epiploic appendages

**Anatomy** - Small (1–2 cm thick, 0.5–5 cm long), pedunculated, serosa-covered outpouchings of subperitoneal fat along the colon, usually in two rows adjacent to the anterior and posterior taeniae coli. Typically 100–150 in number. - Present from the cecum to the rectosigmoid junction; most numerous in the sigmoid and transverse colon. The rectum has none. - Each is supplied by 1–2 small branches of the vasa recta, with a single draining vein through a narrow stalk. This is why they are prone to torsion and ischemia. - Together with the **taeniae coli**, **haustra**, and a **large lumen** (compared with the small bowel), they are a gross feature distinguishing the colon from the small bowel. - Function is uncertain. Proposed roles include cushioning, immune or protective roles, and fat storage.

**Epiploic appendagitis (key clinical correlate)** - Pathophysiology: torsion of the appendage or spontaneous thrombosis of its draining vein leads to ischemia, then aseptic inflammation and fat necrosis. - Risk factors: obesity, hernias, and strenuous exercise. It is most common in ages 20–50. - Presentation: acute, localized, sharp lower quadrant pain. It is most often left-sided (sigmoid), but a right-sided presentation mimics appendicitis. A palpable tender mass may be present. Fever, leukocytosis, nausea and vomiting, and changes in bowel habits are typically absent or minimal, and inflammatory markers are normal or only mildly elevated. - Differential: diverticulitis (left) and appendicitis (right). Omental infarction is also on the differential. - Diagnosis: CT is the study of choice. It shows an oval, fat-attenuation lesion (<5 cm) abutting the colon with a hyperattenuating rim ("hyperdense ring sign") and surrounding fat stranding. Often a central dot (the thrombosed vessel) is visible. There is no bowel wall thickening, which distinguishes it from diverticulitis. - Treatment: conservative, with NSAIDs or analgesics. It is self-limited, usually resolving in 1–2 weeks. Surgery is rarely needed. Antibiotics are not indicated.

**Other associations** - A detached, calcified appendage can become a **peritoneal loose body** ("peritoneal mouse"), usually an incidental finding. - Appendages can act as the lead point for **intussusception** or can twist around bowel and cause **obstruction** (rare). - They can herniate into a hernia sac and become inflamed. - Appendages can be involved in diverticulitis, because diverticula often occur at sites where the vasa recta penetrate the colonic wall, adjacent to the appendages.

**Board pearls** - "Acute, localized lower quadrant pain, afebrile, normal WBC, and a CT showing a fat-density ovoid lesion with a hyperdense rim next to the colon" → epiploic appendagitis → conservative management. - Do not confuse **epiploic appendages** (colon) with the **vermiform appendix** or the **greater omentum** (also called "epiploon"). - Colon features to remember: **taeniae coli**, **haustra**, **epiploic appendages**.