Tracer uptake in mediastinal and paraaortal thoracic lymph nodes as a potential pitfall in image interpretation of PSMA ligand PET/CT
Since the introduction of 68Ga-PSMA-11 PET/CT for imaging prostate cancer (PC) we have frequently observed mediastinal lymph nodes (LN) showing tracer uptake despite being classified as benign. The aim of this evaluation was to further analyze such LN.
Two patient groups with biphasic 68Ga-PSMA-11 PET/CT at 1 h and 3 h p.i. were included in this retrospective evaluation. Group A (n = 38) included patients without LN metastases, and group B (n = 43) patients with LN metastases of PC. SUV of mediastinal/paraaortal LN of group A (n = 100) were compared to SUV of LN metastases of group B (n = 91). Additionally, 22 randomly selected mediastinal and paraaortal LN of patients without PC were immunohistochemically (IHC) analyzed for PSMA expression.
In group A, 7/38 patients (18.4%) presented with at least one PSMA-positive mediastinal LN at 1 h p.i. and 3/38 (7.9%) positive LN at 3 h p.i. with a SUVmax of 2.3 ± 0.7 at 1 h p.i. (2.0 ± 0.7 at 3 h p.i.). A total of 11 PSMA-positive mediastinal/paraaortal LN were detected in nine patients considering both imaging timing points. SUVmax of LN-metastases was 12.5 ± 13.2 at 1 h p.i. (15.8 ± 17.0 at 3 h p.i.). SUVmax increased clearly (> 10%) between 1 h and 3 h p.i. in 76.9% of the LN metastases, and decreased significantly in 72.7% of the mediastinal/paraaortal LN. By IHC, PSMA-expression was observed in intranodal vascular endothelia of all investigated LN groups and to differing degrees within germinal centers of 15/22 of them (68.1%). Expression was stronger in mediastinal nodes (p = 0.038) and when follicular hyperplasia was present (p = 0.050).
PSMA-positive mediastinal/paraaortal benign LN were visible in a notable proportion of patients. PSMA-positivity on the histopathological level was associated with the activation state of the LN. However, in contrast to LN metastases of PC, they presented with significantly lower uptake, which, in addition, usually decreased over time.
KeywordsProstate cancer PET/CT Mediastinal Mediastinal/paraaortal Lymph nodes PSMA Prostate-specific membrane antigen 68Ga-PSMA-11
A large number of people helped to plan, investigate, and analyze the patients in past years. Amongst them are (in alphabetic order): Heidrun Adam, Stephanie Biedenstein, Renate Brück, Elena Dahlke, Larissa Engel, Tanja Gerwert, Prof. Frederik Giesel, Daniela Johna, Dr. Christian Kleist, Dr. Susanne Krämer, Dr. Clemens Kratochwil, Kirsten Kunze, Viktoria Reiswich, Franziska Seybold-Epting, Peter Seybold-Epting, Fabian Spohn, and Natalia Zimmermann.
Compliance with ethical standards
All patients published in this manuscript signed a written informed consent form for the purpose of anonymized evaluation and publication of their data. All reported investigations were conducted in accordance with the Helsinki Declaration and with our national regulations (German Medicinal Products Act, AMG §13 2b). This evaluation was approved by the ethics committee of the University of Heidelberg (S-321-2012).
Conflicts of interest
All authors declare that they have no conflict of interest.
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