Comparison of intradermal and subcutaneous injections in lymphatic mapping

Background. Sentinel node biopsy (SNB) for melanoma, with its intradermal ( ID) injection, has a higher success rate than SNB for breast cancer, which is typically performed with a subcutaneous (SC) or peritumor injection. It is hypothesized that this is in part due to a slower transit time of lympha tic mapping agents through the parenchymal lymphatics of the breast. No stu dy has investigated differences in transit time between different tissues t o account for this clinical observation. The goal of the study was to compa re transit time between ID and SC injections: with common agents used in ly mphatic mapping. Methods. Four injection sites on five domestic pigs were used. Sites were b ilateral and included cervical, forelimb, hindlimb, and flank areas. Agents included technetium sulfur colloid (Tc99, filtered and unfiltered), isosul fan blue (IB) dye, and fluorescein (FL) dye. At each site both ID and SC in jections were made and the transit time to reach the sentinel node was reco rded. The transit time differences were calculated per centimeter distance from the draining lymph node basin. Results. Sentinel nodes were identified draining all sites and found to be hot, blue, or fluorescent (using a Wood's lamp for identification). The cer vical and forelimb injection sites drained to the same cervical lymph node basin and both SC and ID injection sites drained to the same sentinel node. Similarly, the hindlimb and flank injection sites both drained to inguinal lymph node basins. The slowest transit time occurred with Tc99 injected SC and the fastest occurred with Tc99 injected ID, whereas both FL dye and IB traveled rapidly to the sentinel node whether injected SC or ID. Large dif ferences were found using unfiltered Tc99 depending on its injection ID (2. 7 s/cm +/- 0.5) vs SC (249 s/cm +/- 14.7, P = 0.008). Conclusions. Tc99 ID injections were significantly faster than SC injection . The slowest and fastest SC injection agents were unfiltered Tc99 and IB, respectively. Dermal injections provide faster transit of lymphatic agents and may improve the identification rate when applied to patients with breas t cancer. (C) 2001 Academic Press