Magnetic resonance appearance of normal inguinal nodes

To identify adult inguinal lymph node anatomical subgroups using magnetic resonance imaging (MRI), to derive a normal range for nodal number and size and to describe their morphology.

Eighty-three oncology patients with low stage pelvic tumours had inguinal lymph node assessment by MRI. Nodes were divided into proximal superficial (PS), distal superficial (DS) and deep inguinal (DI) subgroups, their number counted in two planes, and their transaxial short axis diameter recorded. Consistency of the largest node was recorded for each anatomical subgroup and two vertical distances measured, between the skin surface and the ipsilateral pubis, and between the skin surface and the deepest node.

Transaxial plane maximum nodal number at the three sites was: PS 5, DS 8, DI 3; and in the coronal plane: PS 7, DS 5, DI 3. Nodal size ranges were: PS 3-10 mm (mean 4 mm), DS 3-15 mm (mean 6 mm) and DI3-10 mm (mean 6 mm). There was no correlation between nodal size or number and age or gender. Nodes were usually uniformly solid (PS 44%; DS 37%, DI 45%), or fatty (PS 39%; DS 33%; DI 25%). The range of distances between the skin and deepest lymph node was 2.5-16 cm depending on patient fatness.

The mean number of nodes counted in the axial plane was six and in the coronal plane five. A maximum short axis diameter of 15 mm was recorded for inguinal lymph nodes.