Gastrointestinal: Absent coeliac axis

Abstract

A66-year old man with obstructive jaundice was found to have an unresectable pancreatic tumour on contrast-enhanced CT scan. Sagittal (Figure 1) and 3-D (Figure 2) reconstructions of the CT scan images revealed complete agenesis of the coeliac axis, with the splenic and hepatic arteries arising directly from the superior mesenteric artery. The arterial supply of the gastrointestinal tract develops in week 4 of embryological life. The future blood vessels of the GI tract are formed from the vitelline system, which is composed of two bilateral arterial plexuses which coalesce to form arteries from the dorsal aorta to GI tract. Above the diaphragm the vitelline channels amalgamate to form about 5 pairs of arteries which supply the thoracic oesophagus. Below the diaphragm the vitelline system condenses to form the three major abdominal arteries of the foregut, midgut and hindgut. The coeliac artery is the most superior of these arteries; it leaves the aorta at the seventh cervical level in the embryo but later descends to the twelfth thoracic level during development. In addition to supplying the abdominal foregut proper, the coeliac artery also supplies its endodermal derivatives; the hepatic diverticulum (future liver), the cystic diverticulum (future gallbladder), and the dorsal and ventral pancreatic bud (future pancreas). It also supplies the mesodermally derived spleen. The anatomical variation in the celiac trunk is assumed to be caused by different patterns of vitelline reduction. However, some animal studies have suggested that the major abdominal arteries arise from medial umbilical roots of the dorsal aorta. Anomalies of the coeliac axis have been described in up to 28% of subjects. The commonest variation appears to be a common hepatosplenic trunk with a separate left gastric artery. Complete absence of the coeliac axis, with the splenic and hepatic arteries originating from the superior mesenteric artery is rare. Identification of these anomalies is particularly important in the event of angiographic or surgical intervention and organ harvest for transplantation, and can be achieved using reconstructions derived from multi-detector CT images.