Sacral tumors: a comprehensive review of imaging, diagnostic challenges, and tumor mimics

The sacrum can harbor a diverse group of both benign and malignant tumors, including metastases. Primary tumors of the sacrum can arise from bone, cartilage, marrow, notochordal remnants, or surrounding nerves and vessels. Among a variety of primary tumors of the spine, chordoma, germ cell tumors and Ewing's sarcoma are recognized for their propensity to occur in the sacrum. Imaging is essential in diagnosis, pretreatment evaluation, and assessment of response to treatment. Radiography, CT and MRI are the primary modalities in assessing morphology and tumor extent whereas PET/CT is crucial in the evaluation of systemic disease in the setting of myeloma, lymphoproliferative disease, and metastasis. A definitive diagnosis is not always achievable by imaging as some tumors lack specific imaging features. However, as we detail in this comprehensive review, many entities have characteristic clinical and epidemiological factors as well as typical imaging findings that can help make either a confident diagnosis or offer a narrow list of differentials. We discuss a wide range of benign and malignant, primary, and secondary tumors that can involve the sacrum, highlighting the pertinent clinical details and typical imaging findings of these entities, enabling the reader to develop and apply a systematic approach to evaluating sacral masses on imaging. We also briefly describe non-neoplastic tumor mimics, which include developmental entities, infections, and insufficiency fractures.