Pediatric Ultrasonography: Differentiating Acquired from Congenital Disease

s Voorjaarsdagen 2007 | 81 Diagnostic Imaging artery. The left adrenal is located cranial to the left renal artery and caudal to the left cranial mesenteric artery. The left adrenal is visualized as a bi-lobed structure with the phrenicoabdominal vein at its waist. With a transverse beam back in the middle of the abdomen, scan caudally to a large hypoechoic structure, the urinary bladder. Evaluate bladder wall and lumen contents, and, dorsal to the bladder, the major vessels (caudal vena cava and aorta). Sub lumbar lymph nodes will be seen at the aortic bifurcation into the iliac arteries, adjacent to the bladder wall. Sagittal scanning of the urinary bladder caudally will allow visualization of the urethra (and prostate in the male). At the edge of the right ribcage at the renal fossa of the liver the right kidney will be found. The right kidney should be evaluated as was the left (renal border, cortical echogenicity and pelvic architecture). By scanning sagittally between the right kidney and the caudal vena cava with a fanning technique, the right adrenal is visualized just lateral to the caudal vena cava. In transverse, find the right kidney, and lateral to the kidney, the duodenum. At the cranial end of the kidney medial to the duodenum will be the right limb of the pancreas. The right pancreatic limb is identified by visualizing the caudal pancreaticoduodenal vein within the structure. Turning to the sagittal plane, follow the pancreas, scanning medially to the angle of the body and left limb, or sagittally scan the caudal border of the stomach. The pancreatic body is seen caudal to the stomach, cranial to the splenic vein. The left limb is found caudal to the splenic vein and midline to the cranial pole of the left kidney. Returning to the transverse plane in mid abdomen at the mesenteric root, scan for mesenteric lymph nodes and small bowel wall changes. It may take 2-3 passes to evaluate the entire abdomen scanning in a uniform serpentine fashion. 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). Renal Agenesis 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. Renal Dysplasia 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 breeds in which morphologic changes are grossly evident (i.e. Persian cats, Cairn Terriers, German Shepherd Dogs). Ectopic Ureter 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 01 p041-170.indd 81 10-04-2007 15:38:01 Scientific Proceedings: Companion Animals Programme 1 | Abstracts Voorjaarsdagen 2007 82 Diagnostic Imaging Diagnostic Imaging 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. Ureterocele An 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 Patent Urachus 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. [7] Urachal diverticula can predispose the bladder to recurrent infection because of abnormal bladder flow in the region, surgical excision can be indicated. Cryptorchidism Ultrasound localization of cryptorchid testis (es) can confirm the condition in pediatric patients with bilateral involvement whose neutering status is unknown, and assist the surgeon in planning the approach (i.e. inguinal vs cranial abdominal). The retained testis can be positioned anywhere between the ipsilateral kidney and the scrotum. A systematic evaluation of the region from the caudal renal pole to the inguinal canal can identify an oval, homogenously echogenic structure with a mildly hyperechoic border representing the parietal and visceral tunics. The epididymis is usually distinctly less echoic than the testicular parenchyma, as in the scrotal testis. The cryptorchid testis will maintain the anatomic structure, the median testes (a hyperechoic slash), and normal testicular echogenicity despite being reduced in size as compared to a scrotal testis. Ultrasound is also the test of choice to detect non descended testicles in adult dogs and cats. Ultrasound may also detect non palpable testicular tumors which are more prevalent in this group of patients. Disorders of the Digestive System Development Hernias Congenital peritoneopericardial diaphragmatic hernias occur in both the dog and cat; ultrasonography provides an additional modality for their diagnosis. As with other diaphragmatic hernias, careful evaluation for continuity of the echogenic diaphragm differentiates a true hernia from mirror image artifacts. Evaluation of the pericardial contents can be made from the subcostal (across the liver) or intercostal (using the heart as an acoustic window) approach. Abnormal pericardial contents can include falciform fat, liver, gall bladder and/or intestines. Congenital inguinal hernias can similarly be confirmed by ultrasonographic identification of intestines in the subcutaneous space of the affected groin. This can be a dynamic finding. Mesenteric fat may alternatively be entrapped through the hernia. Congenital hiatal hernias are more difficult to confirm with ultrasound because of the inherent difficulty imaging the gas filled stomach and the intermittent nature of the disorder. Stomach wall with characteristic rugal folds can be imaged crossing the diaphragm into the thoracic cavity. Fluoroscopic evaluation can be more informative in these cases. Enteric Anomalies Pyloric stenosis secondary to hypertrophic gastritis has been reported in a pediatric dog. Focal circumferential thickening of the pylorus primarily involving the muscularis is typical. Enteric duplication or agenesis can be confirmed ultrasonographically in pediatric patients. Duplication is rare, can occur anywhere in the intestinal tract and the clinical signs may be nonspecific. A fluid filled juxtaintestinal formation with variable peristalsis and contents can be seen. Enteric agenesis usually results in severe clinical signs in the neonatal period. Ultrasonographic findings usually include marked fluid and gas distention of bowel proximal to the defect. Several breeds of dogs have a reported genetic predilection to small intestinal disease. Normally, the small bowel appears sonographically as four distinct layers. The bowel lumen is hyperechoic, as gas and ingesta are compressed. The layer just outside the lumen is the mucosa; it is hypoechoic and normally the thickest appearing section. Outside the mucosa is the submucosa, it is hyperechoic to the mucosa and about one third the thickness. The muscularis, the bowel muscle layer, is outside of the submucosa and appears as a very thin hypoechoic black line. An immunoproliferative enteropathy is seen in the Basenji breed which is characterized by lymphangectasia, intermittent diarrhea, weight loss, hypoalbuminemia and hyperglobulinemia, and lymphoplasmacytic mucosal infiltrates throughout the GI tract. Histopathology is diagnostic, however abdominal ultrasonography can identify bowel in which disruption of the normal layering 01 p041-170.indd 82 10-04-2007 15:38:02