a. Nipple shadow may appear exactly like lung nodule i.e well-rounded opacity up to 1cm in size. However, upon closer look, nipple shadow would have a hollow ring around it. This is due to air that got trapped between the nipple and the skin.
b. Nipple shadow is usually in the 5th intercostals space in the axillary mid-line. This position may change with positioning.
c. Nipple shadows are usually bilateral and symmetrical. However, occasionally only 1 shadow is seen. This is usually the left nipple for some unknown reason.
d. If you are still in doubt, put a nipple marker (any metallic object) and repeat the radiograph.