Embolized meningiomas: risk of overgrading and neo-angiogenesis

Pre-operative embolization (POE) of meningiomas may induce histological changes which simulate malignancy, possibly resulting in overgrading. Aims of the present study were to identify clues to distinguish malignancy-related features from POE-related changes and to test for overgrading the grading scheme currently in use, in embolized meningiomas. In addition, we aimed to analyze whether the POE procedure may stimulate neo-angiogenesis in meningiomas. The histological features of a series of embolized meningiomas were evaluated and considered for grading assessment. In the same cases neo-angiogenesis was quantified by the evaluation of microvessel density (MVD) and correlated with the interval between POE and surgery. Necrosis and macronucleoli represented common findings in embolized meningiomas. Nonetheless, in most of the cases, necrosis showed an abrupt line of demarcation from the viable tumour tissue, and macronucleoli were restricted to peri-necrotic areas. Suggesting that these were POE-associated changes, exclusion of necrotic areas with an abrupt line of transition and focal macronucleoli from grading assessment resulted in increased specificity and positive predictive value in the identification of recurring meningiomas. In our cohort, MVD significantly increased with the time between POE and surgery, suggesting that POE procedure may induce neo-angiogenesis in meningiomas. In conclusion, a risk of overgrading there exists in embolized meningiomas, as a consequence of the frequent evidence of necrosis and prominent nucleoli in these tumours. In order to avoid overgrading, we suggest that necrosis showing an abrupt line of demarcation and focal peri-necrotic macronucleoli are not included in grading assessment. Also, caution should be used in the interpretation of MVD as a prognostic factor in embolized meningioma, as it may also result from POE procedure.