systemic disease, had a generalized tonic-clonic seizure. A head CT examination at the emergency department revealed an ovoidal, slightly hypodense, extra-axial right fronto-temporal mass, causing discrete compression on the surrounding brain structures (fig. 1). The mass showed a strong, homogenous contrast enhancement (fig. 2a) with tortuous vessel-like structures at its cranial and caudal poles (fig. 2b-c). On MR T2-weighted images the lesion was hyperintense and tubular signal void areas were present at its boundaries (fig. 3a-b). The dura at and near the lesion base was thickened and showed marked gadolinium enhancement (fig. 4). A presumptive diagnosis of angioblastic meningioma was posed and a digital subtraction angiography (DSA) study was performed prior to surgery. The lesion had an early arterial contrast enhancement (fig. 5) persisting relatively long in the venous phase (fig. 6) and was fed by vessels originating essentially from the anterior and posterior branches of the right middle meningeal artery (MMA) (fig. 7). Enlarged veins drained blood into the superior longitudinal sinus and the vein of Labbé (fig. 8). Embolization of the anterior and posterior branches of the right MMA was performed by superselective injection of polyvinyl alcohol (PVA) particles (fig. 9a-b) followed by positioning of a small coil into the proximal tract of the posterior branch, obtaining a good arterial deafferentation (fig. 10). Five days later, the patient underwent surgical removal of the mass extended to the adjacent dura. Pathologic confirmation revealed a WHO II atypical meningioma (fig. 11).

Discussion

The 2000 WHO classification divides meningiomas into grade I (typical), grade II (atypical), and grade III (anaplastic). The atypical variant accounts for only 7.2% of meningiomas, with more than 90% typical and 2.4% anaplastic meningiomas, and is more frequent in women between the third and fifth decade, about 10 years before typical meningioma, with a predilection for some ethnic groups such as African Americans. Macroscopically it resembles typical meningioma and consists of an ovoidal or lobulate mass with a tight adhesion to the dura, which is thickened also at some distance from the lesion base, forming the so-called ‘dural tail’. In contrast to typical meningiomas, atypical meningiomas contain few or no calcifications, are not associated with hyperostosis of adjacent bone and can have indistinct margins with irregular projections into the brain tissue (‘mushrooming’). Clinical symptoms can derive from compression on the surrounding brain structures as well as from bleeding, since atypical meningiomas are highly hypervascularized. Extracranial metastases are rare but more frequent compared with typical meningiomas and may involve liver, lungs, pleura, lymph nodes, and bones. In addition, atypical meningiomas have a higher recurrence rate than typical ones (26% vs 9%), which justifies their radical surgical excision together with their dural tail. The definitive differential diagnosis between typical and atypical meningioma is histopathological; however, there are some radiological findings that can suggest the possibility of an atypical meningioma. At CT examination atypical meningiomas are usually mildly hyperdense or isodense, but they can also be hypodense as in our case. Intralesional calcifications are generally absent and skull bone is often intact; in some aggressive atypical meningiomas, as well as in anaplastic ones, bone erosion can be found. On MRI, atypical meningiomas are iso- or hypointense compared with gray substance on T1-weighted images and hyperintense on T2-weighted images, related to their high cellularity and vascularization. On T2-weighted images flow void phenomena can be seen, corresponding to dilated high-flow drainage veins. Atypical meningiomas and their dural tail show a strong, homogenous contrast enhancement. DSA is used to assess lesion vascularization and perform embolization of feeding arteries before surgery, in order to limit intraoperative bleeding. Compared with CT and MR, DSA has the advantage of allowing selective vessel catheterization and real-time evaluation of the lesion contrast enhancement. Atypical meningiomas usually have an early, diffuse and prolonged contrastographic blush, which some authors have ironically called the ‘mother-in-law sign’, as contrast material comes early and stays until late in the vascular bed of those neoplasms. Arterial vessels feeding the meningioma are dilated and may source from the dural or the pial circulation or, more frequently, from both. The presence of artero-venous shunts is a specific sign for non-typical meningiomas, though it does not have high sensitivity. Percutaneous arterial embolization is usually performed by using particulate material, such as PVA, so to close the most distal branches of the feeding arteries. Coils can be also employed to stop flow in more proximal vascular segments in case of residual opacification of the lesion after injection of embolizing particles.

Differential Diagnosis List

Final Diagnosis

Atypical intracranial meningioma.

URL:	https://www.eurorad.org/case/5152
DOI:	10.1594/EURORAD/CASE.5152
ISSN:	1563-4086