The sigmoid colon is the final, S-shaped segment of the large intestine, connecting the descending colon to the rectum. Located on the left side of the abdomen, its primary function is to store fecal matter and absorb the last remnants of water before waste is eliminated. When medical imaging, such as a CT scan, reveals “mural thickening,” it refers to an abnormal increase in the width of the colon wall. This finding is non-specific; it indicates an underlying process like inflammation, infection, or tissue infiltration rather than a diagnosis itself. Investigating the cause of this thickening is necessary to determine the correct diagnosis and management plan.
The Most Common Inflammatory Cause: Diverticulitis
The most frequent cause of isolated sigmoid colon thickening is acute diverticulitis, which stems from diverticulosis. Diverticulosis involves the formation of small, sac-like pouches (diverticula) that protrude through weakened areas of the colon wall. These pouches are common in the sigmoid colon.
Diverticulitis occurs when a diverticulum becomes obstructed, often by hardened stool, leading to inflammation and localized infection. The inflammatory response causes edema within the colon wall tissues, resulting in the thickening observed on imaging. Patients typically experience sudden, persistent pain in the left lower quadrant of the abdomen, often accompanied by fever or a change in bowel habits.
On a CT scan, diverticulitis presents with a thickened sigmoid wall, usually over four millimeters, surrounded by pericolic fat stranding. This stranding indicates inflammation in the adjacent fatty tissue. Uncomplicated diverticulitis involves only inflammation and thickening. Recurrent inflammation can lead to permanent thickening of the muscular layer.
Other Key Causes Requiring Investigation
While diverticulitis is common, other causes of sigmoid thickening require thorough medical evaluation, especially those involving chronic inflammation or malignancy. Colorectal adenocarcinoma, the most common form of colon cancer, causes thickening through the infiltration of malignant cells into the bowel wall layers. Cancerous thickening is often localized, asymmetric, or irregular, which helps distinguish it from the uniform thickening seen in acute inflammation.
Chronic inflammatory bowel diseases (IBD), such as Crohn’s disease or ulcerative colitis, are frequent causes of colonic thickening. Crohn’s disease involves transmural inflammation, affecting all layers of the colon wall and leading to persistent thickening. Ulcerative colitis primarily involves the mucosal lining, which may cause less pronounced wall thickening.
Acute conditions like infectious colitis and ischemic colitis can also cause rapid sigmoid thickening. Infectious colitis results from severe bacterial, viral, or parasitic infections that trigger an inflammatory response within the colon wall. Ischemic colitis occurs when a temporary reduction in blood flow leads to oxygen deprivation and subsequent tissue swelling. Ischemic events often present with acute, cramping abdominal pain followed by the passage of blood in the stool.
Diagnostic Pathway and Medical Evaluation
The discovery of sigmoid colon thickening on an initial imaging study, typically a CT scan, initiates a structured diagnostic pathway. The CT scan assesses the severity of the thickening, identifies associated findings like pericolic fat stranding or abscesses, and rules out acute complications such as perforation. This initial information guides the subsequent evaluation.
Direct visualization of the colon lining is usually required through a colonoscopy or flexible sigmoidoscopy. These endoscopic procedures allow a physician to inspect the internal surface of the sigmoid colon for ulcers, polyps, or masses, and confirm the extent of inflammation. Endoscopy permits the collection of tissue samples (biopsies), which are examined under a microscope to confirm the exact diagnosis, such as identifying cancerous cells or inflammation consistent with IBD.
Laboratory tests provide supplementary information about the body’s systemic response. A complete blood count can reveal an elevated white blood cell count, indicating an active infection or severe inflammation. Inflammatory markers like C-reactive protein (CRP) are also measured to gauge the overall level of inflammation, helping to monitor disease activity and treatment response.
Treatment Strategies Based on Diagnosis
Treatment for sigmoid colon thickening depends entirely upon the confirmed underlying diagnosis, ranging from conservative management to surgical intervention. For most cases of uncomplicated diverticulitis, the management plan focuses on gut rest, often involving a liquid diet, and a course of oral antibiotics. For recurrent or complicated diverticulitis, a sigmoid colectomy may be necessary to remove the diseased segment of the colon.
Malignancy, such as adenocarcinoma, requires prompt treatment, typically involving surgical resection of the tumor, a surrounding margin of healthy tissue, and nearby lymph nodes. This may be followed by chemotherapy depending on the cancer stage. Treatment for chronic inflammatory bowel disease, like Crohn’s disease, involves long-term use of anti-inflammatory medications or advanced biologic therapies to suppress the immune response and promote mucosal healing.
Acute conditions like infectious colitis are managed with supportive care, including intravenous fluids, and specific antibiotics if a bacterial pathogen is identified. Ischemic colitis is frequently self-limiting, with treatment focused on supportive measures like bowel rest and addressing the underlying cause of reduced blood flow.