Radiology for the USMLE: Abdominal Anatomy
- Nov 14, 2018
Imaging anatomy can be high-yield, especially on Step 1. Not only can you answer questions asked directly about what is visible in an image, but you are able to apply the anatomy to sort of “get your bearings” in order to answer higher order questions. For example, by knowing where the liver is in the abdomen when given a CT, and identifying that there is a gross abnormality, then you have instantly aided in cutting down your differential diagnosis by moving from “abdominal pathology” to “liver pathology.”
Cross-sectional abdominal anatomy is probably the most high-yield imaging anatomy to know for the USMLE. Here is a brief guide on how to start identifying organs on cross sectional imaging, particularly on CT of the upper abdomen:
Liver: The liver is one of the easiest organs to identify. You will find it anterior and right sided (remember right sided in radiology is the left side of the image). The liver is large and wedge shaped.
Kidneys: Remember the kidneys are retroperitoneal, so they will be posterior. Also remember there are two kidneys (unless they are showing you a horseshoe kidney). Look for two medium sized posterior organs.
Spleen: The spleen lives on its own laterally on the left side of the abdomen. Look for a left sided solid organ on a slice that also contains the liver.
Pancreas: The pancreas is more amorphous than the other abdominal organs and can assume many shapes based on the slice and the patient’s anatomy. Look for a lobulated bordered organ in the middle of the abdomen.
Aorta: Remember the descending aorta is a left sided retroperitoneal structure. Look for a posterior circular structure that is just anterior to the vertebral bodies.
Inferior Vena Cava (IVC): The IVC is a retroperitoneal right sided structure. Like the aorta it is posterior and circular, but it is right sided just anterior to the vertebral bodies.
Case courtesy of Dr. Ian Bickle, Radiopaedia.org, rID: 38003
Putting it All Together
When you come across a question containing the cross sectional anatomy detailed above, start off by trying to identify the organs. Then look for any obvious pathology. Remember, the USMLE tests obvious abnormalities, you do not need to be a radiologist to do well on USMLE imaging questions. After you have identified the pathologic structure, go back to the vignette and synthesize your new information with the nuggets of information you have already pulled from the vignette to arrive at your answer.