Teaching Case

The patient was presented with hypertension and lumbar pain for 5 months. He had been operated 4 years ago in another Hospital because left obstructive uropathy. Patient underwent MR imaging and percutaneous biopsy.

The patient was admitted because of hypertension and lumbar pain for 5 months. He had been operated 4 years ago in another Hospital because left obstructive uropathy and he refused any further treatment. Sonography demonstrated normal-sized kidneys and a hypoechoic bilateral perirenal halo. MR imaging was performed and the patient underwent a percutaneous biopsy.

Retroperitoneal fibrosis is an uncommon disease characterized pathologically by proliferation of fibrous tissue and various degrees of chronic inflammation in the retroperitoneal space. The etiology of retroperitoneal fibrosis is idiopathic, although drugs (such as methysergide), primary or metastatic tumors, aneurysms, surgery and radiotherapy have been associated with similar pathologic alterations in the retroperitoneum. The plaque of idiopathic retroperitoneal fibrosis (IRPF) typically begins below the aortic bifurcation at the level of the sacral promontory or the fourth or fifth lumbar vertebra and then spreads along the anterior surface of the spine toward the renal hila, where, on rare occasion, it may envelop the renal pelvis and even surround the kidney. This case is a rare form of retroperitoneal fibrosis due to the predominantly perirenal involvement with only a little amount of abnormal fibrosis tissue around the aorta and cava vein. MR imaging is, nowadays, considered the most specific imaging examination to diagnose IRPF due to its characteristic short T2 related to the fibrotic acellular composition of the mass. On MR, IRPF usually has homogeneous signal on T1 and T2 weighted sequences, similar to that of striated muscle, with no increase of signal intensity on T2-weighted images. Contrast enhancement varies depending upon the maturity of the fibrous tissue. In our case, postcontrast T1-weighted images showed peripheral slight enhancement and central intermediate signal intensity within the mass. These areas intermediate signal intensity also appeared to have low signal intensity on T2-weighted image. The MR findings are presumably produced by a mixture of active inflammatory tissue and mature, well-organized fibrous tissue. Medical therapy with steroids is useful in the active inflammatory phase of IRPF and may be used as an adjunct to surgical therapy or alone in IRPF. MR should be used to demonstrate the changes in size of the mass and modification of signal intensity during medical therapy. Perirenal solid masses are rare and the differential diagnosis is practically circumscribed to lymphoma or other retroperitoneal neoplasm. In both cases, MR examination has a homogeneous or heterogeneous hyperintense signal intensity on T2-weighted sequences and signal intensity enhancement on T1-weighted images after Gd-DTPA injection. Hypointensity on T2 weighted images due to the short T2 of masses with significant fibrous elements and marked hypocellularity such as aggressive fibromatosis, cicatricial fibroma, and desmoid tumors is well known. However, when short T2 is identify on MR examination of a retroperitoneal mass, the diagnosis of IRPF should be considered.