Appendiceal abscess is an organized periappendiceal collection that develops as a complication of perforated or gangrenous appendicitis. A pus collection forms around the perforated appendix, walled off by omentum and adjacent bowel loops. CT characteristically shows a rim-enhancing collection with central low density. Treated with percutaneous drainage and/or delayed appendectomy.
Age Range
10-70
Peak Age
30
Gender
Equal
Prevalence
Uncommon
Appendiceal abscess is an advanced complication of acute appendicitis. Bacterial contamination from a gangrenous or perforated appendix spreads to the peritoneal cavity. The body's defense mechanisms (omental migration, fibrin deposition, adhesion of adjacent bowel loops) localize the infection, forming an organized collection. The abscess wall develops a capsule composed of granulation tissue and fibrosis — the pathologic basis for rim enhancement on CT. Abscess contents consist of pus (necrotic debris, bacteria, and neutrophil accumulation), explaining the central low-density (10-30 HU) appearance. Untreated, the abscess may enlarge leading to serious complications such as fistulization, sepsis, or portal pylephlebitis.
On portal venous phase CT, a collection with smooth ring-like enhancing wall and central low-density (10-30 HU) fluid content in the right lower quadrant adjacent to the appendiceal base represents the diagnostic finding of periappendiceal abscess. This pattern represents an organized infection collection encapsulated by granulation tissue.
Rim (ring-like) enhancing organized collection with central low density in the right lower quadrant adjacent to cecum and ileum. Collection typically measures 3-8 cm and wall thickness varies between 2-4 mm. Rim enhancement is smooth and homogeneous.
Report Sentence
A rim-enhancing collection measuring ... x ... cm is identified in the right lower quadrant, consistent with periappendiceal abscess.
Diffuse fat stranding, fascial thickening, and phlegmonous change are seen surrounding the abscess. Phlegmon represents unorganized inflammatory infiltration and indicates inflammation extending beyond the abscess wall. Reactive thickening of adjacent cecum and ileum walls may accompany.
Report Sentence
Widespread phlegmonous change and fat stranding are noted surrounding the collection.
Detection of extraluminal appendicolith within the abscess collection or periappendiceal area strongly supports perforation. The appendicolith has exited the appendiceal lumen and may appear 'floating' within the collection or adherent to the abscess wall.
Report Sentence
An extraluminal calcified appendicolith is identified within the abscess collection, supporting perforated appendicitis.
Reactive thickening and enhancement of the cecal wall adjacent to the abscess is seen. This finding may mimic cecal carcinoma ('appendicitis mimicking cecal carcinoma'). Cecal pole thickening may be focal or symmetric.
Report Sentence
Reactive thickening of the cecal wall adjacent to the abscess is noted; follow-up for malignancy exclusion is recommended.
Ultrasound demonstrates a complex fluid collection in the right lower quadrant. Internal structure is heterogeneous containing debris echoes, septations, and thick wall. Unlike anechoic simple fluid, internal echoes reflect pus and necrotic material.
Report Sentence
A complex collection measuring ... x ... cm with internal echoes and septations in the right lower quadrant is consistent with abscess.
On MRI, the abscess collection shows T2-hyperintense center and hypointense rim on T2-weighted sequences. Marked diffusion restriction on DWI (high b-value, low ADC) strengthens abscess diagnosis and differentiates from phlegmon or unorganized fluid.
Report Sentence
Collection showing T2 hyperintensity with diffusion restriction on DWI is consistent with abscess.
Criteria
Collection <5 cm, smooth-walled, no significant adhesion to surrounding organs
Distinct Features
Percutaneous drainage is usually sufficient. Interval appendectomy is planned at 6-8 weeks. Antibiotic therapy accompanies.
Criteria
Collection >5 cm, septated, multiple loculations, adhesion or fistula to surrounding organs
Distinct Features
Percutaneous drainage may be insufficient; surgical drainage may be required. Emergent surgery should be evaluated in the presence of fistula. Risk of obstruction in adjacent bowel loops.
Distinguishing Feature
In perforation, free air and diffuse free fluid are predominant without organized collection; abscess shows organized rim-enhancing collection and free air is usually absent
Distinguishing Feature
Uncomplicated acute appendicitis shows no organized collection, only dilated appendix and periappendiceal stranding
Distinguishing Feature
In adenocarcinoma, irregular solid mass and wall thickening predominate, rim-enhancing fluid collection is usually absent; however, tumor perforation may be complicated by abscess
Urgency
urgentManagement
interventionalBiopsy
Not NeededFollow-up
3-monthAppendiceal abscess requires urgent intervention. Treatment approach is determined by abscess size and patient condition: abscesses <3 cm may be treated with IV antibiotics alone; abscesses ≥3 cm require percutaneous drainage + antibiotics. Interval appendectomy is planned at 6-8 weeks. Post-drainage follow-up imaging is important to verify collection resolution. Colonoscopy is recommended in patients >40 years to exclude underlying appendiceal neoplasm.
Treatment of periappendiceal abscess depends on size and clinical status. Small abscesses (<3 cm) may be treated with IV antibiotics, while large abscesses require percutaneous drainage. Interval appendectomy is usually planned 6-8 weeks later. In the phlegmon stage, conservative treatment (antibiotics + follow-up) is preferred.