Cloaca is single cavity present in early embryonic development when bladder, genital tract, and bowel are all connected

Spectrum of abnormal anatomy is related to timing of developmental arrest

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  Range from urogenital sinus (2 perineal openings) to cloacal dysgenesis (no perineal opening)

  
  
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  Classic cloaca defined as coalescence of urethra, vagina, and hindgut into common channel draining through single perineal orifice (exclusively in females)

Most common presentation is cystic pelvic mass in female fetus; “cyst” is grossly dilated vagina (hydrocolpos)

Uterine and vaginal duplication is observed in ~ 80% of cases in which hydrocolpos is present

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  Vaginal duplication creates linear septation within conical fluid collection

Abnormal perineum; absent anal dimple

High percentage have additional abnormalities, most commonly genitourinary, bowel, and lumbosacral

Vagina is most distended structure and appears as cystic pelvic mass

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  Scan in coronal plane looking for vertical septum

  
  
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  Even if no septum is present, may still see fluid-debris level (vaginal secretions ± meconium mixing with urine)

Do not confuse with bladder

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  Bladder may be compressed by distended vagina

  
  
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  Be very suspicious if female fetus is sent for “urethral atresia”; far more likely to be cloacal malformation

When any lower GI or GU abnormality is suspected, perform high-resolution images of perineum looking for abnormal genitalia and absent anal dimple

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  If abnormal, highly suspicious for cloacal malformation even if no cystic mass is present