Inguinal lymph nodes: size, number, and other characteristics in asymptomatic patients by CT

The purpose of this study was to establish normative data for the CT appearance of inguinal lymph nodes. After Institutional Review Board approval, search of the radiology information system identified 500 consecutive CT examinations of the pelvis. Patients were included if no lower extremity or perineum pathology, or history of malignancy at the time of CT examination, and a clinical note documenting no tumor at least 2 years after the CT. The final study group was 77 patients. CT examinations were retrospectively reviewed and bilateral inguinal lymph nodes were characterized by size (short axis and largest size in general), number, and presence of fat attenuation. The mean short-axis inguinal lymph node size was 5.4 mm (range 2.1–13.6 mm), measured at 8.8 mm two standard deviations above the mean. The mean number of superficial and deep inguinal lymph nodes was 10.7 (range 3–18) and 1.2 per patient (range 1–2), respectively. Superficial and deep inguinal nodes showed internal fat attenuation in 85 and 78 % of nodes, and were oval in shape in 95 and 78 %, respectively. Inguinal lymph nodes in asymptomatic patients have a mean short axis of 5.4 mm, a short axis of 8.8 mm at two standard deviations above the mean, and are multiple and symmetric in size and number (4–20 per patient). Normal inguinal lymph nodes were commonly oval in shape and contained fat, although such findings may be absent in smaller lymph nodes.