* Gynecologist, Hôpital Félix Guyon, 97400  Saint-Denis, Ile de la Réunion, France. Telephone: 0262 90 55 22; fax: 0262 90 77 30;

** Sonographer, Translator, Editor, Novato, California;

*** Department of Gynecology, GHSR, 97400 Saint-Pierre, Ile de la Réunion, France;

**** Department of Anatomo-pathology, GHSR, 97400 Saint-Pierre, Ile de la Réunion, France. Tél: 0262 90 55 22. Fax: 0262 90 77 30.

Definition

Congenital megaurethra is diffuse dilatation of the anterior urethra due to nondevelopment of erectile tissue of the penis.  It is characterized by dilatation of the penile urethra without distal obstruction (such as phimosis).

We describe prenatal discovery of congenital megaurethra with renal pyelectasis and bladder dilatation, initially thought to be megacystitis with posterior urethral valves.

Case report

A  20-year-old patient, G1P0, was referred after ultrasound findings of bladder dilatation and bilateral pyelectasis at 18 weeks GA. Her medical history was unremarkable.  On sonography at 19 weeks we observed:

• Dilated , thick-walled bladder, with two umbilical arteries in an unusually wide,  convex aspect;
• Bilateral pyelectasis and left ureteral dilatation;
• Megaurethra with intraluminal dilatation;
• Echogenic left myocardium suggestive of fibroelastosis;
• Amniotic fluid volume was normal.

The couple was informed of fetal prognosis and chose interruption of pregnancy at 20 weeks GA;  amniocentesis was performed revealing 46, XY. The parents authorized autopsy. Bilateral dysplastic kidneys and a large bladder were seen. The scrotal sac was present, the penis was distended,  and the distended urethra ended in a blind pouch.

Images 1, 2. Dilated urinary bladder and proximal urethra.

Images 3, 4. Dilated urinary bladder with thick wall.

Images 5, 6. Dilated urinary bladder and urethra.

Images 7, 8. Dilated urethra.

Images 9, 10. Dilated renal pelvises.

Images 11, 12. Pathological specimens.

History

Perinatal discovery of congenital megaurethra was described by Obrinsky in 1949. Benacerraf et al described the first prenatal diagnosis of congenital megaurethra in 1989. Only ten cases of prenatal congenital megaurethra are described in the literature before 2003, according to Ardiet et al. Ardiet cites 100 postnatal discoveries of congenital megaurethra in the literature altogether. Ozukutan et al (2005) cite 80 cases of congenital megaurethra described in the literature.

Prevalence

Congenital megaurethra is a rare anomaly whose prevalence is not well known. Sepulveda et al (2005) described a series of four cases discovered between 20 and 24 weeks GA. Vaux cites another series of cases. All other citations in the literature, however, are described as isolated. In the series of cases by Sepulveda in 2005, all the fetuses died after premature delivery. All had a normal karyotype. Nijagal et al (2005) described one case. The baby died soon after birth.

Etiology

Posterior urethral valves are the most common cause of fetal urethral obstruction in the fetus; anterior urethral valves, though rare, may cause obstruction as well. Other less well recognized causes of distal urethral obstruction are urethral atresia and urethral webs.  However, congenital megaurethra has a different pathogenesis to these entities. Vaux et al (2005) described four cases of congenital megaurethra associated with maternal diabetes mellitus, but this is a correlative, not causative association.

Pathogenesis

Congenital megaurethra is a consequence of deficient fusion of ventral mesenchymal elements of the penis, featuring abnormal development of the corpora cavernosa resulting in massive urethral dilatation. There are two types of megaurethra, according to Dorairajan's and Stephens' classification (1963):

• Scaphoid megaurethra: 80% of cases; this involves the corpus spongiosum;
• Fusiform megaurethra: 20% of cases. The fusiform variety is associated with a poor prognosis and involves both the corpus spongiosum and corpora cavernosa.

Sonographic findings

Prenatal diagnosis of congenital megaurethra is based on visualization of an penis with a cystic urethra; this results in a dilated bladder and sometimes bilateral pyelectasis. The consequences for the upper renal tracts can be different:

• Megacystitis without duplicated collecting system;
• Pyelectasis with or without ureteral dilatation.

Oligohydramnios is possible. In our case at 18 weeks  GA, fetal keratinization had not yet occurred, so amniotic fluid was normal. Most cases of congenital megaurethra are detected between 16 and 24 weeks GA and present with distended bladder and  megaurethra. Frequently the initial diagnosis is megacystitis such as in prune belly syndrome (Eagle-Barrett syndrome).

Differential diagnosis

• Megacystitis;
• Posterior urethral valves;
• Anterior urethral valves;
• Meatal agenesis
• Prune belly syndrome.

Associated anomalies

Approximately 70% of cases of congenital megaurethra present with structural and functional urinary defects. Congenital megaurethra may be associated with other systemic anomalies such as cardiac anomalies or intestinal malrotation, differing in type and severity. These malformations support the hypothesis that the defect in the penile urethra is the manifestation of a diffuse mesodermal abnormality. Congenital megaurethra can lead to urinary retention, incontinence, enuresis,  megacystitis, and, exceptionally, spontaneous bladder rupture.

Associated syndromes

Sonographic examination includes a search for associations and malformations of congenital megaurethra:

• VACTERL (VATER) association: In 2003, Ardiet et al described a case of complete VACTERL association. A distended bladder, dilated anterior urethra, and with thick, hyperechoic urethral walls were seen. Because VACTERL has a pathognomonic vertebral pathology such as hemivertebra or irregular vertebral angulation, in Ardiet's case, vertebral angulation suggeted the final diagnosis. After delivery, the baby was found to have type III esophageal atresia;
• Prune belly syndrome;
• Any upper renal tract abnormality.

Prognosis

Congenital megaurethra has a very poor perinatal outcome. If urethral obstruction occurs, congenital megaurethra is lethal without patent urachus or rectovesical fistula. The prognosis depends upon the severity of accompanying malfomations, in particular, renal malfomations and the degree of renal dysfunction.  Retrograde cysto-urethrogram confirms diagnosis.

Conclusion

Congenital megaurethra can be diagnosed prenatally, the earlier the better, so that interruption of pregnancy, if desired, is possible before viability. If the pregnancy continues, children and adolescents often suffer penile swelling and dysuria. Patients may undergo reduction urethroplasty; the aim of surgical correction is to obtain a visually normal penis. Erectile function is rare; incontinence and sterility are common sequelae. The parents must therefore be educated about the developmental prognosis of their child.