Teaching Case

A 45-year-old male patient presented with history of progressive recurrent headaches.

A 45-year-old male patient presented with history of progressive recurrent headaches. His symptoms were chiefly localised to the occipital region. He also complained of mild tenderness in the occipital region of few weeks duration. There was no other significant past medical history. Neurological examination was essentially normal. General physical examination and laboratory data were non contributory. Magnetic resonance imaging showed a well circumscribed, lobulated, extra-axial mass lesion along the left temporo-occipital cerebral convexity. The lesion was relatively flat and seemed to grow in a radial fashion along the dura. It was isointense to the cortex on T1w and markedly hypointnse on T2-weighted images, and demonstrated intense post-contrast enhancement. It was indenting and mildly compressing the adjacent cerebral parenchyma, and was associated with mild perilesional oedema. The adjacent calvaria was hyperostotic. On post contrast scan there was an abnormal marrow enhancement seen within the expanded calvaria suggestive of osseous hypertrophy and invasion. Based upon the imaging characteristics, the diagnostic possibility of an "en plaque" meningioma was considered which was confirmed on histopathology.

Meningiomas are the most common primary nonglial intracranial tumours. Based upon their configuration, meningiomas can be classified into the commoner globular form known as “meningioma en masse” and the rarer flat variety called “meningioma en plaque”. The term meningioma en plaque (MEP) was coined by Cushing and Eisenhardt in 1938 to differentiate these uncommon sheet-like meningiomas from the more common globular variety. En plaque meningiomas constitute 2-4 % of all intracranial meningiomas. Morphologically these are carpet or sheet-like lesions that grow in a radial fashion along the meninges. They tend to infiltrate the dura and many a times invade the adjacent bones. Enplaque meningiomas are much more commonly associated with adjacent bony hyperostosis, than the larger en masse tumours. They often provoke bony hyperostosis that is disproportionately greater than the relatively size of the intracranial mass. Unlike in globular meningiomas, the bony hypenostosis in enplaque meningiomas is more likely to be secondary to tumour invasion. Due to difficulty in complete resection, the recurrence rate of en plaque meningiomas is higher than the usual counterpart. MEP are more prone to develop malignant change when compared to globular meningiomas. The sphenoid ridge is the most common location. Cerebral convexity, juxtaorbital location, diffuse calvarial or rarely spinal region involvement have been described in literature. These are most commonly found in middle aged females usually in the fourth to fifth decade of life.

Contrast enhanced MRI is the preferred imaging modality. MRI depicts well the extradural soft-tissue component of tumour, which appears isointense on T1-weighted images & iso-to-hyperintense on T2-weighted images and shows intense homogeneous enhancement on the post contrast scan. En plaque meningiomas may have a diverse appearance on the post contrast scan ranging from a smooth thin extra-axial mass to a highly irregular lobulated lesion. The lesion tends to gro radially or in a sheet-like manner along the dura. Dural and osseous invasion are commonly encountered. Calvarial thickening is a common finding seen at imaging as these lesions are well known to invade and expand the adjacent bone. CT scan is superior for viewing the osseous changes which can be at times subtle on MRI scan. Post-contrast fat suppressed T1-weighted images are especially useful to evaluate the orbital or soft tissue extension of the lesion in case of spheno-orbital MEP. The differential diagnosis of an enplaque meningioma includes a wide variety of diseases which may cause abnormal dural thickening and enhancement. This includes neuro-sarcoidosis, granulomatous infection such as tuberculosis, lymphoma, meningeal carcinomatosis and postradiation changes. Analysing the CT finding of hyperostotic bone is useful for differentiation of MEP from other diseases.

To conclude, en plaque meningiomas are a rare flat variety of intracranial meningiomas which grow along the planes of the meninges. Their diagnosis remains difficult but should be considered when linear or lobulated enhancing dural-based mass lesion is seen on neuroimaging. These tumours are often associated with osseous invasion, expansion and hypertrophy.