A CST is assisting a surgeon on a lumbar discectomy procedure. The CST removes tissue from the jaws of the pituitary rongeur that the surgeon is using to remove the disc material. He looks at the specimen and says to the physician, “I think you should stop and look at this—it doesn’t look like disc material to me.” The surgeon asks, “How so?” and the CST responds, “It has a lumen.” The surgeon examines the tissue, has the circulator page a genitourinary specialist, completes the discectomy, and assists on the repair of the ureter. A CST is assisting a surgeon on a lumbar discectomy procedure. The CST removes tissue from the jaws of the pituitary rongeur that the surgeon is using to remove the disc material. He looks at the specimen and says to the physician, “I think you should stop and look at this—it doesn’t look like disc material to me.” The surgeon asks, “How so?” and the CST responds, “It has a lumen.” The surgeon examines the tissue, has the circulator page a genitourinary specialist, completes the discectomy, and assists on the repair of the ureter.

What did the CST have to know in order to make this critical observation?