Rim sign (nuclear medicine) | Radiology Signs

Answer:

The rim sign is a curvilinear band of increased tracer activity in the liver parenchyma immediately adjacent to the gallbladder fossa, persisting on delayed images of a technetium-99m iminodiacetic acid study. It occurs together with the primary finding of non-visualisation of the gallbladder and is therefore an adjunct rather than a stand-alone sign. Its importance is prognostic: the rim sign is present in a minority of cases of acute cholecystitis, of the order of a quarter to a third, but its presence substantially increases the likelihood of gangrenous or otherwise complicated cholecystitis, which is why it should be reported explicitly to the surgical team. Standard practice is imaging for 60 minutes after injection; if the gallbladder has not filled, either morphine augmentation at 0.04 mg/kg with imaging for a further 30 minutes or delayed imaging at 3 to 4 hours is used to distinguish acute obstruction of the cystic duct from chronic cholecystitis and sludge. False non-visualisation occurs with prolonged fasting, total parenteral nutrition, severe intercurrent illness, hepatocellular dysfunction and chronic cholecystitis, so the clinical context must be weighed. Hepatobiliary scintigraphy has the highest sensitivity and specificity of the available tests for acute cholecystitis and is used when ultrasound, the first-line test, is equivocal, and CT correlates the rim sign with pericholecystic inflammatory change.

Why is it called so?

The band of increased activity forms a rim of hot liver around the cold gallbladder fossa.

Pathophysiology

Obstruction of the cystic duct by a stone causes gallbladder distension, wall inflammation and, if unrelieved, mural ischaemia and gangrene. The inflammatory process extends directly into the immediately adjacent liver parenchyma, where hyperaemia and inflammatory infiltration alter hepatocyte handling of the iminodiacetic acid tracer, delaying its clearance into the biliary canaliculi. Activity therefore persists in that segment of liver while the rest of the parenchyma clears normally, producing a focal hot rim. Because the pericholecystic inflammatory change is proportional to the severity of the gallbladder disease, the intensity and persistence of the rim track with gangrenous and perforated cholecystitis.

Alternative names: Hot rim sign; hepatobiliary rim sign; pericholecystic hepatic activity

Other associated named signs: Non-visualisation of the gallbladder, the cystic duct sign, and the sonographic Murphy sign with wall thickening and pericholecystic fluid

References

1. Bushnell DL, Perlman SB, Wilson MA, Polcyn RE. The rim sign: association with acute cholecystitis. J Nucl Med. 1986;27(3):353-6. PMID: 3712052.