Appendiceal diverticulitis is inflammation of a diverticulum (true or pseudo) in the appendiceal wall. True diverticula are congenital and involve all wall layers (including muscularis propria); pseudodiverticula are acquired, representing herniation of mucosa and submucosa through a muscularis propria defect — a mechanism similar to colonic diverticulosis. Incidence is reported as 0.004-2.1% in appendectomy series. Mean age at diagnosis is around 50, with slight male predominance. Its clinical significance lies in mimicking acute appendicitis while having a much higher perforation rate (66% vs 20%) — because the pseudodiverticulum's thin wall, lacking muscularis propria support, cannot resist inflammatory pressure. On CT, findings resemble acute appendicitis, but careful examination reveals focal wall defect or outpouching, asymmetric periappendiceal inflammation, and typically normal or minimally dilated appendiceal lumen as distinguishing clues. Pathological examination is required for definitive diagnosis. Since underlying mucinous neoplasm or carcinoid tumor may trigger diverticulum formation, careful histopathological evaluation of the surgical specimen is mandatory.
Age Range
30-80
Peak Age
50
Gender
Male predominant
Prevalence
Rare
Appendiceal diverticulitis develops through two mechanisms. True diverticula are congenital and involve all wall layers (mucosa, submucosa, muscularis propria, serosa) — arising from focal wall weaknesses during embryological development and rarely seen (0.004-0.01%). Pseudodiverticula are much more common (1-2%) and form through herniation of mucosa and submucosa through weak points in the muscularis propria (especially at vasa recta entry points — on the mesenteric side), caused by increased intraluminal pressure (fecalith, lymphoid hyperplasia) or peristaltic dysfunction. This mechanism parallels colonic diverticulosis. Once a diverticulum forms, the chain of fecal material accumulation in the narrow neck → luminal obstruction → increased intraluminal pressure → mucosal ischemia → bacterial translocation begins as in acute appendicitis. However, the critical difference is that the pseudodiverticulum wall lacks muscularis propria — this thin wall is much less resistant to inflammatory pressure, hence the perforation rate reaches up to 66% (vs 20% in acute appendicitis). On CT, this pathophysiology is reflected as focal defect or outpouching in the appendiceal wall, focal/asymmetric periappendiceal inflammation, and typically preserved appendiceal lumen caliber — because the pathology is localized to the diverticulum and luminal obstruction is focal, not generalized. The underlying pathology is important: mucinous neoplasm or carcinoid tumor can cause luminal obstruction and secondary diverticulum formation.
Focal outpouching or defect in the appendiceal wall — direct imaging finding of the diverticulum. Best evaluated on thin-section CT (1-2 mm) and multiplanar reformats (coronal/sagittal). This finding is the most important clue in differential diagnosis from acute appendicitis — appendicitis shows smooth wall thickening, while diverticulitis shows focal outpouching.
Focal outpouching (diverticulum) of the appendiceal wall appears as a thin-walled focal evagination. The outpouching is typically localized on the mesenteric side (vasa recta entry points — weakest area of muscularis propria). Size may vary from a few mm to 1-2 cm. When inflammation is present, focal increased density in surrounding fat is seen. This finding is the most important CT finding distinguishing from acute appendicitis.
Report Sentence
A focal outpouching (diverticulum) measuring approximately ___ mm is seen in the appendiceal wall with surrounding focal inflammatory changes; consistent with appendiceal diverticulitis.
Periappendiceal fat stranding in appendiceal diverticulitis characteristically shows asymmetric and focal distribution — concentrated on the side where the diverticulum is localized. In acute appendicitis, fat stranding is typically diffuse and circumferential, symmetrically affecting the entire appendiceal circumference. This asymmetry reflects the inflammatory process starting from the diverticulum and spreading focally.
Report Sentence
Asymmetric/focal periappendiceal fat stranding is observed around the appendix, consistent with appendiceal diverticulitis.
In appendiceal diverticulitis, the appendiceal lumen typically remains normal caliber (<6 mm) or minimally dilated — different from the significant luminal dilation (>6 mm, often >10 mm) in acute appendicitis. This is because the pathology is localized to the diverticulum, not the appendiceal lumen. If luminal obstruction is absent or partial, appendiceal caliber is preserved.
Report Sentence
The appendiceal lumen is of normal caliber with accompanying periappendiceal inflammatory changes; this finding may be consistent with appendiceal diverticulitis.
On T2-weighted and fat-suppressed sequences (T2 fat-sat/STIR), focal high signal is seen around the appendix — reflecting inflammatory edema. Focal and asymmetric distribution is characteristic of diverticulitis. The diverticulum itself may be visible as a small outpouching with high T2 signal (fluid content). MRI is an alternative imaging modality when CT is contraindicated (pregnancy, young patients).
Report Sentence
Focal high signal is seen around the appendix on T2/STIR sequences, consistent with focal inflammatory changes; the possibility of appendiceal diverticulitis should be considered.
On US, focal wall irregularity or outpouching of the appendix may be seen. Focal hyperechogenicity in periappendiceal fat (inflammation) is observed. Appendiceal diameter is typically normal (<6 mm) or minimally increased. Appendix is localized using graded compression technique. US diagnostic sensitivity is lower than CT but is the first-choice imaging in pregnancy and young patients.
Report Sentence
Focal wall irregularity and surrounding focal hyperechoic fat are observed around the appendix; the possibility of appendiceal diverticulitis should be considered; CT correlation is recommended.
Due to frequent perforation (66%), focal periappendiceal abscess is an important complication of appendiceal diverticulitis. Abscess appears as a low-density collection with rim enhancement. Small air bubbles (perforation indicator) may be present. Abscess typically develops focally on the side where the diverticulum is localized — diffuse peritonitis is rarer but possible.
Report Sentence
A low-density collection (abscess) measuring approximately ___ cm with rim enhancement is seen around the appendix, consistent with perforated appendiceal diverticulitis; surgical consultation is recommended.
Criteria
Involves all wall layers (mucosa, submucosa, muscularis propria, serosa). Congenital, arising from wall weakness during embryological development. Incidence 0.004-0.01%, very rare.
Distinct Features
Wall thickness may be normal (all layers present). Perforation risk lower than pseudodiverticulum. Usually solitary and located near the tip of appendix.
Criteria
Only mucosa and submucosa herniation — does not include muscularis propria. Acquired, resulting from increased intraluminal pressure or peristaltic dysfunction. Incidence 1-2%, much more common.
Distinct Features
Thin wall (no muscularis propria) — very high perforation risk (66%). Usually localized on mesenteric side (vasa recta entry points). May be multiple. Mechanistic similarity with colonic diverticulosis.
Criteria
Underlying mucinous neoplasm or carcinoid tumor causing luminal obstruction and secondary diverticulum formation. Diagnosis made by detection of neoplasia in pathological specimen.
Distinct Features
Mass or focal thickening in appendiceal wall may be present on CT. Mucinous neoplasm shows low-density cystic dilation; carcinoid shows small enhancing solid nodule. Careful histopathological examination of surgical specimen mandatory.
Distinguishing Feature
In acute appendicitis, appendiceal lumen is diffusely dilated (>6 mm) with circumferential fat stranding; in diverticulitis, lumen is usually normal caliber with focal/asymmetric fat stranding. No focal wall outpouching in appendicitis.
Distinguishing Feature
Colonic diverticulitis is localized to cecum or sigmoid colon; appendiceal diverticulitis is specific to the appendix. Diverticulum is in cecal/colonic wall in colonic diverticulitis, in appendiceal wall in appendiceal diverticulitis.
Distinguishing Feature
Mucinous neoplasm is characterized by chronic cystic appendiceal dilation and low-density mucinous content; diverticulitis has acute inflammatory findings and focal wall defect in the foreground. Mucinous neoplasm is slowly progressive; diverticulitis has acute presentation.
Distinguishing Feature
Carcinoid tumor typically appears as a small enhancing solid nodule at the appendix tip; diverticulitis is characterized by focal wall outpouching and inflammation. Carcinoid is usually an asymptomatic incidental finding.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralAppendiceal diverticulitis requires emergency surgery (appendectomy) due to high perforation risk (66% vs 20% in acute appendicitis). Preoperative diagnosis is rarely made — the vast majority of cases are operated with a preoperative diagnosis of acute appendicitis and diagnosed on pathological specimen examination. Careful histopathological evaluation of the surgical specimen is mandatory — underlying mucinous neoplasm or carcinoid tumor must be excluded as these neoplasms may trigger diverticulum formation. Conservative treatment (antibiotics + percutaneous drainage) may be considered only in patients with high surgical risk.
Due to high perforation risk (66%), early surgery (appendectomy) is recommended. Preoperative diagnosis is rarely made — usually detected on pathologic specimen examination. When appendiceal diverticulitis is identified, careful pathological evaluation is needed to exclude underlying neoplasia.