Primary Intraparenchymal Meningiomas: A Case Report and a Systematic Review.

Background Primary intraparenchymal meningiomas are exceedingly rare and often challenging to diagnose, given their misleading radiologic features. It is hypothesized that they arise from the cap cells of the pia mater that enter the brain via penetrating blood vessels during brain development. We systematically reviewed and analyzed previously reported features of primary intraparenchymal meningiomas in terms of radiography, presenting symptoms, and histopathology. Methods A literature search of the Web of Science and PubMed databases and crossed references was performed in March 2021, per PRISMA guidelines, with no restrictions regarding publication date. Data regarding demographic features, clinical, radiographic, and histopathologic characteristics were extracted. Results A total of 52 patients (including the reported case) were included in this review. The mean age was 21.1 years (range, 0.3–66 years) with a male/female ratio of 1.9:1. The most common localizations of intraparenchymal meningiomas were in the frontal (30.8%) and temporal (21.2%) lobes. Cyst formation was more readily observed and was noted in 51.4% of patients. Histopathology showed a higher incidence of World Health Organization grade II (14/52, 26.9%) and World Health Organization grade III (7/52, 13.5%) of primary intraparenchymal meningiomas. Conclusions We present a comprehensive analysis of every reported primary intraparenchymal meningioma. Because of their rarity and capacity to mimic other more common intra-axial tumors, they represent a diagnostic challenge. This systematic review highlights the importance of paying attention to atypical intra-axial lesions, with a particular reflection on the discrepancy between clinical characteristics and imaging features.