Diverticulosis — the presence of colonic diverticula (mucosal herniations through the muscular wall at the points where vasa recta penetrate) — is present in approximately 50-60% of adults over 60 in Western populations, rising with age. The great majority remain entirely asymptomatic lifelong. Only approximately 4-5% ever develop acute diverticulitis. Distribution differs by geography: left-sided (sigmoid) predominance in Western populations; right-sided predominance in East Asian populations, where it presents younger and can mimic appendicitis.

The most important recent practice change. The AVOD (Br J Surg 2012) and DIABOLO (Br J Surg 2017) randomised trials showed that antibiotics do not accelerate recovery, prevent complications or reduce recurrence in immunocompetent patients with CT-confirmed UNCOMPLICATED acute diverticulitis. AGA, ASCRS, NICE and Danish/Dutch guidelines now recommend SELECTIVE rather than routine antibiotic use. Antibiotics ARE still indicated for: complicated diverticulitis (abscess, perforation, obstruction, fistula); immunosuppression; significant comorbidity or frailty; sepsis or systemic upset; pregnancy; and failure of initial observation.

The long-standing advice to avoid nuts, seeds, corn and popcorn has been formally refuted. The Health Professionals Follow-up Study (Strate, JAMA 2008) prospectively followed 47,228 men for 18 years and found NO increased risk of diverticulitis or diverticular bleeding with nut, corn or popcorn consumption — indeed nut and popcorn intake was inversely associated with diverticulitis. This dietary restriction should be actively de-prescribed; it has no evidential basis and needlessly restricts a healthy, high-fibre food group.

Hinchey classification of perforated diverticulitis: Stage I — pericolic phlegmon or small confined abscess (Ia: phlegmon; Ib: abscess ≤4-5cm — antibiotics ± percutaneous drainage). Stage II — pelvic, retroperitoneal or distant intra-abdominal abscess (percutaneous drainage + antibiotics). Stage III — generalised PURULENT peritonitis (surgery: laparoscopic lavage in selected cases, or resection). Stage IV — generalised FAECULENT peritonitis (emergency resection — Hartmann's procedure or primary anastomosis with or without diverting stoma). Modern practice increasingly favours primary anastomosis with diverting ileostomy over Hartmann's in appropriately selected Hinchey III-IV patients (LADIES/DIVA trial), because Hartmann's reversal rates are low and reversal morbidity is high.

Guidance has narrowed. Colonoscopy 6-8 weeks after resolution is recommended after COMPLICATED diverticulitis, or where the CT features are atypical, or where the patient is otherwise due for colorectal cancer screening — because the rate of underlying colorectal cancer in CT-proven complicated diverticulitis is meaningfully elevated (approximately 7-11%). After a CT-confirmed UNCOMPLICATED first episode, the cancer yield is much lower (approximately 0.5-1.5%, similar to screening populations), and routine interval colonoscopy is no longer universally recommended. Never scope during acute inflammation — perforation risk.

The historical rule of elective sigmoid resection after two episodes has been abandoned. Recurrence does not reliably escalate in severity — most emergency perforations occur at the FIRST presentation, so prophylactic resection after recurrent mild episodes does not prevent the catastrophic event it was intended to prevent. Elective resection is now individualised, based on: frequency and severity of recurrent attacks; persistent symptoms between episodes (smouldering diverticulitis); complications (fistula — colovesical is the commonest, presenting with pneumaturia and faecaluria; stricture with obstruction); immunosuppression; and patient quality of life and preference (LASER and DIRECT trials support surgery for quality-of-life indications in selected patients).