Filly's 11th Law
The clinical history is important!
I know you are thinking. “Seriously… this egg-head professor needs to tell me that ‘the clinical history is important?’” But, in the discussion below, I would like you to think about the clinical history in the context of Filly's Law #9: There are a few important things to know about statistics: Positive predictive value.
In virtually all diagnostic imaging situations you need to know whether it is the positive predictive value or the negative predictive value that should dominate your thinking in any given case. This particularly relevant in the patient sent to R/O Acute Cholecystitis.
If the patient has the correct clinical presentation: right upper quadrant pain, fever, and leukocytsosis, the identification of gallstones puts your positive predictive value for acute cholecystitis over the 90% mark. Make the diagnosis! If the clinical history also documents that the patient has a positive Murphy’s sign, you are probably at a 95% positive predictive value.
Many diagnosticians refuse to make this diagnosis unless they also observe gallbladder wall thickening – and some wait to see pericholicystic fluid. Waiting to see gallbladder wall thickening, pericholicystic fluid or sloughing of mucosa may further (but only slightly) increase your positive predictive value, but it will definitely slash your sensitivity!
An Emergency Medicine professor, with whom I had worked for years, said to me one day, “I don’t even know why I examine a patient with possible Acute Cholecystitis.” I know I am only going to immediately send them for a sonogram. I explained what I have stated above. He had never even considered that as relevant.