The inferior mesenteric artery arising from the superior mesenteric artery demonstrated with 3D-CT: A case report.

The inferior mesenteric artery arising from the superior mesenteric artery is an extremely rare anatomic variation. We report a case with this variation demonstrated with 3-dimensional contrast-enhanced computed tomography, which later was confirmed at surgery. The ordinary inferior mesenteric artery arising from the aorta was absent. Previously reported cases with this variation are reviewed. 3-dimensional contrast-enhanced computed tomography is useful for in vivo visualization of aberrant arterial anatomy.

Introduction

There are 3 unpaired splanchnic arteries arising from the abdominal aorta; the celiac trunk, the superior mesenteric artery (SMA), and the inferior mesenteric artery (IMA). The first 2 occasionally form a common trunk (celiacomesenteric trunk), which is known to exist in approximately 1%-2% of general population [1], [2]. IMA usually arises from the ventral aspect of the aorta at the level of the third lumbar vertebra, and the anatomic variation of its origin is extremely rare. Herein, we report a case of IMA arising from SMA, a rare anatomic variation demonstrated by 3-D reconstructed images of computed tomography (CT).

Case report

A 63-year-old man was admitted to our institution for treatment of rectal cancer. During the preoperative workup, the patient underwent contrast-enhanced CT, which revealed no metastatic lesions. In addition, the arterial-phase CT images showed that IMA arose from the proximal part of SMA (Figs. 1, 2). The volume-rendering 3-dimenstional (3D) CT images demonstrated that IMA arose as the first branch of SMA and ran downwards along with the inferior mesenteric vein (Fig. 3). The left colic artery branched off from IMA at approximately 13 mm from its origin. At the level of the iliac crest, the sigmoid artery branches off from IMA. The ordinary IMA arising from the aorta was absent. The patient underwent laparoscopic high anterior resection. IMA arising from SMA was confirmed during the operation. The postoperative course was uneventful.

Fig. 1

a - l. Arterial-phase contrast-enhanced CT images show IMA (arrow) arising from SMA. The ordinary IMA arising from the aorta is absent

Fig. 2

a – p. Sagittal reformatted images of arterial-phase contrast-enhanced CT show IMA (arrow) arising from SMA. The ordinary IMA arising from the aorta is absent

Fig. 3

a. 3D-CT image of the abdominal arteries. IMA (arrow) arises as the first branch of SMA. b. 3D-CT image from which the celiac trunk, renal arteries, and jejunal branches of SMA are removed for better visualization of colonic arteries. IMA: inferior mesenteric artery, LCA: left colic artery, MCA: middle colic artery, ICA: ileocolic artery

Discussion

According to Adachi [3], the first case of IMA arising from SMA was described by Fleischmann in 1815. Since then, only 11 cases of this rare anatomic variation have been reported in the literature, to our knowledge [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. The reported 12 cases, including our present case, are summarized in Table 1. Nine cases were observed in cadaveric dissection, whereas the other cases, including our present case, were observed in radiologic examinations. In our present case, the variation was first noticed with CT images and later confirmed by surgery. We could not ascertain the detail of branching pattern of SMA in the first case of Fleischmann. In 10 of the other 12 cases, IMA was the first branch arising from SMA. In the case reported by Gwyn and Skilton [5], IMA was the second branch from SMA, before which the middle colic artery arose. In the case reported by Yoo et al [12], IMA was also the second branch of SMA, before which the inferior pancreaticoduodenal artery arose. In the case reported by Maleux et al [11], the common trunk of SMA and IMA arose from the aorta at the level of the fifth lumbar vertebra. In most other cases, SMA arose from the aorta near its usual origin at the level of the first lumbar vertebra.

Table 1

Summary of reported cases of IMA arising from SMA.

Author [References]	Year of publication	Age	Sex	Reported material	Associated anomalies
Fleischmann (in Adachi [3])	1815	child			(details unknown)
Adachi [3]	1930	45	male	Japanese cadaver
Mori [4]	1960	60	male	Japanese cadaver	no other abnormalities
Gwyn [5]	1966	76	male	Causasian cadaver	no other abnormalities
Kitamura [6]	1987	69	male	Japanese cadaver	no other abnormalities
Yamasaki [7]	1990	61	female	Japanese cadaver	anomaly of the middle colic artery
Nonent [8]	2001	39	male	radiologic description	celiaco-bimesenteric trunk
Osawa [9]	2004	79	male	Japanese cadaver	hepatomesenteric trunk
Yi [10]	2008	79	male	Japanese cadaver	gastrophrenic trunk, hapatosplenic trunk
Maleux [11]	2010	64	female	radiologic description	accessory mesenteric artery to the ileum
Yoo [12]	2011	82	female	Korean cadaver	no other abnormalities
Present case		63	male	Japanese (radiologic description)	no other abnormalities

Several investigators explained the embryological basis of the anatomic variation of the celiac and mesenteric arteries by the presence of longitudinal anastomoses connecting the roots of primitive ventral splanchnic branches arising from the aorta in embryo [1], [6], [8], [9], [10], [12], [13]. Some roots and anastomoses disappear during developmental process, eventually forming the celiac trunk, SMA, and IMA. If different parts of the anastomoses persist, various anomalous branching patterns such as celiacomesenteric trunk and hepatomesenteric trunk are formed. Development of IMA arising from SMA may also be explained by this theory. However, this hypothesis remains largely speculative. To our knowledge, presence of the longitudinal anastomosis between the primitive SMA and IMA has never been clearly demonstrated yet, whereas the longitudinal anastomosis between the celiac trunk and SMA was observed in a 9-mm-long human embryo by Tandler [14].

Clinically, IMA arising from SMA does not present any symptom. However, if acute SMA occlusion occurs in these patients, it may cause life-threatening intestinal ischemia because collateral circulation from IMA will not develop. In addition, recognition of unusual vascular anatomy of IMA is important in patients who undergo colorectal surgery. Currently, contrast-enhanced 3D-CT is the best diagnostic tool for preoperative assessment of arterial anatomy. Prior knowledge of anomalous arterial branching will allow surgeons to perform safe and effective surgical procedures.