title: ¹⁸F-fluoro-deoxy-glucose focal uptake in very small pulmonary nodules: fact or artifact? Case reports.
abstract: BACKGROUND
  18F-fluoro-deoxy-glucose (18 F-FDG) positron emission tomography integrated/combined with computed tomography (PET-CT) provides the best diagnostic results in the metabolic characterization of undetermined solid pulmonary nodules. The diagnostic performance of 18 F-FDG is similar for nodules measuring at least 1 cm and for larger masses, but few data exist for nodules smaller than 1 cm.
  
  
  METHODS
  We report five cases of oncologic patients showing focal lung 18 F-FDG uptake on PET-CT in nodules smaller than 1 cm. We also discuss the most common causes of 18 F-FDG false-positive and false-negative results in the pulmonary parenchyma.In patient 1, contrast-enhanced CT performed 10 days before PET-CT did not show any abnormality in the site of uptake; in patient 2, high-resolution CT performed 1 month after PET showed a bronchiole filled with dense material interpreted as a mucoid impaction; in patient 3, contrast-enhanced CT performed 15 days before PET-CT did not identify any nodules; in patients 4 and 5, contrast-enhanced CT revealed a nodule smaller than 1 cm which could not be characterized. The 18 F-FDG uptake at follow-up confirmed the malignant nature of pulmonary nodules smaller than 1 cm which were undetectable, misinterpreted, not recognized or undetermined at contrast-enhanced CT.
  
  
  CONCLUSIONS
  In all five oncologic patients, 18 F-FDG was able to metabolically characterize as malignant those nodules smaller than 1 cm, underlining that: 18 F-FDG uptake is not only a function of tumor size but it is strongly related to the tumor biology; functional alterations may precede morphologic abnormalities. In the oncologic population, especially in higher-risk patients, PET can be performed even when the nodules are smaller than 1 cm, because it might give an earlier characterization and, sometimes, could guide in the identification of alterations missed on CT.
authors.affiliation: Institute of Nuclear Medicine, Università Cattolica del Sacro Cuore, Largo A, Gemelli, 8, 00168 Rome, Italy. ml.calcagni@rm.unicatt.it
authors.forename: Maria Lucia
authors.initials: ML
authors.lastname: Calcagni
authors.forename: Silvia
authors.initials: S
authors.lastname: Taralli
authors.forename: Fabio
authors.initials: F
authors.lastname: Maggi
authors.forename: Vittoria
authors.initials: V
authors.lastname: Rufini
authors.forename: Giorgio
authors.initials: G
authors.lastname: Treglia
authors.forename: Lucia
authors.initials: L
authors.lastname: Leccisotti
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Bonomo
authors.forename: Alessandro
authors.initials: A
authors.lastname: Giordano
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging* / Q000473:pathology; D005188:False Negative Reactions; D005189:False Positive Reactions; D017809:Fatal Outcome; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D064847:Multimodal Imaging; D055613:Multiple Pulmonary Nodules / Q000000981:diagnostic imaging* / Q000473:pathology; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging* / Q000473:pathology; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18