title: Metastases in normal-sized pelvic lymph nodes: detection with diffusion-weighted MR imaging.
abstract: OBJECTIVE
  To prospectively assess the diagnostic performance of diffusion-weighted (DW) magnetic resonance (MR) imaging in the detection of pelvic lymph node metastases in patients with prostate and/or bladder cancer staged as N0 with preoperative cross-sectional imaging.
  
  
  METHODS
  This study was approved by an independent ethics committee. Written informed consent was obtained from all patients. Patients with no enlarged lymph nodes on preoperative cross-sectional images who were scheduled for radical resection of the primary tumor and extended pelvic lymph node dissection were enrolled. All patients were examined with a 3-T MR unit, and examinations included conventional and DW MR imaging of the entire pelvis. Image analysis was performed by three independent readers blinded to any clinical information. Metastases were diagnosed on the basis of high signal intensity on high b value DW MR images and morphologic features (shape, border). Histopathologic examination served as the standard of reference. Sensitivity and specificity were calculated, and bias-corrected 95% confidence intervals (CIs) were obtained with the bootstrap method. The Fleiss and Cohen κ and median test were applied for statistical analyses.
  
  
  RESULTS
  A total of 4846 lymph nodes were resected in 120 patients. Eighty-eight lymph node metastases were found in 33 of 120 patients (27.5%). Short-axis diameter of these metastases was less than or equal to 3 mm in 68, more than 3 mm to 5 mm in 13, more than 5 mm to 8 mm in five; and more than 8 mm in two. On a per-patient level, the three readers correctly detected metastases in 26 (79%; 95% CI: 64%, 91%), 21 (64%; 95% CI: 45%, 79%), and 25 (76%; 95% CI: 60%, 90%) of the 33 patients with metastases, with respective specificities of 85% (95% CI: 78%, 92%), 79% (95% CI: 70%, 88%), and 84% (95% CI: 76%, 92%). Analyzed according to hemipelvis, lymph node metastases were detected with histopathologic examination in 44 of 240 pelvic sides (18%); the three readers correctly detected these on DW MR images in 26 (59%; 95% CI: 45%, 73%), 19 (43%; 95% CI: 27%, 57%), and 28 (64%; 95% CI: 47%, 78%) of the 44 cases.
  
  
  CONCLUSIONS
  DW MR imaging enables noninvasive detection of small lymph node metastases in normal-sized nodes in a substantial percentage of patients with prostate and bladder cancer diagnosed as N0 with conventional cross-sectional imaging techniques.
authors.affiliation: From the Department of Radiology, Neuroradiology and Nuclear Medicine (H.C.T., J.M.F., M.T., L.J.B., P.V.), Institute of Mathematical Statistics (J.H.), Department of Pathology (A.F.), and Department of Urology (U.E.S.), Inselspital, University of Bern, Freiburgstrasse 10, CH-3010 Bern, Switzerland.
authors.forename: Harriet C
authors.initials: HC
authors.lastname: Thoeny
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Froehlich
authors.forename: Maria
authors.initials: M
authors.lastname: Triantafyllou
authors.forename: Juerg
authors.initials: J
authors.lastname: Huesler
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Bains
authors.forename: Peter
authors.initials: P
authors.lastname: Vermathen
authors.forename: Achim
authors.initials: A
authors.lastname: Fleischmann
authors.forename: Urs E
authors.initials: UE
authors.lastname: Studer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008197:Lymph Node Excision; D008207:Lymphatic Metastasis / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D010388:Pelvis; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000473:pathology*; D001749:Urinary Bladder Neoplasms / Q000473:pathology*
chemical_list: D003287:Contrast Media; D058185:Magnetite Nanoparticles