The features of solitary pulmonary nodules of adenocarcinoma on ¹⁸F-FDG PET/CT

Objective: To study the imaging characteristics of SPN of adenocarcinoma (ASPNs) on ¹⁸F-FDG PET/CT. Methods: The morphological and metabolic features of 35 ASPNs on FDG PET/CT were retrospectively reviewed. SUV_max (SUV) was measured and ΔSUV_max was calculated according to ΔSUV_max =(SUV_max on delay imaging - SUV_max on early imaging)/SUV_max on early imaging × 100%. Statistical analysis was performed by software SPSS 11.5 using t-test, analysis of variance and Fisher exact test. Results: (1) Fifteen ASPNs (42.86%, 15/35) presented as nodular pattern on FDG PET imaging, while 20 (57.14%, 20/35) as lamellar, cloudy or ill-defined patterns. The SUV_max of these ASPNs followed a descending order of nodular, lamellar, cloudy and ill: defined on both early and delay imaging (F=30.696 and 24.758, both P<0.001). (2) There were 54.29% (19/35) ASPNs with SUV_max ≥2.5 and 45.71% (16/35) ASPNs with SUV_max<2.5. (3) Of 35 ASPNs, 24 (68.57%) were solid nodules and 11(31.43%) were ground glass nodules with SUV_max =4.54 ±2.69 and 1.30±0.87, respectively (t=-5.234, P<0.001). (4) The SUV_max of ASPNs on delay FDG imaging (4.22 ±3.52) was significantly higher than that on early imaging (3.49 ±2.72) (t=-4.021, P<0.001). However, SUV_max was dependent on SUV_max on the early imaging:when SUV_max ≥2.5, ΔSUV_max was positive in 94.74% (18/19) of ASPNs; while SUV_max<2.5, ΔSUV_max was positive in 56.25% (9/16) of ASPNs (P=0.013). (5) Of 31 ASPNs with cell differentiation data, there were 10/17 well-differentiated ASPNs and 13/14 poorly-differentiated ASPNs with positive ΔSUV_max (P=0.045). The average SUV_max of well-differentiated ASPNs was significantly lower than that of poorly-differentiated ASPNs (1.70 ± 1.51 vs 4.91 ± 2.69, t=-3.951, P<0.001). Conclusions: The morphological and metabolic features of ASPNs are diversified. It is common for ASPN to present with SUV_max<2.5. ΔSUV_max may be helpful for differentiating malignant from benign SPNs. (authors)