This is a really simple way to teach medical students or junior doctors about diagnosing jaundice.
Obviously they should take a history and examine the patient but when we are talking about diagnosis of jaundice this question usually comes along. “If you could do one quick and easy test to tell you what the likely cause of jaundice is, what would that be?” The usual answer I get is liver function tests, but as we all know liver function tests don’t measure liver function! (The subject of a future blog). Ultrasound is readily available in just about all parts of the world and all care environments and can give a broad answer to what the cause of jaundice is. There are basically three different things that an ultrasound can show in the jaundiced patient.
1. There is no duct dilatation either in the liver or in the extrahepatic bile ducts. So basically this means that the cause of the jaundice is at a cellular level or involving microspcopic bile ducts too small to visualize on a scan. Most of the causes for cellular jaundice would be classified as “medical” jaundice such as viral hepatitis, drug induced cholestasis or hepatitis, metabolic disorders, autoimmune hepatitis, primary biliary cirrhosis and so on.
2A. All of the bile ducts inside the liver (intrahepatic) and outside of the liver (extrahepatic) are dilated. The level of obstruction to cause this ultraound picture must be at the lower end of the common bile duct. The most common causes would be benign reasons such as ductal gall stones and malignant causes such as pancreatic cancer. Less common causes might be benign stricture secondary to pancreatitis or malignant distal bile duct cholangiocarcionoma or periampullary cancer.
2B. Only the common bile duct is dilated. This may occur when a gallstone has blocked the lower end of the bile duct but there has not been sufficient time for the intrahepatic bile ducts to become dilated. The same could be true of a tumour but usually by the time clinical jaundice is evident both intra and extraheptic bile ducts will be dilated.
3. The intrahepatic bile ducts are dilated but the extrahepatic bile duct is collapsed and non-dilated. This ultrasound picture is not commonly seen and implies that the cause of obstruction is at the hilus of the liver. The diagnosis that must be considered and excluded in this situation is hilar cholangiocarcinoma. The other less common alternative diagnoses include primary sclerosing cholangitis, Mirrizzi syndrome and gall bladder cancer.
As already mentioned, blood tests don’t help a great deal in the diagnosis of jaundice except of course telling the level of jaundice (bilirubin) and providing some corroborative evidence such as autoantibodies, tumour markers or viral titres in the case of hepatitis. Classifying causes of jaundice on the basis of ultrasound provides a quick and easy schema for diagnosing jaundice which is applicable in primary care as well as hospital based practice. Best of all the students remember it!