Gallbladder sludge

Last revised by Calum Worsley on 16 Feb 2024

Gallbladder sludge, also known as biliary sand, biliary sediment, or thick bile, is a mixture of particulate matter and bile, normally seen as a fluid-fluid level in the gallbladder on ultrasound, corresponding to the precipitate of bile solutes. 

The term biliary microlithiasis is occasionally used as a synonym for sludge, however, this is not strictly correct. Microlithiasis refers to the tiny calculi (<3 mm) undetectable on normal transabdominal ultrasound. Sludge may include these microliths in its composition, but this is only one element of a variable mixture of crystals, proteinaceous debris, lysed cells and mucin 5.

These precipitates consist of cholesterol monohydrate crystals, calcium bilirubinate granules, calcium salts, and mucus secreted by the gallbladder 1

Factors that may contribute to gallbladder sludge include 8:

  • pregnancy - hormonal changes during pregnancy raise cholesterol levels in bile, causing sludge accumulation

  • rapid weight loss increases cholesterol secretion into bile, leading to sludge formation

  • diabetes

  • critical illness

  • organ transplantation

  • total parenteral nutrition

Gallbladder sludge appears as a low amplitude homogeneous echoes, layering on the posterior wall, and frequently forming fluid-fluid level with anechoic bile above it. 

  • it moves slowly with changes in patient position

  • sludge does not cause shadowing unless associated with gallstones 2

Sludge can get compacted forming a mass-like lesion referred to as tumefactive sludge 4

  • hypoechogenic well defined intraluminal mass

  • no posterior acoustic shadowing

  • no internal vascularity at color Doppler

  • mobility is not always demonstrated, therefore, raising differentials with polyps or gallbladder carcinoma 

  • T1: high-signal

  • T2: relatively hypointense compared to bile, though not as hypointense as formed calculi

  • T1 C+ (Gd): no enhancement

  • DWI/ADC: no diffusion restriction

On ultrasound consider

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