MR evaluation of normal retroperitoneal and pelvic lymph nodes

Purpose: To establish guidelines for normal retroperitoneal and pelvic lymph node size at magnetic resonance imaging (MRI) by correlation with computed tomographic (CT) and lymphangiographic (LAG) data.

Materials and methods: Twelve patients previously studied with pre- and post-LAG CT to determine normal pelvic lymph node size [ 1 ] were examined with MRI. All were on surveillance for stage I testicular tumour (minimum follow-up 10 years). Three observers recorded blind the site, size and number of nodes in the retroperitoneum and pelvis at 11 sites. The results were validated with previous CT imaging.

Results: Eight hundred and fifteen nodes in 12 patients were visible on the MRI initially, and a further 44 nodes were identified after comparison with post-LAG CT. More nodes were seen on MRI than on CT. The 95th centile values for maximum short axis diameter (MSAD) of pelvic lymph nodes were common iliac and obturator 4 mm, external and internal iliac 5 mm and hypogastric 6 mm. In the retroperitoneum the 95th centile MSAD values were retrocrural, high left para-aortic, paracaval and interaortocaval 3 mm, post-caval 4 mm and low left para-aortic 5 mm.

Conclusion: MRI criteria for normal retroperitoneal and pelvic lymph node size are defined. Adoption of these recommendations may improve the sensitivity of MRI for the detection of nodal metastases.