Brain Invasion in Meningioma—A Prognostic Potential Worth Exploring

SIMPLE SUMMARY: Meningiomas are benign tumors of the meninges and represent the most common primary brain tumor. Most tumors can be cured by surgical excision or stabilized by radiation therapy. However, recurrent cases are difficult to treat and alternatives to surgery and radiation are lacking. Therefore, a reliable prognostic marker is important for early identification of patients at risk. The presence of infiltrative growth of meningioma cells into central nervous system tissue has been identified as a negative prognostic factor and was therefore included in the latest WHO classification for CNS tumors. Since then, the clinical impact of CNS invasion has been questioned by different retrospective studies and its removal from the WHO classification has been suggested. There may be several reasons for the emergence of conflicting results on this matter, which are discussed in this review together with the potential and future perspectives of the role of CNS invasion in meningiomas. ABSTRACT: Most meningiomas are slow growing tumors arising from the arachnoid cap cells and can be cured by surgical resection or radiation therapy in selected cases. However, recurrent and aggressive cases are also quite common and challenging to treat due to no established treatment alternatives. Assessment of the risk of recurrence is therefore of utmost importance and several prognostic clinical and molecular markers have been established. Additionally, the identification of invasive growth of meningioma cells into CNS tissue was demonstrated to lead to a higher risk of recurrence and was therefore integrated into the WHO classification of CNS tumors. However, the evidence for its prognostic impact has been questioned in subsequent studies and its exclusion from the next WHO classification proposed. We were recently able to show the prognostic impact of CNS invasion in a large comprehensive retrospective meningioma cohort including other established prognostic factors. In this review we discuss the growing experiences that have been gained on this matter, with a focus on the currently nonuniform histopathological assessment, imaging characteristics and intraoperative sampling as well as the overall outlook on the future role of this potential prognostic factor.