JOANNE N. WOOD
HISTORY OF PRESENT ILLNESS
The patient is a 2-year-old male who presents with a 2-day history of vomiting and abdominal pain. The emesis is bilious but nonbloody and the pain is periumbilical. He has had decreased urine output during the last day, although his oral intake has been good. His mother denies any history of fever or diarrhea.
The patient has been evaluated in the emergency department with nonbilious emesis three times in the past month. Each evaluation included normal electrolytes. A urinalysis performed at the last visit was within normal limits. The child was born at term by spontaneous vaginal delivery following an uncomplicated pregnancy. He has never been hospitalized nor had any surgeries. There is no family history of malignancy.
T 37.8°C; RR 24/min; HR 88/min; BP 120/64 mmHg
Weight and Length are at the 75th percentile for age
The patient is resting comfortably and in no acute distress. His cardiac and pulmonary examinations are normal. His abdomen is soft, nontender with absent bowel sounds, and fullness in the left upper quadrant. There is no hepatomegaly or splenomegaly. His rectal examination reveals normal sphincter tone with hard guaiac negative stool in the rectal vault.
Laboratory evaluation revealed 23 000 white blood cells/mm3 with 1% band forms, 47% segmented neutrophils, 45% lymphocytes, and 7% monocytes. The hemoglobin was 12.2 g/dL and the platelet count was 300 000 cells/mm3. Serum electrolytes were normal.
COURSE OF ILLNESS
Abdominal radiographs show a left upper quadrant/flank mass displacing the bowel to the right. What are the most likely causes of an abdominal mass in this child?
DISCUSSION CASE 3-7
Vomiting associated with an abdominal mass is always an emergency and early imaging is imperative. The differential diagnosis of an abdominal mass in children includes organomegaly, malignant and nonmalignant tumors, congenital anomalies, and abscesses. The most likely etiology of an abdominal mass is dependent on the age of the child, location of the mass, and associated symptoms.
In young infants, the most common causes of abdominal masses are hydronephrosis and multicystic kidney which typically present as a flank mass. The most common cause of unilateral hydronephrosis is ureteropelvic junction obstruction, and posterior urethral valves (PUV) is the most common cause of bilateral hydronephrosis. Neonates with posterior urethral valves may also have a large palpable bladder. Hydronephrosis may also result from other causes of distal urinary tract obstruction and from renal vein thrombosis. Gastrointestinal duplications, gastrointestinal obstructions, ovarian cysts, and hydrometrocolpos can present as abdominal masses in neonates. Mesoblastic nephromas, which are usually benign tumors, can be seen in the neonatal period but are uncommon in older infants. Neuroblastoma is the most common malignant tumor in infants but Wilms tumor, extragonadal germ cell tumor, hepatoblastoma, and soft tissue sarcomas can also occur.
The likelihood of an abdominal mass being malignant is higher in older infants and children than in neonates. Neuroblastoma and Wilms tumor are the most common solid abdominal neoplasms in children but hepatocellular carcinoma, genitourinary tract rhabdomyosarcomas, teratomas, and ovarian germ cell tumors can also occur.
The location of the mass can provide clues regarding its likely origin (see Table 3-8). Right upper quadrant (RUQ) masses frequently arise from the liver. Nonmalignant hepatic masses include polycystic liver disease, benign hepatic tumors, vascular lesions, storage disease, abscesses, and hepatitis. Choledochal cysts and gall bladder obstruction may also present with RUQ masses while splenic lesions may present with LUQ masses. Flank and upper quadrant masses may be due to renal or adrenal etiologies. Right lower quadrant masses in a child with signs and symptoms of inflammation suggest an abscess from a ruptured appendix or inflammatory bowel disease.
TABLE 3-8. Malignant and nonmalignant etiologies of abdominal masses in children by location and organ.
In this patient, the location of the mass in the left upper quadrant to flank area is suggestive of a renal, adrenal, or splenic etiology. The history of decreased urinary output despite normal intake raises the possibility of an obstructive uropathy.
The patient was admitted to the hospital and underwent an abdominal sonogram that revealed a large cystic renal lesion. Diuretic renography showed delayed emptying in an enlarged kidney with evidence of obstruction at the proximal ureter suggesting the diagnosis of ureteropelvic junction obstruction. The diuretic renography also demonstrated decreased renal function. A nephrostomy tube was placed and the patient was discharged home with follow-up in 3 weeks for either pyeloplasty or nephrectomy if kidney function remained poor.
INCIDENCE AND EPIDEMIOLOGY OF URETEROPELVIC JUNCTION OBSTRUCTION
Ureteropelvic junction (UPJ) obstruction, the most common obstructive uropathy in children, has an annual incidence of 5 cases per 100 000. There is a 2:1 male to female predominance. In the vast majority of cases (90%) only one kidney is affected with the left kidney being affected in 60% of cases.
Ureteropelvic junction obstruction is characterized by a blockage at the junction of the renal pelvis and the ureter that prevents urine from passing from the renal pelvis to the bladder. The blockage may be intrinsic or extrinsic in nature and can result from congenital or acquired conditions. The majority of cases of UPJ obstruction, however, are congenital and result from an intrinsic obstruction caused by an aperistalitic proximal segment of the ureter. Ureteral polyps, valvular mucosal folds, persistent fetal convolutions, and aberrant arteries are less common causes of congenital UPJ obstruction.
The majority of patients with congenital UPJ obstructions are now diagnosed prenatally on fetal ultrasound. Cases of congenital UPJ obstruction not detected on prenatal ultrasound may present in infancy with a painless palpable flank mass, poor feeding, or failure to thrive. Older children may present with episodes of colicky abdominal or flank pain accompanied by nausea and vomiting. Patients with UPJ obstruction may also present with hematuria after minor trauma or recurrent urinary tract infections.
Although the majority of cases of congenital UPJ obstruction are diagnosed prenatally, the diagnosis can be difficult to make in cases of asymptomatic infants with incidental renal pelvis dilation on prenatal ultrasound.
Renal and bladder ultrasonography. Ultrasonography is usually the preferred primary imaging study when an obstructive uropathy is suspected. A finding of dilated renal pelvis on fetal ultrasound should be evaluated with an ultrasound after birth. If possible, the ultrasound should be performed after the third day of life because of the oliguric state of newborns. If the ultrasonography is normal, it should be repeated in 1 month. Ultrasonography is also used to evaluate suspected cases of UPJ obstruction presenting in childhood. Ultrasonography can provide information on the laterality and severity of the hydronephrosis as well as changes to the renal parenchyma.
Voiding cystourethrography. Voiding cystourethrography (VCUG) is frequently performed in cases of hydronephrosis from UPJ obstruction to evaluate for associated vesicoureteral reflux (VUR).
Diuretic renography. In cases of congenital obstructive uropathy including UPJ obstruction, diuretic renography with 99m-Tc-mercaptoacetyltriglycine (MAG3) is considered the gold standard test for functional imaging. The uptake of the tracer during the diuretic renography provides a measure of the function of the kidney. The diuretic renography is also used to confirm the obstruction and assess the severity of the obstruction.
Magnetic resonance imaging. Magnetic resonance imaging has the potential to assess both anatomy and function but its use in cases of obstructive uropathy has not yet been fully validated.
Historically open pyeloplasty was the treatment of choice for patients with congenital UPJ obstruction and was performed early with the goal of preserving renal function. More recently, however, selected cases of prenatally diagnosed congenital UPJ obstruction are undergoing conservative management. Infants with UPJ obstruction associated with an abdominal mass, bilateral severe hydronephrosis, a solitary kidney, or decreased renal function in the affected kidney still require prompt surgical intervention. Asymptomatic cases with good renal function, however, may be followed with serial renal ultrasounds and repeat diuretic renography. Indications for surgical intervention include symptoms related to UPJ obstruction, worsening renal function, stones, urinary tract infections, or hypertension. In select circumstances a percutaneous nephrostomy may be inserted to allow for drainage of the hydro-nephrotic kidney for a few weeks and then renal function is reassessed.
For patients who do require surgical interventions, less invasive procedures including percutaneous endopyelotomy, ureteroscopic endopyelotomy, and cautery wire balloon endopyelotomy have been developed in recent years as alternatives to open pyeloplasty. Unfortunately, the success rates with these techniques has been lower than with open pyeloplasty. Laparoscopic pyeloplasty, however, has been shown to have success rates similar to open pyeloplasty and is associated with reduced length of hospital stay and decreased morbidity. Laparoscopic pyeloplasty may not be universally available especially for pediatric patients. Robotic-assisted laparoscopic pyeloplasty techniques have also been developed but its advantages over regular laparoscopic pyeloplasty have not been clearly demonstrated.
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