Impact of radiologist interpretation of CT in PET-CT imaging

Abstract

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Objectives: To assess whether radiologists’ reading of the CT portion of the PET-CT identifies significant additional lesions and whether these findings result in major clinical management changes.

Methods: 418 consecutive patients (pts) aged 13-87, 256 male, 162 female, underwent FDG PET-CT scans for known or suspected cancer between 07/05-12/05. Only those pts without a diagnostic CT within 1 month prior to the PET-CT were included. The CT portion of the PET-CT was read by a nuclear medicine or radiology resident or fellow with 1 of 3 designated radiologists and dictated separately from the PET report, which was read with 1 of 5 nuclear medicine faculty physicians. Typically the PET portion was read on the day of scan and CT portion next morning. The radiologists were aware of the PET results and had access to fused PET-CT images. The PET-CT system used was a 2-slice Siemens Biograph. Particular attention was paid to 5 major findings, which are not FDG avid: small pulmonary nodules, lymph nodes, pneumothorax, aortic aneurysm, and renal cell carcinoma. Other CT findings were listed as minor.

Results: The major findings identified by radiologists, but not mentioned by nuclear medicine faculty were FDG-negative lung nodules (typically sub-cm) in 62 pts(14.8%), 28 FDG-negative lymph node/soft tissue masses (6.7%), 1 pneumothorax, 1 pneumoperitoneum, 8 aortic aneurysms (1.9%) and no renal cell carcinoma. These make up a total of 24% of the cases. However, major clinical management changes as a result of these findings only occurred in 3 pts: one with a 7-cm AAA who is now in preparation for surgical repair and another one with enlarged right iliac lymph nodes that were subsequently excised. The pt with pneumothorax did not require chest drain. The pt with pneumoperitoneum underwent laparotomy for perforation of duodenal ulcer. The remaining 7 aneurysms are being followed, as are the cases of small pulmonary nodules. The minor radiology findings were: calcified granulomas 67 (16%), atherosclerotic calcifications 33 (7.9%), kidney/liver cysts 20 (4.8%), emphysema 18 (4.3%), gallstones 14 (3.3%), pericardial effusion 10 (2.4%), lung blebs 9 (2.2%), thyroid nodules 7 (1.7%), pleural effusion 5 (1.2%), adrenal adenoma 5 (1.2%) and kidney stones 5 (1.2%). Other <1% findings include hiatal hernia, ascites, sinus disease, uterine fibroids, hydronephrosis, focal pneumonitis, and ventral hernia. None of these led to major clinical management changes.

Conclusions: The reading of the CT portion of a PET-CT study often identifies FDG-negative lesions; however, it infrequently leads to major clinical management changes in oncology patients. Nevertheless, given the severity of some of these findings, it seems warranted that the CT portion of the examination be carefully examined by a physician with appropriate CT experience.