Diverticulitis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2], Ahmed Elsaiey, MBBCH [3], James Nasr[4]

Diverticulitis is a common disease of the digestive tract that affects the colon. Diverticulitis develops from diverticulosis, which involves the formation of pouches (diverticula) on the outside of the colon. Diverticulitis results when one of these diverticula becomes inflamed, usually due to fecal trapping with bacterial translocation, microperforation, and altered gut microbiome and immune response.^[1][2][3] Diverticulitis is classified as complicated or uncomplicated. In the United States the annual incidence of diverticulitis is around 180 per 100 000 people.^[4] Among those with diverticulosis, only about 1% to 4% will develop diverticulitis in their lifetime.^[5][6] The highest incidence occurs in patients older than 60, with rising incidence in adults younger than 50, particularly among men. Men are more commonly affected before age 50, while females are more commonly affected after age 50.^[7] Risk factors include age, obesity, genetics, connective-tissue disorders, NSAIDs, steroids, opioids, hypertension, and type 2 diabetes.^[8] Diverticulitis can cause many complications as abscess, perforation, peritonitis, and fistula formation. Symptoms of diverticulitis include left lower abdominal pain, fever, cramps, and constipation.^[9] Common physical examination findings include tachycardia, fever, abdominal tenderness, guarding and rebound tenderness, and presence of a palpable mass.^[10][11] Uncomplicated diverticulitis is managed with observation and pain management, with or without antibiotics.^[12] Complicated diverticulitis is treated with intravenous antibiotics and, when indicated, percutaneous drainage or surgical resection.^[13][14]

Diverticulitis was first described by Dr. Lavater in the 1700s. In the 18th century, Dr. Littre was the first person to describe the diverticular disease. Dr. Meckel gave a full description of the diverticulum in 1812.

Diverticulitis may be classified according to the 2014 guidelines by the German Societies of Gastroenterology (DGVS) and of Visceral Surgery (DGAV). They unanimously agreed on a classification system (Classification of Diverticular Disease (CDD)), that takes practical algorithms (symptomatic, asymptomatic, complicated, uncomplicated, acute, recurrent), ongoing surgical aspects (purulent versus fecal peritonitis), and contemporary diagnostic standards in clinical practice into account. As a result, this classification comprises the entire spectrum of diverticular disease. While the CDD system remains in use in some European centers, current U.S. guidance, including the 2025 JAMA review, primarily classifies diverticulitis as uncomplicated or complicated, with severity stratified using the modified Hinchey classification.^[8]

Diverticula are sac-like protrusions of the mucosal and submucosa through weak points in the muscular wall, and occur more commonly in the sigmoid colon. Diverticulitis is the inflammation of a diverticulum. The first steps in the pathogenesis of diverticulitis are an increase in intraluminal pressure, change in intestinal motility, and bacterial colonization.^[3] The inflammation is caused by histamine, tumor necrosis factor, and metalloproteinases, which have been found in diverticulitis patients’ tissue biopsies. Obstruction of the diverticula leads to bacterial colonization, which causes inflammation.

Common causes of diverticulitis include diverticulosis, and is believed to result from obstruction of a diverticulum by fecal material leading to bacterial translocation and mucosal inflammation, increased intraluminal pressure causing microperforation, and alterations in the gut microbiome and bile acids that disrupt the mucosal barrier and immune response.^[1][2][3]

Diverticulitis must be differentiated from other diseases that cause lower abdominal pain and fever, such as appendicitis, inflammatory bowel disease, colon cancer, cystitis, and endometritis. Diverticulitis must be also differentiated from diseases causing peritonitis.

The lifetime risk of diverticulitis among individuals with diverticulosis is approximately 1% to 4%.^[5][6] The highest incidence is in patients older than 60. Men are more commonly affected before age 50, while females are more commonly affected after age 50. The prevalence of diverticulitis has increased in developed countries.^[7] In the United States, approximately 200,000 cases are admitted to the hospitals annually.^[8] In Japan, more cases of right side diverticulitis have been reported than cases of left side diverticulitis.

Risk factors for diverticulitis include older age, obesity, genetic predisposition, connective-tissue disorders (polycystic kidney disease, Marfan syndrome, and Ehlers-Danlos syndrome), hypertension, type 2 diabetes, and use of NSAIDs, corticosteroids, and opioids.^[8]

There is insufficient evidence to recommend routine screening for diverticulitis.

Diverticulitis natural history is still being clarified. Diverticulitis can cause many complications that can be fatal in some cases. These complications include abscess, perforation, peritonitis, and fistula formation. Prognosis of diverticulitis is excellent; more than 90% of patients with uncomplicated diverticulitis improve with conservative management, and recurrence risk is lower than previously believed.^[15]

The most common symptoms of diverticulitis include left lower abdominal pain, fever, cramps, and constipation. A positive history of change in bowel habits is suggestive of diverticulitis. Less common symptoms include flatulence, nausea, and vomiting.^[9]

Patients with diverticulitis usually appear toxic due to pain. Common physical examination findings include tachycardia, fever, abdominal tenderness, guarding and rebound tenderness, and presence of a palpable mass. Diverticulitis diagnosis depends on taking a proper history, performing a physical examination, and imaging conifrmation. The known diagnostic criteria for diverticulitis include abdominal tenderness, especially in the left lower quadrant, and leukocytosis. CT scan findings help in disease confirmation.

Diverticulitis diagnosis starts by taking history precisely and performing a physical examination. Lab tests are important in excluding other causes of abdominal pain and any other gastrointestinal disease. These lab tests include CBC, CRP, urinalysis, and liver tests. Imaging procedures including CT scan and colonoscopy are important measures in diagnosing diverticulitis.^[16][17]

Contrast-enhanced CT scan is the diagnostic test of choice for diverticulitis. It confirms the diagnosis, evaluates for complications such as abscess, perforation, and obstruction, and can guide percutaneous abscess drainage when needed.^{[15] [18]}

On abdominal MRI, diverticulitis is characterized by thickening of the colon wall, the presence of the diverticula, and exudates from the colon. It may also show the presence of multiple abscesses. MRI is a good imaging modality that can be used in the diagnosis of diverticulitis since it has the advantage that it doesn’t involve exposure to radiation and rules out other abdominal causes of acute abdomen.^[19] However, MRI is not the best diagnostic procedure for diverticulitis; CT scan is preferred.^[15]

On abdominal ultrasonography, diverticulitis is characterized by abscess formation, hypoechoic pericolic fat, the presence of diverticula, and thickening of the colon segments. Extra diverticular exudates and fluids can be also observed. ^[20]

On abdominal X-ray, diverticulitis is characterized by multiple air and fluid levels if there is an intestinal perforation. Chest X-ray should be done in patients with diverticulitis to investigate for pneumoperitoneum, which is a harbinger of a critical illness and will lead to a change in the management plan for the case. X-ray can be used if CT is not available and in uncomplicated cases.

There are no other specific imaging findings for diverticulitis. Other studies such as barium enema and colonoscopy are contraindicated in the acute phase of diverticulitis due to the risk of perforation.

There are no other specific diagnostic studies for diverticulitis. Other studies such as barium enema and colonoscopy are contraindicated in the acute phase of diverticulitis due to the risk of perforation.

Uncomplicated diverticulitis is managed with observation and pain management, with or without antibiotics.^[12] Complicated diverticulitis is treated with intravenous antibiotics and, when indicated, percutaneous drainage or surgical resection.^[13][14]

Surgery is not the first-line treatment option for patients with diverticulitis. Emergency or urgent surgery is usually reserved for patients complicated with peritonitis, who are unresponsive to treatment, who have intestinal obstruction, or with abscess formation. Elective surgery may be performed and it depends on many factors like the age of the patient, severity score, and persistence of symptoms.^[12]

Primary prevention of diverticulitis focuses on overall lifestyle improvements. Physical activity, and weight loss to achieve a BMI less than 25.0 may reduce diverticulitis incidence.^[21] High-fiber diets have been associated with general bowel health, although they have not been shown to prevent diverticulosis or diverticulitis.^[22]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2], Ahmed Elsaiey, MBBCH [3] James Nasr[4]

Diverticula are sac-like protrusions of the mucosal and submucosa through weak points in the muscular wall, and occur more commonly in the sigmoid colon. Diverticulitis is the inflammation of a diverticulum. The first steps in the pathogenesis of diverticulitis are an increase in intraluminal pressure, change in intestinal motility, and bacterial colonization.^[1] The inflammation is caused by histamine, tumor necrosis factor, and metalloproteinases, which have been found in diverticulitis patients’ tissue biopsies. Obstruction of the diverticula leads to bacterial colonization, which causes inflammation.

The pathogenesis of diverticulitis is believed to be erosion of the wall of the diverticulum. It is worsened by an increase in intraluminal pressure or food remnants.

• Diverticula are protrusions of the mucosa and serosa intestinal layers and occur more often on the left side than the right side. Diverticulitis is the inflammation of this protrusion.

• Inflammation and focal necrosis ensue, resulting in perforation and inflammation.^[2]
• The pathogenesis of diverticulitis includes three main processes, which are:
  • Change in the intestinal motility
  • Increase in the luminal pressure
  • Secondary infection may be caused by colonic microbial flora^[3]
• In vivo tests showed that adding chemicals to the colonic tissue can lead to diverticulitis. Neuro-alteration of the tissue was noticed during this test. It showed increased contractility and loss of relaxation.^[4] This alteration in the muscle tissue due to inflammation leads to histological changes of the muscle and nerves.
• Inflammation in cases of diverticulitis is caused by histamine, tumor necrosis factor, and matrix metalloproteinases. These substances were detected in colonic tissue biopsies of diverticulitis patients.^[5]
• The collection of feces and undigested food in the diverticula leads to diverticulum obstruction. This obstruction, by increasing intraluminal pressure, leads to diverticulum distension and collection of the bacteria that cause inflammation.
• The presence of lymphocytes and granulomas are predictive of chronic inflammation.

The gross pathology of diverticulitis includes features such as:^[6][7]

• Corrugated – like cardboard
• Wall thickening (reactive)
• Located usually in the sigmoid colon
• May be found in the appendix

The possible histopathological findings of diverticulitis may include the following:

• Abscess at which neutrophils, lymphocytes, and fibrosis are observed.
• Sulfur granules with peripheral inflammatory cells.

• A brief video showing histopathological findings in patients with diverticulitis:

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