The urachus is an embryonic structure connecting the bladder to the yolk sac and if it remains patent, a communication exists between the bladder and the umbilicus, resulting in discharge of urine from the umbilicus.
The urachus arises from the allantois, a protrusion of the yolk sac that develops during the 3rd week of gestation and normally obliterates shortly before birth. A urachus may persist as a patent communication as in this patient, or it may present in 3 other ways: a vesicourachal diverticulum (outpouching of bladder), a urachal sinus (a persistent space surrounding the umbilicus that is predisposed to infection), or a urachal cyst (usually asymptomatic).
Meltzer reviews the differential diagnosis for a newborn with an umbilical mass. The characteristic presentation of a patent urachus is intermittent drainage of urine from the umbilicus. If the drainage contains bilious or fecal material, it may reflect a persistent omphalomesenteric duct, connecting the ileum to the umbilicus.
Cuda et al. discuss traditional and new treatments for patent urachus. While early surgery remains the treatment of choice, initial treatment of urethral catheterization may be a viable alternative, resulting in spontaneous closure of the patent urachus. If urethral catherization fails following a 1-2 week trial, the patient should undergo surgical correction.
Illustration A depicts the embryolgic development of the urachus from the allantois.
Illustration B depicts various urachus abnormalities that can occur.
Answer 1: Myelomeningocele is when the meninges and spinal cord herniate through a defect in the spinal canal.
Answer 2: Gastroschisis is a congenital defect in which abdominal contents protrude through the abdominal wall, NOT covered by peritoneum.
Answer 3: Omphalocele is a congenital defect in which abdominal contents protrude through the abdominal wall, covered by peritoneum.
Answer 4: Meconium discharge from the umbilicus occurs with a persistent vitelline duct (omphalomesenteric duct).
Meltzer DI. A newborn with an umbilical mass. Am Fam Physician. 2005 Apr 15;71(8):1590-2. Review
PMID:15864900 (Link to Abstract)
Cuda SP, Vanasupa BP, Sutherland RS. Nonoperative management of a patent urachus. Urology. 2005 Dec;66(6):1320.
PMID:16360476 (Link to Abstract)
USMLE World Step 1 QBank Question #652. Copyright © USMLEWorld, LLC 2012