A Triangular Intermuscular Space Sentinel Node in Melanoma: Association With Axillary Lymphatic Drainage

Background. Large centers have described triangular intermuscular space (TIS) sentinel nodes (SNs) for some melanomas of the back. However, their management remains controversial and poorly characterized, especially as related to the ipsilateral axillary node basin. The aim of this study was to summarize our experience with TIS SN, which may contribute to defining their appropriate surgical management. Methods. We performed a retrospective review on surgical patients from January 1993 to April 2009. Among 293 patients with upper back melanoma, data were collected on those with TIS SN. Results. Fourteen patients (5%) with melanoma of the upper back had a TIS SN, 6 of whom (43%) were incorrectly identified at lymphoscintigraphy as axillary, and 11 of whom (79%) had a concurrent axillary SN. Micrometastatic disease was identified in TIS SN in two patients (14%) and in an axillary SN in one (9%). We found direct lymphatic drainage independently to the TIS and to the axilla, as well as a more typical pattern of drainage first to the TIS node and then to axillary nodes. Conclusions. We defined three patterns of lymphatic drainage to TIS and axillary nodes. The TIS and axilla are anatomically linked; patients with SN in both locations should undergo biopsies of both for optimal nodal staging. We recommend directed evaluation for TIS SN in patients with upper back melanomas and recommend clearing the TIS at the time of TIS SN biopsy. Melanoma can metastasize to TIS SN, and we discuss considerations for management of the axilla in patients with positive TIS nodes.