Adenomyomatosis

[6] Black pigment gallstones can form in Rokitansky–Aschoff sinuses of the gallbladder after the fourth to fifth decades of life in absence of the typical risk factors for bilirubin supersaturation of bile.

[7] Abdominal ultrasound has low accuracy in differentiating gall bladder adenomyomatosis from cancer and is operator dependent.

Ultrasound findings may show thickened gall bladder wall, tiny anechoic spaces (Rokitansky–Aschoff sinuses or RAS), and twinkling artifact (or comet-tail reverberation).

Comet tail reverberation, which is due to reflections from cholesterol crystals, is a highly specific sign for adenomyomatosis.

[9] In fat-suppression MRI, RAS present with small, rounded, high signal intensity foci, called “pearl necklace sign”.

Adenomyomatosis of the gallbladder as seen on ultrasound [ 2 ]
Non-contrast abdominal ultrasound and contrast-enhanced ultrasound (CEUS) of adenomyomatosis of the gallbladder: [ 3 ]
a The fundus of the gallbladder wall was thickened and the GB wall was obscure.
b The intramural echogenic foci were detected by high frequency transducer.
c CEUS—arterial phase (22 s) —heterogeneous hyper-enhancement and wall was intact.
d CEUS—venous phase (34 s) the anechoic spaces were more clear.