Histologic differences between extrinsic and intrinsic ureteropelvic junction obstruction

OBJECTIVE Ureteropelvic junction obstruction (UPJ) can be caused by intrinsic disorganization or extrinsic compression from crossing vessels (CV). What is not clear is whether there is also intrinsic UPJ pathology in patients with CV. Recent surgeries, such as the Hellstrom vascular hitch procedure, move the CV cephalad without resecting the UPJ, which presumes no intrinsic narrowing. Our aim was to determine whether the histologic features of the 2 types of UPJ obstruction are distinct enough to enable a blinded pathologist to histologically identify the cause of obstruction. METHODS We reviewed all patients undergoing pyeloplasties from 2000 to 2006. All CV cases with available pathology were selected. A random selection of intrinsic cases was used as controls. One blinded pathologist reviewed the histology, specifically scoring muscle and collagen density. RESULTS Sixteen patients were reviewed. Seven had CV and 9 had intrinsic obstruction. Muscle density was different between the 2 groups with CV denser compared with intrinsic (P = .005). The pathologist correctly assigned the cause of obstruction in 5/7 (71%) of CV and 7/9 (78%) of intrinsic cases (P = .039). CONCLUSIONS Identification of a significant CV intraoperatively does translate to a discernible appearance histologically.