Hydronephrosis

Contributors: Cafer Zorkun M.D., PhD.

Overview
Hydronephrosis is distention and dilation of the renal pelvis, usually caused by obstruction of the free flow of urine from the kidney.

Pathophysiology
The obstruction may be either partial or complete and can occur anywhere from the urethral meatus to the  calyces of the renal pelvis.

The obstruction may arise from either inside or outside the urinary tract or may come from the wall of the urinary tract itself. Intrinsic obstructions (those that occur within the tract) include blood clots, stones, sloughed papilla along with tumours of the kidney, ureter and bladder. Extrinsic obstructions (those that are caused by factors outside of the urinary tract) include pelvic or abdominal tumours or masses, retroperitoneal fibrosis or neurological deficits. Strictures of the ureters (congenital or acquired), neuromuscular dysfunctions or schistosomiasis are other causes which originate from the wall of the urinary tract.

Signs and symptoms
The signs and symptoms of hydronephrosis depends upon whether the obstruction is acute or chronic. Unilateral hydronephrosis may even occur without symptoms.

Blood tests can show raised creatinine and electrolyte imbalance. Urinalysis may show an elevated pH due to the secondary destruction of nephrons within the affected kidney.

Symptoms that occur regardless of where the obstruction lies include loin or flank pain. An enlarged kidney may be palpable on examination.

Where the obstruction occurs in the lower urinary tract, suprapubic tenderness (with or without a history of bladder outflow obstruction) along with a palpable bladder are strongly suggestive of acute urinary retention, which left untreated is highly likely to cause hydronephrosis.

Upper urinary tract obstruction is characterised by pain in the flank, often radiating to either the abdomen or the groin. Where the obstruction is chronic, renal failure may also be present. If the obstruction is complete, an enlarged kidney is often palpable on examination.

Diagnosis
Prenatal diagnosis is possible.

Blood (U&E, creatinine) and urine (MSU, pH) tests should be taken. IVUs, ultrasounds, CTs and MRIs are also important tests.

Ultrasound allows for visualization of the ureters and kidneys and can be used to assess the presence of hydronephrosis and/or hydroureter.

An IVU is useful for assessing the position of the obstruction. Antegrade or retrograde pyelography will show similar findings to an IVU but offer a therapeutic option as well.

The choice of imaging depends on the clinical presentation (history, symptoms and examination findings):

In the case of renal colic (one sided loin pain usually accompanied by a trace of blood in the urine) the initial investigation is usually an intravenous urogram. This has the advantage of showing whether there is any obstruction of flow of urine causing hydronephrosis as well as demonstrating the function of the other kidney. Many stones are not visible on plain xray or IVU but 99% of stones are visible on CT and therefore CT is becoming a common choice of initial investigation.

MRI is less commonly used, often when there is a reason to avoid radiation exposure, e.g. in pregnancy.

Patient #1: CT images demonstrate marked left hydronephrosis secondary to a calculus in the proximal right ureter

Images courtesy of RadsWiki

Treatment
Treatment of hydronephrosis focuses upon the removal of the obstruction and drainage of the urine that has accumulated behind the obstruction. Therefore, the specific treatment depends upon where the obstruction lies, and whether it is acute or chronic.

Acute obstruction of the upper urinary tract is usually treated by the insertion of a nephrostomy tube. Chronic upper urinary tract obstruction is treated by the insertion of a ureteric stent or a pyeloplasty.

Lower urinary tract obstruction (such as that caused by bladder outflow obstruction secondary to prostatic hypertrophy) is usually treated by insertion of a urinary catheter or a suprapubic catheter.

Surgery is not required in all cases.

Complications
Left untreated, bilateral obstruction (obstruction occurring to both kidneys rather than one) has a poor prognosis.