Interval nodes - The forgotten sentinel nodes in patients with melanoma

Background: Any sentinel lymph node that receives lymph drainage directly f rom a primary melanoma site, regardless of its location, may contain metast atic disease. This is true even if the sentinel node does not lie in a reco gnized node field. Interval (in-transit) nodes that lie along the course of a lymphatic vessel between a primary melanoma site and a recognized node f ield are sometimes seen during lymphatic mapping for sentinel node biopsy. If drainage to such interval nodes is ignored by the surgeon during sentine l node biopsy, metastatic melanoma will be missed in some patients. Hypothesis: When lymph drains directly from a cutaneous melanoma site to an interval node, that sentinel node has the same chance of harboring microme tastatic disease as a sentinel node in a recognized node field. Design: Preoperative lymphoscintigraphy with technetium Tc 99m antimony tri sulfide colloid was performed to define lymphatic drainage patterns and, si nce 1992, to locate the sentinel lymph nodes for surgical biopsy or for per manent skin marking of their location with point tattoos. Setting: Melanoma unit of a university teaching hospital. Patients: A total of 2045 patients with cutaneous melanoma were studied in 13 years. Results: Interval nodes were found in 148 patients (7.2%). The incidence of interval nodes varied with the sire of the primary melanoma. Interval node s were more common with melanomas on the trunk than with those on the lower limbs. Micrometastatic disease was found in 14% of interval nodes that und erwent biopsy as sentinel nodes. This incidence is similar to that found in sentinel nodes located in recognized node fields, confirming the potential clinical importance of interval nodes. Conclusions: Interval nodes should be removed surgically along with any add itional sentinel nodes in standard node fields if the sentinel node biopsy procedure is to be complete. In some patients, an interval node will be the only lymph node that contains metastatic disease.