Nipple shadow
Nipple shadows refer to the silhouettes of the nipples on frontal chest radiographs, which may mimic solitary pulmonary nodules (SPNs).
Epidemiology
Nipple shadows are apparent on ~7.5% (range 3.5-11%) of frontal chest x-rays .
Pathology
It has been proposed by Miller et al. that solitary pulmonary nodules that reach some or all of the following criteria be considered nipple shadows :
- bilateral and symmetric
- "fuzzy" margins or radiolucent "halo"
- sharp lateral border and poorly defined medial border (may be present only on PA projections )
- nodules are in a characteristic position:
- male: between the 5 and 6 ribs anteriorly
- female: at the inferior aspect of the breast shadow
- were not present on a very recent film
- prominent nipples may be visible on a lateral projection
However, if there is doubt whether a nodular opacity represents a nipple shadow or not, a repeat chest x-ray with nipple markers should be performed , albeit at a financial cost and further radiation dose to the patient.
There is always the rare occurrence of a real solitary pulmonary nodule being overshadowed by a nipple shadow.
Radiographic features
Plain radiograph
On chest radiograph the following features are present:
- nipple shadows are nodular opacities that are consistent in shape, size and position :
- oval or round
- 5-15 mm in diameter
- between the 9 and 10 ribs posteriorly or the 5 and 6 ribs anteriorly
- tend to have incomplete margins due to their attachment to the chest wall
Differential diagnosis
- solitary pulmonary nodule
- pleural or extrapleural lesions
