Within a period of 11 years, we found a prevalence of celiac artery compression by MAL in 12.3% (n = 7) of patients submitted to endovascular embolization of SAAPs at our institution (n = 57). Considering aneurysms only, it was present in 35.2% (greater than the rate reported by Regus et al., although the number of visceral aneurysms in their sample was almost twice the size of ours) [29]. Boll et al. found a much greater prevalence of CA stenosis or occlusion (> 60%) in patients treated with coil embolization, but they only included aneurysms of the GDA or PDA [19]. In their retrospective study of 37 patients with MALS diagnosed at CTA, Heo et al. found SA aneurysms in 24.3% of cases, which were more common in patients with collateral circulation. However, only 2 patients underwent embolization, one due to aneurysm rupture and the other due to complete CA obstruction [5]. These findings suggest that the number of patients with co-existent MALC and SA aneurysms is probably higher than we estimated, given that we only analyzed SAAPs submitted to endovascular treatment, which is still more often performed in the presence of complications.

A high prevalence of MALS has been reported in patients with PDAs aneurysms (33–100%), most probably due to the increased blood flow through these collaterals [1,2,3, 7, 16]. In our study sample, SAAPs in patients with MALC were also more frequent in PDAs (57.1%, n = 4), whereas they occurred in 10% of patients without MALC. This difference was statistically significant (P = 0.009), with a 5.71 higher chance of this location in the first group (95% CI [1.99–16.33]). Besides PDAs, some reports have described aneurysms in other locations in patients with MALS [13, 19, 21, 23, 26, 30,31,32,33,34,35,36,37]. In the present sample of patients with MALC, we also found them in the splenic and gastroepiploic arteries.

The only other statistically significant difference we found between patients with and without MALC, was a greater proportion of aneurysms in patients with MALC (71.4%) when compared with those without MALC (24%), whereas pseudoaneurysms were less common (28.6% vs 76%). The risk of aneurysm instead of pseudoaneurysm was 2.98 times higher in patients with MALC (P = 0.020, 95% CI [1.51–5.88]). This is an expected finding, as the hypothesized physiopathological explanation for the development of splanchnic artery aneurysms in patients with MALC is the weakening of the wall of small collateral arteries connecting the CA and the SMA beds, due to increased blood flow, hypertension, and shear stress, whereas pseudoaneurysms are usually secondary to wall disruption from other causes [1, 2, 8]. In fact, the only pseudoaneurysm we found in patients with MALC was secondary to biliodigestive surgery, although it is possible that the weakness of the vessel walls induced by MALC may still have been contributory.

Caruana et al.found that most PDAs aneurysms (7 out of 8) were associated with severe CA stenosis, defined as 80–100% stenosis or ≥ 8 mm in length [3]. Bonardelli et al.also reported a preponderance of severe stenosis (56%) in their study sample [38]. In our group of patients with MALC, 50% was the lower value of stenosis, in a patient submitted to prophylactic embolization of a splenic artery aneurysm. In the other cases, the grade of stenosis was higher, ranging from 55 to 100% (mean 70.86%). This may suggest that a greater CA stenosis predisposes to the formation of SA aneurysms. Also, the diameter of collaterals was greater in cases of more severe stenosis. These findings are consistent with those reported by others [39]. However, the grade of CA stenosis may have been underestimated, since CTA scans are usually obtained on inspiration, with partial release of the compression.

In their study of PDAs aneurysms, Antoniak et al.also graded the thickness of MAL into severe or nonsevere, with a threshold value of 4 mm. Most cases (10 out of 15) were severe [37]. Adopting the same grading, all cases in our study were severe, and the mean thickness was 6.3 mm, ranging from 4 to 10 mm. This could also suggest that SAAPs are more prevalent in patients with greater CA stenosis. However, no correlation was found between that measure and the grade of stenosis, but both are influenced by the inspiration status, which was not controlled in this study.

Although some authors reported that most patients with SAAPs and MALC were asymptomatic [37], in our 7 patients with MALC, only two of them were, and rupture was the main indication for embolization (71.4%). This is probably explained by the patient selection, given that we analyzed SAAPs submitted to embolization, which is mostly done following complications, namely rupture. In their review of five SA aneurysms associated with MALS, Sugiyama and Takehara found rupture in 60% of them (2 in PDAs and 1 in epiploic artery), successfully treated with transarterial coil embolization [4]. Boll et al.also found a large proportion of symptomatic patients (85%) in their study of embolized PDA and GDA aneurysms, including 45% ruptured cases [19]. These findings reinforce the potential clinical relevance of SA aneurysms in this group of patients. It is important to be aware of the presence of CA stenosis before the endovascular treatment of PDA aneurysm rupture, as it can influence the vascular approach (CA cannulation may be difficult in some patients) [40]. Also, PDA embolization in patients with CA stenosis can cause ischemia of the upper abdominal organs [1, 40]. Simultaneous blood pressure monitoring of the common hepatic artery has been proposed as a safety measure in patients with MALC, to prevent liver ischemia [41]. We found no reported signs of ischemic damage to the liver or other organs, presumably due to the presence of a rich collateral circulation in all cases.

Interestingly, Tétreau et al.found that ruptured aneurysms due to CA stenosis were significantly smaller than other ruptured aneurysms (9 mm vs. 26 mm) [42]. Although the mean size of ruptured SAAPs in our study was also smaller in cases of MALC (12.9 mm) compared with the others (15.5 mm), we found no statistically significant difference (P = 0.538).

Besides CA stenosis secondary to MALC, atherosclerotic disease has also been associated with the presence of PDAs aneurysms. At their article, Bonardelli et al.described 23 patients with concomitant CA stenosis/occlusion and visceral aneurysms, mostly secondary to MALS (44%), followed by atherosclerotic lesions (32%) [38]. Like those authors, we also found that mean age was higher in the atherosclerotic group (76.7 years) compared with MALC group (59.7 years). As expected, the mortality rate was higher in the atherosclerotic group, as these patients have more comorbities and are older.

Management of SA aneurysms remains controversial, given the unpredictability of PDAs aneurysms to rupture, which is neither correlated with the size and multiplicity of the aneurysms, nor the patient’s age [37]. In fact, PDAs aneurysms have a high propensity for spontaneous rupture, regardless of size (as opposed to the other SA aneurysms, in which the risk increases with sizes greater than 2 to 2.5 cm). Also, it as an associated mortality rate of 30% to 50%. Therefore, prophylactic endovascular treatment is recommended to prevent such events [3,4,5].

However, there is no established consensual approach in terms of when and in whom CA stenosis should be addressed in patients with SA aneurysms and MALC [1, 10, 15, 19,20,21]. Some authors have recommended CA decompression to prevent organ ischemia and reduce the risk of aneurysm recurrence, either with endovascular procedures (angioplasty and/or stent placement), or surgery (MAL release and/or bypass grafting) (1,2,10,13,15–18]. Splanchnic artery aneurysms and CA stenosis can be addressed simultaneously (one-stage treatment) or separated (two-stage treatment), although there are no established recommendations regarding the optimal order of and duration of time between the two procedures. Also, it depends on the patient’s condition, grade of stenosis, operator’s preference, and availability of a hybrid operation room [15].

Resolution or stability of collateral circulation and aneurysms after treating CA stenosis alone have been reported, presumably due to reduced flow and thrombosis [12, 14, 43,44,45], but there are reported cases of aneurysm growth after CA decompression [32, 46]. On the other hand, others have obtained good outcomes using aneurysm embolization only [1, 16, 19,20,21,22,23,24,25,26,27]. However, Takase et al.noted a higher mean age in patients with MALS and PDA aneurysms compared to those without aneurysms (56.9 years vs. 44.6 years), suggesting that longer follow-ups (10 years or longer) may be necessary to detect aneurysm recurrence [27].

In the present study, only 1 out of 7 patients with MALC performed surgical MAL incision 16 months after the endovascular treatment of the SA aneurysm, showing less severe residual CA stenosis in the follow-up CTA 3 months later. The remainder patients had no register of aneurysm recurrence or other complications during a mean follow-up of 1967 days (ranging from 401 to 3116 days). Boll et al.also reported no recurrent PDA or GDA aneurysms after coil embolization alone, although their mean follow-up was shorter (12 months). Still, our study sample is small and further studies with more patients and longer follow-up are necessary to provide evidence for the creation of management recommendations.

The major limitations of our study are its retrospective nature and the relatively small number of patients, inherent to the scarcity of embolized SAAPs. Also, CTA studies weren’t specifically performed for evaluation of CA compression by MAL, so no specification is given in terms of inspiration/inspiration status, precluding homogenization of the analysis. For the same reason, the grade of CA stenosis may have been underestimated, since CTA scans are usually obtained on inspiration, with partial release of the compression. Also, different scanners were used, which may have influenced the arterial measurements, although a good resolution was obtained with CTA protocol in all cases. In addition, we did not evaluate the clinical impact of CA stenosis, namely the presence of symptoms associated with MALC, which we could not accurately access retrospectively in all cases. Finally, the number of cases with different causes of CA stenosis other than MALC was very limited (3 cases of atherosclerotic stenosis), precluding an accurate comparative analysis.

Given all these limitations, to better analyze the prevalence, clinical impact, and outcomes of associated MALC and SAAPs, prospective studies with more patients, well-defined and uniformized imaging studies, and consistent clinical and imaging follow-up and management are required.