Surface lines of the front of the thorax and abdomen. (Transpyloric is top horizontal line.)
The transpyloric plane, also known as Addison's plane, is an imaginary horizontal plane, located halfway between the suprasternal notch of the manubrium and the upper border of the symphysis pubis at the level of the first lumbar vertebrae, L1. It lies roughly a hand's breadth beneath the xiphisternum or midway between the xiphisternum and the umbilicus. The plane in most cases cuts through the pylorus of the stomach, the tips of the ninth costal cartilages and the lower border of the first lumbar vertebra.
The transpyloric plane is clinically notable because it passes through several important abdominal structures. It also divides the supracolic and infracolic compartments, with the liver, spleen and gastric fundus above it and the small intestine and colon below it.
Lumbar vertebra and spinal cord
The first lumbar vertebra lies at the level of the transpyloric plane. Despite the conus medullaris, the end of the spinal cord, being understood to terminate at the level of the transpyloric plane, there is significant variability. Up to 40% of people have spinal cords ending below the transpyloric plane.
The horizontal part of the duodenum slopes upwards to the left of the vertical midline, following which the vertical ascending part of the duodenum reaches the transpyloric plane. It ends in the duodenojejunal junction, which lies approximately 2.5 cm to the left of the midline and just below the transpyloric plane.
Despite the right kidney lying 1 cm lower than the left (right just below and the left just above the plane), to be practical, the surface markings are taken the same way. The hilum of the kidney on the left and right is taken as 5 cm from the vertical midline and is on the transpyloric plane.
The lower border of the spleen lies near the transpyloric plane.
- the left and right colic flexure
- the root of the transverse mesocolon.
- cisterna chyli (which drains into the thoracic duct).
The transpyloric plane relates to the three-dimensional mapping of the abdomen founded on more than 10,000 measurements completed on 40 bodies, that surgeon Viscount Addison took at the turn of the 20th century.
Addison reported his findings in a paper titled, "On the anatomical topography of the abdominal viscera in man, especially the gastro-intestinal canal" in which he established a baseline for the anatomy of the abdomen based on the arrangement of the map of the Earth. Using the suprasternal notch as the North Pole of the trunk, and the upper border of the pubic symphysis as the South Pole, he drew a vertical line joining these two points as his meridian. At the meridian's midpoint, he then drew a perpendicular line corresponding to the Equator. As this transverse plane crossed the pylorus, he called it the transpyloric plane.
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