Case prepared by Dr Viren Vaghasiya and Dr Jitendra Nasit
– A single well-circumscribed smooth nodular mass of approximately 4 cm, with a solid tan-yellowish cut surface. Single small point show more brownish color. Single small separate strip of dura is also reveived (not shown here).
– The neoplastic proliferation of variable-size vacuolated cells with a prominent background of variable-sized blood vessels including large staghorn-like vessels (vessels with thin walls, large lumen, and branching appearance) and hyalinized thick-walled blood vessels. But Vascular component is not the dominant component (limited to <50% of tumor area).
– Neoplastic cells have round to oval nuclei with pleomorphism and smudgy dense/degenerative chromatin but lack of mitoses, necrosis, and coarse nuclear chromatin. Few cells show nuclear pseudoinclusions. The cytoplasm of tumor cells have cobweb-like interconnected-looking long processes which are separated by clear spaces giving rise to microcystic architecture.
– Overall tumor looks like edematous tissue.
Practical points of Pathoclinics:
- Microcystic meningiomais WHO grade 1 meningioma.
- The vascular elements especially microvascular pattern should be more than 50% to conclude a meningioma as angiomatous type with a background of microcystic meningioma.
- Microscopic features like mitoses, brain invasion, and atypical features (sheet-like growth, hypercellularity, small cell change, necrosis, and macronucleoli) are use to distinguish grade 1 meningioma from higher-grade tumors. Pleomorphism which is a common feature of microcystic meningioma is not included in atypical features.
- Microcytic meningioma is one of the subtypes of meningioma with prominent peritumor edema in surrounding brain tissue (which is considered a radiological indication of brain invasion) even when there is no brain invasion.
- EMA and PR positivity are commonly used to favor meningioma in an extramedullary intradural tumor. Somatostatin receptor 2a (SSTR2a) is a very sensitive and specific meningioma marker.
- Focal areas of microcytic changes can be seen in other meningiomas. In presence of extensive microcystic clear spaces, it may create confusion with clear cell renal cell carcinoma, hemangioblastoma, and clear cell meningioma.
- Clear cell renal cell carcinoma shows a nesting and alveolar pattern of clear cells with surrounding rich vascularity of capillary-type blood vessels. Clear cell renal cell carcinoma is positive for PAX8, RCC, and CD10. CAIX is not helpful as it is positive in both microcystic meningioma and clear cell renal cell carcinoma.
- Hemangioblastoma is another differential diagnosis. It is a WHO grade 1 tumor and commonly associated with von Hippel-Lindau (VHL) disease. Prominent vascularity is an overlapping feature but cells of hemangioblastoma are bubbly foamy looking (almost like sebocytes). Inhibin, CAIX, S100, and Brachyury are positive in hemangioblastoma while negative for EMA, PR, SSTR2a, PAX8, CD10, and RCC. Here, CAIX is not helpful as it is positive in both microcystic meningioma and hemangioblastoma.
- Clear cell meningioma (WHO grade II) has clear cytoplasm of cells in contrast to microcystic “clear” spaces. In addition, the presence of perivascular and interstitial collagen bands is a helpful finding in clear cell meningioma. On immunohistochemistry, loos of SMARCE1 and negative CAIX are seen in clear cell meningioma, in contrast to retained SMARCE1 and positive CAIX in microcystic meningioma.
Resources for further learning:
- Youtubevideo: https://www.youtube.com/watch?v=XvSQmnRu_bA&t=1007s&ab_channel=pathCast