Background

Three major arteries arise from the abdominal aorta: the celiac artery, the superior mesenteric artery (SMA), and the inferior mesenteric artery (IMA). While there are many various subtypes of the branches from the celiac artery or the superior mesenteric artery reported, there are few reports of those from the IMA [1, 2]. Here, we report a case of advanced sigmoid colon cancer with the IMA arising from the SMA.

Case presentation

A 59-year-old-male presented with a complaint of bloody stools. On physical examination, no mass was felt during palpation. Laboratory data on admission showed that the levels of tumor markers including CEA and CA19-9 were within normal ranges. Colonoscopy revealed a semi-circumscribed irregular elevated lesion in the sigmoid colon that was diagnosed as adenocarcinoma by biopsy (Fig. 1a). Abdominal enhanced CT scan revealed wall thickening of the sigmoid colon, and 3D-CT angiography showed that the IMA originated at 36 mm distal side from the SMA, which was the same level as the second lumbar vertebra, and the first jejunal artery bifurcated further distal side from the IMA origin (Fig. 1b). It also detected that the middle colic artery branched off from the SMA at 27 mm distal side from the IMA origin, and both the left colic artery and the sigmoid colic artery bifurcated from the IMA. No direct branches originating from the abdominal aorta were identified to supply the left-side colon. There were no anomalies or abnormalities detected except for the IMA. On PET-CT, paracolic lymph nodes were suspected of metastasis, but there was no abnormal FDG accumulation in the lymph nodes around the root of the IMA (Fig. 1c). Liver metastasis was also suspected by PET-CT and MRI (Fig. 1d). The patient was diagnosed with sigmoid colon cancer cT4aN2aM1a cStage IVA. Therefore, we planned treatment with laparoscopic low anterior resection followed by resection of the liver metastases to achieve radical resection.

Fig. 1
figure 1

Preoperative imaging findings. a Colonoscopy showed a semi-circumscribed irregular elevated lesion in the sigmoid colon. b 3D-CT angiography showed that the IMA (yellow arrowheads) originated from the SMA (yellow arrow). c On PET-CT, there was no abnormal accumulation in the central lymph nodes around the IMA. d MRI showed findings suggestive of liver metastasis (white arrow)

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Laparoscopically, we can found that the tumor was located in the sigmoid colon and involved the small intestine and the left seminal vesicle. The IMA was identified as running parallel to the abdominal aorta; meanwhile, the colonic autonomic nerve was supplied from the lumbar splanchnic nerve at the caudal side of the duodenum (Fig. 2a). Central lymph nodes around the colonic autonomic nerve were dissected en bloc with the regional lymph nodes, followed by resection of the IMA at the level of the lower duodenal border (Fig. 2b). The left seminal vesicle, the left pelvic plexus and the middle rectum were firmly adhered to the tumor, and thus we performed low anterior resection with combined resection of them (Fig. 2c). Indocyanine green fluorescence system was used for assessment of the blood supply to the colonic stump. Pathological radical resection including the regional lymph nodes metastases was achieved. Two months later, complete resection of the liver metastasis was performed. After adjuvant chemotherapy, no recurrence was observed during the 1.5 years since the liver resection was performed.

Fig. 2
figure 2

Intraoperative findings during laparoscopic low anterior resection. a The IMA ran parallel to the abdominal aorta without branching, while the neural branch (white arrow) arising from the lumbar splanchnic nerves (white arrowheads) supplied the left-sided colon. b The central lymph nodes around the IMA were dissected, followed by transection of the IMA at the level of the inferior edge of the duodenum. c Complete resection was performed

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Discussion

Anatomical variation of the IMA is relatively rare. Kakihara et al. reported that, among 3,182 cases of abdominal angiography, one case (0.03%) had a defective IMA, two cases (0.06%) had abnormal running of the root associated with visceral retroversion, and two cases (0.06%) branched from the SMA. All other cases bifurcated to the left side at the level of the third lumbar vertebra [3]. Several primitive mesenteric arteries arise from the dorsal aorta in a segmental fashion and are distributed against their respective primaries in the early fetal period. Early in development, there is a longitudinal anastomosis connecting the arteries vertically in the dorsal mesentery. According to fetal development, some primitive mesenteric arteries disappear, while the others become the celiac artery, the SMA, and the IMA, which are distributed in the foregut, midgut, and hindgut, respectively [4]. The IMA is initially formed at the twelfth thoracic vertebra but eventually migrates to the level of the third lumbar vertebra [5]. In this case, the IMA bifurcation from the SMA may occur due to both abnormal arterial disappearance and lack of the usual migration. According to the previous reports, the IMA arising from the SMA typically diverges as the first branch supplying the colon (as shown in Table 1) [2, 3, 6,7,8,9,10,11,12,13,14,15,16]. In most cases, the left colic artery arises as a branch of the IMA. One-third of the previous cases were associated with other vascular malformations. In the present case, the IMA was the first branch of the SMA and had the same bifurcation pattern as most previous cases, which included the left colic artery and the sigmoid colic artery. This case also showed a branch from the lumber splanchnic nerve supplying the left-sided colon at the level of the third lumber vertebra where the IMA normally branches. It is possible that the sympathetic nervous system and the vascular system develop asynchronously.

Table 1 Summary of previous cases of the IMA arising from the SMA
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For left-sided colorectal cancer with unusual IMA bifurcation, the optimal definition of the extent of lymph node dissection has not been established [3, 13,14,15,16]. Kakihara et al. performed radical lymph node dissection including around the root of the IMA branching from the SMA for cT3N0M0 cStage II lower rectal cancer [3], while Kondo et al. performed central lymph node dissection up to the level of the inferior edge of the duodenum where the IMA usually branches from the aorta, preserving blood flow to the LCA for rectal cancer cT3N0M0 cStage II [14]. Minamisawa et al. dissected the lymph nodes around the bifurcation of the LCA as the cranial border of the dissection for cT2N0M0 cStage I rectal cancer [15]. In this case, preoperative PET-CT suggested metastases in the para-intestinal lymph nodes, but not in the proximal lymph nodes along the IMA. Pathological examination revealed complete resection; therefore, central lymph node dissection including that at the level of the inferior border of the duodenum would be oncologically sufficient. When the IMA was deficient, the marginal artery from the middle colic artery was the only blood flow to the left-sided colon. Thus, regional lymph node dissection in the direction of the intestinal axis is more important than central lymph node dissection in such cases.

Although anatomical variation of the IMA is infrequent, preoperative assessment using CT and CT angiography is very important because they can provide clear case-specific anatomical information. Even in patients with rare anatomical anomalies, prior confirmation of the anatomy allows us to safely complete radical surgery.

Conclusions

We reported a rare case of sigmoid colon cancer with the IMA directly branching from the SMA. Preoperative confirmation of the anatomy enabled us to safely complete radical surgery even in a patient who had unusual bifurcation of the IMA.