Steal phenomenon-induced lung perfusion defects in pulmonary arteriovenous fistulas: assessment with automated perfusion SPECT-CT fusion images.

PURPOSE

Lung perfusion impairment in patients with pulmonary arteriovenous fistula (AVF) was evaluated by automated deep inspiratory breath-hold (DIBrH) perfusion single-photon emission computed tomography (SPECT)-CT fusion images.

METHODS

Participants were 14 patients with a single (N=6) or multiple nodular AVFs (N=8) diagnosed by contrast-enhanced CT scan and/or pulmonary angiography. After the injection of 185MBq Tc-99m-macroaggregated albumin, a whole-body scan was obtained to quantify an intrapulmonary right-to-left shunt. Subsequently, DIBrH SPECT was obtained using the continuous rotating acquisition mode of a dual-headed SPECT system, which was automatically coregistered with DIBrH CT. The anatomic relationship between AVF and perfusion defects was assessed on the fusion images.

RESULTS

The whole-body scan depicted systemic organs indicating the presence of an intrapulmonary right-to-left shunt in all the patients. DIBrH SPECT showed 34 perfusion defects in these patients, which were located at the AVF and in the surrounding lungs of the AVF on the fusion images, regardless of the absence of morphologic abnormality on CT in all the patients. These defects were considered to be caused by the 'steal phenomenon' associated with the high and fast pulmonary arterial flow to each AVF, which were more extensive and severe in the multiple AVFs compared with a single AVF (P=0.0012), occasionally extending to the entire lobe with AVF or even to the adjacent lobe. In five patients, the fusion images detected a total of six tiny AVFs with unexpectedly extensive 'steal phenomenon'-induced defects, which had been missed by other radiological imaging techniques. The summed value of the shunt index estimated by the whole-body scan and the lung perfusion defect extent estimated by DIBrH SPECT was significantly correlated with PaO2 in all the patients (P < 0.0001), with a better correlation compared with the shunt index alone.

CONCLUSION

In addition to the right-to-left shunt, 'steal phenomenon'-induced perfusion defects are common in the surrounding lung of pulmonary nodular AVF and cause hypoxemia. DIBrH SPECT-CT fusion images contribute to the objective evaluation of 'steal phenomenon'-induced lung perfusion impairment in AVF and the detection of tiny, subtle AVFs that may be missed by other radiological imaging techniques.