Radiographic evaluation of subcutaneously injected, water-soluble, iodinated contrast for lymphography

Sentinel lymph node (SLN) mapping is common in many types of human cancers, and is gaining utility in veterinary medicine. There are currently many different methods described in veterinary medicine for pre-operative SLN mapping, however, most of these are restricted to referral institutions due to cost and need for specialized equipment. The purpose of this prospective, pilot study was to evaluate the feasibility of radiographic evaluation of water-soluble, iodinated contrast (WIC) injected subcutaneously for lymphography in dogs. Eight dogs were injected with 1-2 milliliters of WIC into the subcutaneous tissues overlying the tarsus in 4 separate locations mimicking a circumferential, peri-tumoral injection. Radiographs were taken at select time points up to 50 minutes. Image sequences were evaluated by a single, board-certified radiologist. All 8 dogs had visible contrast-enhancing lymphatic channels. Median time to lymphatic enhancement was immediately post-injection. Seven dogs (88%) had 8 contrast enhancing lymph nodes (7 popliteal and 1 superficial inguinal). Median time to lymph node enhancement was 20 minutes. In this study, the plantar aspect of the pes drained to the superficial inguinal lymph node, and the dorsal aspect of the pes drained to the popliteal lymph node. Subcutaneously-injected WIC was readily identifiable in the lymphatic channels and draining lymph node(s). Subcutaneously injected WIC may offer a practical alternative to previously described pre-operative methods of SLN mapping. Additionally, one cannot assume that the popliteal lymph node alone, drains the distal pelvic limb.