Introduction: Meningiomas, the most common benign brain tumors, comprise 13% to 26% of intracranial neoplasms1. In a series of 1809 meningiomas, Hasselbat et al2 reported the prevalence of microcystic meningioma as 1.6% and the angiomatous variant as 2.1%. On CT and MRI, meningiomas usually appear as solid with a classical appearance. However, meningioma variants, such as microcystic and angiomatous meningiomas, show unusual MRI features, making pre-operative diagnosis and surgical planning more difficult1.

Methods: Seventy patients with meningioma were included in our series. Their tumors were divided by morphology into 3 groups. Group 1 included 12 pure microcystic, 3 pure angiomatoid and 7 mixed tumors. Group 2 was comprised of 28 atypical (WHO Grade II) and 9 anaplastic (WHO Grade III) meningiomas. Group 3 included 3 fibrous and 8 meningotheliomatous (WHO Grade I) tumors. We measured peritumoral edema using the edema index volume. Additionally, the ADC ratio and tumor perfusion values were obtained.

Results: The edema indexes of tumors in Groups 1 and 2 were significantly higher than in Group 3 (p=0.003 between Group 1 and 3, p<0.0001 between Group 2 and 3).The highest meningioma ADC values, as normalized to the lateral ventricle, were compared. The values in the high grade Group 2 were significantly higher than either of the two low grade Groups 1 and 3, with p values of 0.0007 and 0.001, respectively. Groups 1 and 3 were not significantly different with respect to ADC values. The CBV values showed no significant group differences.

Conclusions: The peritumor edema index and CBV values both failed to distinguish microcystic and angiomatous meningiomas from aggressive WHO Grade II and WHO Grade III tumors. This distinction, however, could be accomplished by the use of internal ADC values and will potentially aid surgeons in their pre-operative diagnosis.

Patient Care: It will provide a more definitive framework for a reliable preoperative diagnosis of meningioma tumors based on MRI images aiding pre operative planning and post operative care.

Learning Objectives: To aid physicians in their differential diagnosis by characterizing the MRI features of angiomatous and microcystic meningiomas and comparing them to other types of low and high grade meningiomas.

References: 1.Gasparetto EL, Leite Cda C, Lucato LT, et al. Intracranial meningiomas: magnetic resonance imaging findings in 78 cases. Arq Neuropsiquiatr 2007:65(3A):610-4. 2.Hasselblatt M, Wilhelm K, Paulus W. Angiomatous Meningioma: A Clinicopathologic Study of 38 Cases. Am J Surg Pathol 2004:28(3):390-393.