Diverticulosis of the appendix: CT and MRI findings

Clinical History

An asymptomatic 68-year-old male patient with a previous history of renal tuberculosis was imaged for a non-cyst right renal nodule found in a routine renal ultrasound, at an outpatient facility. Physical examination was unremarkable. No significant laboratory abnormalities were found.

Imaging Findings

An abdominopelvic CT was performed to evaluate a renal nodule found in a routine ultrasound. Apart from the renal findings, caecal and appendiceal diverticulosis were incidentally diagnosed. Several millimetric appendiceal diverticula were found along the entire length of the appendix. They appeared as round air-filled outpouchings around the appendix wall. No signs of diverticulitis (prominent enhancement of the diverticulum wall with surrounding fat stranding) were present.
Due to the rarity of appendiceal diverticulosis and for academic reasons, MRI followed for additional characterization, confirming the CT findings.
An abdominal ultrasound (images not shown) was also performed showing a normal-sized appendix with some millimetric appendiceal diverticula, although these were not clearly depicted due to the appendix being not enlarged and the millimetric size of the diverticula in a patient with a bad sonographic profile.

Discussion

Appendiceal diverticulosis (AD) was first described in 1893 and it is a relatively rare entity. The prevalence of AD in patients undergoing appendectomy is about 1% of all appendectomy specimens. [1]

Most appendiceal diverticula are pseudodiverticula, with herniation of the mucosa through the muscularis. They may be single or multiple, usually measure less than 0.5 cm, and are more often located along the distal third of the appendix. [2]

AD is usually an incidental finding and clinically asymptomatic. [2] It has clinical significance for two reasons: inflammation of diverticula can lead to diverticulitis of the appendix and there is a well-established association of diverticulosis with appendiceal neoplasms.

Concerning diverticulitis of the appendix, this is an entity clinically distinct from acute appendicitis and much rarer. It affects older patients (usually >30 years of age), has a more insidious onset, and lacks the characteristic migratory pain location and the gastrointestinal symptoms seen in classic appendicitis. These features may lead to delayed diagnosis, resulting in a four times higher rate of perforation and a 30-fold increase in mortality when compared with simple uncomplicated appendicitis, owing to a thinner diverticulum wall. [2]

The association with appendiceal neoplasms can be explained by the fact that tumours located proximally in the appendix cause obstruction with increased intraluminal pressure favouring the development of diverticula. Excessive mucous production by the tumour can also contribute to increased intraluminal pressure. [3]

On ultrasound, an appendiceal diverticulum usually presents as a well-defined hypoechoic, rounded or oval-shaped nodular lesion abutting the muscular layer of the appendix. [4]
On CT, it appears as a round outpouching beyond the margin of the appendix that can contain fluid, air, or enhancing soft tissue. Diverticular inflammation is seen as prominent enhancement of the diverticulum wall with surrounding fat stranding. [5]
The literature regarding MRI findings of AD is very sparse. [6] The normal appendix appears as a blind-ended tubular structure on coronal T1WI and T2WI with intensity similar to muscle. [7]

Some authors advocate that prophylactic appendectomy should be considered for incidentally discovered diverticula, either by preoperative radiological investigations or during an exploratory operation, to prevent inflammation with possible perforation and to rule out the possibility of a coexisting neoplasm. [2]

AD is occasionally encountered on imaging. Radiologists should recognize and stress this entity, not only because diverticula may become symptomatic and cause significant complications, but also because a coexisting neoplasm of the appendix should be excluded.

Differential Diagnosis List

Final Diagnosis

Diverticulosis of the appendix

URL:	https://www.eurorad.org/case/12095
DOI:	10.1594/EURORAD/CASE.12095
ISSN:	1563-4086