In a single-center large surgical series of operative meningiomas, cystic meningiomas accounted for a small subset of intracranial meningiomas. Imaging features, histopathological characteristics and outcomes following surgical resection of this relatively rare group of patients with cystic meningiomas is described. We found that the majority of cystic meningiomas were WHO grade I with low Ki-67/MIB-1 proliferation index. These results suggest that cysts in meningioma may not be as aggressive a feature as previously thought [12, 15, 13, 24]. In our study, cystic meningiomas were significantly larger than their non-cystic counterparts and exhibited higher rates of hemorrhage and necrosis. Cystic and non-cystic meningiomas demonstrated no statistically significant differences with regards to histopathological features and outcomes, including extent of resection, readmission, and recurrence. Although single-patient case reports of cystic meningiomas are common in the literature, only a few studies have reported longer term postoperative outcomes following resection of these tumors [25–27].
Prior studies have demonstrated that cystic meningiomas are often accompanied by edema [28, 2],[29]. Approximately half of cystic meningiomas in our study had peritumoral edema, a frequency similar to their non-cystic counterparts. This suggests that the presence of peritumoral edema in meningioma may be unrelated to the cystic component. We noted that cystic tumors had significantly larger median maximal diameter compared to non-cystic meningiomas. The increased tumor size may result in microvascular injury resulting in ischemic necrosis, which can evolve into an intratumoral cyst [30]. Most cysts were intratumoral, either central or peripheral [18, 31, 32]. In our analysis, cystic tumors were associated with higher frequency of necrosis and hemorrhage, which may demonstrate the various stages of cyst formation and shed light on the pathophysiology of intratumoral cyst formation in meningiomas [18, 16, 2, 33]. Further natural history studies are needed to evaluate a causal link between necrosis, hemorrhage, and tumor cyst formation in meningiomas. For peritumoral cysts, the larger tumor size may result in increased compression of the peritumoral brain parenchyma, causing reactive gliosis or entrapment of the CSF in subarachnoid spaces.
A prior study reported that tumor cells are often identified in the cyst wall of cystic meningiomas [25]. Therefore, GTR including removal of the cyst wall is recommended when possible. More than 84% of cystic tumor had GTR in our study. There was no difference in frequency of GTR between cystic and non-cystic meningiomas. This suggests that the presence of cyst may not affect the extent of meningioma resection. The presence of cyst is believed to be reflective of higher grade meningioma [12, 34, 35, 21]. Analogous to Weber et al [29], we noted that most cystic meningiomas were WHO grade I and had low Ki-67/MIB proliferation index. This suggests that cysts associated with the tumor may not be an indicator of aggressive behavior. Recurrence of tumor after GTR is generally used as an additional indicator of aggressive tumor behavior. Our study was underpowered to demonstrate a statistically significant difference in recurrence rates between cystic and non-cystic meningiomas. Therefore, the negative association with recurrence should be interpreted with caution. Nonetheless, we noted that of the seven recurrent meningiomas, six were WHO grade I and underwent GTR at time of initial surgery.
Our study reviews the presentation and behavior of cystic meningiomas in one of the largest cohorts to date, but is not without limitation. The study cohort, although relatively large, was not powered to fully detect and compare recurrence or other outcomes between cystic and non-cystic meningiomas. Given the rarity of these tumors, multi-institutional studies with larger sample sizes could serve to provide additional clarity on the behavior and prognosis of these tumors. Furthermore, the single-center retrospective study design contributes its associated biases. In addition, the use of billing codes to identify patients may have resulted in missing patients in both cystic and non-cystic meningioma groups. Finally, cystic meningiomas were identified based on review of imaging and radiology reports by the authors, who are neurosurgeons, and not reevaluated by a neuroradiologist for this study [36].