John M Froehlich PhD, Presenter: Consultant, Guerbet SA

Maria Triantafyllou MD, Abstract Co-Author: Nothing to Disclose

Achim Fleischmann MD, Abstract Co-Author: Nothing to Disclose

Harriet Carolina Thoeny MD, Abstract Co-Author: Nothing to Disclose

Lymphotropic USPIO visualized by signal decrease occuring on T2-weighted sequences may improve detection/differentiation of metastatic lymph nodes in patients with prostate/bladder cancer. The aim was to quantify lymph node signal decrease to assess whether a cut-off value might be defined to differentiate benign from malignant normal-sized pelvic lymph nodes.

Fifty-eight patients with histological proven bladder/prostate cancer (50 men, 8 females) were examined on a 3T MR-unit (Siemens TRIO) before and 24-36 hours after USPIO. Lymph node signal intensity (SI) quantification was performed on a 3D-T2w-TSE SPACE sequence (TR=640ms,TE=47ms,bandwidth=465Hz/pixel,isotropic voxels=1mm3) on pre- and post-contrast images. Mean signal-to-noise ratios (SNR) were measured three times encompassing the entire lymph node excluding obvious regions of fat. Extended lymphadenectomy was performed in all patients allowing histopathological correlation. Statistical comparison of various groups of lymph nodes was performed with 2-sided, paired Student's t-test. ROC curve was used for threshold assessment.

A total of 2182 lymph nodes were resected; 367 of these (65 inguinal;302 iliacal) were assessed for their respective signal decrease. In proven malignant lymph nodes (n=35) SI (-0.29%±12.9%) and SNR (0.63%±11.9%) changes were significantly (p<0.0001) lower compared to benign lymph nodes (n=267) presenting a mean SI-decrease of 20.7%±25.4% (inguinal) and of 39.7±16.2% (iliacal). SNR-decrease differed significantly (p=0.0008) between inguinal (19.9±22.7%) and iliacal (31.2±25.2%) benign lymph nodes. An optimal cut-off of 20% allowed differentiation between benign and malignant lymph nodes (Figure). Overlap of SNR changes depended on partial-volume effects, histiocytosis, focal hyperplasia and lipomatosis within lymph nodes.

Quantification of SNR/SI-decrease qualifying uptake of lymphotropic USPIO is not sufficient for staging of normal sized lymph nodes. Additional criteria such as morphology, fatty content or localisation of lymph nodes must be considered.

Quantification of lymphotropic uptake of USPIO might allow differentiation of malignant from benign lymph nodes but needs to take into account morphological criteria.

Froehlich, J, Triantafyllou, M, Fleischmann, A, Thoeny, H, Does Quantification of T2 SNR Decrease after USPIO Administration Allow Differentiation between Benign and Malignant Normal-sized Pelvic Lymph Nodes?.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11012390.html