Benedikt Michael Schaarschmidt MD, Presenter: Nothing to Disclose

Johannes Grueneisen, Abstract Co-Author: Nothing to Disclose

Philipp Heusch MD, Abstract Co-Author: Nothing to Disclose

Verena Ruhlmann, Abstract Co-Author: Nothing to Disclose

Gerald Antoch MD, Abstract Co-Author: Speaker, Siemens Medical AG Speaker, Bayer AG Speaker, BTG International Ltd

Christian Buchbender, Abstract Co-Author: Nothing to Disclose

Incidental masses and cysts are frequent findings in abdominal imaging. While clearly malignant or benign findings do not pose a diagnostic problem, indeterminate findings require further diagnostic workup. The aim of this study was to investigate whether 18F-FDG-PET/MRI with its superior soft tissue contrast and functional MRI-data can reduce the number of indeterminate findings compared to 18F-FDG-PET/CT.  

164 patients with full-dose, contrast-enhanced, whole-body (WB) 18F-FDG-PET/CT and subsequent 18F-FDG-PET/MRI were enrolled in this retrospective study. 18F-FDG-PET/CT was performed 60min after the injection of a mean dose of 270MBq followed by 18F-FDG-PET/MRI (mean time after tracer injection: 146min). Two independent readers examined both modalities in separate sessions. Incidentalomas of upper abdominal organs detected on morphological images and incidental tracer uptake were classified in three categories: most likely benign, indeterminate, and most likely malignant. Discrepancies were resolved in a consensus reading. McNemar's test was performed to test for differences between both modalities with regard to classification of incidentalomas.  

A total of 663 incidental findings was recorded (416 in 18F-FDG-PET/CT and 649 in 18F-FDG-PET/MRI, p<0.001). Among these were 276, 250, 14, 17, 0 and 0 cystic and 32, 19, 24, 0, 16 and 1 solid lesions of liver, kidney, spleen, adrenal gland and gallbladder according to 18F-FDG-PET/MRI. Of these incidental lesions 96 were indeterminate in 18F-FDG-PET/CT and 47 in 18F-FDG-PET/MRI, respectively (p<0.001). 70 lesions classified indeterminate in 18F-FDG-PET/CT could be resolved in the corresponding 18F-FDG-PET/MRI examination. On the other hand, 18F-FDG-PET/CT resolved indeterminate PET/MRI-findings in 6 cases.  

Although 18F-FDG-PET/MRI goes along with more incidental findings in the upper abdomen, it has less indeterminate findings than contrast-enhanced 18F-FDG-PET/CT. Patients undergoing 18F-FDG-PET/MRI may profit from a higher diagnostic confidence compared with 18F-FDG-PET/CT.

Incidentalomas require an additional diagnostic workup. This study shows that 18F-FDG-PET/MRI has less indeterminate findings than 18F-FDG-PET/CT and may reduce the number of additional diagnostic procedures required.

Schaarschmidt, B, Grueneisen, J, Heusch, P, Ruhlmann, V, Antoch, G, Buchbender, C, Upper Abdominal Incidentalomas in [18]F-FDG-PET/CT and [18]F-FDG-PET/MRI: Which Modality Has Less Indeterminate Findings?.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045520.html