Imaging evaluation of amyloidosis of the urinary tract and retroperitoneum.

Amyloidosis is a heterogeneous group of disorders and may be classified as systemic or localized on the basis of the distribution of amyloid deposition. Infrequently, the urinary tract and supporting retroperitoneum may be involved, and the imaging findings are nonspecific and diverse. Localized amyloidosis usually involves the bladder and often mimics malignancy. Less frequently, the ureter, renal pelvis, and urethra are involved. The most common findings of amyloid deposition are focal or diffuse wall thickening in the urinary tract with intramural calcification that often results in ureteral obstruction. When the renal parenchyma is involved, patients generally develop nephrotic-range proteinuria, and the kidneys appear atrophic with cortical thinning. In systemic amyloidosis, amyloid may infiltrate the retroperitoneal and pelvic soft tissues, encasing the urinary tract, with diffuse soft-tissue thickening and slowly progressive calcification. In both localized and systemic amyloidosis, amyloid lesions are characteristically hypointense at T2-weighted magnetic resonance imaging. Because myeloma or lymphoma is often present with systemic amyloidosis, biopsy is necessary to diagnose the condition. Amyloid lymphadenopathy characteristically appears as nodal enlargement with calcification and low attenuation at computed tomography. Radiologists should be familiar with the imaging features of amyloidosis that, in the appropriate clinical context, may indicate the diagnosis.