Differential Diagnosis of Pulmonary Fungal Infection and Lung Cancer via 18F-FDG PET/CT: A Retrospective Study

Abstract Background: There is limited evidence regarding the 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) characteristics of lung fungal (LF) infections with nodules or masses, which are often misdiagnosed as lung cancer (LC) with indications for surgery. We aimed to investigate the PET/CT findings of LF infections with nodules in comparison to those of LC and clarify the diagnostic value of 18F-FDG PET/CT in the differential diagnosis of LF infections.Methods: We enrolled 21 patients who presented with pulmonary nodules or masses on CT, were diagnosed with LF infections, and underwent PET/CT as the LF group and randomly selected 42 patients with LC diagnosed by pathology as the LC group. Clinical and PET/CT imaging data were statistically analyzed.Results: LC was the most common misdiagnosed disease in the LF group (52.38%). There were no significant differences in lung imaging features between the two groups. The levels of white blood cells, neutrophils, and IgG and the positive rates for fungal antigen test in the LF group were significantly higher than those in the LC group (P<0.05). Lung masses larger than 3 cm were more common in the LC group (P<0.05). Overall, 80.95% (17/21) of patients in the LF group showed increased 18F-FDG uptake. There were no significant between-group differences in the maximal standardized uptake value (SUVmax, 8.20 [2.70, 12.95] vs. 8.80 [7.00, 12.38]). In the LF group, eight, five, and eight patients had cryptococcal, Aspergillus, and Talaromyces marneffei infections, respectively, with no significant difference in SUVmax among them (5.10 [1.70, 14.40] vs. 8.20 [1.50, 8.20] vs. 8.50 [5.10, 11.30]). Conclusions: Both LF infection and LC can present with increased 18F-FDG uptake on PET/CT. Thus, it is difficult to distinguish between them according to lung PET/CT and CT manifestations. Patients presenting with pulmonary masses should also be suspected to have fungal infection, even those with an increased SUVmax and simultaneous lymph node and bone involvement; particular attention is needed for patients with abnormal inflammation indexes and fungal antigen test. We should be emphasized preoperative pathological examination and fungal etiology.