Diverticulitis: Symptoms, Causes & Complete Treatment Guide

What Is Diverticulitis and How Does It Develop?

Diverticulitis is an inflammation or infection of small pouches called diverticula that form in the walls of the colon, most commonly in the sigmoid colon (lower left side). These pouches develop when weak spots in the intestinal wall bulge outward under pressure, and become inflamed when bacteria become trapped inside.

To understand diverticulitis, it helps to first understand diverticulosis. Diverticula are small, bulging pouches that can form anywhere in the digestive system, but they most commonly develop in the large intestine (colon). When a person has these pouches but no symptoms, the condition is called diverticulosis. This is extremely common, affecting approximately 50% of people over age 60 in Western countries and up to 70% of those over 80.

The pouches form at weak points in the colon wall, typically where blood vessels penetrate the muscle layer. When pressure inside the colon increases - from constipation, straining during bowel movements, or other factors - the inner lining of the intestine pushes through these weak spots, creating the characteristic balloon-like pouches. Each pouch is typically between 5-10 millimeters in diameter, though they can grow larger.

Diverticulitis occurs when one or more of these pouches becomes inflamed or infected. This happens when fecal material or bacteria become trapped inside a diverticulum, leading to a localized infection. The inflammation can range from mild irritation to severe infection with complications such as abscess formation, perforation, or obstruction.

The exact mechanism triggering diverticulitis is still being researched. Current evidence suggests that changes in the gut microbiome, microscopic perforations in the diverticula, and chronic low-grade inflammation all play roles. Interestingly, contrary to long-held beliefs, there is no scientific evidence that eating nuts, seeds, or popcorn triggers diverticulitis episodes.

Uncomplicated vs. Complicated Diverticulitis

Medical professionals classify diverticulitis into two main categories based on severity. Uncomplicated diverticulitis, which accounts for about 75% of cases, involves inflammation and infection confined to the colon wall itself. These cases typically respond well to conservative treatment with rest, dietary modifications, and sometimes antibiotics.

Complicated diverticulitis occurs when the infection spreads beyond the colon wall or causes structural damage. Complications include abscess formation (a walled-off collection of pus), perforation (a hole in the colon wall allowing contents to leak into the abdominal cavity), fistula (an abnormal connection between the colon and another organ like the bladder), and obstruction (blockage of the intestine due to scarring). These complications require more aggressive treatment, often including hospitalization and sometimes surgery.

What Are the Symptoms of Diverticulitis?

The hallmark symptom of diverticulitis is sudden, severe pain in the lower left abdomen that persists for several days. Other common symptoms include fever, nausea, vomiting, constipation or diarrhea, abdominal tenderness, and bloating. The pain often worsens with movement and may temporarily improve after passing gas or having a bowel movement.

Diverticulitis symptoms typically come on suddenly and can range from mild discomfort to severe, debilitating pain. The presentation can vary depending on the location of the inflamed diverticula and the severity of the infection. Understanding the full spectrum of symptoms helps in recognizing when to seek medical care.

The most characteristic symptom is abdominal pain, typically felt in the lower left quadrant of the abdomen. This location corresponds to the sigmoid colon, where most diverticula form in Western populations. However, in some people - particularly those of Asian descent - diverticula may form on the right side of the colon, causing right-sided abdominal pain that can mimic appendicitis. The pain is usually constant rather than crampy, tends to worsen over several days, and is aggravated by movement, coughing, or pressing on the abdomen.

Fever is another common symptom, indicating that the body is fighting infection. Temperatures can range from low-grade (around 100.4°F or 38°C) in mild cases to high fever (above 102°F or 39°C) in severe infections. The presence of high fever, especially combined with chills or rigors (shaking chills), suggests a more serious infection requiring urgent medical attention.

Changes in bowel habits are frequently reported. Some people experience constipation as the inflammation causes the colon to function abnormally. Others develop diarrhea, sometimes alternating with constipation. Bloating and increased gas are also common, and some patients notice a complete change in their normal bowel pattern during an episode.

Common Symptoms of Diverticulitis

• Abdominal pain: Usually constant, located in the lower left abdomen, worsening over 1-3 days
• Fever and chills: Low to moderate fever (100.4-102°F) indicating infection
• Nausea and vomiting: Often accompanies pain, especially in moderate to severe cases
• Constipation: Difficulty passing stool or feeling of incomplete evacuation
• Diarrhea: Some patients experience loose stools instead of constipation
• Bloating and gas: Abdominal distension and increased flatulence
• Loss of appetite: General feeling of unwellness and reduced desire to eat
• Abdominal tenderness: Pain when the abdomen is pressed, especially on the left side

Warning Signs of Complications

Certain symptoms indicate serious complications requiring immediate medical attention. These red flag symptoms suggest that the infection may have spread beyond the colon wall or that other dangerous complications have developed.

What Causes Diverticulitis and Who Is at Risk?

Diverticulitis develops when diverticula (intestinal pouches) become inflamed or infected. Major risk factors include age over 40, low-fiber diet, obesity, lack of physical activity, smoking, and certain medications like NSAIDs. Genetics also play a role, with the condition running in families.

The development of both diverticula and subsequent diverticulitis involves multiple factors, including structural changes in the colon wall, dietary patterns, lifestyle factors, and genetic predisposition. Understanding these causes and risk factors is essential for both prevention and management of the condition.

The primary structural cause relates to increased pressure inside the colon. When the colon must generate more force to move stool along - often due to low-fiber diets that produce hard, dry stools - the pressure can cause the inner lining to bulge through weak points in the muscular wall. These weak points typically occur where blood vessels penetrate the colon wall. Over time, with repeated episodes of high pressure, these bulges become permanent pouches.

Once diverticula form, they can become inflamed through several mechanisms. The most widely accepted theory involves micro-perforations - tiny tears in the thin wall of a diverticulum that allow bacteria to cause infection. Another theory suggests that fecal matter becomes trapped in a diverticulum, blocking it and allowing bacteria to multiply. Recent research also points to the role of chronic low-grade inflammation and changes in the gut microbiome.

Major Risk Factors for Diverticulitis

Age is the strongest risk factor for both diverticulosis and diverticulitis. The condition is rare before age 40 but becomes increasingly common with advancing age. By age 60, approximately half of people in Western countries have diverticula, and by age 80, this rises to nearly 70%. The aging process causes the colon wall to weaken and lose elasticity, making it more susceptible to pouch formation.

Diet low in fiber is considered a major modifiable risk factor. Populations that consume traditional high-fiber diets have much lower rates of diverticular disease. Fiber adds bulk to stool and helps it move through the colon more easily, reducing the pressure needed for propulsion. The typical Western diet contains only 12-15 grams of fiber daily, far below the recommended 25-35 grams.

Obesity significantly increases the risk of diverticulitis and its complications. Studies show that individuals with a BMI over 30 have about a 1.5 to 2-fold increased risk of diverticulitis compared to those at normal weight. Obesity is associated with chronic low-grade inflammation, altered gut microbiome, and physical changes in the abdominal cavity that may contribute to this increased risk.

Physical inactivity also elevates risk. Regular exercise helps maintain normal bowel function, reduces intra-abdominal pressure, and may have anti-inflammatory effects. Studies have found that vigorous physical activity can reduce the risk of diverticulitis by 25-40%.

Smoking increases both the risk of developing diverticulitis and the risk of complications. Tobacco use impairs blood flow to the colon, weakens the intestinal wall, and affects the gut microbiome. Smokers also tend to have worse outcomes when diverticulitis occurs.

Certain medications have been linked to increased diverticulitis risk. Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and aspirin, opioid pain medications, and corticosteroids all appear to increase risk, possibly by affecting the gut lining or masking early symptoms until the disease is more advanced.

Genetic and Other Factors

Diverticular disease has a significant genetic component. Studies of twins suggest that genetics account for approximately 40-50% of the risk. If you have a first-degree relative (parent, sibling) with diverticulitis, your risk is substantially higher than the general population. Researchers have identified several genetic variants associated with connective tissue structure and intestinal motility that may contribute to this inherited risk.

How Is Diverticulitis Diagnosed?

Diverticulitis is primarily diagnosed through a combination of clinical evaluation and CT scan (computed tomography), which is the gold standard imaging test. Blood tests check for infection markers, and other tests may be used to rule out alternative diagnoses. Colonoscopy is NOT performed during acute diverticulitis but is recommended 6-8 weeks after recovery.

Accurate diagnosis of diverticulitis is crucial because the symptoms can overlap with many other abdominal conditions, including appendicitis, ovarian cysts, inflammatory bowel disease, irritable bowel syndrome, and even colon cancer. The diagnostic process involves several steps to confirm diverticulitis and assess its severity.

The evaluation typically begins with a medical history and physical examination. Your doctor will ask about the nature, location, and duration of your pain, associated symptoms like fever and bowel changes, your medical history, and any previous episodes. During the physical exam, the doctor will feel your abdomen, checking for tenderness, muscle guarding, and masses. Classic findings include tenderness in the left lower abdomen, possibly with a palpable mass representing inflamed tissue.

Blood tests are routinely ordered and typically show signs of infection and inflammation. The white blood cell count (WBC) is often elevated, indicating the body is fighting infection. C-reactive protein (CRP), an inflammatory marker, is usually elevated as well. Other blood tests help assess overall health status, kidney function, and electrolyte balance, which become important if hospitalization or surgery is needed.

The CT scan (computed tomography) is considered the gold standard for diagnosing diverticulitis. It provides detailed images of the colon and surrounding structures, allowing doctors to confirm the diagnosis, assess the extent of inflammation, and identify any complications such as abscesses, perforations, or fistulas. CT scanning has a sensitivity of over 90% for diagnosing diverticulitis and is invaluable for treatment planning. The scan is typically performed with oral and intravenous contrast to optimize visualization.

What to Expect During Diagnosis

• History and physical examination: Questions about symptoms, detailed abdominal examination
• Blood tests: Complete blood count (CBC), C-reactive protein (CRP), metabolic panel
• CT scan: Primary imaging test, usually with contrast, takes about 15-20 minutes
• Urinalysis: May be done to rule out urinary tract infection as an alternative cause
• Pregnancy test: For women of childbearing age to rule out ectopic pregnancy

Colonoscopy is NOT performed during an acute diverticulitis episode because the inflamed colon is at risk of perforation from the procedure. However, a follow-up colonoscopy is typically recommended 6-8 weeks after the acute episode resolves. This is important because the symptoms of diverticulitis can overlap with those of colon cancer, and the inflammation during the acute episode can mask small tumors on CT imaging. The colonoscopy ensures there is no underlying malignancy and allows for a thorough assessment of the extent of diverticulosis.

How Is Diverticulitis Treated?

Treatment depends on severity. Mild uncomplicated diverticulitis is often managed at home with rest, clear liquids, and sometimes antibiotics. Moderate to severe cases require hospitalization for IV antibiotics and bowel rest. Complicated cases with abscesses may need drainage procedures, while severe complications like perforation require emergency surgery.

The approach to treating diverticulitis has evolved significantly in recent years, with current guidelines emphasizing individualized care based on the severity of the disease and patient factors. The goal of treatment is to resolve the acute infection, manage symptoms, prevent complications, and reduce the risk of recurrence.

Treatment for Uncomplicated Diverticulitis

For mild, uncomplicated diverticulitis, outpatient management is often appropriate. This typically includes dietary modifications to rest the bowel - starting with clear liquids for 2-3 days and gradually advancing to low-fiber foods as symptoms improve. Interestingly, recent research has questioned whether antibiotics are always necessary for mild cases. Current guidelines suggest that antibiotics can be withheld in select patients with uncomplicated diverticulitis who can be closely monitored, though many doctors still prescribe them.

When antibiotics are prescribed, a course of 7-10 days is typical. Common antibiotic regimens include a combination covering both aerobic and anaerobic bacteria - such as ciprofloxacin plus metronidazole, or amoxicillin-clavulanate alone. Pain management typically involves acetaminophen (paracetamol) rather than NSAIDs, as NSAIDs may increase the risk of complications.

Patients being treated at home should be given clear return precautions: come back or call if fever increases, pain worsens significantly, they cannot keep fluids down, or they develop any warning signs. Most patients with uncomplicated diverticulitis improve within 2-3 days and fully recover within 1-2 weeks.

Hospital Treatment for Moderate to Severe Cases

Hospitalization is needed for patients with moderate to severe symptoms, those unable to tolerate oral intake, patients with significant comorbidities, signs of complications, or failure to improve with outpatient treatment. In the hospital, treatment includes intravenous (IV) antibiotics, IV fluids for hydration, bowel rest (nothing by mouth initially), and pain management. Patients are monitored closely for improvement or deterioration.

For complicated diverticulitis with abscess formation, treatment depends on the size of the abscess. Small abscesses (less than 3-4 cm) may resolve with antibiotics alone. Larger abscesses typically require percutaneous drainage - a procedure where a radiologist uses CT guidance to place a drain into the abscess to remove the infected fluid. This minimally invasive approach often allows patients to avoid emergency surgery.

Surgical Treatment

Emergency surgery is required for the most serious complications: free perforation with peritonitis (infection spreading throughout the abdominal cavity), uncontrolled sepsis, or obstruction. The traditional approach involves a two-stage procedure: first, removing the diseased section of colon and creating a colostomy (bringing the end of the colon to the skin surface), followed by a second surgery months later to reconnect the bowel. However, newer techniques sometimes allow primary anastomosis (reconnecting the bowel immediately) in selected patients.

Elective surgery may be recommended for patients with recurrent episodes of diverticulitis, complicated disease, or persistent symptoms. The decision to operate is individualized, considering factors like the number and severity of episodes, the patient's overall health, and quality of life impact. The surgery (sigmoid colectomy) removes the section of colon most affected by diverticula. When performed electively, it can usually be done laparoscopically with faster recovery than open surgery.

What Should You Eat During and After Diverticulitis?

During an acute diverticulitis flare-up, start with clear liquids only (water, broth, clear juices) for 2-3 days, then gradually progress to low-fiber foods. Once recovered, transition to a high-fiber diet (25-35 grams daily) to prevent future episodes. Contrary to old advice, nuts, seeds, and popcorn are safe to eat and may actually be beneficial.

Dietary management plays a central role both during acute diverticulitis and in preventing future episodes. The approach differs significantly between these two phases, which sometimes causes confusion for patients.

Diet During Acute Diverticulitis

During an acute flare-up, the goal is to rest the digestive system while maintaining hydration. In the first 2-3 days when symptoms are worst, a clear liquid diet is typically recommended. This includes:

• Water and ice chips
• Clear broth (chicken, beef, or vegetable)
• Plain gelatin (without fruit pieces)
• Clear fruit juices without pulp (apple, grape, cranberry)
• Clear sports drinks or electrolyte solutions
• Tea or coffee without milk or cream
• Popsicles without fruit chunks

As symptoms improve (usually within 2-4 days), you can gradually advance to low-fiber foods. This phase typically lasts until you feel significantly better and have had a follow-up with your doctor. Low-fiber foods include:

• White rice, white bread, refined pasta
• Eggs cooked any style
• Fish and poultry without skin
• Well-cooked vegetables without skins
• Canned or cooked fruits without skins or seeds
• Dairy products (if tolerated)
• Smooth nut butters in small amounts

Diet for Prevention

Once you've fully recovered from the acute episode (typically 2-4 weeks later), the dietary goal shifts to preventing future episodes. This means gradually transitioning to a high-fiber diet, which is the single most important dietary intervention for preventing diverticulitis recurrence.

Aim for 25-35 grams of fiber per day, increasing gradually over several weeks to allow your digestive system to adjust. Increasing fiber too quickly can cause bloating, gas, and discomfort. Good sources of fiber include:

• Fruits: Apples, pears, berries, oranges, prunes (with skin when possible)
• Vegetables: Broccoli, carrots, Brussels sprouts, artichokes, sweet potatoes
• Whole grains: Oats, brown rice, whole wheat bread, quinoa, barley
• Legumes: Beans, lentils, chickpeas, split peas
• Nuts and seeds: Almonds, walnuts, chia seeds, flaxseeds (these are SAFE)

Adequate hydration is equally important. When increasing fiber intake, you must also increase water consumption. Fiber absorbs water to form soft, bulky stools - without enough fluid, high-fiber intake can actually cause constipation. Aim for at least 8-10 glasses of water daily.

How Can You Prevent Diverticulitis?

Prevent diverticulitis by eating a high-fiber diet (25-35 grams daily), maintaining a healthy weight, exercising regularly, not smoking, limiting red meat, and staying well-hydrated. These lifestyle modifications can significantly reduce both the formation of new diverticula and the risk of diverticulitis episodes.

While you cannot make existing diverticula disappear, you can significantly reduce the risk of them becoming inflamed. Prevention strategies focus on modifiable lifestyle factors that influence colon health and inflammation.

High-fiber diet remains the cornerstone of prevention. Large population studies consistently show that people who consume more fiber have lower rates of diverticular disease. Fiber reduces intra-colonic pressure by producing softer, bulkier stools that are easier to pass. Aim for 25-35 grams daily from whole food sources rather than supplements when possible. Increase fiber gradually to minimize digestive discomfort.

Regular physical activity has a strong protective effect. Exercise promotes normal bowel function, helps maintain healthy weight, and may reduce inflammation. Studies show that vigorous exercise (running, cycling, swimming) provides greater protection than light activity, though any physical activity is beneficial. Aim for at least 150 minutes of moderate activity or 75 minutes of vigorous activity weekly.

Maintain a healthy weight. Obesity significantly increases diverticulitis risk. Weight loss in overweight individuals can reduce this risk. Even modest weight loss of 5-10% of body weight can have meaningful health benefits.

Don't smoke. Smoking increases diverticulitis risk and the risk of complications. Quitting smoking provides benefits for colon health as well as overall health.

Limit red meat consumption. Some studies suggest that high intake of red meat may increase diverticulitis risk, while diets emphasizing plant-based foods appear protective. You don't need to eliminate red meat entirely, but consider making fruits, vegetables, and whole grains the foundation of your diet.

Stay well-hydrated. Adequate fluid intake keeps stools soft and easy to pass. Aim for at least 8 glasses of water daily, more if you're physically active or in hot weather.

Avoid or minimize NSAIDs. If you regularly take non-steroidal anti-inflammatory drugs like ibuprofen or aspirin, discuss alternatives with your doctor, especially if you have a history of diverticulitis.

What Complications Can Diverticulitis Cause?

Diverticulitis can lead to serious complications including abscess (collection of pus), perforation (hole in the colon), fistula (abnormal connection to other organs), intestinal obstruction (blockage), and peritonitis (life-threatening abdominal infection). About 25% of diverticulitis cases develop complications, requiring more aggressive treatment.

While most cases of diverticulitis are uncomplicated and resolve with conservative treatment, approximately 25% of patients develop complications that require more intensive management. Understanding these complications helps patients recognize warning signs and seek appropriate care.

Abscess is the most common complication, occurring when the infection is contained but creates a walled-off pocket of pus near the inflamed diverticulum. Small abscesses may resolve with antibiotics alone, but larger ones (generally over 3-4 cm) typically require drainage. This is usually performed by interventional radiology using CT guidance to place a thin catheter into the abscess cavity to drain the pus. Abscess drainage is often successful in resolving the acute infection and may allow patients to avoid emergency surgery.

Perforation occurs when the inflamed diverticulum ruptures, creating a hole in the colon wall. If the perforation is small and quickly contained by surrounding tissues, it may form an abscess. However, if colonic contents leak freely into the abdominal cavity, it causes peritonitis - a life-threatening infection of the abdominal lining. Peritonitis causes severe abdominal pain, rigid abdomen, high fever, and signs of shock. This is a surgical emergency requiring immediate operation.

Fistula is an abnormal tunnel-like connection that forms between the inflamed colon and an adjacent organ. The most common type is a colovesical fistula, connecting the colon to the bladder. Symptoms include air or stool particles in the urine (pneumaturia or fecaluria), recurrent urinary tract infections, and abdominal pain. Colovaginal fistulas (to the vagina) cause vaginal discharge or passage of gas/stool through the vagina. Fistulas generally require surgical repair.

Intestinal obstruction can result from the scarring and narrowing (stricture) that occurs with repeated episodes of inflammation. Partial obstruction causes cramping abdominal pain, bloating, and constipation. Complete obstruction is an emergency, causing inability to pass gas or stool, severe abdominal distension, and vomiting. Strictures may be treated with endoscopic dilation or may require surgical resection.

Diverticular bleeding is a separate complication that occurs when a blood vessel in a diverticulum erodes and bleeds. Unlike diverticulitis, diverticular bleeding typically causes painless passage of large amounts of bright red blood from the rectum. While alarming, most episodes stop spontaneously. However, significant bleeding requires hospitalization for monitoring and sometimes intervention to stop the bleeding.