Fig1: CT scan of 57 year old female shows multiple hypodense small lesions of fatty attenuation seen in the gall bladder suggestive of cholesterol gall stones. Fig 2: USG of gall bladder shows multiple calculi in the GB.
Gall stones are of two types: 1. Cholesterol stones and 2. Pigment stones.
Cholesterol stones are made primarily of cholesterol of 70-80%. Where as pigment stones contain only 20% of cholesterol. Ultrasound is the most sensitive and best investigation for the diagnosis of cholelithiasis. CT can pick up calcified gall stones and cholesterol stone which contain more amount of cholesterol. Cholesterol stones appear dark on the background of isoense bile on CT. CT can miss gallstones which are not calcified.