Prenatal diagnosis of renal duplication by magnetic resonance imaging

Troubleshooting Tips for Diagnosing Complex Fetal Genitourinary Malformations

Fetal genitourinary anomalies can present a diagnostic challenge for the radiologist. The absence of a normally located kidney may represent agenesis or be secondary to a fusion or migration abnormality. A dilated renal pelvis should prompt evaluation for a specific cause, including ureteropelvic junction obstruction, reflux, or an obstructed duplicated system. Cystic parenchymal changes are characteristic of a multicystic dysplastic kidney but may also be seen in obstructive cystic dysplasia. There are numerous causes of megacystis including chromosomal (trisomy 18 syndrome), obstruction (posterior urethral valves, urethral atresia), or muscular dysfunction (prune belly syndrome, megacystis microcolon intestinal hypoperistalsis syndrome). Important mimics of a large bladder include hydrocolpos and urogenital sinus or cloacal malformation. Complications of genitourinary malformations are common and include oligohydramnios, urinary ascites, and urinoma. Making an accurate diagnosis often requires additional US views beyond those obtained in the standard fetal survey and occasionally performing fetal MRI. The appropriate use of orthogonal T2-weighted sequences, in conjunction with diffusion-weighted images for evaluation of the kidneys and gradient-recalled-echo sequences for evaluation of T1-hyperintense meconium in the colon, can play an integral role in diagnosis. Accurate diagnosis of fetal genitourinary malformations is vital to direct patient counseling and pregnancy management as outcomes are highly variable. Some conditions can be surgically corrected quite simply, some require multiple complex procedures, and some are lethal. The authors offer troubleshooting tips to narrow the differential diagnosis for four observations: unilateral absent kidney, dilated renal pelvis, cystic renal parenchyma, and megacystis and its mimics. ©RSNA, 2023 Test Your Knowledge questions are available in the Online Learning Center.

Giant neonatal hydronephrosis of the upper pole of a complete duplicated renal system

Ureteropelvic junction obstruction (UPJO) in the upper pole of a complete duplicated renal system is extremely rare. We report a case that was diagnosed prenatally and we review 10 cases published in the literature. Diagnoses of adrenal hematoma and cystic neuroblastoma were suspected on prenatal ultrasound, based on the severity of dilatation and the difficulty of identifying the exact origin of this anomaly. Neonatal magnetic resonance imagery (MRI) was subsequently able to show a normal adrenal gland. Surgical management is similar to that of a single-system pyeloureteral junction obstruction. Since this situation is very rare, we believe cystoscopy can be useful to confirm diagnosis of UPJO associated with complete duplication, especially in the absence of preoperative MRI. Among the 11 surgical cases previously published, seven patients underwent pyeloplasty and four heminephrectomy.