Prevalence and clinical impact of incidental findings on the unenhanced CT images of PET/CT scan in patients with multiple myeloma: the value of radiological reporting in the multimodal hybrid imaging

OBJECTIVE: In the hybrid Positron Emission Tomography/Computed Tomography (PET/CT) method, the functional evaluation is integrated with the morphological information provided by co-registered CT, still performed for attenuation correction and lesion localization. However, co-registered CT images could provide additional diagnostic information that PET alone could underestimate. To optimize the diagnostic potential of this hybrid examination, we evaluated the prevalence and the clinical significance of incidental findings detected on co-registered CT images in a cohort of multiple myeloma (MM) patients. PATIENTS AND METHODS: We evaluated 112 MM patients (mean age 65.8 y), who underwent [18F]FDG-PET/CT during their regular workup. All co-registered CT images were retrospectively reviewed by two expert radiologists and each non-myelomatous incidental finding (nM-IF) was collected and clinically graded according to a nMIF Reporting and Data System (nM-RADS). In addition, nM-IFs were classified according to anatomic localization (skull, lung, mediastinum, abdomen, breast, gastrointestinal, genitourinary and cardiovascular system and muscle/soft tissue). RESULTS: 163 nM-IFs were detected in 94/112 patients (83.9%) (mean value: 1.5 IFs per patient). The most interested anatomic districts were the lung (n=33; 20.2%), genitourinary (n=33; 20.2%) and gastrointestinal (n=30; 18.4%) systems. Focusing on the clinically significant findings (nM3+nM4), 92/163 (56.4%) IFs could have been required further investigations, of which 38/163 (23.3%) were potentially important and detected in 33/112 (29.5%) patients. CONCLUSIONS: The high percentage of potentially clinically significant IFs detected in MM patients emphasizes that co-registered CT images hold precious information often missed. Giving more relevance to co-registered CT with tailored acquisition and reconstruction protocols and dedicated reporting could optimize the potentiality of this multimodality imaging method with impact on clinical management.