Since it is still debated whether 2b acute diverticulitis (AD), according to the World Society of Emergency Surgery (WSES) classification, should be initially treated surgically or conservatively, the COLD2B study has been launched to compare the clinical results of both therapeutic regimens in a multi-institutional cohort of prospectively enrolled patients.

The primary aim of the COLD2B (Conservative vs surgical (either Open or Laparoscopic) approach in the emergency management of acute Diverticulitis WSES 2B) study is to develop a model able to predict the length of hospitalization, comparing the management of WSES 2b AD in the emergency setting (conservative versus surgical approach) (primary endpoint of the first arm of the study).

Moreover, the two groups will be compared regarding mortality and morbidity (secondary end-point).

The second arm of the study will consider the population undergoing surgery, develop a model able to predict the length of hospitalization, and compare the open vs laparoscopic approach (primary end-point), and mortality, morbidity, and surgical outcome indices (secondary end-point).

The COLD2B study is a national, multi-center, prospective observational study of acutely (unplanned and non-elective presentation to hospital for urgent or emergency reasons) presenting patients to the emergency departments of the participating centers with WSES 2b AD (Distant gas - more than 5 cm from inflamed bowel segment).

The study population includes all consecutive adult patients (≥18 years of age) acutely (unplanned and non-elective presentation to hospital for urgent or emergency reasons) presenting at the participating centers with a clinical and radiological diagnosis of WSES 2b AD for 1 year. According to the different management methods, the cohort will be divided into the following categories:

1. Conservatively treated, which will include patients treated with medical therapy (see fluid, anti-pain drugs and antibiotics, except for radiologic drainage) and
2. Surgically resected, which will be devised into the following sub-categories:

2a) Open surgery management, i.e. traditional open surgery approach with any kind of technique: either reconstructive (with or without ileal/colonic stoma protection) or non-reconstructive (see Hartman procedure) 2b) Laparoscopic approach, i.e. emergency laparoscopic resection with the characteristics mentioned above The enrollment period and the overall evaluation will last approximately 1 year.

Inclusion Criteria:

1. Patients of both sexes, ≥ 18 years old.

2. Patients with abdominal CT scan diagnosis of colonic Acute Diverticulitis classifiable as WSES 2B, i.e..

   1. thickening and other phlegmon signs of the left-sided colonic wall (mostly sigmoid) associated with the inflammatory involvement of the surrounding tissues, plus
   2. presence of air bubbles distant more than 5 cm from the primary colonic inflammatory localization, plus
   3. absence of conspicuous free fluid collection or pelvic abscess.

3. Patients fit for surgery.

4. Patients with colonic diverticulitis on postoperative histological examination.

Exclusion Criteria:

1. Right-sided or transverse diverticulitis
2. Concomitant bowel abscess, perforation, or fistula
3. Radiological drainage
4. Elective procedures.
5. Pregnancy or lactation
6. Patients of both sexes, younger than 18 years of age

Patients affected by WSES 2b acute diverticulitis actively present at participating hospitals