Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms

Primary neoplasms that originate in the soft tissue of the retroperitoneum are rare, but they are often malignant and can grow to a substantial size at clinical presentation. Although imaging findings can be nonspecific, knowledge of some distinguishing imaging features and clinical and epidemiologic considerations can aid the radiologist in narrowing the differential diagnosis or, in some cases, providing a specific diagnosis. Some of the more important findings at cross-sectional imaging that can facilitate this assessment include tumor size and location (eg, presacral, paravertebral, or in the organ of Zuckerkandl); tissue composition (eg, fat, fibrous tissue, cystic components, or myxoid matrix), including assessment of the signal intensity of the lesion at T2-weighted MRI; degree of vascularization; and relationship to adjacent structures (ie, invasion of vascular structures such as the inferior vena cava). This assessment is further enhanced by an understanding of the gross and microscopic histologic appearances of these neoplasms. Primary solid retroperitoneal neoplasms are grouped and presented according to their primary soft-tissue element (eg, adipocytic, smooth muscle, fibroblastic, neurogenic, or skeletal muscle). Brief discussions of primary cystic retroperitoneal neoplasms and some miscellaneous neoplasms that do not fit into the aforementioned categories follow. An imaging algorithm to ensure a systematic approach to diagnosis of these lesions is also provided, which will allow the radiologist to provide more accurate interpretations for their referring providers, thus ensuring optimal patient treatment. (C) RSNA, 2020