Perinatology Unit, Carabobo University, Valencia - Venezuela, Maternidad Privada Las Acacias. Valencia Venezuela

Abstract:
Megalourethra, a rare congenital disorder involving the penile urethra, is subdivided into two types, fusiform and scaphoid. We present a case of congenital megalourethra scaphoid type, the corpus spongiosum was absent with normal corpora cavernosa, without obstructive distal urethra, diagnosed prenatally at 21 weeks of gestation. Ultrasound features was an enlarged and deformed penis with urethra dilatation, megacyst, mild hydronephrosis, single umbilical artery and horseshoe kidney were also found. The anomaly of the penile urethra is discussed, and 41 cases from the English and Spanish literature are reviewed.

Case report
A 30-year-old G1 was transferred to the authors after a routine sonogram during early gestation revealed a fetal cystic mass in the abdomen. Subsequent ultrasound revealed fetal megalourethra, megacystis, horseshoe kidney with echogenic renal parenchyma, mild hydronephrosis, single umbilical artery and normal amniotic fluid volume and a fetus consistent with 21 weeks (figures 1-8). Chromosome analysis revealed a normal male karyotype.

These images show the striking cystic structure in the penile urethra and slight distension of the bladder. These 2 findings are characteristic of megalourethra.

...and these of course represented a horseshoe kidney !

Schematic representation of the features

Megalourethra (longitudinal view) and cavernous corpora (arrow) in axial plane.

Definition:
Nesbit (22, 23) was the first described in 1954 as "a congenital dilatation of penile urethra without distal obstructionâ€. This rare abnormality is characterized by severe dilatation of the penile urethra caused by an absence of corpus spongiosum (scaphoid type) or with deficiency of both corpus spongiosum and cavernous corpora (fusiform type).   

               Fusiform type associates a prune-belly syndrome.

 This condition is usually associated with many congenital malformations especially abdominal wall, genitourinary, gastrointestinal and vertebral (1-37). The distinction between scaphoid and fusiform megalourethra seems arbitrary, and the disorder is better viewed as a spectrum rather than as 2 distinct entities (1).
An association between urethral atresia and the prune belly syndrome (PBS) has been recognized (2, 28) but in this case an obstructive phenomenon early in gestation leading to irreversible damage to the genitourinary tract and abdominal wall. In other hand (18) justify categorization of megalourethra how the minor forms of prune belly syndrome.
 
Incidence:
Rare. Fewer than 90 cases of megalourethra had been reported in the literature.

Etiology:
1. Failure of urethral recanalization as a cause of megalourethra (Stephens-Fortune)
2. Temporary obstruction during early development may be a etiologic factor in fusiform type
3. Failure of development of erectile tissue may be a etiologic factor in scaphoid type
4. Abnormal mesodermal development: developmental arrest of the mesenchymal elements of the penis would lead to severe laxity and defective development of the erectile tissue
The pathogenesis of the prune belly syndrome (PBS) remains controversial (2, 28) but two theories predominate. The first theory supports an obstructive phenomenon early in gestation leading to irreversible damage to the genitourinary tract and abdominal wall. The second theory suggests mesodermal injury between the 6th and 10th weeks of gestation as the primary abnormality (34).

Associated anomalies:
Megalourethra often had been associated with other severe anomalies (1-37): Prune-belly syndrome (PBS) in 27%, genitourinary, and intestinal (70%), others systems (30%): Cloacae, vertebral, anal, cardiac, tracheal, esophageal, renal, limb malformations (VACTERL and VATER association), duplication of urethra, renal dysplasia , megacyst, polycystic kidney, brachydactiylia, unilateral renal hypoplasia, colonic malrotation, hydronephrosis, hydroureteronephrosis, duplication of the ureter, cryptorchydism and vesicocutaneous fistula . The urethral stenosis can be observed in Williams-Beuren Syndrome, Fraser synd., and Melnick-Needles syndrome.

Prenatal diagnosis:
Cystic dilatation and enlargement of the penis, in the fusiform type we can not observed both corpus spongiosum and cavernous corpora. In the scaphoid type we can observed the glands penis and the cavernous corpora is displaced by a megalourethra. In the Dillon (5) case, a cystic area was seen arising from the perineum.
Significant concomitant upper urinary tract abnormalities may be present in any patient with megalourethra, a fact that should lead to the routine investigation of the upper urinary tract in all patients with this developmental anomaly (1)

Management:
During pregnancy:
Termination of pregnancy can be offered before viability. Without other malformations and normal chromosomal study, sonographic monitoring of amniotic fluid index, urinary bladder volume, and fetal urine biochemistry and fetal serum beta 2-microglobulin (7) can be used to rule out severe renal impairment. Early decompression of severe bladder obstruction by vesico-amniotic shunt may prevent or attenuate these complications and improving the prognosis. Fetuses that develop mild urinary tract distension have better prognosis. Mild hydronephrosis and megalourethra may be the only manifestations in these cases. 
Neonatal period:
 Imperforated anus can be corrected on the first day. Vesicostomy can be considered early in life. A neonatal penile urethrostomy can be performed. Treatment of megalourethra follows the principles of surgery for hypospadias, with urethroplasty (Nesbit, Johansson, Heaton and others techniques). The surgical treatment of fusiform type of megalourethra involves the placement of penile prosthesis, in the adult period.

Prognosis:
The prognosis depends on the degree of renal function compromise and severity of associated anomalies. Often, patients with fusiform megalourethras have associated lethal congenital malformations, and unfortunately fusiform megalourethra is usually an autopsy finding since this condition often is associated with stillbirths. Associated anomalies determine the prognosis of patients with scaphoid type, ultimately depend on renal damage.
Penis prosthesis can be considered in fusiform type during adult period.

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