Lymph nodes located between a tumor and the natural lymphatic draining basin occur frequently in melanoma patients and indicate a need to perform lymphoscintigraphy in all patients with cutaneous tumors, a Michigan radiologist said at an RSNA scientific session.
So-called "in-transit" lymph nodes occurred in 7.2% of 166 patients with cutaneous tumors, all but two of which were melanomas. Several in-transit nodes harbored metastatic disease.
"Our findings are consistent with reports in the literature, which cite a 5% to 10% incidence of nodes lying outside the classically described lymphatic drainage basin," said Dr. Adam Tonakie, a radiologist at the University of Michigan.
"It has been suggested that lymphoscintigraphy is not necessary for cutaneous appendicular tumors, due to the classical lymphatic drainage pathways that are commonly observed. However, we believe that lymphoscintigraphy should be performed in all cutaneous tumors to ensure all in-transit nodes are identified and excised," he said.
The findings came from a retrospective review of lymphoscintigraphy exams performed for mapping tumor lymphatic drainage routes or identifying sentinel lymph nodes. All the patients were evaluated by gamma scan, using Tc99m HSA, with or without sulfur colloid.
The 7.2% incidence of in-transit lymph nodes comprised nodes identified in the arm, popliteal region, and chest wall. In several cases, the in-transit nodes contained tumor while proximal nodes were tumor-free.
"In-transit nodes are quite common, are often the site of metastatic disease, and may be affected without involvement of the expected primary draining nodal basin," Tonakie said.
The investigators generally employ unfiltered sulfur colloid for lymphoscintigraphy. Whether that practice will continue remains unresolved, Tonakie said, because unfiltered sulfur colloid usually does not propagate upstream after encountering a node. As a result, fewer nodes may be identified.
The findings also have implications for the lymphadenectomy technique. Traditionally, surgeons have not removed popliteal nodes. The Michigan results may point to a need to rethink the approach to node removal, said Dr. Richard Wahl, who chaired the scientific session.
