Prenatal diagnosis of congenital megalourethra with imperforate anus

Fetal megalourethra is rare and mostly associated with severe renal dysfunction and oligohydramnios [1, 2] most probably due to a consequences of lower urinary tract obstruction. Congenital megalourethra is characterized by an enlarged penis caused by cystic dilatation of the urethra, resulting from the absence or hypoplasia of the corpus spongiosum or corpus cavernosum or anterior urethral valves [2, 3]. We present the prenatal sonography and postnatal findings of a fetus at 22 weeks of gestation with a marked dilated penis, megacystis, bilateral hydronephrosis and in combined with imperforate anus.

We report a 30-year-old women, gravida 2, para 1 was referred for an ultrasound examination at 22 weeks gestation for abnormal fetal abdominal dilated cystic lesions. Her family history and prenatal course have been unremarkable.

The ultrasound evaluation revealed very prominent abnormalities over the entire urology system with marked bilateral hydronephrosis, hydroureters and megacystis, with extension of an enlarged cystic and septate lesion in the penis (Fig. 1). In addition to the urology lesions, the posterior perineum region show absence of the anal muscle in which an anorectal anomaly was highly suspected (Fig. 2). The amniotic fluid was decreased but not yet anhydramnios. Other organ systems did not have detectable ultrasonography anomaly. The parents underwent counseling and decided to terminate this pregnancy because of a poor prognosis mainly caused by the high probability of severe renal and sexual malfunctions. The gross examination of the 465 g fetus confirmed the prenatal diagnosis of megalourethra and imperforate anus (Figs. 3 & 4), however, autopsy and genetic study were declined.

Congenital megalourethra was defined by dilatation and elongation of the penile urethra on prenatal sonography with a remarkable postnatal examination. This is an uncommon male urogenital anomaly with only limited numbers of case reports [1‐3].

Among the largest multi-center cohort case collection of fifty cases of congenital megalourethra, none reported prenatal diagnosis of imperforate anus [2, 3]. Most prenatally diagnosed fetuses, nearly 90%, with congenital megalourethra were diagnosed in the second trimester [1‐3]. They are usually associated with varies severity of bilateral hydroureters, hydronephrosis and decreased amniotic fluid. In addition, half of the megalourethra had extra-urogenital anomaly [3]. The major pathogenic cause is obstructive of urine flow, which may be complete or partial, is along with consequent renal and pulmonary failure. Only 10% cases, which had no other genitourinary anomalies, had spontaneous resolution with normal postnatal renal function [3]. Our case was postulated as caused by complete absence of the corpora spongiosa and cavernosa, resulting partially obstructed the flow and had associated renal parenchyma damage. Fetal interventions did not affect either the survival rate or renal function.

On the other aspect, imperforate anus has a low prenatal detection rate. It also has a low incidence congenital defect in the general population (0.04%) but has 30 times frequent incidence in high-risk group of congenital anomaly of urinary tract (1.2%) [4]. Early reports of prenatal diagnosis have relied on indirect sonographic findings such as over distention of the rectum and even to the sigmoid colon. Under the application of high resolution ultrasonography, the earliest detection of anal anomaly was by 20 weeks of gestation [4]. This case was consistent with previous reports with absence of the anal mucosa in the posterior perineal triangle in the trans-perineal axial view is a specific and important sonographic marker for improperly canalized anal canal and a direct prenatal diagnosis of imperforate anus.

As the genetic and autopsy studies were unavailable, the true underlying possible pathogenesis of this case such as chromosome aneuploides, megacystis-microcolon hypoperistalsis (MMIHS) and other genetic syndromes, was uncompleted. The genito-recto malformation originates from the endoderm were identified in some animal studies. The defects in sonic hedgehog signaling and the mutations in the homebox genes will hamper proper functions of the urogenital sinus [5]. Furthermore, the outcomes of megalourethra not only depends on the postnatal renal and pulmonary functions but also on voiding and sexual dysfunction [4, 6]. The prenatal detection of a severe megalourethra with hydronephrosis, as in our case, following an addition of anal anomaly yielded a poorer outcome.

The present case revealed a unique finding: early prenatal onset of a large megalourethra and imperforate anus can be evaluated through ultrasonography. We also demonstrated the usefulness of prenatal sonography in a high-risk patient for having both the urogenital and anorectal lesions as well as to evaluate the severity, and prognosis of the postnatal outcomes. Though prenatal diagnosis remains a great challenge, this case proved feasible and will be beneficial experience in optimizing perinatal care and better parents counseling.