The truncus coeliacus is an unpaired arterial trunk that arises anteriorly toward the abdomen (ventrally) from the abdominal portion of the aorta still above the paired renal arteries. It branches after a few centimeters into three other arteries that supply arterial, oxygenated blood to various abdominal organs as well as part of the mesentery. Because the truncus coeliacus originates just below the passage of the aorta through the diaphragm, the arterial trunk can be affected by compression, Dunbar’s syndrome.
What is the coeliac trunk?
The truncus coeliacus is a common arterial trunk that arises ventrally (abdominally) as an unpaired branch from the abdominal aorta at the level of the twelfth thoracic vertebra below the aortic passage through the diaphragm (hiatus aorticus). The truncal artery branches after a few centimeters into three arteries: the splenic artery, the gastric sinistra artery, and the hepatic common artery. The area of branching into three arteries is also called Haller’s tripod or tripus coeliacus. The three branching arteries supply fresh, oxygenated blood to the abdominal organs of the liver, pancreas, stomach, spleen, duodenum, and associated mesentery. Any dysfunction of the coeliac trunk may be immediately life-threatening.
Anatomy and structure
Haller’s tripod of the truncus coeliacus deserves special attention because “normal” branching into the three arteries mentioned above directly in the tripod is present in only an estimated 55 to 62 percent of people. In the remaining cases with statistically relevant clustering, more than ten different anomalies are found. For example, the frequency of variants II and III is estimated by the anatomist Hellmuth Michels to be 10 and 11 percent, respectively. Variant II refers to the anatomical peculiarity that the common hepatic artery does not arise directly from the tripod, but from the left abdominal aorta, the gastrica sinistra artery. Variant III is present when the right gastric artery, the gastrica dextra artery, does not arise from the common hepatic artery (arteria hepatica communis) but from the superior mesenteric artery, which is a separate branch from the abdominal aorta. Other anatomic anomalies with appreciable frequency of 7 to 8 percent such as variants VI and VII correspond to normal anatomy with an accessory hepatic artery in each case. The wall structure of the coeliac trunk corresponds to that of other large arteries. The three wall layers tunica intima, tunica media and tunica externa can be distinguished from the inside to the outside. The tunica interna or interna consists of a single-layered endothelium followed by loose connective tissue, which is separated from the media by an elastic membrane. The tunica media or media is composed mainly of annular and oblique smooth muscle cells and elastic connective tissue and collagenous fibers. A highly elastic membrane demarcates the media from the tunica externa, which is composed of connective tissue and traversed by “supply lines” such as blood vessels and nerves.
Function and tasks
The main function of the abdominal trunk as the truncus coeliacus is also called, is to transmit oxygen-rich blood to the three arteries that originate from the abdominal trunk in normal anatomy. The three arteries supply the connected abdominal organs through further branches and branches. The walls of the abdominal sinus trunk correspond to the structure of the large elastic arteries near the heart, so that they are also actively involved in smoothing systolic blood pressure peaks and at the same time are involved in maintaining diastolic blood pressure by vasoconstriction during diastole, the resting phase of the two ventricles. Diastolic “residual” blood pressure is enormously important in keeping the narrow arterioles and capillaries from collapsing with subsequent irreversible sticking together of their walls. The smooth muscle cells of the abdominal trunk depend on signals from the baroreceptors in the two carotid arteries for this, because there are no pressure sensors in the intestinal part of the circulation. The truncus coeliacus thus takes over part of the so-called windkessel function of the large arteries near the heart to smooth the blood flow on the arterial side of the circulation.
Diseases
One of the most important diseases or conditions associated with the abdominal trunk is due to mechanical obstruction of blood flow. The phenomenon, called truncus coeliacus compression syndrome or Dunbar’s syndrome, usually results from a minor abnormality of the medial arcuate ligament or a slightly displaced origin of the abdominal trunk. The band of tissue that normally runs above the arterial trunk and reinforces the edge of the aortic passage (hiatus aorticus) through the diaphragm can partially pinch off the abdominal sinus trunk, as well as the coeliac ganglion that lies on top of it, causing additional nerve compression. Occurring symptoms such as cramping abdominal pain, nausea and digestive complaints depend on the degree of obstruction of blood flow. The symptoms therefore range from minor discomfort to severe and unbearable pain and life-threatening conditions. In the presence of chronic compression syndrome, secondary damage also occurs to the organs normally supplied by the pinched artery(s). In some cases, where other arteries such as the superior pancreaticoduodenal artery serve as a substitute artery, aneurysms can form in the “substitute” artery due to overtaxation, which can lead to dangerous internal bleeding. In rare cases, isolated dissection requiring treatment has been observed in the truncus coeliacus. This means that blood seeps in between the inner wall layer, the tunica intima and the tunica media, which can cause significant discomfort. Most commonly, dissections are caused by tears in the intima or by injury.
