Retroperitoneal Fibrosis limited to Perinephric spaces-Rare Disease

78 year old treated case of collagen disorder in the past with immunosuppression on routine USG Abdomen is detected to have perinephric heterogeneous echogenic regions compressing and paging the kidneys (right > left). MDCT study delineates extensive, symmetrical, perinephric spaces, heterogeneous enhancing nodular mass lesions with fat stranding, compression and displacement of the kidneys, with dilated pelvicollecting system on the right along with ureter with rest of the study including great vessels, origins of the main vessels and retroperitoneum in general unremarkable.Retroperitoneal fibrosis limited to the perinephric spaces is likely.

Teaching Points by Dr MGK Murthy, Dr Sumer Sethi, Mr Hariom Sharma :

·RPF is characterized by proliferation of fibrous tissue around the aorta, through a plaque like infiltrative soft tissue process and commonly involves infrarenal aorta and iliac vessels.

·2/3rds are idiopathic with a male preponderance. RPF as an isolated disease or as a part of other autoimmune disorders is known.

·Perirenal involvement could be secondary or may occur as in this case without associated RPF. 3 stages are described ranging from chronic active inflammation to fibrous scaring.

·Imaging could show soft tissue mass that envelops the kidneys with or without displacement. MR is good for demonstrating high T2 signal and early contrast enhancement in active inflammation stage, and low T2 signal with delayed enhancement in fibrosis stage. Isolated perirenal fibrosis is difficult to diagnose and in cases of doubt biopsy would help.