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.