The lower horizontal watershed is located at the level of the T12.

• A. Cannot determine
• B. True
• C. False
• D. Not applicable

Answer: (B)

The idea here is that the trunk has imaginary horizontal watershed lines that separate regions whose lymphatic drainage tends to follow different major channels. The lower horizontal watershed marks the boundary between drainage that mostly follows pathways toward the thoracic duct via the abdomen and lower trunk, and drainage that tends to head toward the pelvic and inguinal channels. In ACOLS MLD teaching, this boundary aligns with the level of the T12 vertebra, around the transpyloric region. That alignment is why stating that the lower horizontal watershed is located at T12 is the correct understanding. Minor individual variation can occur, but T12 is the standard reference level used in training.