Diverticular Disease and Diverticulitis

Diverticula are small pouches that form in the wall of the colon. Most cause no symptoms, while diverticular disease causes chronic symptoms and diverticulitis involves acute inflammation or infection. The terms are not interchangeable, and severe pain, sepsis, obstruction or major bleeding require urgent assessment.

What diverticula are A diverticulum is a small pouch projecting outwards from the wall of the bowel. More than one pouch is called diverticula. They occur mainly within the colon, which is the large bowel. In many Western populations, they are most common within the sigmoid colon on the lower left side. How the pouches form The inner lining can push through weak points within the bowel's muscular wall. These weak points often occur where small blood vessels pass through the muscle. Age related changes in connective tissue and pressure within the colon can contribute. The process is multifactorial and is not explained by one food or one episode of constipation. The sigmoid colon The sigmoid colon is the curved final section of the colon before the rectum. Stool is usually more formed by the time it reaches this region. The sigmoid also develops strong muscle contractions that move contents forwards. These features may help explain why diverticula commonly form there. Right sided diverticula Diverticula can occur elsewhere in the colon. Right sided disease is more common in some Asian populations and can produce right sided pain. This pattern can resemble appendicitis or another right sided abdominal condition. Pain location therefore provides a clue rather than a complete diagnosis. A spectrum with different terms Diverticulosis, diverticular disease and diverticulitis describe different clinical states. They should not be used as interchangeable names. The same person can move between these states over time. Most people with diverticulosis never develop diverticulitis. Diverticulosis Diverticulosis means that diverticula are present without symptoms. The pouches are often found incidentally during colonoscopy or imaging performed for another reason. NICE advises that asymptomatic diverticulosis needs no specific medical treatment. Finding pouches does not mean that the bowel is inflamed or infected. Diverticular disease Diverticular disease means diverticula are present with mild chronic abdominal pain or tenderness and no systemic illness. This is sometimes called symptomatic uncomplicated diverticular disease. Symptoms can include altered bowel habit, bloating and intermittent lower abdominal discomfort. The symptoms can overlap substantially with irritable bowel syndrome. Diverticulitis Acute diverticulitis is sudden inflammation or infection associated with one or more diverticula. Pain is usually more constant and localised than in uncomplicated diverticular disease. Fever, tenderness and raised inflammatory markers can accompany it. Diverticulitis can remain uncomplicated or develop serious complications. Most diverticulosis is asymptomatic Most people with diverticula do not know they have them. The pouches may remain unchanged and never cause a clinical problem. An incidental finding should not automatically explain unrelated pain, diarrhoea or bleeding. Symptoms still require their own assessment. Diverticula become more common with age Age is the strongest recognised risk factor for developing colonic diverticula. The bowel wall and connective tissue change gradually over time. Diverticula can still occur in younger adults, so age is not an absolute rule. New severe symptoms at any age require appropriate assessment. Low fibre dietary patterns A low fibre dietary pattern has long been associated with diverticular disease. Lower fibre can produce smaller, firmer stools and may increase pressure during colonic contractions. However, current evidence does not support a simple rule that low fibre alone causes every diverticulum. Genetic, structural, inflammatory and lifestyle factors also contribute. Obesity Obesity is associated with a higher risk of symptomatic diverticular disease and acute diverticulitis. Possible mechanisms include altered inflammation, diet, movement and abdominal pressure. Weight is one part of risk and should not be used to blame the person for an acute episode. Smoking Smoking is associated with a greater risk of symptomatic and complicated diverticular disease. It also increases cardiovascular, lung and cancer risks. Stopping smoking can reduce wider harm and may reduce future diverticular complications. Reduced physical activity Lower physical activity is associated with a higher risk of symptomatic disease in population studies. Regular movement can support bowel function, weight management and general health. Activity should be increased gradually according to fitness and other medical conditions. NSAIDs Non steroidal anti inflammatory drugs are usually shortened to NSAIDs. Examples include ibuprofen, naproxen and diclofenac. NICE advises avoiding them where possible in diverticular disease because they may increase perforation risk. They can also cause upper gastrointestinal ulcers and bleeding. Opioid medicines Opioids such as codeine and morphine slow bowel movement and commonly cause constipation. They may increase pressure within the colon and are associated with diverticular perforation. NICE advises avoiding opioid analgesia where possible. A prescribed opioid should not be stopped abruptly without reviewing the reason for treatment. Other medicine considerations Corticosteroids and immunosuppressive medicines can increase infection risk or reduce typical inflammatory signs. Anticoagulants and antiplatelet medicines can increase the impact of diverticular bleeding. These medicines may be essential for other conditions. They require clinical review rather than independent stopping. Genetics and bowel structure Family studies suggest that inherited factors influence who develops diverticula and complications. Differences in connective tissue, bowel movement and inflammatory responses may contribute. A health problems in the family changes probability but does not predict one person's course. Symptoms of uncomplicated diverticular disease Pain usually affects the left lower abdomen, also called the left iliac fossa. It may be triggered by eating and improve after passing stool or wind. Constipation, diarrhoea and bloating can occur. The pain is usually intermittent rather than steadily worsening with fever. Left iliac fossa pain The left iliac fossa is the lower left region of the abdomen. The sigmoid colon lies there in many people. Pain in this area has several possible causes, including IBS, constipation, colitis and urinary or gynaecological disease. Its location does not prove diverticular disease. Altered bowel habit Diverticular disease can accompany constipation or diarrhoea. Some people alternate between the two. A sustained new change in bowel habit can also occur with inflammatory disease or colorectal cancer. It should not be attributed automatically to known diverticula. Bloating Bloating is a sensation of fullness, pressure or swelling. Visible enlargement is called distension. Both can occur with diverticular disease, IBS, constipation and several other conditions. Bloating alone is not evidence of inflammation. Rectal bleeding in diverticular disease Diverticula can cause rectal bleeding without diverticulitis. The bleeding results when a small artery associated with a pouch is injured. It can be sudden, painless and substantial. Every new bleed requires assessment because other causes include cancer, colitis, haemorrhoids and vascular disease. Acute diverticulitis pain Acute diverticulitis commonly causes constant lower abdominal pain. The pain is often severe and localises to the left lower quadrant. Movement or pressure over the area may worsen it. Right sided pain can occur when diverticula are located elsewhere. Fever and systemic symptoms Fever, chills, nausea and reduced appetite can accompany acute diverticulitis. A person may feel generally unwell. Older, frail or immunosuppressed people can have serious disease without a high temperature. The whole clinical pattern matters more than fever alone. Localised tenderness Examination can show tenderness over the affected bowel segment. Guarding means involuntary tightening of the abdominal muscles because the underlying tissues are irritated. Localised tenderness can occur in uncomplicated inflammation. Rigidity or widespread guarding raises concern for perforation and peritonitis. Raised inflammatory markers C reactive protein is usually shortened to CRP. CRP and the white cell count can rise during acute inflammation or infection. A raised result supports concern but does not prove diverticulitis. Normal markers reduce the likelihood of complicated inflammation but do not replace clinical judgement. Uncomplicated acute diverticulitis Uncomplicated diverticulitis is inflammation confined to the bowel and nearby tissues without abscess, fistula, obstruction or generalised perforation. The person may have localised pain and mild systemic symptoms while remaining physiologically stable. Many suitable people can be managed outside hospital with careful safety netting. Complicated acute diverticulitis Complicated diverticulitis means the inflammation has produced an important local or systemic complication. Examples include abscess, fistula, stricture, obstruction, perforation, peritonitis and sepsis. These presentations require same day hospital assessment. Abscess An abscess is a collection of pus near the inflamed bowel. It can cause persistent fever, pain, a tender mass or failure to improve. CT shows its size and location. Smaller abscesses may respond to antibiotics, while larger accessible collections may require image guided drainage. Perforation Perforation means a hole has developed through the bowel wall. A small leak can be contained by nearby tissues and form a local collection. A larger leak can spread bowel contents through the abdominal cavity. Generalised contamination can cause peritonitis, sepsis and shock. Peritonitis The peritoneum is the lining of the abdominal cavity. Peritonitis causes severe pain, guarding or a rigid abdomen and marked systemic illness. It is a surgical emergency. The person needs resuscitation, antibiotics and urgent source control assessment. Fistula A fistula is an abnormal connection between the colon and another organ or the skin. A connection to the bladder can cause air in urine, recurrent urinary infection or stool material in urine. A connection to the vagina can cause passage of gas or stool through the vagina. Persistent fistulas often require specialist surgical treatment. Stricture and obstruction Repeated inflammation and scarring can narrow the colon. This narrowing is called a stricture. Obstruction can cause cramping pain, abdominal swelling, vomiting and inability to pass stool or wind. Cancer can cause a similar narrowing and must be considered. Sepsis Sepsis is life threatening organ dysfunction caused by an abnormal response to infection. Warning features can include confusion, rapid breathing, low blood pressure, skin discolouration and very low urine output. A normal temperature does not exclude sepsis. Suspected sepsis needs emergency assessment. Hinchey classification The Hinchey classification is a specialist framework describing the severity of complicated diverticulitis. It was developed to guide surgical management and has several modified versions. The broad concept progresses from local abscess to more distant abscess and then generalised peritonitis. It is not a public self triage scale. Hinchey stages conceptually Classic stage I describes a local abscess next to the affected colon. Stage II describes an abscess farther away, such as within the pelvis or another abdominal space. Stage III describes generalised purulent peritonitis. Stage IV describes generalised faecal peritonitis. Why the classification is not over taught here Modern teams also use CT based systems and the person's physiology. The same radiological stage can affect two people differently because of age, frailty and comorbidity. Treatment is not chosen from a stage number alone. Diverticular bleeding is a separate entity Diverticular bleeding is not the same process as diverticulitis. A vessel crossing the pouch can rupture without surrounding infection or inflammation. The presentation is often painless fresh or dark red rectal bleeding. Pain and fever suggest another process or a coexisting condition. Bleeding can be heavy Some diverticular bleeds stop spontaneously. Others cause repeated large volume blood loss, anaemia or shock. Blood clots, toilet water turning red, dizziness or collapse require emergency assessment. The source cannot be confirmed from blood colour alone. Diverticular bleeding and medicines Anticoagulants, antiplatelet medicines and NSAIDs can increase bleeding severity. These medicines may protect against stroke, heart attack or venous clots. Do not stop them independently. Emergency clinicians decide whether temporary interruption or reversal is needed. Differential diagnosis matters Left lower abdominal pain is not specific to diverticulitis. Possible bowel causes include IBS, constipation, colorectal cancer, IBD, infectious colitis and ischaemic colitis. Urinary and reproductive organ conditions can present similarly. The assessment is broader when the pattern is atypical. Irritable bowel syndrome IBS often causes intermittent pain related to defecation and altered stool form. Fever and raised inflammatory markers are not expected from IBS itself. A person can have both IBS and diverticula. The presence of pouches does not prove that chronic symptoms come from them. Colorectal cancer Cancer can cause altered bowel habit, bleeding, weight loss, anaemia, pain or obstruction. Acute inflammation can also create bowel wall thickening on imaging. Persistent symptoms or NICE suspected cancer criteria require the appropriate pathway. A previous diverticulitis diagnosis does not remove future cancer risk. Inflammatory bowel disease and colitis Crohn's disease and ulcerative colitis can cause pain, diarrhoea, bleeding and systemic illness. Ischaemic colitis can cause sudden pain followed by bleeding, particularly in older adults. Infectious colitis can cause fever and diarrhoea. Stool and endoscopic tests are selected according to the pattern. Appendicitis Appendicitis usually begins centrally and later localises to the right lower abdomen. Right sided diverticulitis can resemble it. CT or ultrasound can be needed when the diagnosis remains uncertain. Urinary conditions Kidney stones can cause severe flank to groin pain and blood in urine. A urinary infection can cause lower pain, frequency and fever. A diverticular fistula to the bladder can cause repeated urinary infection or air in urine. Urine testing provides information but does not diagnose every source. Gynaecological and pelvic causes Ovarian cyst complications, pelvic inflammatory disease and ectopic pregnancy can cause lower abdominal pain. Endometriosis can cause bowel related and cyclical pelvic symptoms. Pregnancy testing and pelvic assessment are used where relevant. Diverticulitis should not be assumed from pain location alone. Clinical assessment in primary care The clinician asks about onset, pain pattern, fever, vomiting and bowel changes. They ask about bleeding, previous episodes, diverticula and colon investigations. Medicines, immune suppression, pregnancy possibility and other diseases are reviewed. Vital signs and abdominal examination determine whether same day hospital assessment is needed. A clinical diagnosis can guide initial care NICE does not require routine immediate CT for every stable suspected uncomplicated episode managed in primary care. A compatible history, localised tenderness and absence of complicated features can support initial management. The person needs clear advice to return if symptoms persist or worsen. Clinical diagnosis remains provisional because several conditions can mimic it. When blood tests help Primary care testing depends on clinical severity and diagnostic uncertainty. FBC can show anaemia, raised white cells or other clues. CRP supports assessment of inflammation. Kidney function becomes important with dehydration, contrast imaging or particular medicines. CT is the key complication test Contrast enhanced CT can confirm inflammation and show abscess, perforation, fistula or obstruction. NICE recommends CT within 24 hours in hospital when complicated diverticulitis is suspected and inflammatory markers are raised. It also helps plan drainage or surgery. CT is not required merely because incidental diverticula are known. When CT may be needed beyond complications Imaging can help when the diagnosis is uncertain, symptoms are severe or the person fails to improve. It can distinguish diverticulitis from cancer, appendicitis, urinary disease and gynaecological conditions. Radiation and contrast risks are considered against the likely benefit. Alternatives to contrast CT If intravenous contrast is contraindicated, NICE allows non contrast CT, MRI or ultrasound according to local expertise. Ultrasound avoids radiation but is more operator dependent. MRI can be useful in selected situations but is less available for acute assessment. Colonoscopy during acute inflammation Colonoscopy is generally avoided during active severe diverticulitis because distension and instrumentation can increase perforation risk. Later lower bowel investigation is selected when cancer, colitis or another diagnosis remains possible. The decision depends on previous investigations, imaging findings and the continuing symptom pattern. Cancer pathways remain separate Rectal bleeding, iron deficiency anaemia, weight loss, an abdominal or rectal mass and persistent bowel habit change can meet current NICE testing or referral criteria. FIT may guide colorectal referral in selected symptomatic adults. A presumed diverticular explanation must not delay the cancer pathway. Outpatient management principles A systemically well person without complicated features may be managed outside hospital. Management includes suitable pain relief, fluids and food as tolerated, and reliable follow up. The person must be able to obtain urgent help if symptoms worsen. Social circumstances and comorbidities influence whether outpatient care is safe. Antibiotics are not automatic Older teaching treated every episode with antibiotics. NICE now advises considering no antibiotics for a systemically well person with acute diverticulitis. Many uncomplicated episodes improve without antimicrobial treatment. Avoiding unnecessary antibiotics reduces adverse effects and antimicrobial resistance. When oral antibiotics are considered NICE advises an antibiotic strategy when the person is systemically unwell, immunosuppressed or has significant comorbidity. Oral treatment is used when the person does not meet criteria for suspected complicated disease. The prescriber considers allergy, kidney function, interactions and local resistance guidance. The medicine should not be selected or shared without assessment. When hospital care is needed Same day hospital assessment is needed for uncontrolled pain with signs of abscess, peritonitis, sepsis, fistula or obstruction. Admission is also more likely when oral intake is poor, vomiting persists or outpatient monitoring is unsafe. Frailty, immune suppression and major comorbidity lower the threshold. Intravenous treatment Complicated diverticulitis usually receives intravenous antibiotics in hospital. Fluids, pain relief and sepsis management are provided as needed. NICE recommends reviewing intravenous antibiotics within 48 hours or after scanning if sooner. Treatment steps down to oral medicine when clinically appropriate. Managing an abscess CT determines the abscess size and position. NICE considers percutaneous drainage or surgery for an abscess larger than 3 cm when anatomically feasible. Smaller abscesses can often switch to oral antibiotics when the person improves. Failure to improve can prompt repeat imaging. Image guided drainage A radiologist passes a catheter through the skin into an accessible abscess using imaging guidance. Pus is drained and sent for microbiological testing. The result can help tailor antibiotics. Not every collection can be reached safely. Emergency surgery Generalised peritonitis, uncontrolled sepsis, ongoing perforation or failed non surgical care can require emergency surgery. The diseased bowel segment may be removed. The surgeon may reconnect the bowel or create a temporary or permanent stoma depending on safety. The decision reflects physiology, contamination and individual risk. Elective surgery Surgery is not automatically required after a fixed number of uncomplicated episodes. It can be considered after complicated disease when a fistula, stricture or continuing symptoms remain. Quality of life, recurrence pattern, operative risk and patient preference all matter. Pain relief NICE recommends simple analgesia such as paracetamol when appropriate. NSAIDs are avoided where possible because of perforation and bleeding concerns. Opioids are also avoided where possible because they slow the bowel and may increase complications. Severe pain despite simple treatment requires reassessment rather than repeated self medication. Antispasmodics An antispasmodic can be considered for chronic cramping in diverticular disease. It is not a treatment for peritonitis, obstruction or uncontrolled acute pain. A pharmacist or clinician checks contraindications and interactions. Bulk forming laxatives Bulk forming laxatives can help when constipation persists or dietary fibre is not tolerated. They work by increasing stool water and bulk. They require adequate fluid and are not appropriate during suspected bowel obstruction. Eating during an acute episode A person with mild uncomplicated disease can usually eat and drink according to tolerance. Temporary simpler foods may feel easier during pain or nausea. Prolonged fasting is not a routine home treatment. Vomiting, dehydration or inability to eat requires clinical review. Fibre after acute symptoms settle Once acute inflammation has settled, a healthy balanced diet with adequate fibre is encouraged. Whole grains, fruit, vegetables, pulses, nuts and seeds can contribute. Fibre is increased gradually to reduce bloating and discomfort. Adequate fluid is important as intake rises. Fibre is not an emergency treatment Increasing fibre during severe acute pain does not treat an abscess or perforation. Prevention advice applies to longer term bowel health after the acute episode settles. Individual tolerance and other bowel conditions affect the most suitable amount. Nuts, seeds and popcorn Current NICE guidance states that people do not need to avoid seeds, nuts, popcorn or fruit skins. The older idea was that small particles entered a pouch and triggered inflammation. Research has not supported routine exclusion. A person can still avoid an individual food that repeatedly causes symptoms for another reason. Hydration Adequate fluid helps increased fibre remain soft and easier to pass. Fluid needs differ with weather, activity, kidney disease and heart failure. Forced excessive drinking is not necessary. Vomiting or reduced urine can indicate dehydration and need assessment. Physical activity Regular activity supports bowel function, muscle health and cardiovascular wellbeing. NICE advises discussing exercise as part of reducing symptomatic disease and diverticulitis risk. The plan should be realistic and progressive. Weight management Weight loss can reduce risk when a person is living with overweight or obesity. Support should be non stigmatising and based on sustainable eating and activity. Rapid restrictive diets are not required for diverticular prevention. Smoking cessation Stopping smoking can reduce the risk of symptomatic and complicated disease. It also lowers the risk of cancer, COPD and cardiovascular disease. Behavioural and medicine support improve cessation success. Preventive antibiotics are not recommended NICE advises against antibiotics to prevent recurrent acute diverticulitis. Long term exposure can cause adverse effects and resistance without established preventive benefit. Aminosalicylates are also not recommended for this purpose. Recurrence Diverticulitis can recur, but recurrence is not inevitable. A future episode may be milder, similar or more complicated. New symptoms still require reassessment because another disease can develop. Persistent symptoms after diverticulitis Pain and bowel changes can continue after inflammation settles. Possible explanations include altered bowel sensitivity, constipation, IBS or an unresolved complication. Persistent symptoms should prompt reconsideration rather than repeated empirical antibiotics. Prognosis Most people with diverticulosis remain asymptomatic. Most uncomplicated diverticulitis episodes resolve without surgery. Complicated disease is less common but can be serious. Clear safety netting allows proportionate care without presenting every pouch as a future emergency. Living with diverticular disease Chronic symptoms can affect food confidence, work and travel. The aim is a broad balanced diet and a manageable symptom plan rather than fear of eating. A diagnosis should provide useful guidance without turning normal bowel variation into constant surveillance. What this lesson should not be used for This lesson cannot diagnose diverticulitis from pain location, fever or a previous scan alone. Do not start leftover antibiotics or use antibiotics preventively. Do not take NSAIDs or opioids repeatedly for worsening abdominal pain without clinical advice. Do not assume rectal bleeding is caused by diverticula. Call 999 for major bleeding, severe pain with a rigid or swollen abdomen, collapse or signs of sepsis.

Diverticulosis means symptom free colonic pouches, diverticular disease means chronic symptoms without systemic inflammation, and diverticulitis means acute inflammation or infection. Stable uncomplicated episodes may be managed without routine CT or antibiotics, while abscess, perforation, sepsis, fistula, obstruction or major bleeding require urgent hospital care.