Diverticulitis is a condition characterized by the inflammation or infection of small, bulging pouches that form in the lining of the large intestine, known as diverticula. The mere presence of these pouches is called diverticulosis, which is quite common, especially in older adults, and often causes no symptoms. Diverticulitis occurs when one or more of these pouches become irritated and infected, leading to noticeable physical signs of illness. This distinction is important because diverticulosis is a structural finding, while diverticulitis is an acute disease state requiring medical attention.
The Acute Manifestation of Symptoms
The illness generally announces itself with an acute onset of abdominal pain, which is the most frequent symptom. In Western populations, this discomfort is classically felt in the lower left quadrant of the abdomen, corresponding to the sigmoid colon where diverticula most often form. The pain is often persistent and can range from a mild ache that gradually worsens to a severe, intense sensation.
Tenderness upon touch in the affected area is a common finding during a physical examination. Patients may also develop a fever and chills, which are systemic signs of infection. Nausea and vomiting frequently accompany the abdominal pain as the inflammation irritates the digestive tract.
Changes in normal bowel function are also typical, with many patients experiencing constipation, though some may develop diarrhea instead. The combination of localized pain, fever, and altered bowel habits points toward an infection within the colon. In a small number of cases, particularly among people of Asian descent, the pain may be felt in the lower right quadrant due to a different anatomical distribution of diverticula.
Anatomical Basis and Confirmatory Imaging
The disease process begins when a diverticulum becomes blocked, possibly by hardened stool or undigested food particles, leading to bacterial overgrowth and subsequent inflammation. Pathologically, the condition appears as a swollen, infected pouch, often with surrounding fat inflammation. The inflamed colon wall itself may also thicken noticeably.
Medical professionals rely on imaging to confirm the presence and extent of the disease. Computed tomography (CT) of the abdomen and pelvis is considered the gold standard for diagnosis. A CT scan allows for clear visualization of the inflamed segment of the colon, showing wall thickening and the characteristic haziness, or “fat stranding,” in the surrounding pericolic fat.
CT imaging confirms the presence of diverticula and distinguishes the infection from other conditions that cause abdominal pain. During an acute flare-up, procedures like a colonoscopy are avoided because the inflammation makes the colon wall fragile and increases the risk of perforation. Internal examination is typically delayed until the inflammation has resolved to safely assess the colon.
Recognizing Severe Presentations
Diverticulitis is classified as either uncomplicated, meaning localized inflammation without major complications, or complicated, involving more severe outcomes. Severe presentations indicate that the infection has progressed beyond the colon wall. One such complication is the formation of an abscess, which is a localized pocket of pus that forms near the inflamed diverticulum.
Abscesses can be seen on a CT scan as a fluid collection with a defined wall, sometimes requiring percutaneous drainage. A much more serious presentation is perforation, which occurs when the infected pouch tears, allowing intestinal contents to leak into the abdominal cavity. This spillage can lead to peritonitis, a widespread infection of the abdominal lining, causing heightened systemic symptoms like a rigid abdomen and signs of septic shock.
Fistula development is another severe, though often more chronic, complication where the infection creates an abnormal connection between the colon and a nearby organ. The most common type of fistula connects the colon to the bladder, which can cause symptoms such as recurrent urinary tract infections or air in the urine. These severe manifestations require immediate and aggressive medical intervention, often including surgery.