MEGALOURETHRA MIMICKING AN ANTERIOR ABDOMINAL WALL MASS ROSALIA MISSERI, MARK P. CAIN,* , † MARY PELL ABERNATHY, CAROLYN BRADBURY AND LILLIE MAE PADILLA From the Departments of Pediatric Urology (RM, MPC), and Obstetrics and Gynecology (MPA, CB, LMP), Indiana University, Indianapolis, Indiana KEY WORDS: urethral obstruction; prenatal diagnosis; ultrasonography, prenatal Megalourethra is an uncommon congenital anomaly. His- torically, the majority of males with megalourethra are diag- nosed at birth. However, with the increased use of prenatal ultrasound more cases may be diagnosed prenatally. We describe a unique case of megalourethra presenting with early bladder outlet obstruction that resolved in utero. Two hypotheses regarding the etiology of the anomaly have been proposed. One suggests that there is an arrest in mi- gration and fusion of mesenchymal elements that form the corpora spongiosa leading to a patulous urethra. 1 The other suggests that the anomaly is the result of an obstructing uncanalized epithelial glanular plug. 2 Our unusual case demonstrates one of these hypotheses. CASE REPORT A 37-year-old gravida III, para I female underwent prena- tal ultrasound at 15 weeks of gestation, which showed anhy- dramnios and an enlarged cystic mass in the fetal abdomen consistent with a bladder measuring 4.0  3.2  4.3 cm. Aspiration of the structure yielded 24 cc clear yellow fluid. Ultrasounds were repeated weekly, each revealing anhydr- amnios with a distended bladder (fig. 1, A). Bladder aspira- tion was performed after each study. Urine sodium, chloride and osmolality were within normal limits. At 18 weeks of gestation ultrasound demonstrated small pockets of amniotic fluid. The bladder appeared distended but it could not be tapped due to fetal positioning and ma- ternal body habitus. Amnioinfusion with indigo carmine was performed to facilitate ultrasound examination and rule out amniotic fluid leakage. At 19 weeks of gestation the bladder was decompressed with normal amniotic fluid volumes. Ul- trasound at 22 weeks of gestation showed normal amniotic fluid volume with a nondistended bladder (fig. 1, B). Ultra- sounds were obtained at 2-week intervals and remained nor- mal during the following months. At 32 weeks, 4 days of gestation ultrasound revealed a cystic structure on the anterior abdominal wall measuring 2.7  5.8  5.0 cm (fig. 1, C). The bladder and kidneys were visualized and appeared normal. One week later the anterior cystic structure (6.4  3.2 cm) was again visualized low on the anterior abdominal wall. A small stump-like structure visualized was presumed to be the fetal penis. The newborn was delivered via cesarean section at 38 weeks of gestation. At birth the neonate was noted to have a large phallus consistent with a scaphoid megalourethra (fig. 2). Renal/bladder ultrasound demonstrated a normal upper urinary tract. The bladder appeared normal without evi- dence of vesicoureteral reflux on voiding cystourethrogram. The newborn underwent an anterior urethrotomy to facili- tate voiding and to prevent pooling of urine in the dilated anterior urethra. DISCUSSION By week 14 of development the urethral folds fuse to form the tubular penile urethra. However, the glanular urethra forms by a different mechanism and is likely to be the result of 2 separate processes. Proximally the glanular urethra is formed by fusion of the urethral folds, while distally it is due to the invagination of the epithelial tag. The epithelial tag is of ectodermal origin and is present at the tip of the genital tubercle. By week 18 canalization of the epithelial core (ie formation of the distal glanular urethra) with union to the penile urethra should be complete. Based on autopsy studies of fetuses with megalourethra, Stephens and Fortune suggest that a defect in the sequence of embryological events leading to urethral formation causes the abnormality. 2 Their findings suggest late onset of canalization of the epithelial core or a possible arrest in development leading to over distention of the urethra with compression and arrest in formation of the corpus spongiosum. Attenuation of the corpora cavernosa may result from prolonged distention. Other theories regarding the etiology of megalourethra suggest that it is due to an arrest in embryogenesis of the Accepted for publication May 21, 2004. * Financial interest and/or other relationship with Sanofi and Boehringer Ingelheim. † Correspondence: Department of Pediatric Urology, Riley Hospi- tal for Children, 702 Barnhill Dr., ROC 4230, Indianapolis, Indiana 46202 (telephone: 317-274-0171; FAX: 317-274-7481; e-mail: mpcain@iupui.edu. FIG. 1. Prenatal sonograms. A, estimated gestational age 16 weeks. Distended bladder with anhydramnios. B, estimated gesta- tional age 22 weeks. Decompressed bladder with normal amniotic fluid volumes. C, estimated gestational age 32 weeks, 4 days. Cystic anterior abdominal mass later found to be phallus with megaloure- thra lying on anterior abdominal wall. FIG. 2. Scaphoid megalourethra 0022-5347/04/1724-1454/0 Vol. 172, 1454–1455, October 2004 THE JOURNAL OF UROLOGY ® Printed in U.S.A. Copyright © 2004 by AMERICAN UROLOGICAL ASSOCIATION DOI: 10.1097/01.ju.0000138212.27587.0b 1454