Origin, Course and Associated Congenital Anomalies of Type 2 Single Umbilical Artery: A Fetal Anatomic Study

Abstract

Umbilical arteries normally originate from a pair of allantoic arteries. A failure of allantoic vascular system in early fetal life results in substitution by the vitelline vascular system, an inherent safety mechanism. This gives rise to anomalous course and origin of the umbilical artery. In these cases, the umbilical artery originates from the abdominal aorta and continues as a single umbilical artery. Aim: The aim of this study is to elaborate upon our current understanding about the origin, course and associated anomalies of Type2 single umbilical artery. Material and Methods: Fifty five foetuses, terminated for severe congenital anomalies over a period of 10 years, were sent to the department of anatomy for academic evaluation of congenital anomalies. All the foetuses were dissected systematically to delineate the abnormalities. Results: Thirty fetuses had two umbilical arteries with normal course on either side of allantois (urachus) and urinary bladder. Single umbilical artery was observed in 25 cases. Twenty had type 1 single umbilical artery and coursed normally. Five cases had single anomalous origin and course of umbilical artery, which was similar to type 2 single umbilical artery (SUA). After opening the abdominal cavity, the umbilical artery was not seen beside the urachus: instead it coursed posteriorly between the coils of intestine. When it was traced further, its origin was from the abdominal aorta. The aorta was hypoplastic below the origin of the single umbilical artery. All these cases were associated with cardiac, gastro-intestinal, vertebral, renal and limb abnormalities. Conclusion: Very few cases of this abnormality have been described in literature. Only a few of these cases were diagnosed prenatally as a vitelline artery abnormality: our study will thus help refine prenatal diagnosis and management.

Case report of a type II single umbilical artery seen in the first trimester anomaly scan

“…Due to this steal phenomenon, the amount of blood circulating through the distal aorta is minuscule, resulting in caudal regression. Thus, further evaluation for caudal regression on an antenatal scan becomes essential if the presence of a vitelline origin of an umbilical artery is noted [2].…”

“…Our case is of type II SUA, which has a reported incidence of 1.5% of all SUAs [1]. In a few case reports of Type II SUA published in literature [2][3][4][5][6], rarely normal fetal development was seen. Most of these cases were detected in the second trimester and had an unfavorable prognosis due to multiple fetal developmental anomalies.…”

Abnormalities of the Umbilical Cord

“…There is an increased incidence of severe malformations associated with type II SUA with the implication of the caudal body wall (sirenomelia, omphalocele-exstrophy-imperforate anus-spinal defects) and urorectal like exstrophy of the bladder, anal atresia, or urogenital agenesis [13].…”