When is contrast needed for a CT scan of neck?

Contrast. Needed to look for cancer or infection and to see extent of penetrating trauma. Cta uses dye yo look at vessels in more detail.
Almost always. The neck has many anatomical structures in a very small space, without a lot of fat around them. Contrast helps to show differences in tissue blood flow (contrast enhancement), and shows where the vessels are, which better defines the anatomy. Sme diagnoses also cause contrast enhancement, which makes the diagnosis easier. If the concern is only with the spine, the ct can be without contrast.