Postrenaal

Postrenaal, or postrenal, refers to disorders caused by obstruction to urine flow distal to the kidneys, involving structures such as the ureters, bladder, and urethra. It is one of the three broad categories of acute kidney injury, alongside prerenal and intrinsic (intrarenal) causes.

The obstruction raises intraluminal pressure, reducing glomerular filtration rate and leading to hydronephrosis if persistent. Prolonged obstruction can cause tubular injury and interstitial damage, and renal function may recover after relief of the blockage, though chronic obstruction can lead to lasting impairment.

Common causes include kidney stones and ureteral stones, ureteropelvic or ureterovesical junction obstructions, ureteral strictures, bladder outlet obstruction from benign prostatic hyperplasia or tumor, neurogenic bladder, pelvic tumors, and urethral stenosis. External compression from retroperitoneal fibrosis or malignant processes can also produce postrenal obstruction.

Clinical presentation varies with the site and duration of obstruction. Patients may have reduced urine output, flank pain, abdominal distension, or signs of urinary tract infection. Laboratory findings typically show a rise in serum creatinine and BUN, with variable electrolyte abnormalities. Imaging, especially renal ultrasound, can reveal hydronephrosis; CT urography or functional studies may be used if needed. A key diagnostic feature is improvement in urine output following relief of the obstruction, such as catheterization or decompression procedures.

Management centers on relieving the obstruction (catheterization, ureteral stenting, or percutaneous nephrostomy) and treating the underlying cause, with supportive care for kidney function. Prognosis depends on the duration of obstruction; prompt relief often allows recovery, while prolonged obstruction risks irreversible damage.