1993-06-04-19 Urethral meatus agenesis © Fuller www.thefetus.net/
Urethral meatus agenesis
Beverly F. Fuller, MD*, Philippe Jeanty, MD, PhD
Prevalence: Unknown but rare.
Definition: Absence of urethral meatus.
Pathogenesis: Unknown, probably secondary to failure of development of the glandular plate and/or its canalization with the spongy urethra.
Associated anomalies: Other GU anomalies, Prune-belly syndrome.
Resulting anomalies: Megacystis, hydroureter, hydronephrosis, renal dysplasia and the oligohydramnios sequence (pulmonary hypoplasia, Potter"s facies, limb deformities).
Differential diagnosis: Posterior urethral valves, congenital urethral membranes, urethral agenesis, detrusor hypertrophy, urethral agenesis, megacystis-microcolon-intestinal hypoperistalsis syndrome.
Prognosis: Incompatible with life unless an alternate bladder outlet develops, such as a patent urachus or rectovesical fistula.
Recurrence risk: Not known to be increased.
Management: See text.
MESH Urethral-Obstruction-diagnosis; -etiology; -complications ICD9 753.6 CDC 753.630
(*) Address correspondence to Beverly F. Fuller, MD Department of Obstetrics & Gynecology, Vanderbilt University Medical Center, 21st and Garland, Nashville, TN 37232-2519. Phone: (615) 322-2308 Fax (615) 343-8881 (§) Department of Radiology and Radiological Sciences, Ultrasound Section, Vanderbilt University Medical Center, 21st and Garland Nashville, Tennessee 37232-2675 USA
Urethral meatal atresia is a rare genitourinary anomaly incompatible with life unless an alternate bladder outlet develops. It is generally associated with other incidental or resulting genitourinary anomalies. Its ultrasound appearance is very similar to that of posterior urethral valves with which it is easily confused.
This 19 year old G1 was referred at 22 weeks of gestation because of an ultrasound finding of oligohydramnios. Her past medical history was unremarkable. The examination at our institution revealed anhydramnios at 22-23 weeks with a 2-vessel umbilical cord. Other findings included a dilated bladder (fig. 1), enlarged and cystic kidneys (fig. 2), echogenic myocardium suggestive of endocardial fibroelastosis, pericardial effusion, and a left ventricular chamber that was larger than the right.
Fig. 1: Distended bladder.
Fig. 2: Cystic dysplasia of the kidney.
A prostin termination resulted in the delivery of a 660g stillborn male fetus.
The autopsy revealed an absent right kidney, ureter and testis with urethral meatus atresia. A large left multicystic dysplastic kidney was present. The urinary bladder was distended and in the lower left abdomen. The scrotal sac was absent and the urethra ended in a blind pouch in a markedly distended penis (fig. 3).
Fig. 3: Markedly distended penis due to meatal atresia and reflux of urine in the spongious bodies.
The only other anomalies were a 2-vessel cord and undescended but normal left testis. The rest of the examination was normal (including the abdominal musculature, cardiac and skeletal systems). The chromosome analysis was normal (46XY).
Generally, urethral meatus atresia occurs in association with other genitourinary anomalies as seen in this case1-3.
Urethral meatus atresia maybe associated with the prune-belly syndrome1 (deficiency of abdominal musculature, cryptorchidism and obstructive uropathies). Obstructive uropathies are responsible for approximately 35% of cases of prune-belly syndrome3. Urethral obstruction is lethal without a patent urachus or rectovesical fistula3. Some authors consider that urethral meatus atresia is always associated with renal dysplasia and that the severity of cortical anomaly relates directly to the degree of obstruction8,9.
Secondary nomalies are due to the urinary tract obstruction (hydronephrosis, hydroureter, renal dysplasia, megacystis, cryptorchidism, limb atrophy and gangrene secondary to ischemia from compression by the bladder) and the resulting oligohydramnios sequence (pulmonary hypoplasia, Potter"s facies, limb deformities–equinovarus and dimple in the elbow and knee joint). Other anomalies seen in association with urethral meatus atresia are those that may have occurred at the same embryological period, such as renal and testicular agenesis and ureter anomalies.
Renal agenesis is quite common (10:10,000). It is usually found in association with other genitourinary anomalies, and results from failure of formation of the metanephric diverticulum or from early degeneration of this diverticulum. The faulty diverticulum formation prevents fusion with the metanephric mesoderm4.
The urethra in the male consists of the prostatic, membranous and spongy portion which expands into the glands and forms the meatus at its apex (navicular fossa). The epithelium of the prostatic, membranous and spongy urethra is derived from the endoderm of the urogenital sinus. However, the epithelium of the glandular portion of the spongy urethra develops by canalization of an ectodermal cord of cells–the glandular plate–that extends into the glands from its tip. Faulty connections or development of this plate probably account for meatus atresia4 (see fig. 4).
Fig. 4: The urethra is composed of a spongious portion of endodermal origin and a portion of ectodermal origin: the glandular plate. The glandular plate canalize to form the external urethral ostium. The normal connection between the two results in the normal urethra (top right) while the failure of connection results in meatal atresia (bottom right).
The explanation for the prune-belly syndrome is massive bladder distension leading to pressure atrophy of the abdominal wall muscles6.
Renal dysplasia is defined as abnormal nephrogenesis resulting in focal to diffuse dilated ducts lined with cuboidal or columnar epithelium. This is associated with abundant mesenchymal tissue that has retained the ability to form dysontogenetic derivatives such as cartilage and smooth muscle. Urinary formation begins at 7-8 weeks post-conception and a progressive back-up of flow during a crucial period of nephrogenesis is felt to lead to the cystic renal dysplasia5, 7. This fetus has classic renal dysplasia by gross and microscopic examination.
Cryptorchidism results from impaired descend of the testicles due to the distended bladder5.
The differential diagnosis of oligohydramnios and a distended bladder could include other lower obstructive uropathy such as posterior urethral valves, detrusor hypertrophy, urethral agenesis or congenital urethral membranes. The megacystis-microcolon-intestinal hypoperistalsis syndrome consists of the association of a distended unobstructed bladder, a dilated small bowel and distal microcolon, secondary to degeneration of smooth muscle involving these organs10. It is usually seen in association with normal or increased amniotic fluid and therefore can easily be differentiated.
Posterior urethral valves are much more common than urethral meatal atresia and occur in the prostatic urethra and can lead to a similar sequela of anomalies. However, since the obstruction is the proximal portion of the urethra, the urethral dilatation and megaphallus are absent11.
Urethral meatal atresia and its associated findings are incompatible with life unless another urinary outflow tract develops. If this is the case, urethral dilatation or urethrotomy at birth has been used to create a functioning urethra. However, only the infants with minimal renal dysplasia do well11. There is one case report of an infant with unsuspected urethral atresia who underwent fetal urinary decompression by intrauterine placement of a vesicoamniotic shunt at 30 weeks with delivery at 36 weeks followed by surgical correction1.
1 Steinhardt G, Hogan W, Wood E, Weber T, Lynch K. Long term survival in an infant with urethral atresia. J Urol 143:366-367, 1990
2 Kroovand R, Al-Ansari R, Perlmutter A. Urethral and genital malformations in prune-belly syndrome. J Uro, 127:94, 1982
3 Rogers L, Ostrow P. The prune-belly syndrome, J Pediat 83:786-793, 1973
4 Moore Keith. The Developing Human 3rd Edition, W. B. Saunders Co. 1982, 261-262 and 267-268
5 Jones KY. Recognizable Patterns of Human Malformation 4th Edition, W. B. Saunders Co. 1988, 562-565
6 Pagon R, Smith D, Shepard T, Urethral obstruction malformation complex: A cause of abdominal muscle deficiency and the prune-belly, J Pediatr, l94:900, 1979
7 Heptinstall R, Pathology of the Kidney, 3rd Edition Little/Brown and Co., 1983, 96-108
8 Campbell M, Campbells Urology, W. B. Saunders Co., l986, 1791-1797.
9 Risdon R, Renal dysplasia and associated abnormalities of the urinary tract in Rubin M, and Barratt T, Ped. Nephrology, Baltimore, Williams and Williams Co., 1975, 346
10 Puri P, Lake B, Gorman F, et al, megacystis-microcolon-intestinal hypoperistalsis syndrome: a visceral myopathy. J Ped Surgery 18:64, 1983
11 Romero R, Pilu G, Jeanty P, et al: Prenatal diagnosis of congenital anomalies, Appleton and Lange, 1988, 283-4