The block faces of specimens with obvious lumen openings.
Any specimen that is a transverse section of a hollow structure or a specimen containing a lumen will almost always be placed in the block face to show the lumen or other opening in cross-section on the final slide. For any organs with very large lumen's in which the tube has been transected, you will embed on the cut surface to demonstrate the lining and layers present. Of special concern are specimens with very tiny lumen openings, such as temporal arteries or vas deferens. Since the lumen opening is so tiny, it is sometimes difficult to see. Some laboratories may lightly dip the end of the tiny tube opening in black ink. This indicates the "end" that should be placed down in the block face. Some laboratories may submit such tiny tubes whole and ask that they be cut into cross-section at embedding. This allows the histologist to clearly see the opening during dissection. Other means to flag these specimens can be by using an abbreviation on the cassette such as "vas" for vas deferens, alerting the histologist that the specimen contained will need to be embedded on end to show the lumen in cross-section.