DYNAMIC LYMPHOSCINTIGRAPHY TO IDENTIFY THE SENTINEL AND SATELLITE NODES

Lymphoscintigraphy is increasingly used to identify the first draining node (sentinel node) in patients with malignant melanoma or breast ca ncer. If the sentinel node is tumor free then the remainder of the nod es in that specific nodal bed are likely to be free of metastases. Loc alization and biopsy of the sentinel node with an intraoperative surgi cal probe may obviate more radical lymph node dissection. Lymphoscinti graphy is conventionally performed by injecting the radioactive tracer in the four quadrants around the primary tumor and imaging the approp riate nodal beds approximately 30 minutes later, The visualized node n earest the tumor usually is assumed to represent the sentinel node. To test this assumption, a dynamic acquisition was obtained in 16 patien ts with malignant melanoma to determine if the node nearest the tumor was actually the first draining node, In one of 16 patients, the radio active tracer injected around a thigh melanoma drained first to an ing uinal node and then drained inferiorly to a second inguinal node locat ed closer to the tumor. The distinction between the sentinel and satel lite (secondary draining nodes) may have important clinical implicatio ns regarding the number of nodes that require surgical excision. In su mmary, static images do not define the pattern of lymph flow and the n ode nearest the tumor is not necessarily the sentinel node. Failure to obtain dynamic images may lead to misdiagnosis of the sentinel node i n a small percentage of patients.