Angiography of the SMA is necessary for the diagnosis of NOMI. Angiographic findings suggestive of mesenteric vasospasm are (1) narrowing at the origins of the major branches of SMA, (2) irregularities in the intestinal branches with segmental narrowing, (3) spasm of the intestinal arcades, and (4) impaired filling of intramural vessels . After mesenteric vasospasm is confirmed by angiographic examination, prostaglandin or papaverine hydrochloride injection generally improves the vasoconstriction . However, angiography is an invasive and time-consuming examination that cannot be performed in cases with serious conditions such as severe hypotension.
CT is often used to diagnose NOMI by detecting the signs of intestinal ischemia such as attenuated enhancement of the intestinal wall, dilated intestine, and intramural gas [7–10]. Vasospasm of the SMA, as indicated by the SMA diameter and through analysis on multi-planar reconstructed (MPR) images, was also reported as a diagnostic finding of NOMI [8, 9], which was detected in this case. However, the usefulness of CT angiography has not been evaluated thus far. In the present study, angiographic examination was difficult to perform because of hypotension, and the ability of CT angiography to detect SMA irregularity and narrowing of the origin of the MCA and ICA was very useful in the early diagnosis.
Although there are only a few reports on the pathological features of NOMI, Sarda et al. reported congestion and flattening of the plicae with inflammatory exudates in the substantia propriae in less advanced cases as well as necrosis and ulceration of the mucosa, submucosa, and muscularis. Typical macroscopic findings show well-defined multiple circumferential ulcers of variable depths. In the present case, congestion and flattening of the mucosa and edema of the submucosal layer were observed . Although no multiple ulcers were detected, there was necrosis of variable depths with clear margin and regional transmural necrosis with peripheral ghost-like disappearance of the mucosal glands was identified. These ischemic changes and the absence of thrombus in resected specimens were consistent with NOMI.
Ischemic colitis is also known to sometimes cause bowel necrosis despite the absence of thrombosis or embolism in the mesenteric arteries. In many studies, NOMI was not distinguished from ischemic colitis. Wittenberg et al. reported that NOMI typically occurs in the area of the bowel perfused by the SMA, whereas ischemic colitis usually presents in the area perfused by the inferior mesenteric artery . Usually, a long range of the bowel becomes discontinuously necrotic in a patient with NOMI. Intraoperative endoscopy is useful for the evaluation of extent of mucosal necrosis. However, because of the risk of contamination of operation field, extended mucosal necrosis was evaluated by the inspection of the resected specimen in this case. No extended mucosal necrosis was observed in the present case.
Only a few cases of NOMI localized in the colon were reported [7, 12], and the ascending colon was the most frequently reported site. There was no report of a case localized in the transverse colon. Although narrowing of the ICA was observed in the present case, the narrowing of the MCA was more severe than that of the ICA, and the blood flow of the MCA was not detected by CT angiography (Fig. 2). Moreover, in the present case, the LCA could not be detected by CT angiography, which suggested the absence or occlusion of the LCA (Fig. 2), although we could not confirm that during the emergent operation. In our previous study, the absence of the LCA was observed in only 5.1% of the cases . The absence of the LCA, which could be a collateral artery of the transverse colon, may contribute to this rare case of ischemia localized in the transverse colon. The descending colon was not ischemic, which implied that the sigmoid artery assumed the role as a collateral artery. Being less invasive, CT angiography was superior to traditional angiographic examination in acquiring information on multiple arteries.