Epiploic Appendagitis
Epiploic appendagitis is inflammation of one of the small fat-filled pouches that hang from the outer surface of the colon. It occurs when a pouch twists on its narrow stalk or when the vein draining it clots, cutting off its blood supply and causing localized inflammation. The result is sudden, sharply localized abdominal pain in an otherwise well person—most often on the left, where it closely mimics diverticulitis, and sometimes on the right, where it mimics appendicitis. It is entirely self-limiting, resolving on its own within one to two weeks with nothing more than pain relief. Its importance lies almost entirely in recognizing it, since a characteristic CT appearance can spare a patient antibiotics, hospital admission, or an unnecessary operation.
What is it?
The outer surface of the colon carries roughly 50 to 100 small pouches of fat, each covered by peritoneum and attached to the bowel by a narrow stalk. These are called epiploic appendages, or appendices epiploicae. They typically measure one to two centimetres in length, hang in two rows along the colon, and are most numerous and largest along the sigmoid and transverse colon. Their function is not fully established, though they have been proposed to act as cushioning, to play a role in immune defence and in absorbing material from the peritoneal cavity, and to contribute to blood supply of the colon wall.
Their structure is what makes them vulnerable. Each appendage receives its blood supply through one or two small arteries running through a narrow stalk, and drains through a single small vein. This combination—a pendulous, mobile, fat-filled structure supported by a thin pedicle carrying a limited blood supply—leaves them susceptible to two closely related events.
Torsion occurs when an appendage twists on its stalk, mechanically compressing the vessels within it. Spontaneous venous thrombosis occurs when the draining vein clots without any twisting. In both cases the result is the same: the appendage loses its blood supply, becomes ischaemic, and generates a localized inflammatory reaction in the peritoneum immediately surrounding it. That inflammation, in a small area of peritoneum with rich sensory innervation, produces pain that is disproportionately sharp and precisely localized relative to the small size of the structure involved.
The condition is described as primary when it arises this way, spontaneously. Secondary epiploic appendagitis refers to inflammation of an appendage caused by an adjacent process—diverticulitis, appendicitis, cholecystitis, or pancreatitis—inflaming it from outside. The distinction matters, because secondary appendagitis is a marker of another disease that requires its own treatment, whereas primary appendagitis needs nothing but analgesia.
Risk factors are modest and not always present. Obesity is the most consistently reported, presumably because larger appendages are more prone to twisting. Recent rapid weight loss is also associated, possibly because appendages become more pendulous as surrounding fat diminishes. Unaccustomed strenuous exercise and sudden vigorous movement or position change are reported precipitants. Hernias have been implicated occasionally. Many patients have no identifiable risk factor at all.
The typical presentation is fairly distinctive once known.
Pain begins suddenly, is sharp, and is remarkably well localized—patients can often indicate the exact spot with a fingertip, which is unusual for most abdominal conditions. It is constant rather than colicky, and it may be aggravated by coughing, deep breathing, stretching, or bending. The lower left abdomen is the most common location, followed by the lower right.
Examination reveals focal tenderness over that same point, sometimes with mild rebound, and occasionally a small palpable tender mass. Importantly, guarding and rigidity are absent, and the abdomen elsewhere is soft.
The most useful diagnostic feature is what is missing. Patients with epiploic appendagitis look and feel well apart from the pain. Fever is absent or minimal. Nausea, vomiting, and loss of appetite—prominent in appendicitis—are uncommon. Change in bowel habit is unusual. Blood tests are typically normal or barely abnormal, with a normal white cell count and normal or only slightly raised inflammatory markers. The mismatch between significant localized pain and an otherwise entirely unremarkable clinical and laboratory picture is the pattern that should prompt consideration of this diagnosis.
Because the condition was described long before cross-sectional imaging existed, it was historically diagnosed only at surgery, when a surgeon operating for suspected diverticulitis or appendicitis found a small twisted, infarcted appendage and nothing else. CT has changed this entirely. The condition now has a characteristic appearance that allows confident diagnosis without any intervention, and much of its clinical importance now lies in radiologists and clinicians recognizing that appearance.
CT of the abdomen and pelvis with intravenous contrast demonstrates a small oval lesion, typically one to four centimetres across, lying immediately adjacent to the outer wall of the colon. Its centre has the density of fat, matching the appendage’s contents. It is surrounded by a thin ring of higher density corresponding to the inflamed peritoneal covering—often described as a hyperattenuating rim. Surrounding fat shows inflammatory stranding. A small central dot of higher density is often visible, representing the thrombosed central vein, and is a particularly helpful sign when present.
Two negative findings are as informative as the positive ones. The wall of the adjacent colon is normal or only minimally thickened, which argues strongly against diverticulitis, where wall thickening is typically prominent. And the appendix is normal, excluding appendicitis. Radiologists also assess for the features of omental infarction, a closely related condition producing a similar but generally larger lesion.
Ultrasound can demonstrate a non-compressible, hyperechoic ovoid mass at the exact point of maximal tenderness, without internal blood flow on Doppler. It is operator-dependent but useful in younger and thinner patients and where radiation avoidance matters.
MRI shows the same features without radiation and is used selectively, including in pregnancy.
The differential diagnosis includes diverticulitis, which is the most common misdiagnosis and typically involves colonic wall thickening, more diffuse inflammation, and a more systemically unwell patient; appendicitis, which involves a thickened appendix and more prominent nausea, anorexia, and inflammatory response; omental infarction, which is closely related, more often right-sided, and typically produces a larger area of inflamed fat; mesenteric panniculitis; and in appropriate patients, ovarian pathology including torsion or a ruptured cyst, ureteral stone, and inflammatory bowel disease. Because it is uncommon and unfamiliar, epiploic appendagitis is frequently not considered until CT suggests it.
Important to Know
The single most important fact about epiploic appendagitis is that it is benign and self-limiting, and that recognizing it prevents unnecessary treatment rather than enabling any treatment. Care is typically managed by emergency physicians and primary care clinicians, with surgical or gastroenterology input only where the diagnosis is uncertain.
Treatment consists of oral analgesia and reassurance. Nonsteroidal anti-inflammatory drugs are generally effective where not contraindicated, and paracetamol is an alternative. Patients can eat normally and resume usual activity as comfort allows. No dietary restriction, bowel rest, or activity limitation is required.
Antibiotics have no role. This point deserves emphasis because unnecessary antibiotic courses are commonly given in practice, almost always because the episode has been diagnosed as diverticulitis. Antibiotics do not shorten the illness, do not affect outcome, and expose the patient to side effects, resistance, and cost without benefit. Where CT has established the diagnosis confidently, withholding antibiotics is appropriate.
Hospital admission is not required for typical cases. Patients are managed as outpatients with advice on what to expect and on when to seek reassessment.
The expected course is reliable. Pain typically improves substantially within two to four days and resolves within one to two weeks. Some patients have milder residual discomfort for longer. The imaging abnormality persists well beyond symptom resolution, sometimes for months, gradually shrinking. In a proportion of cases the infarcted appendage calcifies and may detach, occasionally persisting as a small calcified body loose in the peritoneal cavity or adherent to a peritoneal surface—an entity known as a peritoneal loose body or, informally, an abdominal mouse. This is entirely benign, though it occasionally appears on later imaging and can cause confusion if its origin is not recognized.
Because the imaging changes outlast the symptoms, repeat imaging is generally unnecessary in a patient recovering as expected, and a persistent abnormality on a scan performed weeks later does not indicate treatment failure.
Surgery has essentially no role in typical cases. Historically, most cases were diagnosed at operation, and laparoscopic removal of the affected appendage does relieve symptoms promptly. But given that the condition resolves on its own, operating on a correctly diagnosed case exposes a patient to the risks of surgery for no benefit. Surgery is now reserved for the rare situation where the diagnosis remains genuinely uncertain despite imaging, where symptoms fail to resolve over an extended period, or where a complication such as abscess formation or adhesion-related obstruction develops—all of which are uncommon.
Recurrence is uncommon but reported, and a second episode at a different site is possible since there are many appendages. Recurrent episodes do not generally change management.
An important caveat concerns secondary appendagitis. When CT shows an inflamed appendage alongside features of another condition—significant colonic wall thickening, diverticular changes, an inflamed appendix, or gallbladder disease—the appendage inflammation is a secondary phenomenon and the primary condition drives treatment. Attributing everything to the appendage in that setting would be a diagnostic error, which is why the state of the adjacent bowel and organs is assessed carefully rather than the appendage viewed in isolation.
Patients should be advised on when to return: worsening rather than improving pain, spreading pain, fever, vomiting, or systemic illness all warrant reassessment, since they suggest either an alternative diagnosis or an uncommon complication.
Care is typically coordinated by emergency or primary care clinicians with radiology input, which in this condition is decisive. Imaging, laboratory, and clinical findings are interpreted together, with the combination of focal pain and an unremarkable systemic picture being as informative as the scan itself.
Patient education plays an important role, largely because the condition is unfamiliar and its name unhelpful. Understanding that it involves a small fatty structure on the outside of the colon rather than the colon itself, that it has nothing to do with the appendix despite the similar name, that it is not an infection and does not require antibiotics, that it resolves on its own within a couple of weeks, and that lingering scan findings do not mean lingering disease all contribute to appropriate care and prevent unnecessary anxiety and treatment.
Red flag symptoms include pain that is worsening rather than improving after several days; pain that spreads or becomes generalized; fever with chills; persistent vomiting; abdominal distension with inability to pass gas or stool; a rigid, exquisitely tender abdomen; rapid heart rate, low blood pressure, or confusion; and rectal bleeding. These warrant prompt reassessment, as they suggest an alternative diagnosis such as diverticulitis, appendicitis, or perforation rather than uncomplicated epiploic appendagitis.