About 5 weeks ago I taught the second-year level undergraduate anatomy students their first class on to the anatomy of the trunk, something we would usually teach using fantastically prosected cadaveric specimens and full-bodied plastic models. This time however we had about 50 mins to chat all-things-trunk online… we did our best!
From the duodenum (ju-o-dee-num NOT du-wah-de-num thank you Mericans) all the way to the ascending colon, our journey started with the transpyloric plane.
The transpyloric plane
An integral landmark for gastrointestinal surgeons who have their hands deep in/around a persons foregut, but a very difficult feature for the average clinician (without x-ray vision). You see, this line runs horizontal through the most distal part of the stomach (the pylorus) and is impossible to identify with any certainty from the outside.
To the everyday MSK clinician, knowing where the transpyloric plane is about as useful as a wet sock. The most interesting thing about it is that it was invented by a guy named Viscount Addison who was also into topography (using 10,000 measurements from 40 bodies, Addison discovered that a horizontal line drawn exactly between the jugular notch and the pubic symphysis went directly through the pylorus #eureka?).
But for the clinician seeking that little bit more to spice up their life, the transpyloric plane aligns horizontally with the body of L1, the first and fourth parts of the duodenum, the start of the superior mesenteric artery, the hila of the kidneys, the L) and R) colic flexures and the conus medullaris).
BUT this plane is just too difficult to find without futuristic CT or MRI goggles so unless you’re reading abdominal MRI/CT scans then this won’t come up much in clinic, but for the the MSK clinicians out there of more use is the subcostal plane, the line that bridges the antero-inferior most parts of the left and right ribcage (usually the anterior border of rib 10).
The Subcostal Plane
At LEAST a clinician can identify the subcostal plane by palpating the inferior most aspects of the ribs on either side (not ribs 11 and 12, those pseudo tricksters!) and by visualising a line between them. Even so, when would identifying the subcostal plane be useful?
As aforementioned, this plane tells us the position of the 10th rib (specifically it’s costal cartilage). Using this we can work up 1 more rib (onto rib 9) to find the level of the transpyloric plane (don’t you love a full circle).
The subcostal plane also aligns with the body of L3, so by anteriorly palpating rib 10 (the inferior-most rib element) and working directly posterior from here (note: not following the bone of the rib) we will end up on the spinous process of L3 (probably more accurately the L2/3 interspinous space because the lumbar vertebral bodies are slightly inferior relative to their spinous process).
The subcostal plane also forms the inferior border for the epigastric region of the abdomen (a region where referred pain from the foregut/the liver, pancreas, gall bladder and stomach is common), and the superior border of the umbilical region (where referred pain from the midgut/ the distal duodenum, jejunum, ileum, ascending colon and proximal half of the transverse colon is felt).
The Takeaway
A clinician who was born a FON (freak of nature) with MRI vision can visualise the transpyloric plane through a patient’s skin to identify the positions of a myriad of foregut intestinal and vascular structures.
A boring human clinician can confidently forget about the transpyloric plane, BUT a normal human clinician CAN confidently use the SUBCOSTAL plane to identify lumbar vertebral levels, identify lower rib levels and identify sources of abdominal pain.
We hope this enlightened you to a new anatomical feature that might come in handy during your next patient consultation!