Mediastinal lymph node uptake in patients with prostate carcinoma on F18-choline PET/CT

Fluorine-18-methyl-choline (F18-choline) PET/computed tomography (CT) is routinely performed in our hospital for patients with significantly increased or rapidly increasing prostate-specific antigen (PSA) levels to detect and localize recurrent prostate carcinoma. We observed uptake of this PET tracer in mediastinal lymph nodes in a significant number of patients. The aim of this study was to assess the frequency of this finding and to determine whether it is correlated with tumour and nontumour-related aspects.

A total of 48 consecutive men (mean age: 65.6 years; range: 50-79 years, standard deviation: 7.1) with histopathologically proven prostate cancer were referred for F18-choline PET/CT imaging for restaging from March 2009 to October 2010. All patients had a suspicion of tumour recurrence because of an increased PSA or a rapidly increasing PSA. All studies were reviewed, and the results were correlated with general data such as age; smoking; chronic obstructive pulmonary disease; tumor, lymph nodes and distant metastases stage; Gleason Score and PSA level; with a maximum interval of 3 months between serum PSA and the PET/CT scan.

In 27 patients (56.3%), F18-choline PET/CT showed positive lymph nodes in the mediastinum (mean standardized uptake values: 3.75; range: 1.7-13.8, standard deviation: 2.4). No histological biopsy was carried out in F18-choline-positive lymph nodes, but in none of the patients was mediastinal recurrence or pulmonary infection observed during a 6-month follow-up. Only one patient had histologically proven pulmonary metastasis. No significant relationship was observed between mediastinal F18-choline lymph node uptake and serum PSA level (P=0.785), initial T stage (P=0.555), N stage (P=0.548), M stage (P=0.426), smoking (P=0.537), chronic obstructive pulmonary disease (P=0.115) or the presence of tumour recurrence on F18-choline PET/CT.

Mediastinal lymph node uptake of F18 choline is frequently observed, without any significant relationship with tumour characteristics. Therefore, interpretation of positive mediastinal lymph node uptake should be done carefully.