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Hydronephrosis
Pang-Yen Fan, MD
image BASICS
DESCRIPTION
  • Hydronephrosis refers to a structural finding—dilatation of the renal calyces and pelvis.
    • May occur with urinary tract infection (UTI), vesicoureteric reflux (VUR), high urine output, or physiologic changes in pregnancy
    • Sometimes accompanied with hydroureter
    • Presentation varies from incidental finding to discovery during workup for UTI or for flank or abdominal pain.
  • Hydronephrosis should not be used interchangeably with obstructive uropathy, which refers to the damage to renal parenchyma resulting from urinary tract obstruction (UTO).
EPIDEMIOLOGY
  • UTO is more common in men than women and in children than adults (congenital anomalies).
  • Acute unilateral obstruction is more common than bilateral.
ETIOLOGY AND PATHOPHYSIOLOGY
  • Hydronephrosis develops with increased pressure in the urinary collecting system.
  • Increased pressure within the renal collecting system can cause calyceal fornix rupture and urinary extravasation.
  • Over time, pressures return to normal, but kidney function declines from intense renal vasoconstriction.
  • With concomitant urinary infection, bacteria can enter the renal vasculature, resulting in sepsis.
  • UTO: may be acute/chronic, partial/complete, uni-/bilateral
    • Intraluminal obstruction: calculi, sloughed renal papillae, blood clot, fungal ball
    • Intrinsic abnormality of the urinary collecting system: transitional cell carcinomas, benign prostatic hypertrophy, prostate cancer, congenital ureteropelvic junction (UPJ) obstruction, ureterocele, neurogenic bladder (functional obstruction), urethral stricture or tuberculosis (TB) (can cause ureteral narrowing)
    • Extrinsic compression of the urinary collecting system: extraurinary malignancy (lymphoma, colon, cervix), aortic/iliac aneurysm, retroperitoneal fibrosis, uterine prolapse (15% affected), endometriosis, ovarian vein syndrome, IgG4-related disease
    • Transplant hydronephrosis: Consider BK virus.
  • UTO in transplanted kidneys is commonly due to ureteral strictures, lymphoceles (ureteral compression and bladder dysfunction).
  • VUR resulting in varying degrees of hydroureteronephrosis
  • Physiologic hydronephrosis of pregnancy
  • Hydronephrosis due to high urine output (e.g., diabetes insipidus, psychogenic polydipsia)
  • Hydronephrosis of infection: due to bacterial toxins inhibiting smooth muscle contraction of the renal pelvis and ureter
Pediatric Considerations
  • Antenatal hydronephrosis is diagnosed in 1-5% of pregnancies, usually by US, as early as the 12th to 14th week of gestation.
  • Children with antenatal hydronephrosis are at greater risk of postnatal pathology.
  • Postnatal evaluation begins with US exam; further studies, such as voiding cystourethrogram (VCUG), based on the severity of postnatal hydronephrosis
  • In neonates, it is the most common cause of abdominal mass.
  • Common etiologies in children are VUR, congenital UPJ obstruction, neurogenic bladder, and posterior urethral valves.
  • Pediatric diagnostic algorithm differs from adult due to different differential diagnosis necessitating age-appropriate testing.
Pregnancy Considerations
  • Physiologic hydronephrosis in pregnancy is more prominent on the right than left and can be seen in up to 80% of pregnant women.
  • Dilatation is caused by hormonal effects, external compression from expanding uterus, and intrinsic changes in the ureteral wall.
  • Despite high incidence, most cases are asymptomatic.
  • If symptomatic and refractory to medical management, ureteric calculus should be considered and urinary infection must be excluded.
image DIAGNOSIS
Symptoms vary according to cause, chronicity, location, and degree of obstruction.
PHYSICAL EXAM
  • General signs
    • Volume overload (edema, rales, hypertension [HTN]) from renal failure
    • Diaphoresis, tachycardia, tachypnea with pain
    • High-grade fever, if infection
  • Abdominal exam: CVA tenderness, palpable bladder, rarely palpable abdominal mass (may be visible, particularly in thin children)
  • Pelvic exam: pelvic mass, uterine prolapse, palpable enlarged prostate (cancer or benign), urethral meatal stenosis, phimosis
DIAGNOSTIC TESTS & INTERPRETATION
  • Urinalysis with microscopy: hematuria, proteinuria, crystalluria, pyuria
  • Midstream urine culture and sensitivity: Exclude UTI.
  • Basic metabolic panel: Elevated urea and creatinine may indicate obstructive uropathy. Hyperkalemic nonanion gap metabolic acidosis may indicate type 4 distal RTA due to obstruction.
  • CBC: Anemia of CKD, leukocytosis; if infection, check platelet count prior to considering ureteral instrumentation.
  • Prostate-specific antigen (PSA): adult males age >50 years or with abnormal digital rectal exam or bladder outlet obstruction signs or symptoms
  • Urine cytology: for malignant cells in urothelial malignancies
  • US and noncontrast CT scan are effective in diagnosing presence and cause of obstruction in most cases.
  • US: screening test of choice for hydronephrosis
    • Sensitivity 90%, specificity 84.5% compared with IVU. Does not assess function and rarely detects cause and level of obstruction. Degree of hydronephrosis does not correlate with duration or severity of the obstruction.
    • Advantages: detects renal parenchymal disease (decreased renal size, increased cortical echogenicity, cortical thinning, cysts); no exposure to radiation or contrast; safe in pregnancy, contrast allergy, and renal dysfunction
    • False-positive findings 15.5% (for UTO): normal extrarenal pelvis, parapelvic cysts, VUR, excessive diuresis
    • False-negative findings 10%: dehydration, acute obstruction, calyceal dilatation misinterpreted as renal cortical cysts, and retroperitoneal fibrosis
  • Noncontrast helical CT (NHCT): test of choice for suspected nephrolithiasis
    • Reported sensitivity 94-96%, specificity 94-100%. Stone is most commonly found at levels of ureteric luminal narrowing: UPJ, pelvic brim, and the vesicoureteric junction.
    • Typical findings in acute obstruction are hydronephrosis with hydroureter proximal to the level of obstruction, perinephric stranding, and renal swelling. If chronic, renal atrophy may be noted.
    • Advantages: no contrast exposure, time-saving, cost-effective, identifies extraurinary pathology
    • Disadvantages: does not assess function or degree of obstruction; higher radiation exposure, although low radiation dose protocols have shown comparable accuracy
  • P.503

  • DTPA or MAG-3 radionuclide renal scan (diuretic renal scintigraphy)
    • Indicated only for evaluation of hydronephrosis without apparent obstruction
    • Determines presence of true obstruction as well as total and split (right vs. left) renal function
    • Furosemide is given 20 minutes after the tracer and the T1/2 for the tracer's washout is measured. T1/2; <10 minutes is unobstructed, >20 minutes is obstructed, and 10 to 20 minutes is equivocal; some experts consider <15 minutes normal.
    • Advantages: no contrast exposure, safe in contrast allergy and renal dysfunction
    • False-positive findings: delayed excretion due to renal failure, massive dilatation causing a water-reservoir effect of delayed excretion without obstruction
    • False-negative findings: dehydration or inadequate diuretic challenge
  • Multiphase contrast-enhanced CT
    • Nonenhanced phase detects stones and swelling.
    • Parenchymal phase demonstrates decreased enhancement of renal parenchyma with acute obstruction; can identify extraurinary causes of obstruction and determine the relative glomerular filtration rate (GFR) of each kidney with accuracy equal to radionuclide renal scan
    • Delayed phase allows visualization of the collecting system and soft tissue filling defects (e.g., urothelial cancer).
  • Magnetic resonance urography (MRU): indicated when US and NHCT are nondiagnostic
    • Provides anatomic, functional, and prognostic information. Sensitivity not superior to US or NHCT for nephrolithiasis (70%) but superior for soft tissue causes including strictures.
    • Advantages: no radiation exposure, safe in young children and pregnant women
    • Disadvantages: more expensive and time-consuming (35 vs. 5 minutes) and less available compared with CT. Gadolinium is contraindicated in renal failure due to risk of nephrogenic systemic fibrosis.
Diagnostic Procedures/Other
Cystoscopy, retrograde pyelogram ± ureteroscopy, and biopsy are occasionally used to determine the cause of obstruction (e.g., small urothelial cancer missed on imaging) or to confirm a normal distal ureter prior to pyeloplasty. In addition, such procedures are often needed to establish a definitive pathologic diagnosis for mass lesions.
image TREATMENT
GENERAL MEASURES
  • Medical treatment: correction of fluid and electrolyte abnormalities, pain control, antibiotics as an adjunct to drainage if infection present
  • Relief of obstruction: prompt drainage indicated in the presence of UTI, compromised renal function, or uncontrollable/persistent pain
    • Bladder outlet obstruction: urethral or suprapubic catheter
    • Ureteric obstruction: retrograde (cystoscopic) or antegrade (percutaneous) stenting
  • VUR is often managed conservatively with antibiotics; surgical management required in severe cases in children or women of childbearing age
  • Medical expulsive therapy (MET) with &agr;-blockers or calcium channel blockers indicated for urethral stones <10 mm in patients with controlled pain, no signs of sepsis, with good renal function
SURGERY/OTHER PROCEDURES
  • Hydronephrosis due to obstruction
    • Congenital UPJ obstruction: Pyeloplasty (open or laparoscopic) and minimally invasive stricture incision (endopyelotomy) are used with comparable results.
    • Nephrolithiasis: Extracorporeal shock wave lithotripsy (ESWL) is the initial treatment of choice for management of impacted upper urethral stones ≤2 cm. Ureteroscopy with or without intracorporeal lithotripsy has lower retreatment but higher complication rates and longer hospital stay. Ureteral stenting pre-ESWL or postureteroscopy associated with no additional benefit and more discomfort and morbidity (1)[A]
    • Transitional cell cancer: nephroureterectomy
    • Idiopathic retroperitoneal fibrosis: ureterolysis (frees ureters from inflammatory mass)
    • Prostate disorders: various treatment modalities, including transurethral resection of the prostate (TURP) and radical prostatectomy
  • Nonobstructed hydronephrosis
    • VUR: ureteric reimplantation, endoscopic suburethral injection
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
Obstruction coexisting with infection (pyonephrosis) is a true urologic emergency requiring urgent drainage. Typically, this requires placement of percutaneous nephrostomy tube(s), as retrograde (cystoscopic) stenting is often difficult, but both are equally effective.
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
  • Serial monitoring of kidney function (electrolytes, BUN, and creatinine) and BP until renal function stabilizes. Frequency of monitoring depends on severity of renal dysfunction.
  • Follow-up US after stabilization of renal function to assess for resolution of hydronephrosis. If hydronephrosis persists, consider diuretic radionuclide study to rule out persistent obstruction.
PROGNOSIS
  • Recovery of renal function depends on etiology, presence or absence of UTI, and degree and duration of obstruction.
  • Significant recovery can occur despite days of complete obstruction, although some irreversible injury may develop within 24 hours. Delays in therapy can lead to irreversible renal damage (2).
  • Diagnostic testing is of poor predictive value. Course of incomplete obstruction is highly unpredictable.
REFERENCES
1. Aboumarzouk OM, Kata SG, Keeley FX, et al. Extracorporeal shock wave lithotripsy (ESWL) versus ureteroscopic management for ureteric calculi. Cochrane Database Syst Rev. 2011;(12):CD006029.
2. Cohen EP, Sobrero M, Roxe DM, et al. Reversibility of long-standing urinary tract obstruction requiring long-term dialysis. Arch Intern Med. 1992;152(1):177-179.
Additional Reading
&NA;
  • Ramsey S, Robertson A, Ablett MJ, et al. Evidence-based drainage of infected hydronephrosis secondary to ureteric calculi. J Endourol. 2010;24(2):185-189.
  • Seitz C, Liatsikos E, Porpiglia F, et al. Medical therapy to facilitate the passage of stones: what is the evidence? Eur Urol. 2009;56(3):455-471.
  • Shen P, Jiang M, Yang J, et al. Use of ureteral stent in extracorporeal shock wave lithotripsy for upper urinary calculi: a systematic review and meta-analysis. J Urol. 2011;186(4):1328-1335.
  • Worster A, Preyra I, Weaver B, et al. The accuracy of noncontrast helical computed tomography versus intravenous pyelography in the diagnosis of suspected acute urolithiasis: a meta-analysis. Ann Emerg Med. 2002;40(3):280-286.
Codes
&NA;
ICD10
  • N13.30 Unspecified hydronephrosis
  • N13.39 Other hydronephrosis
  • Q62.0 Congenital hydronephrosis
Clinical Pearls
&NA;
  • US and noncontrast CT identify most causes of hydronephrosis.
  • Relief of obstruction, when present, is the primary treatment.