Retroperitoneal and Pelvic Lymph Nodes in Children: What Is Normal?

OBJECTIVE. The purpose of this study was to evaluate size criteria for retroperitoneal and pelvic lymph nodes in healthy children. MATERIALS AND METHODS. We identified all trauma patients younger than 18 years old without underlying disease and with CT scans without abnormalities in the abdomen and pelvis during 2014-2015. Two pediatric radiologists reviewed the studies independently and recorded the number of retroperitoneal and pelvic lymph nodes with a long diameter 5 mm or greater and the size (two perpendicular diameters) of the largest lymph node in five anatomic locations. Discrepant results were reviewed in consensus. The relationship of short diameter to age and interobserver variability was evaluated. RESULTS. A total of 166 patients (86 boys) with a mean age of 7.2 years old (range, 0.1-18.0 years old) were identified. More than 95% of lymph nodes in the retroperitoneum and pelvis had a short diameter measuring at most 7 and 8 mm, respectively, by consensus. The size of the largest short diameter of lymph nodes did not vary with age. More than four lymph nodes were identified in any anatomic location in only three patients, by only one of the radiologists. Agreement for lymph nodes with largest diameter of 5 mm or greater between radiologists ranged from 70.5% to 97.6% for the five anatomic locations with poor interobserver agreement (κ, 0.2-0.3). CONCLUSION. The size and number of retroperitoneal and pelvic lymph nodes in children are less than in adults. A short diameter threshold of 7 mm (retroperitoneal) and 8 mm (pelvic) and more than four lymph nodes with long diameter of 5 mm or greater in one location may define disease.