The most effective treatment of malignant melanoma is thought to be a surgical excision of primary tumor and metastatic lesion. The extent of excision should be necessary and sufficient from the perspective of tumor recurrence and postoperative complications, and the determination of indication for lymph node dissection is sometimes difficult.
Lymphatic drainage of cutaneous melanoma targets cervical, axillary, or inguinal lesions in many cases, but some melanomas initially drain to unexpected areas, such as the epitrochlear region or popliteal fossa [2
]. Lymph nodes in these lesions have been described as interval or in-transit nodes, including drainage to the popliteal nodes for a distal lower extremity. According to classical anatomical theory, drainage from the dorsum and medial aspect of the foot passes parallel to the course of the great saphenous vein to the inguinal lesion, and drainage from the posterolateral aspect of the heel, sole, and lateral malleolus follows the lesser saphenous vein to the popliteal legion. Thompson et al. [3
] showed that positive nodes in the popliteal fossa can occur from a lesion anywhere below the knee. Biopsy of these interval nodes in melanoma indicates that they are as frequently involved with metastatic disease as the nodes in the conventional lymph node basin [4
]. However, the rate of popliteal nodes detection was reported [2
] to be from 1.8% to 9.6%, so popliteal nodal metastasis is relatively uncommon. Furthermore, the popliteal metastasis-positive and inguinal-negative rate of all melanomas located below the knee is estimated to range from 0.16% to 0.94% [2
In these popliteal-positive and inguinal-negative cases, the issue of which lesions should be dissected is important. There is no established evidence on this subject. Because we considered popliteal nodes as a regional, not interval, lymph node basin and defined the popliteal status independent of the inguinal nodal status, only popliteal lymph node dissection without dissection of the next nodal basin was performed. As a result, good postoperative course with no recurrence or complication was achieved in our institution. Lymphedema is an unpleasant complication of inguinal and ilioinguinal lymph node dissection, which may cause a chronic feeling of heaviness, discomfort, and pain, sometimes resulting in limitation of patient activity. This is reported to occur in 9% to 55% of patients, but lymphedema is rarely seen after only popliteal lymph node dissection [9
]. In our case, only “interval” node dissection is thought to be an adequate treatment. Because Steen et al. reported that two popliteal node-positive and inguinal-negative cases had nodal recurrences in the groin after disease-free intervals of about 60 months [6
], further long-term followup and prompt treatment for recurrence are necessary in our patient.
Lymphoscintigraphy is now used routinely for sentinel lymph node biopsy and sometimes identifies popliteal nodal drainage, which can be the only site of nodal metastasis in some cases [4
]. The first site of drainage of a lesion is the sentinel node by definition, so the popliteal node can be a sentinel lymph node, not an “interval node.” The inguinal node is not the sentinel node in all lower extremity melanomas, and all sentinel nodes identified by a lymphoscintigram should be removed. There are thought to be some patterns of lymphatic drainage from the foot to the inguinal and popliteal lymph nodes [5
]. More detailed investigation of anatomical predictions of nodal drainage should be performed, and more appropriate surgical treatment is expected to improve patient's quality of life.