What is the sonographic Murphy sign on ultrasound of the gallbladder?
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Answer:
The sonographic Murphy sign is maximal tenderness elicited by direct pressure of the transducer over the sonographically localised gallbladder, which is what distinguishes it from the clinical Murphy sign obtained by palpation over the right upper quadrant. Together with gallstones it forms the core of the ultrasound diagnosis of acute cholecystitis, and the combination of stones with a positive sonographic Murphy sign has a high positive predictive value. Supporting findings are a gallbladder wall thicker than 3 mm, pericholecystic fluid, gallbladder distension beyond about 4 cm in transverse diameter, an impacted stone in the neck or cystic duct, wall hyperaemia on Doppler and sludge. Important limitations must be stated: the sign is unreliable or falsely negative in the patient who has received opioid analgesia, in the elderly or obtunded, in diabetic and other neuropathies, and above all in gangrenous cholecystitis, in which mural necrosis destroys the nerve endings and the sign is characteristically lost just as the disease becomes most dangerous. Wall thickening is itself non-specific and occurs with hepatitis, heart failure, hypoalbuminaemia, ascites and a contracted postprandial gallbladder. When ultrasound is equivocal, hepatobiliary scintigraphy is the most accurate test and contrast-enhanced CT or MRI assess complications such as perforation, emphysematous change and abscess.
Why is it called so?
The sign is the ultrasound equivalent of Murphy’s clinical sign of arrest of inspiration on palpation of the inflamed gallbladder.
Pathophysiology
Obstruction of the cystic duct by a calculus causes the gallbladder to distend and its wall to become inflamed and oedematous. The visceral peritoneum overlying the gallbladder and the adjacent parietal peritoneum are supplied by somatic afferents, so once inflammation reaches the serosal surface the pain becomes sharply localised and is provoked by direct pressure over the organ, which is what the transducer applies. In gangrenous cholecystitis the wall becomes ischaemic and necrotic, intramural nerve endings are destroyed and the pain may paradoxically diminish, so the loss of the sign in a systemically unwell patient with striated or irregular wall thickening, intraluminal membranes and absent mural flow should raise rather than lower concern.
Alternative names: Ultrasound Murphy sign
Other associated named signs: Rim sign on hepatobiliary scintigraphy, the WES sign of a stone-packed gallbladder and the hole sign of gallbladder perforation
References
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