Visceral artery aneurysms (VAAs) are usually asymptomatic; however, they can prove fatal if they rupture. Superior mesenteric artery (SMA) aneurysms (SMAAs) account for approximately 7% of all VAAs [1]. The rates of SMAA rupture range from 38% to 50%, with an associated mortality of 30% to 90% [2]. The Society for Vascular Surgery guidelines recommend immediate treatment of SMAA regardless of the diameter due to a high risk of rupture and associated mortality. The guidelines also suggest endovascular therapy (EVT) as the first choice of treatment because of its minimal invasiveness, if the anatomical complexity and patency of organ perfusion allow it [3]. We report a case of endovascular treatment of a giant SMAA with challenging anatomy in a 92-year-old female. Reintervention was required to rectify a postoperative endoleak; however, a favorable outcome was achieved with EVT. This case report was approved by the Institutional Review Board of Sapporo Teishinkai Hospital (IRB no. 2021-126). The study participant provided written informed consent for publication.

A 92-year-old female was referred to our department due to a markedly enlarged SMAA, which was identified incidentally on computed tomography (CT) during treatment of a urinary tract infection. Although the white blood cell count was 7,450 cells/μL and the C-reactive protein level was 11.27 mg/dL at admission, the patient responded to the antibiotic treatment, and her inflammatory status normalized. She had a medical history of hypertension, dyslipidemia, and chronic atrial fibrillation. The aneurysm was identified as a saccular mass with well-defined margins and a maximum diameter of 96 mm (Fig. 1A, B). Nonetheless, any other symptoms such as abdominal pain and vomiting were not observed. In this case, CT angiography demonstrated that EVT was not a suitable treatment option for SMAA because of the short proximal sealing zone, measuring 5.0 mm in length from the origin of the SMA, revealing a reverse tapered anatomy with a diameter of 6.0-6.8 mm. Furthermore, the neck of the aneurysm was 3 mm in diameter and opened vertically into the SMA. The right hepatic artery (HA) developed from SMA approximately 25 mm after its origin, and there was no collateral artery connecting to the HA to continuously perfuse the right lobe of the liver. The distal landing zone was 17.0 mm in length and 6.5 mm in diameter (Fig. 1C). Based on the favorable response to antibiotic treatment for urinary tract infection and the contrast-enhanced CT findings, an infectious aneurysm was considered unlikely. Considering the patient’s age and the invasiveness of an open surgery, EVT was selected as the initial plan despite the anatomical difficulties. Moreover, treatment was performed on the 9th day after confirmation of negative blood cultures.

Figure 1. Preoperative computed tomography findings and the anatomical schematic of the superior mesenteric artery (SMA) aneurysm (SMAA). The SMAA was a saccular aneurysm measuring 96 mm in diameter (A, B). The proximal landing zone was 5.0 mm long with a 6.5-6.8 mm SMA main trunk. The right hepatic artery (HA) branched 17.0 mm distally from the site of the aneurysm (C).

EVT was performed through the right femoral artery using a 7 Fr Introducer (Flexor Tuohy-Borst Sidearm Introducer; Cook Medical). The sheath was placed into the SMA (Fig. 2A), and a 7×25 mm VIABAHN stent graft (SG) (W. L. Gore & Associates) was implanted at its origin, sparing the right HA. It was then dilated with a 7×40 mm Rx-Genity balloon (Kaneka Medix Corporation). However, a type Ia endoleak was identified in the aneurysm (Fig. 2B). An additional 8×25 mm VIABAHN SG was added to the proximal side and post-dilated with an 8×40 mm ULTRAVERSE balloon catheter (Becton Dickinson). Following the proximal dilation, the type Ia endoleak disappeared and the procedure was completed (Fig. 2C). Postoperative CT angiography a week after EVT showed an endoleak partly into the aneurysm (Fig. 2D). The patient was discharged after a thorough postoperative examination. Postoperative CT 4 months after EVT demonstrated patency of the SG and disappearance of the endoleak (Fig. 2E). The patient was started on a direct oral anticoagulant for chronic atrial fibrillation 6 months after EVT. The maximum transverse diameter of the aneurysm decreased from 71 mm to 68 mm.

Figure 2. The initial endovascular treatment for the superior mesenteric artery aneurysm (SMAA). Angiography was performed distal from the site of SMAA development. The right hepatic artery (HA) was identified (A). Angiography demonstrated a substantial type Ia endoleak after placement and post-dilation of the first stent graft (SG). The black arrow shows the proximal edge of the SG (B). An additional SG was deployed to treat the endoleak. The white arrow shows the proximal edge of the additional SG. The black arrow shows the proximal edge of the first SG (C). Postoperative computed tomography (CT) 1 week after the treatment showed persistent flow into the aneurysm (D). CT performed 4 months after the treatment demonstrated the patency of the SGs and disappearance of the endoleak (E).

However, 19 months after the initial treatment, contrast-enhanced CT revealed endoleak recurrence (Fig. 3A). The maximum transverse diameter of the aneurysm had increased to 73 mm. Additional treatment was chosen to identify other possible endoleaks, including types Ia, Ib, and III. An 8×25 mm VIABAHN SG was implanted just proximal to the origin of the right HA for type Ib endoleak (Fig. 3B), and an 8×50 mm VIABAHN SG was implanted to protrude into the aorta for type Ia and III endoleaks (Fig. 3C). They were both dilated with an 8×40 mm ULTRAVERSE balloon catheter. No evident endoleaks were observed during the procedure. Postoperative CT angiography performed 21 months after the initial treatment showed no endoleak or enlargement of the aneurysm (Fig. 3D-F). The patient was asymptomatic before and after EVT. Although a postoperative endoleak was identified after initial EVT, the patient experienced no impact on her daily activities during follow-up.

Figure 3. Recurred endoleak and subsequent reintervention 19 months after initial treatment. Computed tomography (CT) showed sac growth due to the endoleak (A). A stent graft (SG) was placed to cover the distal landing zone and overlapped with the previous SGs. The black arrowhead shows the proximal edge of the third SG. The black arrow shows the proximal edge of the first SG. The white arrow shows the proximal edge of the second SG (B). A SG was also added to cover the proximal part with protrusion into the aorta. The black arrowhead shows the proximal edge of the third SG. The black arrow shows the proximal edge of the first SG. The white arrow shows the proximal edge of the second SG. The white arrowhead shows the proximal edge of the fourth SG (C). Postoperative CT angiography showed the patency of the right hepatic artery (HA) and the well-excluded aneurysm (D, E). The fourth SG was placed protruding into the aorta (F).

Catheter-based treatment options are better for treating patients with limitations such as advanced age and a hostile abdomen. The treatment choice for VAAs has notably shifted from open surgery to EVT as experience with the technique has increased and clinical outcomes have improved. Advancements in EVT have enabled the treatment of various aneurysms. Although not limited to SMAA, the endovascular approach is associated with a shorter hospital stay and fewer cardiovascular complications [4]. The reported technical success rate of EVT for VAAs exceeds 95% [5]. Transcatheter embolization using coils is a common procedure; however, new procedural techniques and devices, such as covered stenting, continue to emerge. In the EVT era, anatomical feasibility is always considered when making a decision on the treatment strategy for VAAs; reintervention might be required to control endoleaks, but this is dependent on anatomical issues, location, branches from the aneurysm, and proximal and distal sealing zones [3,6]. Therefore, careful follow-up using postoperative imaging is recommended in patients with anatomical difficulties. We performed contrast-enhanced CT approximately 3 months postoperatively and followed up with a plain CT every 6 months. A plain CT was used in the subsequent follow-ups because the endoleak had disappeared initially. Contrast-enhanced CT was performed 19 months postoperatively because the aneurysm showed a growing trend, which led to the detection of a new endoleak.

The catheter-based strategy for small VAAs is an established treatment with satisfactory outcomes. However, as shown in the current case, giant VAAs, defined as those measuring >5 cm in diameter, are substantially more complex. Although the technical success rate was 91% in 11 patients in a previous study, 27% experienced perioperative complications, including rupture, organ ischemia, and abscess formation [7]. A variety of endovascular tools, such as coils, may be required for a successful treatment. Coil packing using a microcatheter outside of the SG was technically feasible in our case; however, the procedure was not performed since coil compaction was difficult and recanalization after coil packing was highly unpredictable given the giant aneurysm [8]. Liquid embolic agents, such as N-butyl cyanoacrylate (NBCA), are available for embolizing VAAs [9]. However, little is known about the safety of NBCA for the treatment of SMAA. Postembolization syndrome has rarely been reported because of the specific techniques involved and limited indications [10]. In the current case, the use of NBCA might have been effective in decreasing the persistent flow in the aneurysm. Additionally, vascular plugs within the SMAA can help the thrombosis of SMAA. However, cannulation of the aneurysm was considered difficult, and we did not intend to strain the aneurysm. Therefore, the treatment plans mentioned above were not selected.

SGs allow long-term exclusion of the aneurysm, preserving the flow through the affected visceral artery and thus reducing the potential risk of target organ ischemia [11]. The patency rate was approximately 90% at 6 months after the procedure. The long-term patency rate was also good (>90% at a mean follow-up period of 20 months). Furthermore, SG occlusion due to intimal thickening in the remote stage may be less likely to cause organ ischemia due to the development of collateral blood vessels [5].

In the current case, persistent flow of the SMAA with short neck distance was excluded with multiple SGs. To prevent endoleaks in the current case, an initially larger SG may be preferable (the 7 mm SG is oversized by 102%, and the 8 mm SG is oversized by 117% in our case). In addition to size selection, protruding the SG into the aorta helped extend the proximal sealing zone as much as possible. Moreover, to prevent type Ib endoleaks, HA embolization might be performed to extend the distal landing zone. In this regard, the presence of reserved collateral vessels after HA embolization lowers the risk of hepatic complications, regardless of portal venous flow. However, 13% of the patients with poor collateral vessels after HA embolization, such as the patient in the current case, experience segmental hepatic infarction, even if portal venous flow is preserved. In total, 75% of the patients with poor collateral vessels after HA embolization and compromised portal venous flow experienced multisegmental hepatic infarction or hepatic failure. Thus, arterial collateral vessels and portal venous impairments should be evaluated when the HA is planned to embolize [12]. Regarding the selection of SGs, self-expanding and balloon-expandable ones are available. In the current case of SMAA, we took advantage of the increased flexibility of the self-expanding SG compared with that of the balloon-expandable SG in the SMA. Balloon-expandable SGs are sometimes difficult to place because their rigidity precludes adequate advancement and placement. However, balloon-expandable SGs could be used in procedures by partially extending the SG into the aorta and performing post-dilatation in stages of varying sizes.

Although reintervention was required to correct an endoleak during follow-up, a giant SMAA, which was anatomically unfavorable for EVT, was successfully treated using SGs. SGs may be useful for overlapping short proximal and distal sealing zones.

None.

Shinsuke Kikuchi has been the editorial board member of the VSI since 2019. He was not involved in the review process. Otherwise, no potential conflict of interest relevant to this article was reported.

Concept and design: RO, NO. Analysis and interpretation: RO, MT. Data collection: RO, NO. Writing the article: RO, HK. Critical revision of the article: SK. Final approval of the article: all authors. Statistical analysis: none. Obtained funding: none. Overall responsibility: RO.