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Image : “Diverticulosis, Ascending Colon” by Ed Uthman. License: CC BY-SA 2.0

Definition and Background

Diverticulosis and diverticulitis explained

Diverticulosis (diverticular disease) is the condition of having diverticula in the colon. Diverticula are outpouchings of the mucosa and submucosa due to the weakness of the muscular layers of the colonic wall.

Large bowel (sigmoid colon) showing multiple diverticula

Image: “Large bowel (sigmoid colon) showing multiple diverticula. Note how the diverticula appear on either side of the longitudinal muscle bundle (taenium),” by Haymanj. License: Public domain.

Diverticulitis is a very serious condition that involves the inflammation of diverticula and can occur in the small and large intestine or the colon. Diverticulitis can occur at any age when diverticula are present, e.g., Meckel’s diverticulum in infants, or in the elderly, with diverticular disease.

It is crucial that these diseases are noticed early to ensure prompt diagnosis and treatment. Serious complications of diverticulitis can arise if rapid action is not taken. Thus, diverticulitis is a common examination topic.


Occurrence of diverticulosis and diverticulitis

Diverticulosis has a notable correlation with the low-fiber Western diet; hence, this condition is very common in the US, UK, Canada, and Australia but is relatively uncommon in Africa and Asia.

In the US, 10% of 40-year-olds and more than 50% of over-60-year-olds have the disease. Certain conditions increase the chances of developing diverticulosis, such as Marfan’s syndrome, Ehlers Danlos syndrome, and scleroderma.

Diverticulitis most commonly affects the middle-aged to the elderly, although it also affects the young. Ninety-five percent of patients have diverticulitis of diverticula found in the sigmoid colon. Some of the epidemiology of diverticular disease is related to diverticulitis, as approximately 15–25% of patients with diverticulosis develop diverticulitis at some point in their lives; 10–20% of the patients with Meckel’s diverticulum (embryological condition) develop diverticulitis as a complication.

Etiology and Risk Factors

Causes of diverticulosis

Large Intestine

Image: Large intestine. By Phil Schatz. License: CC BY 4.0

Diverticulosis is thought to be caused by a number of factors. It commonly occurs in the older population because increasing age causes a decrease in the strength of the connective tissue that makes up the walls of the colon. The connective tissue, which is mostly made up of collagen types 1 and 2, decreases in tensile strength with age and the elastic mucosa pushes outwards.

The weaker connective tissue fails to maintain the structure of the colon and creates diverticular outpouchings. This is why genetic conditions that result in dysfunctional connective tissue (e.g., Marfan syndrome and Ehlers-Danlos syndrome) increase the chances of developing diverticulosis.

If a patient has a family history of diverticulosis, then it is more likely that they will develop the condition. Family members may also share environmental factors (e.g., low-fiber diet) which are thought to play a role in diverticulosis.

Whole slide of a transverse section of left colon with diverticulosis

Image: Whole slide of a transverse section of the left colon with diverticulosis, scanned. By Alex_brollo. License: CC BY-SA 3.0

Constipation causes the colon walls to be exposed to higher pressures than normal. If this occurs in the elderly or those with weaker connective tissue, it is likely to result in the formation of diverticula. Younger patients who suffer from chronic constipation may also get diverticular disease despite having connective tissue of normal strength.

Some studies have shown that a low-fiber diet plays a role in the causation of diverticular disease. A low-fiber diet causes the muscles of the colon to contract strongly. This results in an increased pressure that leads to herniations (diverticula) in weaker parts of the wall, where blood vessels enter. Recent studies have provided evidence that questions this theory and claims that a high-fiber diet may even increase the chance of diverticular disease as it increases the frequency of bowel movements.

Causes of diverticulitis

The etiology of diverticulitis is not well known and is thought to be a balance between genetics and environmental factors. The evidence to support the low-fiber diet theory is unclear, although it is commonly accepted as a reasonable theory. Diverticulitis is more prevalent in obese patients. It is more likely to occur in patients with Meckel’s diverticulum as a complication of this embryological outpouching.


Pathophysiology of diverticulosis

The sigmoid colon is the most common site for diverticulosis as it is the site where the most pressure builds up. If the patient is constipated or has particularly hard stools,  over time, the walls of the colon are put under constant strain, and eventually, the mucosa and submucosa punch through the weakened muscular layer and form outpouchings. The outpouchings usually occur at the weakest spots in the wall of the colon, such as where blood vessels enter. These are most common in the elderly as it requires less strain to herniate through their weakened structural tissue.

Most people with diverticulosis are asymptomatic. However, these outpouchings can sometimes bleed and lead to anemia from continuous GI blood loss. This can be a very serious complication if the blood loss is significant, and surgical treatment may be necessary. All rectal bleeds should be thoroughly investigated as there are other causes such as colon cancer, inflammatory bowel disease, and polyps that need to be ruled out.

Patients usually visit the toilet more times than they usually would, and a common complaint is that they pass rabbit-pellet stools in the morning time; this is caused by feces that have been stored and shaped by the spherical diverticula of the sigmoid colon. Diverticulosis can cause cramping, bloating, flatulence and a change in bowel habit; these symptoms mimic conditions such as irritable bowel syndrome and the distinction has to be made through investigations so that the right treatment can be provided.

Diverticulosis is usually painless, and this is one of the main distinctions between this condition and diverticulitis. However, there can be an occasional start-stop pain in the left lower quadrant.

Pathophysiology of diverticulitis

Diverticulitis occurs when a diverticulum becomes inflamed. It most commonly occurs in the diverticula found in age-related diverticulosis. The diverticula can become obstructed with a fecolith or foreign body. This can pass naturally or start to irritate the colonic wall and cause an inflammatory reaction.

Bacteria found in the stool become trapped in the diverticula and begin to thrive, causing a neutrophilic response. Common bacterial agents include anaerobes (such as E. coli) and Bacteroides – these bacteria are commonly found in the gut as part of the normal commensal flora.

The size of the diverticula increases due to distension caused by the edema and inflammation and this causes severe lower left quadrant pain. The patient will present with a fever due to the infective aspect of the diverticulitis and will also feel nauseated and may even vomit. The bowel movements of the patient will change and become more frequent and diarrhea may eventually occur. The patient may also be bloated and the passage of stools and flatulence may provide some pain relief.

The pain begins over approximately 1 or 2 days and usually starts in the central umbilical region before spreading to the lower left quadrant in western populations, or the lower right quadrant in East Asians (genetic predisposition to right-sided diverticula and diverticulitis). Diverticulitis can progress and be life-threatening if not treated rapidly. Complications include abscesses, a build-up of gas, rupture, peritonitis, and sepsis.

If the patient presents in the late stages of diverticulitis or the condition progresses rapidly, patients may experience a rupture of their infected diverticula, and this can lead to peritonitis, resulting in a rigid abdomen and guarding. This is a surgical emergency and patients need to be referred immediately for the Hartmann procedure.

Signs and Symptoms

Signs of diverticulosis

It is uncommon for patients to suffer any symptoms from this condition. If patients have never experienced abdominal pain or diarrhea, they are likely to never develop any symptoms in the future. Diverticulosis is mostly a painless condition, unlike diverticulitis.

Diverticulosis can sometimes mimic irritable bowel syndrome and other GI conditions – bloating, flatulence, cramps, and change in bowel habit (diarrhea or constipation). Patients can pass rabbit-pellet stools and, rarely, can pass dark blood from the rectum; blood loss from the rectum usually occurs after a notable episode of cramping pain and patients usually require a visit to the hospital. This occurs when a blood vessel ruptures and bleeds out.

If these episodes continue and/or are neglected, the patient can develop anemia over time and experience symptoms including:

Patients are usually very anxious to find the cause of the bleeding and are usually worried about diseases such as colon cancer (which need to be ruled out). Unlike colon cancer, diverticulosis does not cause weight loss.

Note: 10–25% of those with diverticulosis eventually experience diverticulitis.

Signs of diverticulitis

The presentation of diverticulitis is very different and noticeable when patients present with the following symptoms:

  • Severe left lower quadrant pain
  • Fever
  • Malaise
  • Tiredness
  • Nausea and vomiting

The pain is noticeable over 1 or 2 days and can begin in the umbilical region before localizing to the lower left quadrant in most western countries (lower right in most East Asians).

On physical examination, the abdomen will be tender in the affected lower quadrant. The patient’s face should be observed as the abdomen is gently palpated. If the patient has a rigid abdomen with guarding, peritonitis should be suspected. Signs of peritonitis include:

  • Reduced movement
  • Reduced breathing volume
  • Guarding
  • Rebound and percussion tenderness
  • Absent bowel sounds
  • Tympanitic (resonance)
  • Distended abdomen

Additionally, signs of sepsis must not be neglected and these include:

  • High-flow oxygen
  • Blood cultures
  • IV antibiotics
  • Fluid challenge
  • Measure lactate
  • Measure urine output
Note: If suspected, the sepsis pathway should be followed immediately.


Diverticulitis has the following common complications:

  • Rupture and consequent peritonitis
  • Sepsis
  • Abscess
  • Fistula between adjacent structures (e.g., bladder)
  • Bleeding — blood vessel rupture
  • Strictures (due to surgery)
  • Risk of surgical procedures that may be required.
Note: The main complications include rupture, peritonitis, and sepsis; these conditions are potentially fatal.


Detecting diverticulosis

The diagnosis of this condition involves good history-taking skills and some investigations. As this condition has serious differential diagnoses, it is important to rule these out (e.g., colon cancer). Asymptomatic diverticulosis is mostly found incidentally on radiological images.

Detecting diverticulitis

The diagnosis of diverticulitis needs to be rapid to prevent further progression and complications. A full GI physical examination is required. Signs of peritonitis and sepsis should be evaluated. Once the patient is stable, a detailed history should be taken to assess risk factors, symptom duration, onset, and any family history or genetic conditions.

Differential Diagnosis

Symptomatic Diverticulosis

Differential diagnosis for diverticulitis



Abdominal X-ray

  • Thickened walls
  • Constipation
  • Not sufficient to diagnose diverticulosis (may be an incidental finding)

CT scan with contrast

  • Gold standard to accurately diagnose diverticulosis and any complications.


Endoscopic image of diverticulosis

Image: “Endoscopic image of diverticulosis,” by Samir (The Scope). License: CC BY-SA 3.0

It is important to rule out any other diseases that may mimic symptomatic diverticulosis – cancer, inflammatory bowel disease, etc.

If the patient had an acute flare-up, the patient should be allowed to recover for up to 6 weeks before undergoing this investigation (reduces the risk of iatrogenic perforation).

Enables the visualization of diverticula.

Barium enema

  • Can reveal any strictures or diverticula present
  • Useful where colonoscopy is contraindicated

MRI scan

  • Not as useful as contrast CT scan
  • Clearer picture of soft tissue but most costly compared to CT and colonoscopy

Full blood test

  • If the patient experienced/experiences any rectal bleeding, they may have anemia that needs treatment.
Note: Barium enemas and colonoscopies should never be performed in an acute episode of diverticulitis or symptomatic diverticulosis as there is an increased risk of complications such as rupture and perforation. Barium fluid may leak into the abdominal cavity in colonic rupture. Significant time must be allowed to pass before these investigations can be performed.


CT Scan with contrast

CT scan of Diverticulitis

Image: “Diverticulitis in the left lower quadrant,” by James Heilman, MD. License: CC BY-SA 3.0

  • Gold standard test for diagnosing diverticulitis
  • 98% accurate
  • Should not be delayed in any suspected case.
  • Can identify the extent of the disease and any complications, such as abscesses.

Blood test

A blood test will reveal any signs of infection, e.g., leukocytosis, an increase in the number of white cells due to the infection. If there is any GI blood loss, a full blood count will reveal any anemia.

Temperature: The patient’s temperature should be checked regularly to monitor for any change (e.g., temperature spike if there is progression to peritonitis and sepsis).

Note: Barium enema and colonoscopy should never be performed during an episode of diverticulitis.



As most patients are usually asymptomatic, no treatment is required. It is recommended that patients increase the amount of fiber in their diet and ensure that their diet is well-balanced. Weight loss through improved diet and increased exercise is recommended to increase general health. Certain foods are thought to worsen diverticulosis and patients are sometimes referred to a dietician for diet plans. If possible, patients should also avoid aspirin or NSAIDs as this increases the risk of complications.


The following treatments are possible:

Nil by mouth

Patients experiencing an acute episode should stop eating/drinking immediately to prevent further irritation of the colon. Once the patient is fully recovered, they should follow the treatment pathway for diverticulosis in terms of increasing the amount of fiber in their diets.

Nasogastric tube

This removes food from the stomach and tries to prevent further strain on the inflamed colon, which may be caused by food passage. Gas is also allowed to escape from the stomach, preventing a dangerous build-up.


If bacterial infection is suspected, antibiotics are usually given as treatment. Common antibiotics, which work against the causative bacteria, include metronidazole and fluoroquinolones (e.g., cefotaxime).


If treatment is started early enough, surgery is usually not required. If CT scans reveal complications such as bleeding, rupture, peritonitis, abscesses, or fistulas, then surgery may be necessary. Depending on the complication, some cases are suitable for elective surgery. One such complication is rupture. This is because intestinal rupture leads to infective peritonitis and potentially, sepsis.

Emergency procedures include primary bowel resection or bowel resection with a colostomy (Hartmann’s procedure). They can be done laparoscopically (preferred) or by open surgery. Laparoscopic offers a fast postoperative recovery rate amongst other advantages.

In Hartmann’s procedure, the end of the resected bowel is attached to the abdomen and exits at the skin surface where the feces pass into a colostomy bag. This is usually temporary until the surgeon can reverse the colostomy once the inflammation and infection have settled. The time for the reversal depends on the severity of the case and can be months later.

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