Definition

• the presence of outpouchings of the colonic mucosa that have herniated through the circular muscular layer of the large bowel and are therefore only pseudodiverticula.

 • the vast majority of cases are seen in the sigmoid colon.

 Epidemiology

 • Very common. Mostly a disease of patients aged >60 y.

 Aetiology

 • A diet low in fibre and high in meat is the strongest risk factor.

 Pathogenesis

 • firm stools require higher intraluminal pressures to propel.

• high intraluminal pressure forces pouches of the colonic mucosa through an anatomical weak point in the muscular layer where blood vessels pass through to supply the mucosal layers.

 Presentation

 • Intermittent abdominal pain, altered bowel habit, iron deficiency anaemia. * Note these symptoms may closely mimic colorectal carcinoma.

 • Acute inflammation in a diverticulum (acute diverticulitis) presents with severe left iliac fossa pain.

 • Occasionally, erosion of a large submucosal vessel can cause severe rectal bleeding.

 Macroscopy

 • Diverticula are seen herniating out between the taenia coli of the sigmoid colon. • the circular muscle layer is often markedly thickened and numerous redundant mucosal folds are present, projecting into the lumen.

 • In acute diverticulitis, an inflammatory mass may be visible surrounding a diverticulum.

 • Diverticular strictures cause fibrous narrowing of the bowel lumen which can closely mimic a stenosing carcinoma.

Histopathology

 • Diverticula are seen herniating through a thickened circular muscle layer. Only a thin coating of longitudinal muscle separates the diverticulum from the pericolic fat.

 • In cases of acute diverticulitis, there is superimposed acute inflammation associated with a diverticulum; severe cases may show pericolic abscess formation.

Prognosis

• Acute diverticulitis can be complicated by pericolic abscess formation, fistula formation, and free perforation.

• free perforation causes generalized peritonitis which can be fatal in frail elderly patients.