Adenomyomatosis of the gallbladder

Adenomyomatosis of the gallbladder is a hyperplastic cholecystosis of the gallbladder wall. It is a relatively common and benign cause of diffuse or focal gallbladder wall thickening. It is most easily seen on ultrasound and MRI. 

Epidemiology

Adenomyomatosis is relatively common, found in ~9% of all cholecystectomy specimens ⁵. It is typically seen in patients in their 5^th decade. The incidence increases with age, presumably the result of protracted inflammation (see below). There is a female predilection (M:F=1:3).

It is most often an incidental finding and usually requires no treatment. It may be found more often in chronically inflamed gallbladders (which are at higher risk for carcinoma), but it is not a premalignant lesion in itself ⁵.

Clinical presentation

Adenomyomatosis per se is usually asymptomatic. It is, however, frequently associated with chronic biliary inflammation, most commonly gallstones (25-75%), but also seen in cholesterolosis (33%) and pancreatitis ².

Pathology

Adenomyomatosis is one of the hyperplastic cholecystoses. There is hyperplasia of the wall with the formation of Rokitansky-Aschoff sinuses (intramural diverticula lined by mucosal epithelium) penetrating into the muscular wall of the gallbladder, with or without gallbladder wall thickening. Cholesterol accumulation in adenomyomatosis is intraluminal, as cholesterol crystals precipitate in the bile trapped in Rokitansky-Aschoff sinuses.

Radiographic features

Three morphological types of adenomyomatosis are described:

• fundal (localised)
• segmental (annular)
• generalised (diffuse)

Ultrasound

• mural thickening (diffuse, focal, annular)
  • segmental/annular form is especially difficult to distinguish from gallbladder carcinoma
• comet-tail artefact: echogenic intramural foci from which emanate V-shaped comet tail reverberation artefacts are highly specific for adenomyomatosis, representing the unique acoustic signature of cholesterol crystals within the lumina of Rokitansky-Aschoff sinuses ⁴

CT

• abnormal gallbladder wall thickening and enhancement are common but non-specific CT features of adenomyomatosis
• Rokitansky-Aschoff sinuses of sufficient size can be visualized; a CT rosary sign has been described, formed by enhancing epithelium within intramural diverticula surrounded by the relatively unenhanced hypertrophied gallbladder muscularis

MRCP (or oral cholecystography)

Historically, oral cholecystograms were performed; however, due to low sensitivity and a high rate of contrast hypersensitivity, they have now been largely replaced by MRCP which does not rely on contrast opacification of the gallbladder lumen. MRCP is also able to detect:

• mural thickening
• focal sessile mass
• fluid-filled intramural diverticula (pearl necklace sign)
• hourglass configuration in annular types

MRI

• pearl necklace sign refers to the characteristically curvilinear arrangement of multiple rounded hyperintense intraluminal cavities visualized on T2-weighted MR imaging and MRCP  ⁴

Nuclear medicine

• FDG-PET
  • metabolic characterization with PET has been suggested as a useful adjunct in problematic cases ⁴, but there have also been cases with increased uptake in areas of adenomyomatosis, leading to false positive results ⁶

Treatment and prognosis

Cholecystectomy may be performed as a result of one or more of the following:

• patient symptomatic with right upper quadrant pain (often due to gallstones)
• appearances (especially when focal) may be difficult to distinguish from malignancy

Differential diagnosis

General imaging differential considerations include:

• gallbladder carcinoma
• Phrygian cap
• gallbladder polyp (cholesterol polyp)
• cholelithiasis
• papillomatosis ⁸

Exclusion of gallbladder cancer may be most problematic in segmental and focal cases. Focal adenomyomatosis may appear as a discrete mass, known as an adenomyoma.