Imaging spectrum of meningiomas: a review of uncommon imaging appearances and their histopathological and prognostic significance.

Meningiomas are the most common primary non-glial intracranial neoplasms. In most cases, meningiomas have typical imaging appearances and locations, enabling a straightforward radiological diagnosis. However, a myriad of unusual appearances potentially complicate the imaging picture. Furthermore, certain imaging features can also predict the specific histopathological nature and WHO grade of the meningioma. 'Typical' meningiomas include meningothelial, fibrous, and transitional variants and have the characteristic imaging features described for meningiomas. Several 'atypical' variants exist, which, although less common, also generally have a less favourable prognosis and necessitate early diagnosis. In addition, meningiomas can occur in a variety of unusual intracranial and even extra-cranial locations and need to be distinguished from the more common tumours of these regions on imaging. Any associated oedema or haemorrhagic changes may alter the prognosis and have to be carefully assessed and reported. Cystic changes in meningiomas have been divided into five subtypes, and accurate characterisation is essential to predict the prognosis. An extensive review of the several possible variations in imaging appearances of meningiomas including the differential features of common and uncommon variants would facilitate informative radiological reporting of meningiomas. This would be expected to improve pre-operative planning prior to surgical biopsy and thereby improve disease prognosis and patient outcomes.