1. Generally, medical words derived from Latin or Greek are pluralized according to guidelines in the recommended references. Occasionally, some physicians prefer to pluralize Latin terms in the same way that English words are pluralized, and the transcriptionist follows the dictator's preference unless it is incorrect. Many physicians dictate an incorrect plural for diverticulum; it is diverticula, not -ae or -i, as frequently dictated.
fistulas or fistulae fossas or fossae
hernias or herniae scleras or sclerae
2. See Apostrophes for further guidelines on plurals.