The celiac trunk usually divides into three branches—the LGA, CHA and SA. However, many variant patterns of the celiac trunk have been described. In a review of the literature, on 2,141 cadavers, 87.6% of celiac trunks had the classical trifurcation, 12.2% presented an incomplete bifurcated celiac trunk and 0.2% was absent . On a large series of patients (10,750 patients from 19 studies), the typical three branched celiac trunk (complete celiac trunk) occurred in 90.70% of patients, the incomplete celiac trunk in 6.09% of patients, and the absence of the celiac trunk only in 0.19% of patients . The absence of celiac trunk was extremely rare, existing classifications were rarely described excepting some case reports [2, 4–6, 12].
There have been many attempts to classify the different branching patterns of the celiac trunk. Lipshutz  seems to have been the first and suggested a classification of the celiac trunk into four types. Adachi  presented a more detailed classification, whereas two other commonly used classifications were suggested by Morita  and Michels . The first classification system that included an absent celiac trunk as a morphological type was that of Morita. Regrettably, Morita considered the possibility of such a variant, but none was described. Recently, Marco-Clement et al  created a new and simple classification, they proposed four types with eight subtypes, including complete celiac trunk, incomplete celiac trunk, absence of the celiac trunk, and celiacomesenteric trunk.
However, all these existing classifications failed to describe the anatomic details or further classify for the absence of the celiac trunk. In these studies, the absence of the celiac trunk was narrowly defined as that each of all its branches arise separately from the abdominal aorta, but excluded any HM trunk + LGA + SA, SM trunk + LGA + CHA, or GM trunk + CHA + SA. Our new classification defines the absence of the celiac trunk as that the celiac trunk is not exist, more specifically, there is not such an arterial trunk containing at least two major branches of the celiac trunk. This definition indicates that the absence of the celiac trunk should also include HM trunk + LGA + SA, SM trunk + LGA + CHA, GM trunk + CHA + SA, and any other variant that conforms to the definition, in addition to LGA + CHA + SA + SMA, which thus results in a higher prevalence (0.76%) in our study population.
The absence of the celiac trunk was found in 19 patients in our 2,500 patients studied by the MDCT angiography which should be the most samples so far. Here, we first describe the anatomic details of the absence of the celiac trunk and further classify it into different types which have not been seen in the previous literature. By reviewing previous studies and combining with the present findings on the absence of the celiac trunk, we propose a new and useful classification: Type I, LGA + CHA + SA + SM; type II, HM trunk + LGA + SA; type III, SM trunk + LGA + CHA; type IV, GM trunk + CHA + SA; and type V, other type. The new definition and classification are not only helpful for assessing its variant patterns, but also to analyze the potential embryological mechanisms which led to variant formation.
Tandler  stated that four primitive ventral vascular roots (namely LGA root, CHA root, SA root, and SMA root) stem form the abdominal aorta during the early phase of embryogenesis and that these roots are interconnected by a longitudinal anastomosis. During normal development the longitudinal anastomosis is interrupted between roots 3 and 4, thereby resulting in anatomic separation of the celiac trunk from the SMA (Fig. 2a). The misplacement of the longitudinal anastomosis leads to the development of variants in the celiac trunk and SMA. Our new classification on the absence of the celiac trunk enables us to further analyze the embryological mechanisms of its various types.
Type I of the absence of the celiac trunk may be a primitive type, in which LGA, CHA, SA and SMA originate separately from abdominal aorta. This type can be due to abnormal interruptions of the longitudinal anastomosis among all four roots during embryonic development (Fig. 2b). Since the origins of the LGA, CHA and SA approximate at the same level, the up and down position among the three arteries may not be invariant in human embryos. If the root 3 is CHA and the abnormal interruptions occur among roots 1–3, a type II (HM trunk + LGA + SA) would form (Fig. 2c); if the root 3 is SA, the abnormal interruptions would result a type III (SM trunk+ LGA + CHA) (Fig. 2d); however, only very rarely, the root 3 could be LGA, an extremely unusual type IV (GM trunk + CHA + SA) may occur (Fig. 2e). The type IV may also be attributed to a complete regression or absence of root 1, with a replaced LGA arising from SMA, while the abnormal interruptions occur among roots 2–4. Usually, the LGA root is the highest one and the SMA root is the lowest one, they cannot interconnection with each other. Therefore, the type IV is not found in our study, but it is theoretically possible.
The type V can also be explained by abnormal interruptions and persistence of the longitudinal anastomosis, and regression of vascular root and emergence of replaced artery during embryonic development (Fig. 2f). Such as one of our patients, a SM trunk + LGA with the CHA arising from the distal segment of the SMA, may be attributed to a complete regression or absence of root CHA, with a replaced CHA arising from SMA. The type V is often presented as a variety of very complex and rare variants. Iyori et al  reported a special patient, abdominal aortography did not show the celiac trunk, selective arteriography of the SMA showed a dilated and elongated pancreaticoduodenal artery, which led to the gastroduodenal artery, CHA, proper hepatic artery, SA, and other arteries originating from the celiac trunk. It may be attributed to complete regression or congenital absence of the celiac trunk.
The absence of the celiac trunk has important clinical significance in abdominal vascular surgery, such as in liver transplantation , acute mesenteric occlusion, laparoscopic surgery and interventional procedures in the upper abdomen, specifically when considering the Appleby procedure . Identification of celiac trunk variants may avoid vascular complications during procedures or lead to target embolization in transcatheter arterial chemoembolization. Although abdominal aortic aneurysm with absence of the celiac trunk is extremely rare, complete preoperative MDCT angiographic visualization of the visceral vessels is needed to achieve vascular control of the upper abdominal aorta in patients with significant intraperitoneal bleeding caused by a ruptured aortic aneurysm [16–18]. The variants of absent celiac trunk may be decisive when planning surgical or radiological upper abdominal procedures. The MDCT is a safe and reliability, convenient and rapid way to assess the celiac trunk variants. We hope that the present study would help to minimize complications related to abdominal surgery, including bleeding and necrosis, as well as facilitate better and more accurate radiological interpretation.
The present study has some limitations. First, it was performed retrospectively. Second, it was conducted based on image interpretations performed by means of consensus opinion. Third, the Type IV (GM trunk + CHA + SA) of absence of the celiac trunk was not found in our patients, we need more data to see if it exists. However, the new classification enables us to describe in detail various types of absence of the celiac trunk, and discuss their probable embryological mechanisms.