AIM: To evaluate our experience of the clinical management of spontaneous isolated superior mesenteric artery dissection (ISMAD).

METHODS: From January 2008 to July 2013, 18 patients with ISMAD were retrospectively analyzed, including 7 patients who received conservative therapy, 9 patients who received reconstruction with bare stents, and 2 patients who underwent surgical treatment. The decision to intervene was based on anatomic suitability, patient comorbidities and symptoms.

RESULTS: Intestinal ischemia-related symptoms completely resolved in 7 patients who received conservative therapy. Stent placement was successful in 9 patients. Of the 9 patients who received endovascular stenting, abdominal pain was alleviated after the procedure and gradually disappeared within 3 d. Follow-up computed tomography and computed tomography angiography were available in all patients during the first month and the first year after the procedure, which revealed patent stent and patent involved superior mesenteric artery branches with complete obliteration of the dissection lesion. In the 2 patients who underwent surgical treatment, good clinical efficacy was also observed.

CONCLUSION: ISMAD may be managed successfully in a variety of ways based on the clinical symptoms. ISMAD should be treated by conservative management as the first-line option, however, in those with bowel necrosis or imminent arterial rupture during conservative therapy, endovascular or surgical therapy is indicated.

Since the first description by Bauersfeld[1] in 1947, occasional cases of spontaneous isolated superior mesenteric artery dissection (ISMAD) have been reported. However, early identification in the acute stage is increasingly possible due to the development of advanced imaging technology, in particular, abdominal computed tomography (CT) scanning[2,3]. Therapeutic options include conservative management[4-7], endovascular treatments or open surgery such as bypass or direct surgical reconstruction of the lesion, although no consensus has been reached with regard to the best treatment modality[8-13]. From January 2008 to July 2013, 18 patients with ISMAD received treatment in our center. We adopted a treatment algorithm based on the current literature and report our results in these patients.

As described by Yun et al[14], ISMAD was classified into three types based on the presence of dissection re-entry and SMA main trunk patency at initial diagnosis. Four patients were type I, five were type IIa, six were type IIb, and three were type III. The entry sites were all located within a short distance of the ostium. The distance from the SMA ostium to the origin of the dissection ranged from 0.6 cm to 4.8 cm (mean, 2.1 cm). The medium percentage of true lumen compression by the false lumen was 27.1% (range: 0%-62%) (Table 1). Two patients had aneurysmal dilatation of the SMA at the time of presentation. The diameter of these SMA aneurysms was 1.0 and 1.3 cm, respectively.

Stent placement was successful in 9 patients. A single stent was used in six patients, the overlapping stent technique was used in two patients (Figure 1), and the triple overlapping technique in one patient (Table 2). The diameter of the dissection proximal normal artery, the length of the dissection and the SMA branches involved are shown in Table 2.

Intestinal ischemia-related symptoms completely resolved in the patients who received conservative therapy. Of the 9 patients receiving endovascular stenting, abdominal pain was alleviated after the procedure and gradually disappeared within 3 d. Follow-up CT and CTA were available in all patients during the first month and the first year after the procedure, which revealed patent stent and patent involved SMA branches with complete obliteration of the dissection lesion. The patient with ISMAD who underwent resection plus vascular prosthesis grafting and another patient who underwent thrombectomy plus intimectomy recovered well, without intestinal ischemia-related symptoms.

Although an increasing number of ISMADs have been reported in recent years due to the development of advanced imaging technology[2,3], the natural history of ISMAD is not well understood due to the complexity and rarity of the condition. In the present study, six patients (6/18) presented with hypertension, however, there was no atherosclerotic change in the orifice and the proximal segment of SMA. It seems that different mechanisms are involved in ISMAD as compared with aortic dissection. With regard to the causes of ISMAD, hemodynamic abnormalities in the SMA at the transitional point may be a major cause of ISMAD[15-17].

Isolated SMA dissections are most commonly diagnosed by CT scanning, but may also be diagnosed by ultrasound imaging, MRI, or angiogram[10]. The clinical presentation in our ISMAD patients was acute abdominal pain. This pain is related to stenosis of the true lumen causing mesenteric ischemia[18], or to rupture of the dissection causing a mesenteric hematoma[3]. Yun et al[14] classified ISMADs into three types based on their imaging findings. In our eighteen ISMAD patients, four were type I, five were type IIa, six were type IIb, and two were type III. Endovascular procedures were performed in type I (1), type IIb (4), type IIa (3) and type III (1). Surgery was required in two patients (type III). This indicated that ISMAD with SMA occlusion can be monitored carefully and the patient can undergo endovascular or surgical treatment if necessary. Therefore, the treatment of ISMAD should be partially based on imaging findings[19].

The treatment methods for ISMAD are not universally agreed[19-22]. In the present study, symptomatic patients were treated by conservative management as first-line treatment, including hypotensive and antiplatelet measures, bowel rest, intravenous fluids, and nutritional support, which showed favorable efficacy in 7 patients in whom abdominal pain was gradually alleviated within 5 d. However, if conditions such as aneurysmal false lumen dilation, rupture of artery, persistent abdominal pain, or ISMAD-induced severe intestinal ischemia during conservative therapy are observed, surgical or interventional therapy is indicated. Surgery was required when there was non-viable bowel or where endovascular techniques were considered inappropriate or failed. The surgical procedure for ISMAD included thrombectomy and intima resection.

Recently, interest has centered on endovascular treatment with the use of bare stents for ISMAD[10,16,19,22-25]. There are two aims of endovascular treatment：one is to prevent the extension of dissection and the other is to increase blood flow into the small intestine by obliterating the false lumen[9,16]. The choice of stent diameter was based on the proximal normal artery diameter. The types of bare stents were determined according to the operator’s preference and availability of the stent. In our study, we chose the self-expandable carotid bare metal stent, due to its radial strength, multisegmental design, and good compliance. This stent is generally appropriate for the SMA, which is characterized by weakened vascular wall and curved original site[19]. A balloon-expandable stent (Palmaz Blue) is also useful if the dissection is short.

A bare stent is sometimes sufficient for compressing the septum of an ISMAD, opening the stenotic segment and increasing inflow to remedy the ischemia, and with gradual endothelialization of the stent, the thrombosis or the occlusion inside the false lumen can be observed. However, in some cases, such as ruptured, expanding, or large pseudo-aneurysms, and in cases of remodeling failure with single stent treatment, multiple stents are required. In our multiple stent series, 3 ISMADs were treated by a balloon-expandable stent plus a self-expandable stent, however, 1 ISMAD with a pseudoaneurysm was treated using one self-expandable stent (Figure 2). Our experience showed excellent immediate and long-term (11-32 mo) results[14]. The patency rates of the involved stented SMA and SMA branches were determined in all patients during the first month and the first year after the procedure.

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Figure 2 Single bare stent technique. A: An isolated superior mesenteric artery dissection detected by computed tomography angiography (indicated by the arrow); B: Patent true lumen and the disappearance of the false lumen at 3 mo after single bare stenting.

In conclusion, symptomatic ISMADs should be treated by conservative management, however, in patients with persistent abdominal, ISMAD-induced severe intestinal ischemia, and chronic intestinal ischemia-related symptoms during conservative therapy, rupture of artery, and obvious aneurysmal false lumen dilation at high risk of rupture, endovascular or surgical therapy is indicated. Although a larger sample and expanded follow-up are needed, our series shows that percutaneous endovascular bare stent placement can be easily manipulated with a high success rate and can be achieved with excellent prognosis and no severe adverse effects.

We acknowledge the assistance of Su-Ping Geng in collection of patient data, and the assistance of Wen-Nuo Huang.