What are hypodensities?

Answer 1

Thyroid nodules are fluid-filled or solid lumps that form within the thyroid. A hypodense nodule is simply a less dense nodule.

Answer 2

Density is a measurement of mass per unit of volume, so a hypodense area has less mass for a given volume.

Typically this means it weighs less for a particular size. The implications of this depend on the particular tissue being asked about, and by what is causing the hypodensity.

Answer 3

Since hypo means "less, lower, too little, etc." (as opposed to hyper, meaning "too much", more", etc.) it means less dense, or lower denseness.