Planar scintigraphy and SPET with 99Tcm-HMPAO-labelled leukocytes in patients with median sternotomy: normal patterns

The aim of this study was to determine the normal planar and SPET patterns of the thoracic distribution of 99Tcm-hexamethylpropylene amine oxime (99Tcm-HMPAO) in 20 patients who had undergone a previous median sternotomy and without infectious complications at follow-up. The study included anterior and oblique anterior planar views at 4 and 20 h. SPET of the chest was also carried out at 4 and 20 h. At 4 h, the planar views showed low background vascular activity in the lungs and cardiac region in addition to the sternal uptake, which showed two patterns: homogeneous in five patients and heterogeneous in 15. A long and narrow defect of uptake along the sternal midline was the most characteristic finding. At 4 h, in addition to the background vascular activity in the lungs and cardiac region, the greatest uptake on SPET was in the sternum anteriorly and the marrow spine posteriorly without any focal uptake, allowing visualization of the mediastinum free of focal activity. At 20 h, both the planar and SPET images showed a higher organ-to-background ratio. Knowledge of these post-surgical patterns will make it easier to interpret planar and SPET images when 99Tcm-HMPAO-labelled leukocytes are used in the diagnosis of mediastinitis and sternal infections in patients who had previously undergone median sternotomy. Planar views were better for the assessment of sternal uptake, but SPET views were better for the direct visualization of the mediastinum by eliminating overlapping sternal uptake.