Normal mediastinal lymph node size and number: CT and anatomic study.

Normal lymph nodes were studied retrospectively by computed tomography (CT) in 39 patients and by dissection at autopsy in 12 cadavers. The mediastinum was divided arbitrarily into four zones relating to the left innominate vein (zone 1), pretracheal space (zone 2), precarinal/subcarinal compartment (zone 3), and aorticopulmonary window (zone 4). Of 225 lymph nodes from all zones in the CT study, 99% measured less than 16 mm in largest diameter. The average lymph node size in the four zones in the cadavers was 12.6 X 8.3 mm (length X width). Using contiguous 10-mm CT scans, lymph nodes were detected in 65%-95% of patients, depending on the zone studied. The mean number of lymph nodes on a representative section was 1.1 (range, 0-6); 72.4% of CT patients showed one to three lymph nodes per zone. There was a significant size difference (p less than 0.001) between lymph nodes residing in the superior mediastinum compared with those in the middle mediastinum contiguous to the carina. Thus, only 7% of lymph nodes in zone 1 were larger than 5 mm, whereas 90% and 67% of lymph nodes in zones 3 and 4, respectively, were larger, in the 6-10 mm range.