CONGENITAL MEGALURETHRA

Megalourethra is a rare congenital anomaly resulting in elongation and dilatation of the penile urethra due to partial or complete agenesis of the erectile tissue (1,2). It is characterized by the congenital absence of the corpus spongiosum and/or corpus cavernosum, leading to dilatation of the urethra.

CLASSIFICATION

(based on the severity of the defects in the corpus spongiosum and cavernosum)

• Scaphoid type (most common and least severe form, due to a defect in the corpus spongiosum).
• Fusiform type (complete absence of the corpus spongiosum and cavernosa resulting in a markedly dilated sac-like urethra covered by skin and subcutaneous tissue).
• Normal corporeal bodies of the penis (3).

PATHOGENESIS

Link to Pathogenesis

ULTRASOUND

• Seven prenatally detected cases (1-7). Most cases are diagnose at 18 weeks and over with a single report of the diagnosis made at 13 weeks of gestation (12)
• Male fetuses.
• Cystic area in the anterior penis.
• Abnormal dilatation of the anterior penile urethra (functional obstruction may occur when the displaced tunica acts as a valve like flap resulting in an anterior urethral diverticulum) (8).
• Deviated penile shaft.
• Distended bladder with a thickened wall (7).
• Posterior urethra may be dilated (7).
• The portion between the dilated anterior and posterior urethra may be hyperechogenic (7).
• Bilateral hydronephrosis and hydroureter, multicystic renal dysplasia and renal hypoplasia may be present in varying degrees depending on the degree of obstruction.
• Amniotic fluid volume may be normal, increased or decreased (5).

Bilateral Hydronephrosis
Mildly dilated thick walled bladder Normal Amniotic fluid
Deviated Penis Dilated penile urethra
Dilated penile urethra at 18 wks (image on right) Normal non dilated penile urethra at 20 wks (as this appears to be a functional rather than true obstruction the urethra appears non dilated after fetal micturition, which is probably passive micturition due to pressure build up in the urinary bladder) (see images above)

ASSOCIATED ANOMALIES

• Genitourinary tract malformations occur in the fusiform type in 100% and in the scaphoid type in 74% (9).
• Imperforate anus.
• Prune-belly syndrome (10).
• Posterior urethral valves. Congenital megalourethra is commonly associated with obstructive uropathy and prune belly syndrome, although true anatomic obstruction of the urethra has not been consistently demonstrated (13).
• Esophageal atresia, VATER complex, trisomy 21 and malformations of the teeth, heart, intestines and musculoskeletal system (13).
• Associated malformations are more common in the fusiform type and the prognosis is worse (13).

DIFFERENTIAL DIAGNOSIS

• Urethral diverticulum (saccular and localized protrusion of mucosa from the urethral valve into the corpus spongiosum located in the floor of the urethra.
• Anterior meatal agenesis (failure in the development of the connection between the epithelium of the glandular portion and the epithelium of the spongy urethra) (11).
• Posterior urethral valves.
• Urethral agenesis.

PROGNOSIS

Perinatal mortality rate may be as high as 60% for the fusiform type and 22.5% for the scaphoid type.

REFERENCES

1. Nesbitt TE. Congenital megalourethra. J Urol 1955;73:839-842.
2. Dorairajan T. Defects of spongy tissue and congenital diverticuli of the penile urethra. Aust NZ J Surg 1963;32:209-214.
3. Adamson AS, Burge DM. Megalourethra - a spectrum of disease. Pediatr Surg Int 1990;5:449-450.
4. Fisk NM, Dhillon HK, Ellis CE et.al. Antenatal diagnosis of megalourethra in a fetus with the prune-belly syndrome. J Clin Ultrasound 1990;18:124-128.
5. Sepulveda W, Berry SM, Romero R et.al. Prenatal diagnosis of congenital megalourethra. J Ultrasound Med 1993;12:761-766.
6. Stephens FD, Fortune DW. Pathogenesis of megalourethra. J Urol 1993;149:1512-1516.
7. Wu M-H, Wu R-C, Kuo P-L et.al. Prenatal ultrasonographic diagnosis of congenital megalourethra. Prenat Diagn 1995;15:765-768.
8. Burstein JD, Firlit CF. Megalourethra. In: Clinical Pediatric Urology. Kelalis, King, Belman (eds). 2nd ed. Philadelphia: WB Saunders 1985:574-576.
9. Appel RA, Kaplan GW, Brock WA et.al. Megalourethra. J Urol 1986;135:747.
10. Krueger RP, Churchill BM. Megalourethra with posterior urethral valves. Urology 1981;18:279-281.
11. Fuller BF, Jeanty P. Urethral meatus agenesis. Fetus 1991;1:7536-1.
12. Y.H. Lam and M.H.Y. Tang. Sonographic diagnosis of congenital megalourethra at 13weeks of gestation. Ultrasound Obstet Gynecol 2000;16(6): 585 
13. Sharma AK, Shekhawat NS, Agarwal R, Upadhyay A, Mendoza WX, Harjai MM. Megalourethra: a report of four cases and review of the literature. Peidatr Surg Int 1997; 12: 458-60