One of the most common types of ultrasound studies is evaluation of the right upper quadrant, henceforth referred to as the RUQ. The other quadrants are surely jealous, as the RUQ is the only one to have a namesake imaging study. But the RUQ looms large for a reason—several reasons, actually. Before we get to that, some of you may be asking…
…”the right up quadrant of what, exactly, good sir?”
Well, imagine you have fallen asleep at a frat party and your good friend Connor decided to draw on your abdomen with a permanent marker. Connor was neither too mean nor particularly creative, and drew vertical and horizontal lines intersecting at your belly button. The four roughly rectangular regions created by this cross form the four quadrants of the abdomen. You get a gold star if you guessed the right upper quadrant is the upper one on the right.
Let’s see what’s behind quadrant number one!
The gallbladder, which lies inside the RUQ of your abdominal cavity, is a common cause of abdominal pain. While much abdominal pathology is better evaluated with CT, the gallbladder is particularly well seen with ultrasound.
Other structures routinely evaluated on RUQ ultrasound include the pancreas, liver, bile ducts, and right kidney. The first three structures—along with the gallbladder—have close functional and anatomic relationships to each other (see illustration below). Parts of the stomach, small bowel, and colon also extend into the RUQ, but these structures are usually difficult to evaluate with ultrasound (because they contain air) and not routinely imaged on RUQ ultrasound.
Why do I need all these organs?
Before we address problems that can occur in the RUQ, it is first necessary to understand the normal anatomy and function of the underlying structures. The liver, gallbladder, bile ducts, and pancreas help with digestion. Apologies in advance to the hepatologists (liver doctors) out there; if I oversimplify too much, I’ll buy you a drink.
One of the functions of the liver—a large organ occupying much of the RUQ—is bile production. Bile helps to digest food, and needs to get from the liver to the first part of the small intestine, where it does its job. Bile ducts start as small branches throughout the liver—like tributaries of a river—and combine as they exit the liver to form first the common hepatic duct and, further down, the common bile duct. The common bile duct dumps into the small intestine at a place called the ampulla of Vater (yes, that’s a real thing).
Bile is also stored in the gallbladder, a sac-like structure beneath the liver which connects to the side of the common bile duct. After a meal, the body may need more bile than the liver can immediately produce, and the gallbladder contracts to push more bile into the common bile duct and small intestine.
The pancreas produces enzymes—amylase and lipase—to aid in digestion, and also excretes bicarbonate (i.e.baking soda) to neutralize stomach acid. The pancreas spans the middle of the upper abdomen just below the sternum, but part of it—called the head—extends into the RUQ. Pancreatic juices collect in branching ducts (analogous to bile ducts in the liver) and drain via the main pancreatic duct through that same ampulla of Vater (my favorite ampulla) into the small intestine.
The right kidney just happens to be in the neighborhood of the RUQ, but is not involved in digestion. Kidneys filter blood to produce urine, and problems with the right kidney can also cause RUQ pain.
When bad things happen to good gallbladders
Our magical journey through the RUQ now complete, let’s find out what happens when we throw some wrenches into the system.
- Gallstones and Cholecystitis: The most common culprit behind RUQ pain is the gallbladder, that worthless sac of bile causing more trouble than it’s worth sometimes (sorry, gallbladder, the truth hurts). Two related and sometimes coexisting abnormalities affecting the gallbladder are gallstones and acute cholecystitis.
- Gallstones are stones that form inside the gallbladder, in part due to imbalances in cholesterol and bilirubin (a pigment which gives bile its yellowish color). Too much cholesterol=formation of cholesterol gallstones. Ditto with bilirubin. Bile sitting around in the gallbladder too long is also felt to contribute to gallstone formation. Gallstones appear bright (echogenic) on ultrasound, and a shadow often projects behind them because they block the ultrasound beam.
- Stones inside your body are never good, and gallstones are no exception. Acute cholecystitis—inflammation of the gallbladder—occurs most commonly when a gallstone becomes lodged near the gallbladder neck, where it connects to the common bile duct. This obstructs the ability of the gallbladder to empty; the wall becomes thickened and inflamed, and the patient will often experience a jolt of pain when the ultrasound tech scans over the gallbladder. Acute cholecystitis can more rarely occur when no gallstones are present.
- Gallstones can sometimes pass into the common bile duct and get stuck near the ampulla of Vater, obstructing both the common bile duct and the pancreatic duct. Obstructing the common bile duct can back up the entire biliary system and prevent the normal excretion of bile. Radiologists measure the diameter of the common bile duct, and anything more than 6mm could mean it is obstructed. Bilirubin—a byproduct of the break down of red blood cells by the liver—is normally excreted in the bile. When the common bile duct is obstructed, bilirubin builds up in the blood and causes jaundice, a yellowish discoloration of the skin and whites of the eyes.
- Pancreatitis: If a gallstone blocks the pancreatic duct, pancreatic enzymes back up and the pancreas can actually start to digest itself (!), manifested as pancreatitis, or inflammation of the pancreas. Pancreatitis is usually better evaluated on CT, but we can sometimes see evidence—such as fluid around the pancreas—on ultrasound. A variety of other random fun things can cause pancreatitis, my favorite being the sting of a scorpion.
- Cysts: Cysts—focal collections of fluid—occur in the RUQ, most commonly in the liver and kidney. Cysts are well characterized on ultrasound, which is often used to troubleshoot suspected cysts that were initially seen on CT or MRI.
- Fatty Liver: If you have ever had fois gras, you have eaten fatty liver of a goose or duck. Humans get fatty livers too; perhaps Hannibal Lecter knows if “humain fois gras” is any good (see footnote for bonus “Silence of the Lambs” medical trivia). Fatty liver occurs when lipids, particularly triglycerides, accumulate in liver cells. It is often idiopathic, meaning we don’t know what caused it, but other causes include alcoholism, diabetes, and obesity. On ultrasound, a fatty liver looks diffusely bright (echogenic). Interestingly, this condition is reversible if the factor causing it can be removed.
- Kidney Abnormalities: I discussed bleeping renal cysts in another post, so I won’t go into more detail other than to say they are common. Two additional abnormalities that can be seen in the kidney on ultrasound are hydronephrosis and kidney stones.
- Hydronephrosis: As the kidneys filter blood, urine is produced and collects in the central part of each kidney, then flows through thin tubes called ureters down to the urinary bladder. If this drainage system becomes blocked, most commonly by a kidney stone, the resulting dilation can be seen on ultrasound.
- Kidney stones: Also known as renal calculi, kidney stones are common and can cause acute symptoms if they move into the ureters. On ultrasound, they are usually echogenic and produce a shadow, similar to gallstones. Very small stones—less than about 3mm—can be difficult to see on ultrasound, and CT is a better option if small stones are suspected.
- Cancer: Discovering cancer in one of the organs of the RUQ is fortunately a rare occurrence. The biliary system can become obstructed by cancers in the head of the pancreas or in the biliary system itself. Just like when a gallstone blocks the common bile duct, cancers can dilate the biliary system and cause jaundice. Different types of cancer can occur away from the biliary system as well, involving any of the organs in the right upper quadrant.
Other rare and unusual things show up in the RUQ, but they need to fill medical textbooks with something, so I will stop here. I hope you enjoyed the whirlwind tour through what is, in my opinion, the best quadrant of the abdomen (shh, don’t tell the appendix).
Questions? Comments? Please post below!
1. Hannibal Lecter’s famous quote, “I ate his liver with some fava beans and a nice chianti,” is actually a nerdy psychiatry joke. Monoamine oxidase inhibitors (MAOIs), some of the first antidepressants developed, work by increasing blood levels of tyramine, an amino acid. However, if tyramine levels rise too high, it can dangerously increase blood pressure, so one who takes MAOIs needs to limit foods that are high in tyramine. Guess what foods are famously high in tyramine? Liver, fava beans, and wine. So when Lecter says his famous line, some think he is indirectly telling us that he is not taking his MAOIs.