The popliteal fossa - a problem zone for sentinel lymphonodectomy

Background: The impact of lymphatic drainage to popliteal sentinel lymph nodes (SLNs) has yet to be explored in detail.

Patients and methods: We performed lymphoscintigraphy on 663 patients with cutaneous melanomas. The following day sentinel lymphonodectomy was performed. SLNs were studied on serial sections with both histology and immunohistochemistry.

Results: 166 patients had a melanoma located on the foot, the lower leg or the knee, i. e., the potential of lymphatic drainage to the popliteal lymph nodes. On lymphoscintigraphy, only 16 patients (9.6 %) showed popliteal SLNs. A popliteal SLN was surgically identified in only 6 of the 16 patients. The reason for the poor identification rate was exhausted radioactivity in the small popliteal nodes the day after lymphoscintigraphy. In 3 cases, popliteal SLN metastasis was diagnosed. All but one patient had an additional drainage to the inguinal lymph nodes; inguinal SLN metastasis was diagnosed in 7 patients. Even all 16 patients showed lymphatic drainage to iliac lymph nodes, metastasis in the pelvis was diagnosed in 4 patients.

Conclusions: Popliteal SLNs are observed in less than 10 % of the patients with melanomas of the distal leg. In the case of suspected popliteal drainage, lymphoscintigraphy should be performed on the day of sentinel lymphonodectomy because the radioactivity of the small and deeply situated popliteal nodes diminishes rapidly. With respect to complete lymphadenectomy, decision-making is difficult since three nodal basins (popliteal, inguinal and iliac) may harbor metastases.