Mesenteric lymph nodes: detection and significance on MDCT.

OBJECTIVE Unsuspected mesenteric lymph nodes are frequently found on abdominal CT scans in everyday clinical practice. What to do with these findings has not been well established. The purpose of this study is to document the incidence of mesenteric lymph nodes in a previously healthy population and to provide guidelines for further management. MATERIALS AND METHODS We examined the CT scans of 132 consecutive patients (84 men and 36 women; age range, 12-90 years; mean age, 43 years) who presented to the emergency department after experiencing blunt abdominal trauma. Twelve patients were excluded because they had disease processes known to be associated with lymphadenopathy. All imaging was performed using 3.2-mm collimation on MDCT scanners with IV contrast material. Two radiologists evaluated the images by consensus and recorded the presence of mesenteric lymph nodes greater than 3 mm in the short axis. Lymph node size, number, and location (central, peripheral, or right lower quadrant) were documented. All studies were reviewed on a PACS workstation. RESULTS Of the 120 patients with otherwise normal CT scans, 47 had mesenteric lymph nodes greater than 3 mm. Of these 47 patients, 22 (47%) had five or more lymph nodes detected. Twenty-five (53%) of the 47 patients had four or fewer nodes. The mean size of the largest nodes was 4.8 mm (range, 3-9 mm), and the mean size of the nodes found per patient was 3.6 mm (range, 3-6 mm). These nodes were identified only at the mesenteric root in 32 patients (68%), only in the mesenteric periphery in eight patients (17%), and only in the right lower quadrant in five patients (11%). Nodes were identified in more than one location in two patients (4%). CONCLUSION Incidental finding of mesenteric lymph nodes is common, reflecting more widespread use of thin-collimation MDCT and PACS workstations. In general, these nodes are small, measuring less than 5 mm. Such nodes when found in an otherwise healthy population are clinically insignificant and require no further imaging.