Rare form of a common intracranial lesion - Atypical meningioma

A 51-year-old woman presented with headache and progressive scalp swelling in the right frontoparietal region since eight years. On examination, the swelling was firm with mild tenderness.

CT head showed a large enhancing extra-axial lesion with its epicentre at the right side of the frontal and right parietal bones. There was a large intracranial and smaller extracranial component extending into the scalp with associated calvarial destruction (Figures 1 and 2). The patient later underwent an MRI of the brain. It showed a T1/T2 isointense extra-axial dural-based lesion with avid enhancement and a dural tail. There was mass effect in the form of compression of the underlying brain parenchyma effacement of the right lateral ventricle and midline shift to the left (Figure 3). There was no diffusion restriction on diffusion-weighted (DWI) images (Figure 4).

Background

Meningiomas are meningothelial cell neoplasms, typically dural-based, in the brain and spine. They are usually well-circumscribed, sessile or lentiform, extra-axial lesions with broad-based dural attachment [1]. On imaging, typical meningiomas are dural based avidly enhancing lesions with hyperostosis of the overlying calvarium, while atypical meningiomas appear as dural-based lesions with lytic destruction of the overlying bone, with or without extracranial component [2]. Large intraosseous meningiomas present as lytic destruction of the bone with a larger extracranial and a smaller intracranial component. Atypical meningiomas are WHO grade II tumours [3].

Clinical Perspective

The most common, non-specific symptom in the majority of the patients is headache. Intradural meningiomas may present with seizures due to irritation of the underlying cortex, while atypical meningiomas with calvarial and extracranial extension are more likely to present as an enlarging palpable mass. In skull base meningiomas, the expansile nature of the lesion may lead to cranial nerve palsy presenting as visual disturbance or exophthalmos for lesions involving the orbital wall/sphenoid [4].

Imaging Perspective

Conventional radiographs are generally of limited value in the diagnosis of atypical meningiomas because of the superimposed bony structures. CT with bone windows help to detect the lesion and determine its intra- and extraosseous extension. MRI provides better anatomic delineation of the soft-tissue component and extradural extension of the lesion.

Outcome

Wide surgical excision of the lesion with resection of the involved dura is the most common surgical approach for atypical meningioma. The location of the tumour determines the approach and extent of resection, keeping in mind the preservation of function [5]. CT and MRI play an important role in determining the location and extension of the lesion, thus aiding pre-operative planning.

Histopathology in our case revealed atypical meningioma (Bone invasive) – WHO grade II.

Take Home Message / Teaching Points

Atypical meningioma should be considered in patients with dural-based lesions with osteolytic skull changes associated with an extra-calvarial soft-tissue component. CT and MRI are important in the diagnosis and evaluation of the soft-tissue component and extradural extension.