CT imaging equipment was upgraded during trial enrollment. Old imaging protocols were no longer compatible with new generation CT. As these were not comparable to previous imaging, study was suspended for analysis and reporting of imaging so far.

This study focuses on the use of contrast enhanced low-dose CT imaging as a modality to differentiate between uncomplicated and complicated acute appendicitis. Accurate differential diagnosis allows the assessment of all available treatment options. Complicated acute appendicitis requires emergency appendectomy, while uncomplicated acute appendicitis can be safely and efficiently treated with antibiotics in the majority of patients. Our study group already published the results of the initial OPTICAP trial enrolling patients with BMI under 30 showing similar accuracy between the low-dose and the stadard dose CT, but a significant dose reduction associated with the low-dose CT. All patients will undergo both imaging protocols as the standard CT is also optimized for a low as possible radiation dosage and imaging sequence per patient is randomized due to the optimization of contrast media injection timing. All patients participating in this study will be treated operatively with a laparoscopic appendectomy to obtain histological confirmation for the diagnosis to evaluate the accuracy of the CT imaging. The aim of this study is to optimize a well-performing low-dose CT imaging protocol to use in the diagnosis of uncomplicated acute appendicitis in patients with body mass index over 30 kg/m2.

Acute appendicitis is one of the most common causes of abdominal pain in emergency departments as well as one of the most common indications for emergency abdominal surgery. The clinical diagnosis has been based on patient history, physical examination and laboratory findings as well as the "clinical eye" of the surgeon. Still the diagnosis remains challenging. One of the main problems is that many other disorders can mimic the clinical presentation of appendicitis, thus increasing the role of imaging techniques to aid in diagnostic accuracy. Now preoperative imaging in patients with suspected acute appendicitis is currently widely accepted as the gold standard and CT has been shown to clearly outperform US in terms of diagnostic performance. Currently CT imaging is considered the primary imaging modality in the diagnosis for acute appendicitis as it is appraised for its high sensitivity and specificity. The main disadvantage of CT imaging is exposure to radiation. Thus the favorable diagnostic performance of CT imaging has encouraged optimization of protocols to minimize exposure to radiation through the development of low-dose CT protocols. Initial studies have indicated that contrast enhanced low-dose CT was not inferior to standard-dose contrast enhanced CT with no statistical significance in negative appendectomy rates, appendiceal perforation rates or patients requiring additional imaging.

This study focuses on the use of contrast enhanced low-dose CT imaging as a modality to differentiate between uncomplicated and complicated acute appendicitis in patients with BMI over 30 kg/m2. Accurate differential diagnosis allows the assessment of all available treatment options. Complicated acute appendicitis requires emergency appendectomy, while uncomplicated acute appendicitis can be safely and efficiently treated with antibiotics in the majority of patients. Our study group already published the results of the initial OPTICAP trial enrolling patients with BMI under 30 showing similar accuracy between the low-dose and the stadard dose CT, but a significant dose reduction associated with the low-dose CT. All patients will undergo both imaging protocols as the standard CT is also optimized for a low as possible radiation dosage and imaging sequence per patient is randomized due to the optimization of contrast media injection timing. All patients participating in this study will be treated operatively with a laparoscopic appendectomy to obtain histological confirmation for the diagnosis to evaluate the accuracy of the CT imaging. The aim of this study is to optimize a well-performing low-dose CT imaging protocol to use in the diagnosis of uncomplicated acute appendicitis in patients with body mass index over 30 kg/m2.

Inclusion Criteria:

• Age 18-60 years
• Clinical suspicion of acute uncomplicated appendicitis based on history, physical examination, laboratory findings evaluated by a senior surgeon
• Body mass index over 30 kg/m2

Exclusion Criteria:

• Age <18 years or > 60 years
• Pregnancy or breastfeeding
• Allergy to contrast material or iodine
• History of appendectomy
• Renal failure, creatinine-value greater than the upper reference value
• Diabetes mellitus and metformin medication
• Suspicion of peritonitis and appendiceal perforation
• Incapability to cooperate and give consent to participate in the study

Available from the study PI upon request.