A. Hydronephrosis: an anatomic entity describing an enlargement or dilation of any portion of the collecting system of the kidney.

B. Pelviectasis: dilation of the renal pelvis only.

C. Caliectasis: dilation of the renal calyces only.

D. Pelvocaliectasis: dilation of both the pelvis and calyces.

E. Pyelocaliectasis: equivalent to caliectasis.

F. Hydroureteronephrosis: includes dilation of any portion of the collecting system of the kidney, plus dilation of the ureter as well.

G. Ureterectasis or ureteronephrosis: dilation of the ureter only.

H. Obstruction: a restriction of urinary outflow. A complete obstruction will lead to renal damage. An incomplete obstruction may be physiologic (i.e., normal and not affecting renal function) or pathologic (i.e., abnormal and leading to renal injury). Obstruction and hydronephrosis are not synonymous. A patient may have an enlarged renal collecting system but not have a pathologic obstruction.

Hydronephrosis is present in up to 1.4% of fetuses and persists postnatally in half (0.7%).

One must distinguish whether the hydronephrosis or ureteronephrosis is secondary to an ongoing obstruction (in which case there may be progressive renal deterioration), or secondary to a prior obstructive event that both occurred and resolved antenatally (in which case there will be no further renal damage). In the former, if the obstruction is severe, surgical treatment to correct the obstruction may be necessary to preserve renal function; in the latter, surgical treatment is unnecessary.

Before one can debate whether the child with hydronephrosis needs surgical treatment, one must first determine the etiology of the hydronephrosis. Sometimes the etiology is straightforward (e.g., posterior urethral valves, ureteroceles) and thus the treatment options are clear (i.e., relieve the obstruction). In most cases, however, the hydronephrosis is secondary to a ureteropelvic (64%) or ureterovesical (13%) junction obstruction. In such cases, the treatment options are less clear. Many of these patients are not truly pathologically obstructed and the hydronephrosis or ureteronephrosis may be transient, resolving in time or persisting without clinical consequence; thus surgical intervention is not warranted or necessary.

Vesicoureteral reflux and posterior urethral valves are discussed in Chapters 7 and 15. Neonatal hydronephrosis is discussed in Chapter 13.

A. Ureteropelvic Junction (UPJ) Obstruction

1. Incidence: The UPJ is the most common site of obstruction in the upper urinary tract (Fig. 14-1). Approximately 64% of the 0.7% of children born with hydronephrosis will have a UPJ obstruction.

2. Pathophysiology: Successful conduction of urine from the renal pelvis to the ureter requires an anatomically patent ureteropelvic junction as well as an undisturbed transmission of peristaltic contractions in the proximal ureter. Thus, UPJ obstruction can result from an anatomic abnormality or from poor conduction of peristalsis (Fig. 14-1A). The abnormality can be either extrinsic or intrinsic. Intrinsic obstruction secondary to a narrow segment with muscular discontinuity is the most common cause. Extrinsic causes include aberrant vessels, kinks, or a high insertion of the ureter into the pelvis. There may also be a combination of intrinsic and extrinsic obstruction, for example, an intrinsic ureteral obstruction leading to a dilated pelvis which then results in a kink in the ureter (extrinsic). Rarely, a ureteral polyp may grow from just below the ureteral pelvic junction and intermittently obstruct the flow of urine by a ball valve mechanism.

3. Clinical presentation

a. Infants: Most cases of UPJ obstruction are diagnosed in utero (Chapter 13). If not noted in utero, infants will present with abdominal mass, hematuria, urinary tract infection, or gastrointestinal
discomfort. Of all abdominal masses in infants less than 1 year of age, 50% are renal in origin and 40% of these are secondary to a UPJ obstruction.

b. Older children: Older children will present with abdominal or flank pain, chronic nausea, or hematuria. This may occur after excessive hydration or following mild trauma, or urinary tract infection. Younger children tend to have more generalized lower abdominal pain, and older children will have more conventional flank pain (Dietl’s crisis). The flank pain may worsen with diuresis (e.g., after caffeinated beverages). Any child with gross hematuria after minor trauma should be evaluated for a UPJ, as should any boy with a frank urinary tract infection.

4. Associated anomalies: Patients with imperforate anus, contralateral multicystic kidney disease, congenital heart disease, VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities) syndrome, or esophageal atresia should be screened with a renal ultrasound to rule out hydronephrosis. Also, 10% of patients with UPJ obstruction have ipsilateral ureterovesical reflux.

5. Workup

a. Hydronephrosis discovered antenatally: see Chapter 13.

b. In older children:

(1) Ultrasound: Although an ultrasound should be performed as a screening test for an older child with a suspected UPJ obstruction, it may not always show hydronephrosis. If it does not show hydronephrosis, it should be repeated when the patient is having pain. If the ultrasound is done during an episode of pain, it will almost always show hydronephrosis if a UPJ obstruction is present.

(2) Diuretic renography: A MAG 3 Lasix renogram is performed if the ultrasound shows significant hydronephrosis (society of fetal urology grade 3 or 4). This will document the function of the normal and affected kidney and may on occasion provoke pain (secondary to the diuresis from the Lasix) if the obstruction is intermittent (Fig. 14.2).

(3) Voiding cystourethrogram (VCUG): Historically, all patients with suspected UPJ obstruction underwent a VCUG. Without evidence of a dilated ureter on sonography, the yield in detecting clinically significant reflux in either the affected kidney or contralateral kidney is minimal. Therefore in potty-trained children, routine VCUG is no longer indicated.

(4) CT scan: With the ubiquitous use of CT scans in the emergency room setting, UPJ obstruction may be diagnosed in the workup for acute abdominal pain. Follow-up sonogram or diuretic renogram may be near normal once the pain/obstruction has resolved consistent with the intermittent nature of UPJ blockage.

(5) MR urogram: This is another technique to diagnose UPJ obstruction. The anatomic resolution and ability to perform 3-dimensional reconstruction can localize the precise site of the obstruction as well as document the presence of a crossing vessel.

6. Treatment

a. Natural history and patient selection

(1) Symptomatic: An older child with a ureteropelvic junction obstruction may have intermittent abdominal or flank pain, at times associated with nausea and vomiting. Younger children tend to have more generalized lower abdominal pain, and older children will have more conventional flank pain. The pain may worsen during a brisk diuresis (after caffeine or alcohol). If the
pain is intermittent, sonography should be performed during an attack of pain. If the sonogram reveals the hallmarks of a UPJ obstruction, then surgery is indicated to relieve the obstruction and consequently the pain.