Aim of this study is to evaluate the effect of different treatment strategies on overall complications, health related-Quality of Life (hr-QOL) and costs among two subtypes of complex appendicitis in children (<18 years old).

Main research questions: What is the difference in overall complications at three months between:

Subgroup 1 (complex appendicitis without abscess/mass formation): Laparoscopic (LA) and open appendectomy (OA) Subgroup 2: (complex appendicitis with abscess/mass formation): Non-operative treatment (NOT) and direct appendectomy

Up till now initiated research projects worldwide mainly focus on simple appendicitis (questioning the necessity of an appendectomy). However, complex appendicitis is associated with significant morbidity (up to 30%), prolonged hospital stay and high costs. Identification of the optimal treatment strategy for children with complex appendicitis is therefore essential. Heterogeneity in the treatment of complex appendicitis still exists in daily practice and reflects the lack of high-quality data and emphasizes the need for well-designed studies. Complex appendicitis can be divided into two subtypes:

1. Complex appendicitis without mass/abscess. (subgroup 1) Although (inter)national guidelines agree that appendectomy should be usual care, the optimal approach (open or laparoscopy) is unclear. Laparoscopic appendectomy (LA) is increasingly applied both in adults (80%) and children (60%). Benefits reported for LA in children are, but not limited to, less superficial site infection (SSI), reduced length of hospital stay and significant less postoperative bowel obstruction compared with open appendectomy (OA). Reluctance for usage of LA in this specific subgroup, however, remains due to the potential higher incidence of post-appendectomy abscess formation (PAA) reported. However, the quality of studies on this topic is low and there is considerable inconsistency in results.
2. Complex appendicitis with mass/abscess. (subgroup 2) The recommendation made in our national guideline (to perform direct appendectomy in this subgroup) is not in line with the available literature. A recent Cochrane review on this topic could only include two trials and stated that no firm conclusions could be drawn. An older systematic review, including 7 studies in children, concluded that non-operative treatment (NOT) led to fewer complications, specifically SSI and PAA, when compared to direct appendectomy. Still the recommendation from our national guideline is to perform a direct appendectomy based upon good experiences in the pediatric academic centers.

In order to investigate the optimal treatment for children with complex appendicitis we will perform a nationwide, multi-center, comparative, prospective cohort study. For the purpose of this study, treatment strategies will be standardized among the participating hospitals in order to reduce heterogeneity. Prospectively derived, high quality data will be sufficient to answer the research questions regarding the optimal treatment strategy for each subtype of complex appendicitis in the pediatric population. As it is a non-randomized prospective cohort study, propensity score matching technique will be performed in order to estimate the effect of the treatments adjusted for potential confounders.

Inclusion Criteria:

Eligible for inclusion are all children <18 years old that need to undergo treatment for the suspicion of complex appendicitis. Suspicion of complex appendicitis is based upon the following predefined criteria:

4 or more points on our scoring system developed to predict complex appendicitis. The diagnostic accuracy of this scoring system is 91% (Range: 84-98%). This scoring system consists of five variables (clinical, biochemical and radiological,each awarded points). In case the total score is 4 or more points, the patient is likely to have complex appendicitis. Variables included in the scoring system are:

• Diffuse abdominal guarding (3 points)
• CRP level more than 38 mg/L (2 points)
• Signs on ultrasound / imaging indicative for complex appendicitis (2 points)
• More than one day abdominal pain (2 points)
• Temperature more than 37.5 degrees Celsius (1 point)

Or

High index of suspicion of complex appendicitis by the treating physician. If this is the case, the treating physician will make pre-treatment note upon what clinical, biochemical or radiological variable the high index of suspicion is based.

Exclusion Criteria:

• Adult patients (=18 years old)
• Children with a suspicion of simple appendicitis (based upon the previous mentioned scoring system and radiological features)

All children that present with a preoperative suspicion of complex appendicitis. This suspicion is based on 4 points or more on the abovementioned complex appendicitis scoring system OR a high index of suspicion of complex appendicitis by the treating physician.