Normal variants of a photon-deficient area in the lower sternum demonstrated by bone SPECT

A highly variable normal appearance of the sternal area makes interpretation difficult on planar bone imaging. These normal variants occur especially in the area above the xiphoid process of the sternum in which an oval photopenic area on anterior planar images may be seen. This finding is most likely caused by localized incomplete fusion.

Of a group of 188 patients, 35 patients (33 men, 2 women; age range, 30 to 85 years; mean age, 57 years) were examined with sternal SPECT and planar bone imaging. These patients, who had no history of sternal trauma, surgery, radiation, or infection, were referred for bone scan for metastatic work-up (n = 20), back pain (n = 6), and other conditions (n = 9). Thus 11 of 35 (31%) patients had a SPECT study that showed a photopenic area in the lower sternum.

The incidence of this normal variant was higher than the 2% to 7.7% previously reported, indicating improved detection by SPECT. The normal variant appears to be less apparent on planar bone images and is seen more clearly on SPECT images.

Differentiation from malignancy appears to be related to lesion symmetry, location, midline, and evenly distributed radioactivity surrounding the edge of the photopenic area.