Intraosseous schwannomas involving the sacrum: Characteristic imaging findings and review of the literature.

Background and purpose Sacral intraosseous schwannomas represent a rare subset of schwannomas. The existing literature detailing the radiographic appearance of intraosseous schwannomas is limited. The aim of this study is to formally characterize the radiological appearance of sacral intraosseous schwannomas to differentiate them from other lytic lesions. Materials and methods Imaging studies of 13 pathologically proven intraosseous schwannomas were reviewed from multiple institutions by fellowship-trained radiologists. A PubMed search was performed and identified four papers pertaining to the imaging characteristics of sacral intraosseous schwannomas. The results of these papers were compared to findings from our cases. Results All tumors had heterogeneous signals and were predominately solid but cystic components with fluid-fluid levels were present. The tumors caused a mass effect but none infiltrated the surrounding soft tissues. Post-contrast T1-weighted images revealed heterogeneous enhancement in all 13 tumors and four possessed non-enhancing cysts. A literature review identified 16 other cases of sacral intraosseous schwannomas forming a total of 29 cases examined. Conclusions Sacral intraosseous schwannomas should be considered in the differential diagnosis for both radiologists and pathologists when dealing with large expansile, lytic lesions, with well-defined sclerotic margins involving the sacrum. This is particularly important in middle-aged adults presenting with pathology centered around S2-3.