Pediatric abdominal ultrasonography (Proceedings)
Pediatric patients are commonly presented to the veterinarian because of signs referable to the abdominal cavity due to congenital anomalies, dietary indiscretion, parasitic infestation and infectious disease. Abdominal ultrasound provides valuable clinical information about the peritoneal cavity, great vessels, abdominal viscera and lymph nodes obtained in a non invasive fashion and usually not necessitating sedation or anesthesia. Ultrasonography thus greatly facilitates diagnostic differentiation between congenital and acquired disorders; techniques will be described in this paper.
Disorders of Urogenital Development
Veterinary pediatric ultrasonography has been hampered by the small size of neonatal organs, but advances in pediatric veterinary ultrasonography have been encouraging. Abdominal ultrasound can facilitate the diagnosis of congenital urogenital disorders, because ectopic, distended ureters and changes in renal architecture are usually readily seen. The presence and location of cryptorchid testes can often be detected with ultrasound. Ultrasonographic examination of the bladder disclosing urolithiasis can provide information suggesting congenital hepatic vascular anomalies.The most common familial disorders in cats and dogs include renal agenesis, renal dysplasia, polycystic kidneys, renal amyloidosis, basement membrane disorders, and tubular dysfunction (Fanconi's syndrome).
Congenital renal agenesis resulting in the absence of a kidney can be confirmed with ultrasound. The contralateral kidney typically has normal internal anatomy, but is enlarged as a consequence of obligatory hypertrophy. Renal function of the pediatric patient does not equate that of the adult until 4-6 months of age, compensatory renomegaly may not be apparent until that time.
Until reliable genetic markers are available for the various breed specific congenital renal dysplasias, ultrasound provides the best method of screening young dogs and cats for these likely heritable disorders. Early ultrasonographic screening is possible in platycephalic breeds in which morphologic changes are grossly evident (i.e. Persian cats, Cairn Terriers, German Shepherd Dogs).
Congenital ectopic placement of the distal ureter into the urethra, vestibule or vagina is usually associated with ureteral dilation with or without renal pelvic dilation. Dilation of the ureter improves the sensitivity of the ultrasound study; however, the diagnosis can be elusive. Visualization of a non vascular fluid filled structure with a hyperechoic wall passing dorsal to the urinary bladder, or obvious insertion of the structure into the proximal urethra suggest the diagnosis. Visualization of the ureteral jets in the bladder suggests normalcy, however some ectopic ureters insert initially into the bladder and additionally tunnel distally to terminate in an abnormal site. Visualization of the dilated ureter usually occurs near the urinary bladder. Visualization of the bladder neck and proximal urethra may be obscured by pubic bone, making identification of such termination difficult.
Hydronephrosis can eventually result from an uncorrected ectopic ureter due to flow impedance at the abnormal site of insertion. Urinary tract infection is commonly associated with ectopia, due to accompanying urethral sphincter mechanism anomalies, and if not detected and treated, can progress to pyelonephritis and ureteritis. Infection and its associated inflammation in the tract can further alter the ultrasonographic appearance of the kidneys, bladder, ureters and urethra (see below).
Contrast enhanced computed tomography is the most sensitive and specific modality for the diagnosis of ectopia, but, like double contrast radiography, requires anesthesia, making initial evaluation with ultrasound desirable when ectopia is suspected clinically. The condition is thought to be heritable, and is more common in females.
A ureterocele is an uncommon congenital dilation of the ureter near the bladder, appearing as a cystic structure within the bladder lumen or wall. The ureterocele occurs most commonly in association with an ectopic ureter. Diagnosis can be made by scanning the urinary bladder in the transverse plane and watching for strong peristalsis of the adjacent ureter
The urachus permits the flow of urine from the bladder into the allantoic sac of the fetus, and normally atrophies at birth. A patent urachus in the neonate is characterized clinically by urine dribbling from the umbilicus. The fluid filled urachus can be identified ultrasonographically, extending cranially from the cranioventral bladder wall. If an incompletely patent urachus is present in the neonate, a urachal diverticulum may result, seen as a divot in the apex of the bladder.  Urachal diverticula can predispose the bladder to recurrent infection because of abnormal bladder flow in the region, surgical excision can be indicated.