D128. Collateralization of Forearm Lymphatic Drainage is afforded by a Long-Bundle Lateral Upper Arm Pathway: Novel Insights from Combined ICG Lymphography and Lymphoscintigraphy

PURPOSE: The lateral upper arm/Mascagni-Sappey (MS) pathway is theorized as a collateral route of lymphatic drainage that is protective against breast cancer related lymphedema (BCRL). This study examines patterns of functional drainage between MS pathway phenotypes to establish whether a long-bundle MS pathway can collateralize forearm drainage to the deltopectoral lymph nodes. METHODS: Healthy female volunteers underwent bilateral arm ICG lymphography. Volunteers underwent two bilateral arm lymphoscintigraphy studies with tracer injections in the upper arm over the cephalic vein at first visit and in the hand/wrist at second visit. MS pathway phenotypes (long-bundle, short-bundle, absent) were recorded from ICG lymphography. Lymph nodes with tracer uptake were recorded from SPECT/CT for each study. RESULTS: 64 arms of 32 volunteers were included. 73.4% had a long-bundle, 25% had a short-bundle, and 1.6% did not have the MS pathway. Functional drainage to the deltopectoral lymph nodes was seen in 33% of arms after upper arm cephalic injection. 100% of arms with deltopectoral drainage after the upper arm cephalic injection had the MS pathway. Functional drainage to the deltopectoral lymph nodes was seen in 20% of arms after hand/wrist injections. 92% of arms with deltopectoral drainage after hand/wrist injection demonstrated the long-bundle phenotype. CONCLUSION: This study demonstrates that the MS pathway drains to the deltopectoral lymph nodes. This pathway is a potential protective factor against BCRL by routing arm drainage to lymph nodes spared in an axillary lymph node dissection. A long-bundle may be more protective for additionally connecting forearm drainage to this pathway.