Cloacal Malformation
Cloacal malformation is fortunately the rarest of the urogenital sinus anomalies, with a reported incidence of 1 in 40000 to 50000 newborns and occurring only in genotypic girls. Though its embryologic development is not clearly understood, cloacal malformation represents persistence of an early embryonic state in which the urinary, genital and gastrointestinal tracts all drain through a common perineal channel. It results from failure of the urorectal septum (that separates the allantois from the hindgut) to join the cloacal membrane during the fourth to sixth week of embryonic life. Clinical and radiologic investigation can be most challenging, as children with this anomaly can present with a very broad spectrum of physical manifestations. The newborn can present with a near-normal female appearance, to much more unusual presentations such as an enlarged phallic structure suggestive of ambiguous genitalia, genital transposition or a blank-appearing perineum. The single perineal opening may exit a normal appearing perineal introitus, or may extend to the tip of a phallic structure. Variations of cloacal malformations have been described that differ depending on how the three systems conjoin. The length and morphology of the urethra, its communication with the cloaca, and presence of a urethral sphincteric mechanism are important for reconstructive purposes. The literature indicates that a urethra is present in the majority of malformations, is of varying lengths and can enter the cloaca in varying locations relative to the urogenital diaphragm. The rectal confluence can be equally as complex, with the rectal communication usually entering at the level of the vaginal confluence. Less frequently the rectum enters the vagina or bladder itself, with no direct communication to the cloaca. Vaginal anatomy can be complex and variable as well, with midline vaginal septation common. The vaginas may be of different sizes, and most frequently enter side by side with a single opening into the cloaca. A cervical impression can be seen at the superior margin of both vaginas. Post-natal radiographic evaluation begins with plain film radiography for evaluation of abdominopelvic soft tissue masses, and for initial identification of associated organ system abnormalities such as bony spine and/or sacral anomalies. Ultrasound is indicated to visualize pelvic anatomy and to assess the upper urinary tract. Obstructive hydronephrosis is very common. Genitography with water soluble contrast injected into the cloaca is mandatory to delineate anatomy, including identification of insertion of the bladder/urethra, vagina and colon into the cloacal tract, as well as the length and morphology of these structures. After cloacal channel investigation, a catheter should be advanced into the bladder and a VCUG performed. A high association of vesicoureteral reflux in cloacal malformations is noted. Spinal cord ultrasound in the newborn or MRI in the older child is necessary as well. Plain film radiography, though good for initial assessment, does not exclude spinal cord abnormalities. MRI can also assist in definition of degree of sphincteric muscle development. Clinical investigation includes endoscopy and echocardiography. Reference: Campbell’s Urology, 7th ed, pp 2443-2447. Practical Pediatric Imaging; Diagnostic Radiology of Infants and Children, 3rd ed, pp 1104.
A
B
C
D
E
A. Bladder
B. Urethra
C. Vagina
D. Rectum
E. Cloaca
Differential Diagnosis
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Urogenital sinus