Patterns of lymphatic drainage from the skin in patients with melanoma.

An essential prerequisite for a successful sentinel lymph node biopsy (SLNB) procedure is an accurate map of the pattern of lymphatic drainage from the primary tumor site in each patient. In melanoma patients, mapping requires high-quality lymphoscintigraphy, which can identify the actual lymphatic collecting vessels as they drain into the sentinel lymph nodes. Small-particle radiocolloids are needed to achieve this goal, and imaging protocols must be adapted to ensure that all true sentinel nodes, including those in unexpected locations, are found in every patient. Clinical prediction of lymphatic drainage from the skin is not possible. The old clinical guidelines based on Sappey's lines therefore should be abandoned. Patterns of lymphatic drainage from the skin are highly variable from patient to patient, even from the same area of the skin. Unexpected lymphatic drainage from the skin of the back to sentinel nodes in the triangular intermuscular space and, in some patients, through the posterior body wall to sentinel nodes in the para-aortic, paravertebral, and retroperitoneal areas has been found. Lymphatic drainage from the head and neck frequently involves sentinel nodes in multiple node fields and can occur from the base of the neck up to nodes in the occipital or upper cervical areas or from the scalp down to nodes at the neck base, bypassing many node groups. The sentinel node is not always found in the nearest node field and is best defined as "any lymph node receiving direct lymphatic drainage from a primary tumor site." Lymphatic drainage can occur from the upper limb to sentinel nodes above the axilla. Drainage to the epitrochlear region from the hand and arm as well as to the popliteal region from the foot and leg is more common than was previously thought. Interval nodes, which lie along the course of a lymphatic vessel between a lesion site and a recognized node field, are not uncommon, especially in the trunk. Drainage across the midline of the body is quite common in the trunk and in the head and neck. Micrometastatic disease can be present in any sentinel node regardless of its location, and for the SLNB technique to be accurate, all true sentinel nodes must be biopsied in every patient.