More than a dozen conditions can produce the same left-sided abdominal pain, fever, and bloating that define a typical diverticulitis flare. Some are minor and resolve on their own; others, like colorectal cancer, are serious enough that a missed diagnosis changes outcomes. Knowing what else could be causing your symptoms helps you have a more informed conversation with your doctor and understand why additional testing may be recommended.
Why Diverticulitis Is Easy to Confuse
Diverticulitis causes inflammation in small pouches along the colon wall, most often in the lower left abdomen. But the sigmoid colon can loop across the pelvis, pushing pain to the right side or the center of the lower belly. Right-sided diverticulitis can even mimic conditions in the upper abdomen. That variability in location, combined with symptoms (pain, nausea, changes in bowel habits, low-grade fever) shared by many abdominal conditions, means the initial clinical picture alone is rarely enough to pin down the diagnosis.
Colorectal Cancer
This is the mimic that matters most. About 1.9% of patients diagnosed with diverticulitis are found to have colorectal cancer within the following year. That number sounds small, but the consequences of missing it are severe, and the preoperative diagnostic rate of cancer hidden behind diverticulitis is strikingly low, around 37%. Both conditions can cause wall thickening on imaging, localized pain, and changes in stool. The key difference is that cancer tends to cause progressive narrowing of the bowel, unexplained weight loss, and iron-deficiency anemia, while diverticulitis usually presents more acutely with fever and localized tenderness. A follow-up colonoscopy after a diverticulitis episode is standard practice precisely because imaging during an acute flare can mask an underlying tumor.
Epiploic Appendagitis
Small, fat-filled pouches hang off the outside of the colon. When one of these twists or loses its blood supply, it becomes inflamed, producing sharp, localized pain that looks and feels almost identical to diverticulitis, especially on the left side. This condition, called epiploic appendagitis, is one of the most commonly confused diagnoses on CT imaging.
A few clinical patterns can help separate the two. Patients with epiploic appendagitis tend to be younger (average age around 50, compared to 62 for diverticulitis) and more likely to have a higher BMI. Their blood work also tells a different story: white blood cell counts are usually normal, and inflammatory markers stay low. In one study, only about 6% of epiploic appendagitis patients had elevated white cell counts, compared with 67% of those with diverticulitis. The practical difference for you: epiploic appendagitis resolves on its own with anti-inflammatory pain relief and does not need antibiotics or surgery.
Irritable Bowel Syndrome
IBS and diverticular disease overlap so much in symptoms (cramping, bloating, irregular bowel habits) that distinguishing them without imaging can be genuinely difficult. The single most reliable clinical difference is pain duration. Pain lasting more than 24 hours is far more common in diverticular disease than in IBS. In one comparison, 80% of diverticular disease patients with prolonged pain episodes needed medical attention, versus 33% of IBS patients. IBS pain also tends to improve after a bowel movement and fluctuate with stress, while diverticulitis pain is more constant and usually accompanied by fever or tenderness that worsens with pressure.
Inflammatory Bowel Disease
Both Crohn’s disease and ulcerative colitis can inflame the same stretch of colon where diverticulitis strikes. Crohn’s in particular can be tricky because it causes patchy, deep inflammation that may look like complicated diverticulitis on a CT scan. Endoscopy helps sort this out: Crohn’s typically shows a cobblestone pattern, small shallow ulcers, and sometimes granulomas on biopsy. Ulcerative colitis, by contrast, spreads continuously from the rectum upward, a pattern that doesn’t match the localized pouch inflammation of diverticulitis.
A stool test measuring calprotectin, a protein that rises with intestinal inflammation, can offer a clue. In patients with inflammatory bowel disease, calprotectin levels average about four times higher than in those with diverticular disease. However, there is enough overlap that the number alone isn’t definitive. Doctors weigh it alongside age, symptom patterns, and imaging before deciding whether to pursue colonoscopy.
Segmental Colitis Associated With Diverticulosis
This condition, sometimes called SCAD, sits in an unusual diagnostic space. It involves inflammation of the colon lining between diverticula, but it is not the same as diverticulitis and behaves more like a mild form of inflammatory bowel disease. It mainly affects men over 50. The hallmark finding is that the rectum looks completely normal on endoscopy while the sigmoid colon shows diffuse inflammation, a pattern called “rectal sparing.”
SCAD tends to follow a benign course. In long-term studies spanning over 20 years, more than 80% of well-defined cases either resolved spontaneously or responded to a mild anti-inflammatory medication alone. Antibiotics, the standard treatment for acute diverticulitis, are not typically needed. The distinction matters because misdiagnosing SCAD as recurrent diverticulitis could lead to unnecessary procedures.
Urogenital Conditions
The colon sits close to the urinary tract and reproductive organs, so problems in those systems frequently mimic lower abdominal pain from diverticulitis. Kidney stones passing through the ureter can cause severe left-sided pain that radiates to the groin, closely resembling a diverticulitis flare, though the pain is usually more colicky (coming in waves) rather than constant. A bladder infection can produce suprapubic pain and urgency that overlaps with the urinary symptoms diverticulitis sometimes causes when an inflamed colon irritates the bladder wall.
In women, several gynecological conditions enter the picture. Ovarian cysts, particularly when they rupture or twist, cause sudden lower abdominal pain with nausea. An ectopic pregnancy produces similar pain with vaginal bleeding, and endometriosis can create chronic left-sided pelvic pain that waxes and wanes with the menstrual cycle. In men, prostate infections and inflammation of the seminal vesicles can send pain into the same region. A urine test, pregnancy test, or pelvic ultrasound is often enough to shift the diagnosis toward one of these conditions.
Other Bowel Conditions
Several less common gastrointestinal conditions round out the list of mimics:
- Ischemic colitis occurs when blood flow to a segment of the colon drops, causing sudden pain and bloody diarrhea. It tends to affect older adults with vascular risk factors and often involves the same left-sided territory as diverticulitis.
- Appendicitis is the classic right-sided abdominal emergency, but when the appendix sits in an unusual position or the sigmoid colon loops to the right, the two conditions can look remarkably similar.
- NSAID colitis results from long-term use of anti-inflammatory painkillers, which can erode the colon lining and produce localized inflammation that mimics a diverticulitis flare.
- Infectious colitis from bacterial or parasitic infections can cause fever, pain, and bowel wall thickening that overlap with diverticulitis on imaging.
How Doctors Tell the Difference
A CT scan of the abdomen and pelvis with contrast is the primary tool for sorting diverticulitis from its mimics. It can identify the inflamed diverticula, detect abscesses or perforations, and often reveal alternative diagnoses like epiploic appendagitis, ovarian pathology, or kidney stones in the same study. Blood work showing elevated white blood cells and inflammatory markers supports an active infection or inflammation but does not pinpoint the source on its own.
When the acute episode resolves, a colonoscopy is typically recommended, especially for a first episode, to rule out colorectal cancer and inflammatory bowel disease. The timing matters: colonoscopy during an active flare carries a higher risk of complications, so it is usually scheduled six to eight weeks after symptoms settle. For cases where the picture remains unclear, stool calprotectin testing, urine analysis, or pelvic imaging can help narrow the field further.