In total, we reviewed 21 articles and 16 case reports. The presence or absence of a middle hepatic artery (MHA) was regarded as normal. It was also considered normal anatomy regardless of where the MHA originated from (either the LHA or RHA). Regardless of whether the ARHA and RRHA occurred alone or accompanied by other arterial variations, all were taken into account. In addition, in Winston et al's article, 3 cases of ARHA were documented without a description of their origins, so it was marked “NG” in Table 1. Some publications have noted additional, previously unclassified variations of hepatic arterial supply that are not included in Michels’ classification. However, no published detailed description of these exits, so they were not taken into account. Three points require further illustration. First, in Table 1, an ARHA arising from the LHA or PHA was defined as a kind of anatomic variation based first upon the existence of a normal RHA. When a normal RHA exists, then another artery supplying the right hepatic lobe is called an ARHA, and can be considered a variant artery. Without the presence of an RHA, the artery supplying the right hepatic lobe originating from the LHA or PHA cannot be classified as an ARHA, rather, it is an RHA. Second, in Kishi et al's article, an accessory hepatic artery branch supplying segment VI was termed as “A6,” but is actually an ARHA, which can arise from the CT, PHA, or SPA. Third, additionally, Ahn et al has mentioned that a right posterior hepatic artery arising from the LHA or SMA is also an ARHA owing to the fact that it supplies the right liver but arises from arteries other than the RHA.
For the 21 articles, according to our statistical results, the total number of cases included was 10966, of which 7365 (67.2%) had standard anatomy. An ARHA was identified in 748 (6.8%) cases. The most common origin of an ARHA was the SMA (718 cases, 6.5%), followed by the AA (8 cases, 0.07%), CT (6 cases, 0.05%), PHA (4 cases, 0.04%), GDA (2 cases, 0.02%), LHA (2 cases, 0.02%), LGA (1 case, 0.01%), CHA (1 case, 0.01%), RPA (1 case, 0.01%), RA (1 case, 0.01%), SPA (1 case, 0.01%), and SA (0 cases, 0.00%) (Table 1). An ARHA arising from the SA was not been reported in these articles, but was reported separately by de Albuquerque Martins in 2010 and Al Zahrani et al in 2017 (Table 2).
An RRHA was identified in 1069 (9.7%) cases. As with an ARHA, an RRHA most commonly originated from the SMA (1009 cases, 9.2%), and followed by the CT (33 cases, 0.3%), GDA (8 cases, 0.07%), CHA (8 cases, 0.07%), AA (8 cases, 0.07%), LGA (1 case, 0.01%), RPA (1 case, 0.01%), IMA (1 case, 0.01%), SA (0 cases, 0.00%), and RA (0 cases, 0.00%) (Table 1). An RRHA originating from the SA or RA was not been reported in these 21 articles, but Braun et al reported a rare anatomic variation of an RRHA arising from the RA in 1991, and Caruso et al reported a similar case in 2016 (Table 2). Among this research, the incidence of ARHA and RRHA is very different. For ARHA, the incidence ranges from 24.3% to 0.8%. For RRHA, the incidence ranges from 19.7% to 1.6% (Table 1). This heterogeneity may be related to a difference in the number or characteristics (races and ethnicities, region, or genetic traits) of the patients included in the studies. A literature search did not reveal any relevant studies regarding a correlation between hepatic artery variation and any such characteristics.
According to our statistics, an RRHA has 2.9% higher incidence than an ARHA, corresponding to 1069 cases (9.7%) and 748 cases (6.8%), respectively. For both an ARHA and an RRHA, they most usually originate from the SMA. Interestingly, an RRHA originating from the CT is significantly more common than an ARHA originating from the same artery, corresponding to 33 cases (0.3%) and 6 cases (0.05%), respectively. The other origins are relatively rare. More detailed data are shown in Table 1.
The origins of the ARHA have been well-described in previous articles except for the SA and LHA. Similarly, except for an RRHA originating from the SA and RA, the other origins of RRHA have also been previously described. More detailed data are shown in Table 2.
In reviewing the literature, we found that ARHA and RRHA typically exist independently. Anatomic variation involving both an ARHA and an RRHA has not been reported. Furthermore, Caruso et al conducted an extensive literature review in 2010 of 27 articles with detailed descriptions of anatomic variation in hepatic arteries. In their article, the variation involving both an ARHA and an RRHA was still not reported. According to the above publications, the most common variation reported is the presence of an RRHA without an ARHA, or the presence of an ARHA with a normal RHA. To the best of our knowledge, there have been no published reports to date describing an ARHA branching from the GDA with an RRHA arising from the SMA in the same patient. This is the first report about this type of variation in hepatic arterial anatomy.
The origins and course of the hepatic artery, especially anatomic variations, have important clinical significance for gastric resection, liver resection, liver transplantation, and TACE. Each hepatic artery is functionally essential for providing blood supply to the liver, and so are variant arteries. Inadvertent ligation or embolization of an accessory or replaced hepatic artery during surgery could cause ischemic necrosis of the liver with fatal results. Early in 1989, Brown et al reported a case of a patient who underwent LGA embolization and suffered complications of hepatic ischaemic necrosis owing to a replaced left hepatic artery arising from it. Miura et al also documented 11 patients in 2010 who had postoperative hepatic infarction after undergoing pancreato-biliary surgery and analyzed the underlying causes. In 2 of the 11 patients, the cause of hepatic infarction was inadvertent ligation of the RHA during surgery, and one patient 1 a variant RRHA originating from the SMA. Such serious complications may have been avoided if the variant arterial supply was identified before surgery.
Therefore, a thorough understanding of the normal anatomy of the hepatic artery and its anatomic variation is crucial for surgeons and interventional radiologists to avoid inadvertent injury while performing hepatic surgery and arteriography. These anomalous hepatic arteries should be identified preoperatively and carefully avoided during surgery to prevent unintentional injury, massive hemorrhage, or hepatic infarction. Before liver transplantation, the extrahepatic arterial anatomy must also be precisely understood to assure safety and prevent recipient complications.
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