In the present study cohort, the rate AA with abscess was 9.4%, similar to the reported rate of 2–10% [17]. Surgery was performed with fewer complications in the IA group than in the EA group, ileocecal resection, which was not needed in any patient who underwent IA, was required in some patients who underwent EA.

In previous studies, Andersson et al. reported that EA was associated with higher morbidity compared to conservative treatment (odds ratio, 3.3; 95% confidence interval, 1.9–5.6; P < 0.001) [9]. Simillis et al. showed that conservative treatment for complicated appendicitis was associated with lower rates of complications and reoperation compared to EA [13]. Furthermore, Miyo et al. demonstrated that single-site laparoscopic IA was a safer, more viable, and less invasive approach than EA [18]. In contrast, in a study of patients presenting with appendiceal phlegmon or abscess, Helling et al. reported that EA was preferable to conservative treatment with antibiotic administration in reducing the length of hospital stay and the need for readmissions in cases where laparoscopic expertise was available [19]. In a retrospective study by Young et al. EA was associated with superior outcomes compared to initial conservative treatment [20]. In that study including a cohort of 95 patients presenting with complicated appendicitis, 60 patients underwent EA and 35 patients initially received conservative treatment. All patients who failed conservative treatment (25.7%) underwent laparotomy, with most of the patients requiring ileocecal resection. The incidence of ileocecal resection was lower in patients who underwent EA compared to all patients who initially underwent conservative treatment (3.3% vs 17.1%, P = 0.048). Moreover, the Cochrane review by Cheng et al. has revealed that whether EA is superior to IA in terms of complications in patients with appendiceal phlegmon or abscess remains an unresolved question [17]. However, in these studies, the study cohorts included patients with phlegmon [9, 13, 17, 19], perforation [18], or both [20], in addition to those with abscesses. The current study findings suggest that EA is not superior to IA in patients with AA and abscess and that the findings of previous studies depend on the number of patients with AA and abscess. In the present study, IA was more effective than EA in a cohort limited to patients with AA and abscesses.

Conversely, a high-quality randomized control trial (RCT) by Mentula et al. demonstrated that laparoscopic EA was a safe and feasible first-line treatment option for AA with abscess if performed by experienced surgeons [21]. In that study, laparoscopic EA was associated with fewer readmissions (3% vs. 27%, P = 0.026) and fewer additional interventions (7% vs. 30%, P = 0.042) than conservative treatment, with a comparable length of hospital stay between the two groups. For patients in the laparoscopic EA group, the risk of ileocecal resection was 10% and the risk of incomplete appendectomy was 13%. Conversion to open surgery was necessary in 10% of the patients who underwent laparoscopic EA and in 13% of the patients who received conservative treatment [21]. The authors suggested that laparoscopic EA could be performed by experienced surgeons in the near future. On the other hand, we previously demonstrated that laparoscopic IA could aid in appendix removal and abdominal inspection [12]. Thus, we considered that implementing IA would be easier than laparoscopic EA. In addition, ileocecal resection was performed in 10% of the patients who underwent laparoscopic EA in the RCT by Mentula et al [21], whereas ileocecal resection due to the preoperative suspicion of an appendiceal tumor was performed in only one patient who underwent IA in the present study cohort. Extended resection should be avoided to the greatest extent possible in patients with benign clinical conditions such as AA. Further, the conversion rate was 3% in the current study, which was lower than the conversion rate of 10% reported in the laparoscopic EA group in the RCT. As a procedure that is less dependent on operator skills. IA might be easier and safer compared to laparoscopic EA.

Despite its success, IA after conservative treatment for AA with abscess remains a topic of debate. In cases of perforated AA and phlegmon, the recurrence rate after conservative treatment ranges from 12% to 24% [22, 23]. After initial conservative management, routine selective IA is sometimes advised to reduce the high risk of recurrence [14]. Therefore, IA was performed in all patients who underwent conservative treatment in the present study. Two of the patients (5.9%) experienced relapse after IA but improved with conservative treatment. The low recurrence rate was likely due to the fact that appendectomy was performed before recurrence in all patients who underwent IA.

Another consideration in choosing IA is the possibility of a tumor as an underlying cause of AA. Renteria et al. reported that the rate of unexpected malignancy was 3% in elderly patients with a mean age of 66 years and 1.5% in young patients with a mean age of 39 years among those who underwent appendectomy as primary treatment for AA [24]. Jonge et al. reported that appendiceal neoplasms were diagnosed in up to 11% of adult patients undergoing IA, in contrast to 1.5% of patients undergoing EA [25]. Recently, an RCT by Mällinen et al. comparing IA to follow-up with magnetic resonance imaging after initial successful conservative treatment of peri-appendicular abscess was prematurely terminated because of ethical concerns. During the interim analysis, the authors reported the unexpected finding of a high neoplasm rate (17%), with all neoplasms found in patients older than 40 years [26]. Moreover, Hayes et al. reported that the rate of appendiceal neoplasm was 11% in patients 30 years and older who underwent IA after complicated appendicitis and that the risk of appendiceal neoplasm increased with age, reaching 16% in patients 50 years and older [27]. In the present study, the neoplasm rate was 9% in the IA group, which was similar to the rate of 3%–17% reported in previous studies [24,25,26,27]. Therefore, neoplasm should be considered as a potential cause of AA with abscess and patients aged 40 years or older who present with AA by abscess should receive conservative treatment in addition to colonoscopy to rule out. In the present study, one patient underwent ileocecal resection due to the suspicion of appendiceal neoplasm based on colonoscopy. Therefore, we consider that IA is more effective than EA because it can be performed in parallel with colonoscopy during the waiting period. The presence of a tumor in one patient in the IA group may be related to chronic inflammation; however, further investigation is warranted.

In the future, IA after conservative treatment should become the first treatment option for AA with abscess and is expected to clearly reduce the rate of postoperative complications and ileocecal resection [9, 28, 29] while potentially reducing wasted medical resources. Avoiding EA in patient’s AA and abscess would also provide great benefit to healthcare providers. In addition, the possibility of a tumor can be confirmed by performing colonoscopy during the waiting period for IA, which would be beneficial to the patient.

The present study has several limitations that should be acknowledged. First, this was a retrospective, single-center study and we acknowledge the potential bias in the selection of information from the medical records. We believe that further prospective randomized multicenter investigations developed by dedicated associations and tertiary centers (high volume and strict protocols) are required to establish reliable EBM guidelines. Second, no clearly delineated criteria were utilized to determine the course of treatment for AA with abscess, which was determined by the attending surgeon treating each patient. In particular, many of the surgeons who performed the procedures included in the study could not provide a clear reason for choosing EA. Third, whether differences in the clinical course of patients were due to the involvement of different attending surgeons could not be ruled out. However, many of the attending surgeons participating in the present study were gastroenterological surgeons. In the future, to ensure the quality of surgery, it is necessary to limit the surgeons to specialists in gastroenterological surgery. Finally, laparotomy and laparoscopic approach can drastically influence the outcome of patients. The method of appendiceal root resection may also be relevant, particularly the triple-row stapler, which may be effective. However, it is unlikely that emergent surgery for appendicitis with abscess can reduce complications simply based on using a different approach or resection method. As EA crosses the abscess, residual abscess and paralytic intestinal obstruction are more likely to occur than IA.