MENINGOTHELIAL MENINGIOMA WITH LIPOMATOUS AND RHABDOID DIFFERENTIATION.
Meningiomas are well known entities with frequent histological variants, such as meningothelial, fibroblastic, syncytial, and transitional, among others. However, unusual aggressive subtypes such as papillary meningiomas and rhabdoid meningiomas might constitute a problem in the differential diagnosis with other central nervous system tumours, mainly ependymomas, PNETs, oligodendrogliomas and teratoid/rhabdoid tumors of the CNS (1,2,3,4).
The rhabdoid differentiation, defined as sheets of loosely arranged cells with eccentric nuclei and eosinophilic cytoplasm containing hyaline paranuclear inclusions, seems to constitute a hallmark of malignancy (5,6).
Lipotamous and lipoblastic meningiomas constitute a controversial group among the metaplastic meningiomas (1,2,3,4). Ferracini et al (7) reported the presence of pluripotential primitive cells of the neural crest in perivascular areas of the leptomeninges, which are the probable source of metaplastic mesenchymal differentiation in meningiomas. Lipomatous meningiomas affect adults, and their biological behavior is similar to the classic meningothelial meningiomas (8). However, the recognition of this metaplastic variant is important, since they can be misdiagnosed as liposarcomas, metastatic mucinous adenocarcinomas and chordomas (1,2,3,4).
The rhabdoid differentiation was first described in a renal tumor affecting the kidney of infants (5). Since that description, this morphology has been described in several other types of tumors outside the kidney, such as intracranial gliomas, carcinomas, sarcomas and skin melanomas. It is inferred that this differentiation, occurring at extrarenal sites, might represent poorly-differentiated tumors with a common phenotype. Recently, Keppes et al (6) and Perry et al (5) described a series of the meningothelial meningiomas with rhabdoid differentiation, and suggested that it might constitute a hallmark of malignant progression in meningeal neoplasms, due to the high recurrence rate, documented extracranial metastases, as well as the presence of rhabdoid features only after the first recurrence in 40% of all reported cases (5). In the present case, the rhabdoid morphology was observed only after the third recurrence, supporting the concept of malignant progression. This phenomenon might be linked to the radiotherapy performed prior to the last biopsy.
Contributed by LF Bleggi-Torres, MD, PhD, MIAC; JS Reis-Filho, MD; LN Faoro, BM; L Noronha, MD, MSc; MR Montemor-Netto, MD; R Ramina, MD