The severity of diverticulitis is usually graded with the use of modified Hinchey Criteria. However, there is a condition often seen in the CT scan that is not included in this classification itself; 1-2 pericolic bubbles but no free air or fluid into the abdomen or above the liver. Outcome in these patients remains unknown. We aim to analyse the treatment that these patients and their evolution over the first year after the diagnosis in order to predict the disease related outcome.

The study is set up as a retrospective multicentre observational study. Inclusion criteria are Patients over 18 years old, Diagnosed of acute diverticulitis with a CT scan reported as 1-2 pericolic bubbles with or without free fluid. Exclusion criteria: 1) CT scan showing free distant bubbles in the abdomen. 2) CT scan showing abscess.

Accepting an alpha risk of 0.05 and a beta risk of 0.2 in a two-sided test, 137 subjects are necessary in the observed group to recognize a difference in morbidity greater than or equal to 10%. A proportion in the reference group has been estimated to be 20%. It has been anticipated a drop-out rate of 0%.

Primary outcome is 30-day morbidity and mortality. Secondary outcomes include malignancy and 1 year morbidity including recurrences and ongoing disease. Data will be collected in an online repository. The CT scans will be reviewed by 2 experienced independent radiologists. The management of these patients at the moment of the diagnosis will be recorded, as well as their evolution over the first year during the outpatient clinics. Figure 1 represents the study flow chart.

Data will be collected in an online secure and protected repository (Castor edc). The planned study period is 2 years (01/06/2020 - 31/12/2021).

CT scans will be reviewed by 2 experienced radiologists. Every other CT scan performed during the follow-up will be reviewed by the same radiologists.

The management of these patients at the moment of the diagnosis will be recorded, as well as their evolution over the first year during the outpatient clinics.

This study protocol is a new approach to an unknown entity in diverticulitis. We are convince that the outcomes are clinically relevant to patients and interesting for all physicians treating diverticulitis.

Diverticular disease of the colon is a common disease that includes diverticulosis and diverticulitis. Most patients who have diverticulosis remain asymptomatic; however an estimated 15-20% will develop acute diverticulitis (AD).(1) AD is an inflammatory condition affecting at least one colonic diverticula, often associated with pericolonic inflammation.(2) Diverticulitis can range form mild to severe. Severe, complicated cases with perforation may be associated with intra-abdominal abscess, generalized, purulent peritonitis, fistula formation, bleeding or obstruction. The extent of the perforation determines the clinical behavior. Microperforations remain localised because they are contained by pericolic fat and mesentery, leading to the formation of small pericolic abscesses.

The gold standard for the diagnosis of diverticulitis is the Computed Tomography (CT). It has a sensitivity ranging form 85% to 97% (3,4) and it is very accurate identifying colonic perforation, which can have a direct impact on the management of the patient. The severity of diverticulitis is usually graded with the use of modified Hinchey's Criteria, based on CT imaging and on preoperative findings.(5) It distinguishes four stages of acute complicated diverticulitis. Several modifications to the Hinchey classification have been proposed due to the advancements in imaging modalities. New subcategories have been added that take radiological findings into consideration.(6) However, there is a condition often seen in the CT scan that is not included in this classification itself; a single pericolic bubble.

The management of AD depends on its severity and complexity, and it requires hospitalization, bowel rest and surgery in selected cases. Antibiotic therapy is part of the management of complicated diverticulitis and recent guidelines are in accordance at recommending broad-spectrum antibiotics. Biondo and colleagues evaluated 92 papers in a systematic review, concluding that patients with severe AD without need of emergency surgery, should be treated with hospitalization, parenteral fluids and a single intravenous antibiotic active against aerobic and anaerobic bacteria.(7) Approximately 15-20% of patients admitted with AD have an abscess on CT scan.(8) The size of 3-6 cm has been generally accepted to be treated with antibiotics vs. percutaneous drainage.(8-10) However, clinical monitoring is mandatory and a CT scan should be repeated if the patient does not show clinical and laboratory improvement.

In the 1990s laparoscopic lavage (LL) was proposed to treat patients affected by peritonitis due to perforated AD.(11) Initial results encouraged surgeons to perform LL;(12-14) however, in the 2000s three Randomized Control Trials (RCT) were published with mixed results.(15-17) Two of them suggested that the traditional surgical treatment (segmental resection and stoma formation) achieves more successful results.(16,17) In summary, there are several guidelines for the treatment of AD regarding its severity; however, there is no consensus in the management of those patients with 1-2 pericolic bubbles but no free air into the abdomen. The treatment that these patients receive is widely variable.

For this reason, patients admitted in the emergency unit and diagnosed of acute diverticulitis with a free pericolic bubble of air, regardless the Hinchey's criteria assigned and the treatment received, would be included in this study. We aim to analyse the treatment that they underwent and the evolution of these patients over the first year after the diagnosis. The patients will not undergo any treatment or test that would not be necessary during their follow-up out of this observational and retrospective study.

Inclusion Criteria:

• Patients over 18 years old
• Informed consent
• Diagnosed of acute diverticulitis
• CT scan reported as 1-2 pericolic bubbles with or without free fluid.

Exclusion Criteria:

• CT scan showing free distant bubbles in the abdomen
• CT scan showing abscess

Emergency unit Hospitalization

Study Protocol Statistical Analysis Plan (SAP) Informed Consent Form (ICF) Clinical Study Report (CSR)