What is the pelvic lymph node normal size? Determination from normal MRI examinations.

Purpose: There are few previous reports on maximal pelvic lymph node sizes and no data on normal mesorectal nodes. Therefore, the aim of the study was to estimate the normal size of pelvic lymph nodes and to determine the upper limits of the normal range.

Materials And Methods: Pelvic magnetic resonance imaging (MRI) examinations were prospectively carried out using a Intera 1.5 T magnet (Philips, the Netherlands), on 36 healthy volunteers (22 females, 14 males, mean age 25 years). A balanced fast field echo (b-FFE) sequence was used with the following parameters: 3-mm-thick contiguous slice, matrix 512 × 512. Short axis diameters of pelvic and inguinal lymph nodes were measured in each anatomic territory (internal iliac, external iliac, common iliac, mesorectum and inguinal). After normalization of the measurements, the influences of age, gender, laterality and territory were evaluated. Upper limits (95th percentile) were then calculated.

Results: A total of 1147 lymph nodes were measured. Age, gender and side (right/left) had no significant influence on size. The upper limits of the normal range were, respectively, 5.3, 4.4, 6.3 and 3.9 mm for the external and common iliac, internal iliac, inguinal and mesorectum nodes.

Conclusion: This work presents maximal normal values for each pelvic area, and the values for mesorectum nodes are reported for the first time.

Advances In Knowledge: The mesorectum nodes should be considered as abnormal when they are over 4 mm in short diameter. For the other node areas, the upper limits of the normal range were, respectively, 6, 6, 5, 7 mm for the external and common iliac, internal, iliac and inguinal nodes for the short axis.