Adenomyomatosis of the Gallbladder: 'Comet Tail' Artifact and Rokitansky–Aschoff Sinuses
Pathogenesis and Morphology
Adenomyomatosis belongs to the group of hyperplastic cholecystoses. It is based on the thickening of the gallbladder wall due to the formation of intramural diverticula (Rokitansky–Aschoff sinuses) with accompanying proliferation of smooth muscle and epithelium. The condition is characterized by mucosal hyperplasia and thickening of the muscular layer of the wall. Cholesterol crystals may deposit within these sinus pockets.
Ultrasound Features
The key ultrasound feature is multiple 'comet tail' artifacts emanating from debris in the Rokitansky–Aschoff sinuses; the sinuses themselves may not always be visualized. Additionally, a twinkling artifact is described with color Doppler mapping. Small cystic spaces and intramural echogenic foci are determined in the wall.
Forms of Adenomyomatosis
| Form | Localization / Characteristic |
|---|---|
| Focal (most common) | More often in the fundus area; may appear as a mass with internal cystic spaces, intramural echogenic foci, and 'comet tail'/twinkling artifacts |
| Segmental | Annular thickening or strictures of the gallbladder forming an 'hourglass' appearance |
MRI Confirmation
The diagnosis is easily confirmed on MRI: T2-bright cystic spaces with a characteristic 'string of beads appearance' are demonstrated.
Differential Diagnosis
According to ExpertDDx and Diagnostic Ultrasound, when the gallbladder wall is thickened, the differential includes:
• Gallbladder carcinoma;
• Chronic cholecystitis;
• Xanthogranulomatous cholecystitis;
• Emphysematous cholecystitis;
• Cholesterosis;
• Adenomatous polyp.
The key to a benign diagnosis is the 'comet tail' artifacts from Rokitansky–Aschoff sinuses and the 'string of beads' appearance on MRI.
Nature of the 'Comet Tail' Artifact
The 'comet tail' is a V-shaped reverberation artifact emanating from a hyperechoic point. In the context of the gallbladder, it arises from debris/cholesterol crystals in the Rokitansky–Aschoff sinuses and, unlike microcalcifications, does not produce a pronounced acoustic shadow.
Frequently asked questions
What artifact is pathognomonic for adenomyomatosis?
'Comet tail' artifacts emanating from debris in the Rokitansky–Aschoff sinuses, as well as the twinkling artifact. The sinuses themselves may not be visualized.
Where is focal adenomyomatosis most commonly located?
In the fundus area of the gallbladder. It may appear as a mass with internal cystic spaces and intramural echogenic foci.
How to confirm the diagnosis if in doubt?
On MRI: T2-bright cystic spaces with a characteristic 'string of beads' appearance are demonstrated.
What does the segmental form cause?
Annular thickening or strictures of the gallbladder forming an 'hourglass' appearance.
What should be primarily differentiated?
From gallbladder carcinoma, chronic, xanthogranulomatous, and emphysematous cholecystitis, cholesterosis, and adenomatous polyp.