A 63-year-old man was admitted to our hospital with epigastralgia. Ultrasonography showed thickening of the wall of the gall bladder fundus. Magnetic resonance cholangiopancreatography revealed a cystic lesion on the fundus suggesting Rokitansky-Aschoff sinus (RAS) . Endoscopic retrograde cholangiopancreatography illustrated an elevated lesion on the fundus. No abnormal signal was detected by positron emission tomography. These diagnostic imaging results suggested adenomyomatosis, but the differential diagnosis of cancer remained. The patient opted for surgery instead of strict monitoring as his brother had died of gallbladder cancer. The patient underwent laparoscopic cholecystectomy. The surgically-obtained specimen revealed RAS in the thickened wall of the gall bladder fundus. Around the RAS, small muscle proliferation and lymphocyte infiltration were observed. The pathological diagnosis was adenomyomatosis of the gall bladder with chronic cholecystitis. No evidence of malignancy was found.
