Prenatal diagnosis of congenital megalourethra in the second trimester of pregnancy

Congenital megalourethra is typically characterized by the aplasia of penile erectile tissue, leading to abnormal dilation of the anterior urethra without structural obstruction^(1,2). This terminology was first used in 1955 to describe an infant with abnormally enlarged penis and worsening renal function⁽²⁾. In 1989, Benacerraf et al.⁽³⁾ diagnosed megalourethra for the first time on fetal ultrasound. Congenital megalourethra is a rare condition. The prevalence is not known since most studies were solely focused on case reports and pathological autopsies^(1,4).

A 31 year-old primigravid pregnant woman with unremarkable history was referred to the Tu Du Hospital, Vietnam, with diagnosis of fetal megacystis detected on routine sonography. Ultrasound scan at 17 weeks 6 days reported the following findings: echogenic kidneys, right pyelectasis (3.6 mm), dilated right ureter (3.2–3.6 mm) (Fig. 1), left pyelectasis (3.2 mm), dilated urinary bladder (33 × 24 mm) with keyhole sign (Fig. 2), dorsally curved penis with largely dilated penile urethra (18 × 5 mm) (Fig. 3). The amniotic fluid volume was normal. No other abnormalities were found. Based on such abnormal sonographic findings, including hydronephrosis, hydroureters, megacystis and dilated penile urethra, we came to a diagnosis of scaphoid congenital megalourethra. After parental counseling, termination of pregnancy proved the prenatal findings (Fig. 4).

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Congenital megalourethra belongs to a group of disorders called lower urinary tract obstruction (LUTO). The most common etiologies are structural obstructions such as posterior urethral valve and urethral atresia^(5,6). Obstruction in congenital megalourethra, however, is functional rather than structural, hence featuring a different pathogenesis. Malformation occurs early in pregnancy and disrupts the combining process of mesoderm-derived structures including corpus spongiosum on the ventral side and corpus carvenosum on the dorsal side of the penis. This leads to aplasia of the erectile tissue, which normally supports the urethra on micturation. As a result, the penile urethra gradually dilates, causing urine stasis and retrograde obstruction^(2,4,7).

According to Dorairajan and Stephens, congenital megalourethra was morphologically divided into two types⁽²⁾:

All cases were diagnosed prenatally via ultrasound. Most diagnoses were made in the second trimester (86%), followed by third (12%) and first trimester (2%)⁽¹⁾. The high rate of detection in the second trimester could be explained by the emergence of complications (megacystis, hydroureters, hydronephrosis, oligohydramnios) or detection of other associated anomalies⁽⁷⁾.

The rate of live births was reported to be about 60–70%^(1,2). Most patients suffered from sequelae such as abnormally large penis, erectile and urinating dysfunction, recurrent urinary tract infection, renal failure, etc.^(4,7). Postnatal follow-up revealed that renal impairment rate was up to 42%, with three prenatal risk factors including:

When congenital megalourethra is suspected on ultrasound, it is necessary to rule out other conditions of similar sonographic presentation, yet much higher prevalence.

Similar presentation of megacystis:

In summary, congenital megalourethra is a rare condition with poor prognosis. Isolated cases without severe associated anomalies may have better perinatal outcomes, however long-term life quality is still compromised due to severe sequelae. Along with early diagnosis, ultrasound also provides helpful data for clinicians to prognose, consult and decide the optimal treatment modality for each case.