title: 18F-FDG PET in malignant lymphoma: significance of positive findings.
abstract: OBJECTIVE
  The aim of this study was to evaluate the significance of increased uptake of 18F-fluorodeoxyglucose (FDG) in patients with malignant lymphoma (ML) studied by positron emission tomography (PET).
  
  
  METHODS
  A total of 1,120 consecutive scans carried out in 848 patients were reviewed; all patients had a diagnosis of ML [574 non-Hodgkin's lymphoma (NHL) and 274 Hodgkin's disease (HD)] and were studied at completion of therapy, for suspected recurrence or during follow-up. PET was carried out after intravenous injection of 370 MBq of 18F-FDG; images were recorded after 60-90 min. Patients were selected whose reports indicated areas of increased FDG uptake. PET findings were considered positive for lymphomatous localisation when uptake occurred at sites of previous disease, in asymmetrical lymph nodes or in nodes unlikely to be affected by inflammation (mediastinal, except for hilar, and abdominal). PET findings were adjudged negative for neoplastic localisations in the following instances: physiological uptake (urinary, muscular, thymic or gastrointestinal in patients without MALT), symmetrical nodal uptake, uptake in lesions unrelated to lymphoma that had already been identified by other imaging methods at the time of PET scan, uptake at sites atypical for lymphoma, very low uptake and non-focal uptake. PET findings were compared with the results of other diagnostic procedures (including CT and ultrasound), biopsy findings and follow-up data.
  
  
  RESULTS
  Overall, 354 scans (in 256 patients) showed increased FDG uptake (244 scans in NHL and 110 in HD): in 286 cases, FDG uptake was considered pathological and indicative of ML, in 41 cases the findings were described as uncertain or equivocal and in 37 cases, FDG uptake was considered unrelated to ML (in ten scans, concurrent findings of abnormal FDG uptake attributed to ML and uptake assigned to other causes were obtained) . Of the 286 patients with positive PET findings, 274 (95.8%) were found to have residual or recurrent ML (i.e. true positives). Four of the 41 patients with inconclusive findings turned out to have ML, while in 13 patients, pathological processes other than ML could be identified as the cause of FDG uptake. ML was excluded in all patients with findings reported as non-pathological (100% true-negative rate). Therefore, the false-positive rate in our series was about 5%. The main cause of increased FDG uptake mimicking ML was inflammation.
  
  
  CONCLUSIONS
  Our data confirm that 18F-FDG-PET has very high but not absolute specificity for ML. As already suggested, increased FDG uptake may also be observed in patients without active disease; in most cases, however, non-pathological FDG accumulation is properly identified. Less frequently, inconclusive scans are encountered; these cases are usually caused by inflammation, which subsequently resolves.
authors.affiliation: UO Medicina Nucleare, Policlinico S.Orsola-Malpighi, Via Massarenti, Bologna 40100 Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Castellucci
authors.forename: PierLuigi
authors.initials: P
authors.lastname: Zinzani
authors.forename: Michael
authors.initials: M
authors.lastname: Pourdehnad
authors.forename: Lapo
authors.initials: L
authors.lastname: Alinari
authors.forename: Cristina
authors.initials: C
authors.lastname: Nanni
authors.forename: Mohsen
authors.initials: M
authors.lastname: Farsad
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Battista
authors.forename: Monica
authors.initials: M
authors.lastname: Tani
authors.forename: Vittorio
authors.initials: V
authors.lastname: Stefoni
authors.forename: Romeo
authors.initials: R
authors.lastname: Canini
authors.forename: Nino
authors.initials: N
authors.lastname: Monetti
authors.forename: Domenico
authors.initials: D
authors.lastname: Rubello
authors.forename: Abass
authors.initials: A
authors.lastname: Alavi
authors.forename: Roberto
authors.initials: R
authors.lastname: Franchi
authors.forename: Stefano
authors.initials: S
authors.lastname: Fanti
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005189:False Positive Reactions; D005260:Female; D019788:Fluorodeoxyglucose F18; D006689:Hodgkin Disease / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008207:Lymphatic Metastasis; D008223:Lymphoma / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology*; D008228:Lymphoma, Non-Hodgkin / Q000175:diagnosis / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18