Diagnosis and differentiation of bronchioloalveolar carcinoma from adenocarcinoma with bronchioloalveolar components with metabolic and anatomic characteristics using PET/CT.

UNLABELLED (18)F-FDG PET has been reported to have reduced sensitivity in detecting bronchioloalveolar carcinoma (BAC) versus lung cancers with other histologies. However, there are CT characteristics that are suggestive of BAC, and potentially these could be useful to refine diagnostic criteria so PET/CT can be more accurate in the diagnosis of BAC. We correlated tumor size and density obtained with CT and glucose metabolism obtained with (18)F-FDG PET in patients with BAC and adenocarcinoma with BAC components (Adeno+BAC) to determine the roles of both the anatomic and the functional components of the PET/CT examination in diagnosing this disease. Also, the correlation between tumor size and (18)F-FDG uptake or Hounsfield unit (HU) value was determined in these 2 groups. METHODS This was a retrospective study on a consecutive series of 53 patients with 57 pathology-proven lesions (26 BAC, 31 Adeno+BAC) who underwent (18)F-FDG PET/CT scans. The standardized uptake value (SUV) and average HUs reported were obtained for the tumors. The tumor size, (18)F-FDG uptake, and HU values in both groups were compared. The correlation between metabolic (SUV) and CT (HU) characteristics for the lesions and tumor size was assessed using the Pearson correlation coefficient. RESULTS A total of 26 lesions with pure BAC had a median SUVmax of 1.48 (range, 0.63-4.54). A total of 81% of patients with BAC (21/26 lesions) had SUVmax values of less than 2.5. Thirty-one lesions diagnosed as Adeno+BAC had a median SUVmax of 6.03 (range, 2.45-24) (P < 0.0001 vs. BAC). The mean SUVmax (1.77 +/- 0.99) of BAC was much lower than that of Adeno+BAC (6.55 +/- 4.33) (P < 0.0001). Maximum HU in BAC lesions (-111.96 +/- 123.92) was substantially lower than that in Adeno+BAC (82.03 +/- 33.77) lesions (P < 0.0001). The average maximum tumor dimension in the lung window was much smaller for BACs (17.63 +/- 5.5) than for Adeno+BACs (49.38 +/- 27.5) (P < 0.0001). A strong positive correlation between tumor size and HU was observed in the Adeno+BAC group (P = 0.0002). CONCLUSION PET/CT can help differentiate between BAC and Adeno+BAC by using tumor size, CT density, and metabolic activity. Pure BAC exhibits smaller size, lower (18)F-FDG uptake, and lower tumor density than does Adeno+BAC. Many BACs have low SUVs (<2.0), but their low HU on CT aids in their proper identification.