Abdominal Adhesions and SIBO: How Scar Tissue Creates Bacterial Overgrowth

Every abdominal surgery leaves behind more than a skin scar. Inside the abdomen, the body's wound healing process produces bands of fibrous tissue called adhesions that connect surfaces that are not normally connected. These internal scar tissue bands form between loops of intestine, between the intestine and the abdominal wall, and between abdominal organs. In a landmark 1999 study published in the Lancet, Ellis and colleagues found that adhesions develop in 93% to 100% of patients after open abdominal surgery. Even laparoscopic procedures, which cause less tissue trauma, produce adhesions in 50-70% of cases. For SIBO patients, adhesions represent one of the most underrecognized structural root causes, creating areas of intestinal stagnation where bacteria accumulate and proliferate.

How adhesions form

Adhesion formation is the body's response to peritoneal injury. The peritoneum is the thin membrane lining the abdominal cavity and covering the abdominal organs. When this membrane is damaged by surgical incision, retraction, cauterization, drying (exposure to air during surgery), infection, or inflammation, the body initiates a repair process. Fibrin, the same protein involved in blood clotting, is deposited at the injury site. Under normal circumstances, the body's fibrinolytic system breaks down this fibrin within 72 hours, and the peritoneum heals cleanly.

When the fibrinolytic system is overwhelmed or impaired, typically because of extensive tissue damage or ongoing inflammation, the fibrin matrix persists. Fibroblasts migrate into the fibrin deposit and lay down collagen, transforming the temporary fibrin bridge into a permanent band of scar tissue. Blood vessels grow into the adhesion, making it a living structure that can contract, thicken, and remodel over time. The result is a fibrous band connecting two surfaces that should glide freely against each other. These bands can range from thin, filmy connections to thick, vascular cords capable of compressing or distorting the structures they attach to.

How adhesions cause SIBO

Adhesions cause SIBO through mechanical disruption of normal intestinal flow. The small intestine relies on unimpeded forward movement of its contents, driven by peristalsis and the migrating motor complex, to prevent bacterial stagnation. When an adhesion band kinks, compresses, or tethers a loop of small bowel, it creates a partial obstruction. Contents slow down or pool proximal to the restriction point. This stagnation provides bacteria with time to proliferate in a nutrient-rich environment that would normally be swept clean every 90-120 minutes by the MMC.

Which surgeries carry the highest risk

While any abdominal surgery can produce adhesions, the extent and clinical significance of adhesion formation varies with the type of procedure, the surgical approach (open versus laparoscopic), and the degree of peritoneal injury. Surgeries involving extensive dissection, bowel handling, or peritoneal contamination produce the most adhesions. Lower abdominal and pelvic surgeries are particularly associated with adhesions that affect the distal small intestine and ileocecal region.

Open abdominal surgeries carry the highest adhesion burden. Colorectal surgery, gynecological procedures (hysterectomy, ovarian cyst removal, endometriosis excision), and complex appendectomy are among the most adhesion-prone procedures. Cesarean sections are notable because of their frequency: with over 1.2 million C-sections performed annually in the United States, they represent the single largest source of abdominal adhesion formation. Bariatric surgery, particularly open Roux-en-Y gastric bypass, also produces significant adhesions. Even cholecystectomy (gallbladder removal), though often laparoscopic, can produce adhesions in the right upper quadrant that affect the duodenum and proximal small bowel.

Position-dependent symptoms: a key clue

One of the most distinctive features of adhesion-related SIBO is position dependence. Because adhesions are physical bands attached to specific locations, they exert their effects differently depending on body position. Patients may notice that symptoms worsen when sitting (particularly hunched forward), when bending at the waist, or when lying on a specific side. Standing or lying flat may partially relieve symptoms by changing the angle of the adhesion-related kink or compression. This positional pattern is unusual in motility-driven SIBO, where symptoms are more consistently related to meals and time of day rather than body position.

The imaging challenge

One reason adhesions are underdiagnosed as a SIBO root cause is that they are notoriously difficult to visualize on standard imaging. CT scans, MRI, and ultrasound can detect the consequences of adhesions (such as dilated bowel loops proximal to a point of obstruction, or bowel fixation in an abnormal position) but typically cannot visualize the adhesion bands themselves. Adhesions are definitively diagnosed only during surgery or laparoscopy, when they can be directly observed. This diagnostic limitation means that adhesion-related SIBO is often a clinical diagnosis based on surgical history, symptom patterns, and exclusion of other causes.

Cine MRI, a dynamic MRI technique that captures bowel movement in real time, shows promise for assessing adhesion-related bowel restriction. By observing whether segments of bowel move freely or are tethered in place, radiologists can infer the presence and location of adhesions. However, this technique is not widely available and is not yet part of standard clinical practice for SIBO evaluation.

Treatment implications for adhesion-related SIBO

Standard SIBO treatment protocols (antimicrobials followed by prokinetics) address bacterial overgrowth and motility but do not address the structural component of adhesion-related SIBO. If an adhesion is kinking the small bowel and creating a stagnation point, killing the bacteria without relieving the obstruction will lead to recurrence as bacteria repopulate the stagnant segment. This is why adhesion-related SIBO often requires a multimodal approach: antimicrobial treatment to reduce current bacterial load, visceral manipulation or surgical adhesiolysis to address the structural restriction, and prokinetic therapy to optimize motility between treatment sessions.