Visible male nipple shadows in chest radiographs.

Objective: Annual company employee physical examinations are performed in Japan and include a chest X-ray. Among nodular shadows observed in the lower lung field, nipple shadow is a normal structure to be differentiated, and understanding its characteristics in chest X-rays aids in the interpretation of solitary nodular shadows.

Methodology: Chest X-rays from male employees over 35 years of age at two different companies were analysed for anatomical location, morphology, and size of nipple shadows. If unilateral or bilateral solitary nodular shadows in the lower lung field coincided with the lead nipple marker, we defined it as 'definitive' nipple shadow. If the nodular shadow was observed to be stable for at least 2 years at the typical nipple position, we defined it as 'possible' nipple shadow without confirmation with nipple marking.

Results: Typical nipple position, from the analyses of definitive nipple shadows (n = 15), was between the ninth and tenth posterior ribs and within 60 mm from the inner margin of the rib. The nipple was oval or round and did not exceed 15 mm in size. Incidence of definitive and possible (n = 25) nipple shadows was estimated as 3.5% of examined males (n = 1150). Thoracic computed tomography scanning was conducted in four cases, of which three cases involved solitary nodular shadows that did not coincide with the nipple marker, and one was for a newly formed nodular lesion not detected in previous chest X-rays.

Conclusion: Visible male nipple shadows are not rare and need to be differentiated among the solitary nodular shadows in the lower lung field.