Makindo Medical Notes

Kidney can be obstructed anywhere between collecting ducts and the urethral meatus. Unilateral ureteral obstruction usually causes no detectable change in urine flow or serum creatinine levels, and renal failure occurs only if the drainage of both kidneys is significantly compromised.

About

• Kidney obstruction may occur anywhere from the collecting ducts to the urethral meatus.
• Imaging often reveals proximal dilatation of the urinary tract.

Causes

• Renal: Renal papillary necrosis, staghorn calculus, tumour, clot, bleeding.
• Ureteric: Renal stone, extrinsic tumour (e.g., cervical cancer), intrinsic tumour, retroperitoneal fibrosis.
• Bladder: Stones, intrinsic tumour, clot, neuropathic bladder, retention (e.g., due to constipation).
• Urethra: Prostatic hypertrophy, prostate cancer, stone, phimosis, stricture.

Clinical Presentation

• Symptoms may include acute kidney injury and increased creatinine levels.
• Above the bladder: Flank fullness.
• Partial bladder outlet obstruction presents with urinary hesitancy, decreased urine flow rate, polyuria, and nocturia.
• At or below the bladder: Acute retention, bladder distension, and pain.
• Physical Exam: A rectal exam may reveal an enlarged prostate or hard stool, and a palpable bladder may be present.

Investigations

• Blood Tests: Full blood count (FBC), urea & electrolytes (U&E) to assess renal function. Marked acute kidney injury (AKI) with elevated creatinine levels, metabolic acidosis, and significant hyperkalaemia are common.
• Imaging: Renal tract ultrasound (USS) to determine the level of obstruction and detect hydronephrosis or hydroureter.
• Additional tests, such as spiral CT and radionuclide studies, may be required.
• A postvoid residual volume of more than 200 mL is considered abnormal and suggests bladder outlet obstruction.

After the relief of a complete obstruction, a post-obstructive diuresis may occur. This must be closely monitored and treated with volume repletion when necessary. The diuresis is caused by the sodium and urea retained during the obstruction and impaired tubular concentrating ability.

Management

• Catheterization: Relieve acute retention and measure urine output.
• Imaging: Perform an ultrasound to identify the level of obstruction and the suspected cause.
• Monitor for marked diuresis after obstruction relief and manage accordingly.
• For bladder outflow obstruction in males, consider an α1 antagonist such as tamsulosin or an α-reductase inhibitor like finasteride to improve urine flow. In severe cases, surgery may be necessary to relieve prostate obstruction.
• Surgical Intervention: Surgical stenting or other procedures may be required to relieve obstruction and prevent renal damage.