Lecture 23: Obstructive Uropathy

Consequences of urinary tract obstruction

Hydronephrosis

Hydroureter

↑ risk of infection

↑ risk of stone formation

Kidney Injury, Renal Failure

Clinical presentation of urinary tract obstruction

Often manifests as pyelonephritis

Many asymptomatic

Some may be diagnosed in prenatal ultrasound

Some are diagnosed during evaluation of urinary tract infection, urinary tract obstruction or trauma

Hydronephrosis Pathogenesis

Downstream obstruction of urine outflow

Kidney(s) continue filtering and producing urine

Pressure builds up in collecting system backs up tubules

Increase pressure in tubules causes atrophy and vascular obstruction

Obstruction triggers interstitial inflammation and interstitial fibrosis

Rapid obstruction – mild dilation → pain → diagnosis

Intermittent or subtotal obstruction – hydronephrosis with chronic changes

Hydronephrosis Clinical presentation

Acute Obstruction – pain, symptoms may be due to cause of the obstruction

Unilateral hydronephrosis – May remain asymptomatic if other kidney can compensate, detected in imaging

Bilateral partial obstruction – Increased tubular pressure inhibits urine concentrating ability → polyuria, nocturia

Complete bilateral obstruction – Anuria leading to uremia, coma and death

Renal Calculi

Pain

Renal colic – intense, waxes and wanes, crampy abdominal pain

Flank tenderness progressing to groin pain depending on stone location

Hematuria – blood in the urine (red, pink or brown urine)

Vomiting, nausea

Frequent need to urinate

Urinating small amounts of urine

Diagnosis:

CT can sometimes determine stone type from density

Lab tests – Metabolic panel for renal function, urinalysis for hematuria, pyuria, bacteria

Calcium Stones

Hypercalcemia & hypercalciuria

Hyperoxaluria: Acquired – intestinal over absorption in patients with enteric disease/crohn’s disease

Hypocitraturia associated with acidosis & chronic diarrhea of unknown cause

Diffuse bone disease: Metastatic carcinoma to bone

Granulomatous disease: Sarcoidosis

Hypervitaminosis D & A

Addison disease

Calcium oxalate

Radiopaque; colorless or white

Dumb bell or envelope shaped crystals

Form in near neutral or acidic pH urine

Ethylene glycol (antifreeze) ingestion poisoning

Magnesium Stones

Rectangular coffin lid shape crystals

UTI by urea-splitting organisms

Urea → ammonia → alkaline urine → precipitation of magnesium ammonium phosphate

Proteus mirabilis, some staphylococci, & klebsiella

Vitaminosis A

Desquamated cells from the metaplastic epithelium of collecting duct act as a nidus

Mostly in women

Radiopaque

Staghorn calculi (Large branching calculi filling the renal pelvis & at least 2 calyces)

Uric Acid Stones

Radiolucent; red orange brown

Rhomboids, rosette

Common in individuals with hyperuricemia → Gout

Leukemia, lymphoma (tumor lysis syndrome); rapid cell turnover → high uric acid levels in urine

Hyperuricosuria may be due to:

Vitamin C, Thiazides & other drugs

Diet rich in purines (animal proteins)

Acidic urine pH < 5.5 may predispose to uric acid stones (uric acid is insoluble in acidic pH)

Cysteine Stones

Can form staghorn calculi

Significant fraction of pediatric calculi

Hexagonal crystals – 6 sides

Faintly radiopaque; amber color

Causes:

Genetic defect in the renal reabsorption of amino acids → cystinuria

Liver disease

Stones also form at low urinary pH/ Acidic urine

Calcium oxalate stones

Magnesium stones

Magnesium stones

Magnesium stones

Uric acid stones

Cystine stones