Date Published: September 28, 2017
Publisher: John Wiley and Sons Inc.
Author(s): Takaaki Nakano, Toshitaka Ito, Tetsuhiro Takei, Masaaki Takemoto.
The smaller superior mesenteric vein (SMV) sign is a well‐known computed tomography (CT) parameter for acute superior mesenteric artery (SMA) occlusion. This CT sign is potentially beneficial for the early diagnosis of acute SMA occlusion; however, few reports have documented this sign. The present study aimed to determine the accuracy of the smaller SMV sign for the detection of acute SMA occlusion.
We retrospectively reviewed CT images from 20 patients with acute SMA occlusion and 1,216 controls. We measured the external diameters of the SMV and SMA, and calculated the SMV/SMA diameter ratio. A ratio ≤1 indicated a positive smaller SMV sign.
Of the 20 patients, 14 had the smaller SMV sign, whereas of the 1,216 controls, 88 had the smaller SMV sign. Of the 88 controls with a positive sign, 79 had apparent reasons for the decreased flow in the SMA and nine patients had no reason for the decreased flow. The sensitivity and specificity of the smaller SMV sign for acute SMA occlusion were 70% and 99.2%, respectively.
The smaller SMV sign is an accurate and important CT parameter for the detection of acute SMA occlusion.
Acute superior mesenteric artery (SMA) occlusion is rare, and accounts for less than 1 of every 1,000 hospitalizations. Its mortality rate has been reported to be up to 60–80%, and a delay in diagnosis can result in life‐threatening consequences.1 This disease should be evaluated early, and the time to recanalization is extremely important.1, 2 There are various clinical findings in patients with this disease; therefore, diagnosis can be extremely difficult. For the diagnosis of acute SMA occlusion, imaging techniques, such as ultrasonography, computed tomographic angiography (CTA), and magnetic resonance angiography, are useful.1, 3, 4 However, each of these methods has limitations. Ultrasonography is highly dependent on the skill of the technologist, and it can be difficult to carry out in patients with obesity, bowel gas, and heavy calcification in the vessels. Computed tomographic angiography has a high accuracy for the diagnosis of SMA occlusion (up to 95–100%). However, there might be issues with the use of contrast agents.5, 6 Magnetic resonance angiography requires a long time for imaging.1 Therefore, a quick and accurate diagnostic indicator for acute SMA occlusion is required. The smaller superior mesenteric vein (SMV) sign has been often discussed in textbooks.7
The present study aimed to determine the accuracy of the smaller SMV sign for the detection of acute SMA occlusion.
A total of 20 patients treated for acute embolic occlusion of the SMA between 2005 and 2014 were reviewed retrospectively. The diagnosis was confirmed based on surgical findings, CTA, or catheter angiography. The control group included 1,220 individuals who presented to the emergency department for other reasons and did not have acute SMA occlusion. The control group included 116 patients with abdominal pain. All CT studies were undertaken with a 64‐section helical scanner (pitch, 0.6; 5‐mm intervals). Computed tomography images of patients and controls were evaluated.
A smaller SMV sign was identified in 14 of the 20 patients (Table 1). The mean time from onset to CT imaging was 10.5 h. Mogi class A occlusion was present in 17 patients; of these, 12 had a smaller SMV sign. Class B occlusion was present in two patients, and one had a smaller SMV sign. Class C occlusion was present in one patient, who had a smaller SMV sign (Table 2). There were no significant differences between occluded segments. In patients with a smaller SMV sign, the mean time from onset to CT imaging was 13.4 h, whereas in patients without a smaller SMV sign, the mean time from onset to CT imaging was 3.4 h; however, the difference was not significant.
A smaller SMV sign is usually described in the section regarding acute upper mesenteric artery occlusion in radiology textbooks.7 However, few articles have discussed its definition and usefulness. Acute intestinal ischemia has been diagnosed with CTA and angiography, and endovascular treatment is often carried out prior to surgical intervention.10 A previous study reported that interventional radiology before surgical intervention can increase the survival rate.11 The amount of contrast agent used will increase owing to CTA or interventional radiology treatment. Cigarroa et al.12 reported that administration of contrast agent beyond the maximum acceptable dose (contrast agent 5 mL/kg × body weight [kg]/serum creatinine) can increase the risk of nephropathy. A high incidence of contrast nephropathy has been reported at doses >100 mL.5 The onset of acute renal failure in ischemic bowel disease has been reported to increase the mortality rate.6 Therefore, the use of a contrast agent should be limited as much as possible. A smaller SMV sign can be determined using plain CT images, and the use of a contrast agent can be avoided.
The smaller SMV sign is an important CT parameter for the detection of acute SMA occlusion, with a sensitivity of 70% and a specificity of 99.2%. This sign can be easily detected with plain CT images, allowing for early diagnosis and treatment of acute SMA occlusion.
This study was approved by the clinical research committee of Yokohama City Minato Red Cross Hospital, Japan (2016‐48).