Between 1999 and 2023, 125 patients with RAAs were identified in our hospital database (tracking rate, 84%). The subjects of this analysis were 105 of these patients with a collective total of 151 RAAs, who met the study inclusion criteria. The average age on admission was 61.8 ± 12.4 years (range, 27–89), and 54% of the patients were women. Concomitant diseases included hypertension (56%), diabetes mellitus (12%), and dyslipidemia (27%). Notably, there was a high incidence of current or former smokers (42%) (Table 1). Co-existing aneurysms were most commonly identified at the splenic artery (n = 10), followed by the common iliac (n = 4), hepatic (n = 4), celiac (n = 3) arteries, internal iliac artery (n = 2), and cerebral arteries (n = 2), as well as at other arteries including the carotid and lateral thoracic arteries, ascending and abdominal aortae, and superficial femoral artery (n = 1, each). Multiple aneurysms were found in seven patients (Table 1). Co-existing vascular lesions were likewise identified with renal artery stenosis (n = 5), renal arteriovenous fistula (n = 4), celiac artery stenosis (n = 2), superior mesenteric artery stenosis (n = 2), pelvic arteriovenous fistula (n = 2), and others (n = 1), including celiac artery dissection, subclavian artery stenosis, and thoracic aortic dissection (Table 1).

Half of the RAAs were located on the right side (53%) ipsilaterally, and 15% were located bilaterally. Multiple RAAs were present in 26% of the patients. The mean diameter of the RAAs was 14.9 ± 7.0 mm (range: 5–40 mm) on admission, which increased to 15.2 ± 6.7 mm at the most recent follow-up. The median observation period was 35 ± 57.3 months (range: 0–201 months) and the average expansion rate was 0.055 ± 0.46 mm/month. Most RAAs had no evidence of substantial growth during the observation period. We considered RAAs showing expansion during a follow-up period of less than 3 months to be inappropriate for observing the natural history of RAA expansion, and we performed a sensitivity analysis after excluding them as outliers. In this analysis, the correlation of expansion rates in RAA cases was expressed as the equation: y = 0.0028x + 0.2621 (R2 = 0.0187) (Fig. 2). Most RAAs had a saccular morphology (90%) and 33 (21%) of aneurysms had an “egg-shell” calcification appearance. Although no significant differences were observed, the expansion rate was even lower in patients with “egg-shell” calcification (0.0005 ± 0.003 mm/month, p value = 0.098) (Table 1). Most of the RAAs exhibited no substantial growth during the observation period. The patients remained asymptomatic during follow-up. Rupture occurred in only one patient with a renal artery pseudoaneurysm coexisting with a superficial femoral artery pseudoaneurysm, but they did not suffer shock. No surgical intervention was performed in any patient with “egg-shell” calcification.

Correlation between the expansion diameter and follow-up periods

Surgical interventions were performed in 24 patients with a collective total of 34 RAAs. The mean largest aneurysm diameter of the RAAs in patients with multiple RAAs was 24.6 ± 6.8 mm (range: 15–40 mm), measured during surgery. There was one case of symptomatic pseudoaneurysmal rupture with symptoms. The mean age, proportion of women, and percentage of concomitant diseases were similar to those in the overall population although a lower rate of current or former smokers (42% vs. 27%) was observed (Table 2).

Aneurysmectomy with renal artery reconstruction, including bypass, was performed in 15 patients, and aneurysmorrhaphy was performed in 8 patients. Ex vivo aneurysm repair was performed in two patients, whereas endovascular repair using a stent graft or coil embolization was performed in two others (Table 2).

Post-operative complications developed in 16 (67%) patients as renal infarction in eight patients, renal artery stenosis in five, and bypass occlusion in four. The range of infarction was classified using computed tomography (CT) images in 25% increments of the total kidney volume. The infarcted lesions were within 25% in five of the eight patients (Table 3).

To reveal the effect of infarction or graft occlusion on renal function, we analyzed changes in eGFR. The eGFR decreased to 80% (range: 67–99%) of the preoperative level in the eight patients with infarction and to 76% (range: 55–77%) in the four patients with bypass graft occlusion cases (Table 3).

We summarize the case of a complex bypass (Fig. 3). The patient was a 63-year-old woman with no deterioration of renal function. CT revealed two RAAs (32 mm and 6 mm in diameter) with one afferent renal artery and three efferent branches. Following RAA resection, the small branches were anastomosed to the trunk of the main renal artery. The clamp time was 39 min. Based on our experience with bypass graft occlusions, we confirmed the anastomotic morphology carefully, ensuring that the graft was not twisted or kinked, particularly after removing the towel beneath the kidney that had been inserted to aid surgical exposure (Fig. 3). The bypass has remained patent for 5 years.

A case of multiple renal arterial aneurysms treated with surgical intervention