Lipomatous meningiomas [Neurosurgery Wiki]

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=====Lipomatous meningiomas=====
Lipomatous [[meningioma]]s are rare subtypes of meningiomas. First described by Bailey and Bucy in 1931 
((Bailey P., Bucy P. C. The origin and nature of meningeal tumours. The American Journal of Cancer. 1931;15:15–54.))
, “lipomatous” or “lipoblastic” refers to the cells observed in meningothelial neoplasms resembling adipocytes or lipoblasts, without the implication that those cells are immature or malignant 
((Enzinger F. M., Weiss S. W. Liposarcoma. In: Enzinger F. M., Weiss S. H., editors. Soft Tissue Tumors. St. Louis, Mo, USA: Mosby; 1995. pp. 431–466.)).

Lipomatous meningiomas are a metaplastic form of meningioma ((Perry A., Louis D. N., Scheithauer B. W., Budka H., Von Diemling A. Meningioms. In: Louis D. N., Ohgaki H., Wiestler O. D., Cavenee W. K., editors. WHO Classification of Tumours of the Central Nervous System. Lyon, France: IARC Press; 2007. pp. 164–172.))
although there is ongoing debate regarding meningioma's pathogenesis as true metaplasia of the meningothelial cells or accumulation of lipids within the cells 
((Roncaroli F., Scheithauer B. W., Laeng R. H., Cenacchi G., Abell-Aleff P., Moschopulos M. Lipomatous meningioma: a clinicopathologic study of 18 cases with special reference to the issue of metaplasia. The American Journal of Surgical Pathology. 2001;25(6):769–775. doi: 10.1097/00000478-200106000-00008.))
((Colnat-Coulbois S., Kremer S., Weinbreck N., Pinelli C., Auque J. Lipomatous meningioma: report of 2 cases and review of the literature. Surgical Neurology. 2008;69(4):398–402. doi: 10.1016/j.surneu.2006.11.072.))
((Ohba S., Yoshida K., Akiyama T., Ikeda E., Kawase T. Lipomatous meningioma. Journal of Clinical Neuroscience. 2007;14(10):1003–1006. doi: 10.1016/j.jocn.2006.03.011.)).

Lipomatous meningiomas are classically WHO grade I tumours with good prognosis following complete removal. There is very limited data on these tumours with less than 50 cases of lipomatous meningiomas being described throughout the literature
((Jaiswal A. K., Mehrotra A., Kumar B., et al. Lipomatous meningioma: a study of five cases with brief review of literature. Neurology India. 2011;59(1):87–91. doi: 10.4103/0028-3886.76876.)) 

Metaplastic lipomatous meningiomas can be defined as meningiomas with striking focal or widespread mesenchymal areas, including osseous, cartilaginous, lipomatous, myxoid, or xanthomatous tissue components ((Roncaroli F., Scheithauer B. W., Laeng R. H., Cenacchi G., Abell-Aleff P., Moschopulos M. Lipomatous meningioma: a clinicopathologic study of 18 cases with special reference to the issue of metaplasia. The American Journal of Surgical Pathology. 2001;25(6):769–775. doi: 10.1097/00000478-200106000-00008.)).

Lipomatous meningiomas reveal low mitotic rates. In our case the Ki-67 was 0.5%, which is in keeping with the findings of Tang et al., 2013, in which 14 out of 15 metaplastic meningiomas showed Ki-67 rates of less than 1%, including the two lipomatous meningiomas
((Tang H., Sun H., Chen H., et al. Clinicopathological analysis of metaplastic meningioma: report of 15 cases in Huashan Hospital. Chinese Journal of Cancer Research. 2013;25(1):112–118. doi: 10.3978/j.issn.1000-9604.2013.01.10.)). 
Bone invasion can be seen in meningiomas, yet it is not considered as a part of the grading classification. Recently there have been suggestions that lipomatous meningiomas occur from lipid accumulation due to metabolic abnormality of the neoplastic cells rather than true metaplasia of the meningioma cells 
((Matyja E., Naganska E., Zabek M., Jagielski J. Meningioma with the unique coexistence of secretory and lipomatous components: a case report with immunohistochemical and ultrastructural study. Clinical Neuropathology. 2003;10(6):712–714.)).

Throughout the English literature 41 cases of lipomatous meningiomas have been described 
((Jaiswal A. K., Mehrotra A., Kumar B., et al. Lipomatous meningioma: a study of five cases with brief review of literature. Neurology India. 2011;59(1):87–91. doi: 10.4103/0028-3886.76876.))
, one associated with a secreting meningioma 
((Yamada H., Hanada T., Okuda S., Yokota A., Haratake J. Secretory meningioma with lipomatous component: case report. Brain tumor pathology. 1999;16(2):77–80. doi: 10.1007/BF02478906.))
and another with a cerebral arteriovenous malformation
((Kasantikul V., Brown W. J. Lipomatous meningioma associated with cerebral vascular malformation. Journal of Surgical Oncology. 1984;26(1):35–39. doi: 10.1002/jso.2930260109.)). 
No cases were associated with intraosseous extension, although there has been a previous report of a meningioma occurring at the site of an intraosseous lipoma
((Hayashi Y., Kimura M., Kinoshita A., Hasegawa M., Yamashita J. Meningioma associated with intraosseous lipoma. Clinical Neurology and Neurosurgery. 2003;105(3):221–224. doi: 10.1016/s0303-8467(03)00014-3.)).

see [[Intraosseous lipomatous meningioma]]