Primary ectopic meningiomas: Report of 6 cases with emphasis on atypical morphology and exploratory immunohistochemistry.

Aims: To investigate the histological and immunohistochemical features of primary ectopic meningiomas (PEMs), especially those of primary ectopic atypical meningiomas (PEAMs).

Methods And Results: We examined 6 cases of PEM, including 2 PEAM cases, which occurred separately in left nasal cavity, left lower lung, right neck, left orbit, right upper lung, and left upper lung by histological and immunohistochemical analysis. In general, of the 6 PEM cases analyzed, 4 cases exhibited morphology of Grade Ⅰ, including 1 fibrous, 1 meningothelial, and 2 transitional variant. The remaining 2 cases shared similar atypical morphology of Grade Ⅱ. The tumors were distributed in sheet-like patterns with loss of architecture of classic meningiomas. Significant hypercellularity, multi-focal necrosis, and thin-walled blood vessels were identified. The mitotic figures were estimated at 6 per 10 high-power fields in one case, and 8 mitotic figures in another. Immunohistochemically, the 6 PEM cases were all positive for Vimentin and EMA, while none showed immunostaining for CKpan, S-100, CD34, STAT6, SMA, Syn or Bcl-2. 4 PEM cases of Grade Ⅰ were immunoreactive for PR but negative for P53, while the 2 PEAM cases displayed negative staining for PR but positivity for P53. As for Ki-67, the positive staining of 4 Grade Ⅰ cases was no greater than 2%, while the positive rates of the 2 PEAM cases were 10% and 20%.

Conclusions: Our study has expanded cases of PEMs, especially the 2 PEAM cases in rare sites. Our study has also further summarized the pathological features of PEMs, focusing on the histological features of PEAMs, and the immunohistochemical features worthy of further investigations.