Suburothelial and extrinsic lesions of the urinary bladder: radiologic and pathologic features with emphasis on MR imaging.

OBJECTIVE: The purpose of this article is to present a contemporary review of the imaging appearance of diseases which affect the deeper layers of the urinary bladder, including both suburothelial and extrinsic pathologies, using radiologic-pathologic correlation. CONCLUSION: Compared to the more common urothelial lesions, at cystoscopy, suburothelial and extrinsic diseases of the urinary bladder wall often have a non-specific appearance or may be occult. Cross-sectional imaging, in particular MRI, plays an integral role in diagnosis. Mesenchymal tumors have distinct imaging features on MRI. Leiomyomas are characteristically low signal intensity on T2-weighted (T2W) imaging and progressively enhance. Lipomas and lipomatous hypertrophy are diagnosed by the presence of macroscopic fat. Neurofibromas, hemangiomas, and paragangliomas are hyperintense on T2W sequences and hypervascular. Reactive lesions occur in the setting of chronic inflammation and include: nephrogenic adenoma, cystitis cystica, and cystitis glandularis. Imaging findings are commonly non-specific; however, a mass with internal cystic spaces in association with pelvic lipomatosis is suggestive of cystitis glandularis. Urachal anomalies may be complicated by infection or malignancy. Urachal mucinous adenocarcinoma has a poor prognosis and may present as a T2-hyperintense suburothelial/extrinsic mass centered in the bladder dome. Other diseases may extrinsically involve the urinary bladder by hematogenous and peritoneal spread, including infection, endometriosis, and malignancy. A familiarity with suburothelial and extrinsic pathologies of the urinary bladder is critical for the radiologist, who may be the first to suggest these diagnoses.