Extracardiac findings on computed tomography attenuation correction: Is it worth paying extra attention?

Abstract

Due to the profound impact of attenuation artifacts on diagnostic accuracy, especially specificity, 1 several methods like computed tomography attenuation correction (CTAC), 2 prone myocardial perfusion image (MPI) acquisition, 3 or external radionuclide sources like 153 Gd 4 have been developed. CTAC has evolved as the most common standard used, since it not only improves diagnostic accuracy and outcome prediction by reducing attenuation artifacts 1,5,6 but also enables the evaluation of coronary calcium scoring, 7 offering substantial added diagnostic and prognostic value. 8,9 Furthermore, the application of a CTAC can discriminate defects caused by left bundle branch block from real perfusion defects in SPECT MPI 10 and allows diagnosis of pulmonary hypertension by determining the diameter of the main pulmonary artery in CTAC. 11 Moreover, incidental findings can be found in CTAC with a high prevalence. 12,13 These early results on incidental findings in CTAC have recently been confirmed by a systematic review and meta-analysis demonstrating a prevalence of 44% incidental extracardiac findings, 16% major incidental extracardiac findings, and 0.7% previously unknown malignancies. 14 Although most of these findings might be negligible, some are of clinical relevance. In fact, it is recommended by the EANM procedural guidelines for radionuclide MPI with SPECT and SPECT/CT that noncontrast-enhanced CT scans for AC and also scouts should be additionally screened by a physician fully trained in CT readings. 15 Accordingly, the review of all visible non-cardiovascular structures is recommended by the Society of Cardiovascular Computed Tomography in patients undergoing non-contrast calcium scoring and coronary CT angiography. 16 Despite these recommendations, the field still remains controversial. Considering the high prevalence of these findings, concerns are reported about increased cost and radiation exposure due to follow-up scans, morbidity of biopsy or resection, and anxiety of both the patient and the physician about a non-significant pathology. In addition, only a minority of incidental findings that seem clinically significant in CTAC might actually be detrimental to patient outcome. 17 Hence, considering doubtful clinical relevance, the debate is ongoing whether it is worth paying extra attention to extracardiac findings.In the current issue of the Journal of Nuclear Cardiology, Zadro et al. investigated the prevalence of extracardiac findings on CTAC for MPI by SPECT and evaluated the prognostic outcome. The authors retrospectively screened 1506 patients who underwent MPI SPECT and low-dose CTAC. Extracardiac findings of CTAC were captured and classified as major or minor abnormalities. The prevalence of minor and major extracardiac findings was high, which were found in 830 (55.1%) and 212 (14.1%) patients, respectively, whereas 464 (30.8%) patients had no abnormality. Aneurysm of the aorta (33.8%), liver cirrhosis (27.2%), non cystic hypodense lesions of the liver (18.5%), and suspicious nodules in the ...