Imaging of the Retroperitoneum.

The retroperitoneum, a complex abdominal compartment encompassing the anterior and posterior pararenal spaces, perirenal spaces, and great vessel space, is involved by both organ-based and non-organ-based pathologies. Imaging characteristics are invaluable in localizing pathologies to the either the retroperitoneum or one of its organs. A wide array of primary and metastatic neoplasms, including those of mesodermal, neurogenic, germ cell, sex cord-stromal, and lymphoid origin, may arise in this region. Frequently encountered non-neoplastic entities include fluid collections and retroperitoneal fibrosis. Integrating key clinical and imaging features is essential for the nuanced differentiation of this heterogeneous spectrum of pathologies.