Minimally invasive lymphatic mapping using fluorescently labeled vitamin B12

We examined the usefulness of a new agent in the mapping and dissection of inguinal lymph nodes in the pig. Cy5-cobalamin bioconjugate is blue under visible light and fluoresces brilliant red with laser stimulation. The wavelength of the emitted red light is sufficiently long that it is visible through blood, subcutaneous fat, and fascia. Currently available surgical techniques of minimally invasive dissection are well suited for using fluorescent detection in a dark operating field with minimal modification of an existing Hopkins surgical telescope.

We tested this concept in the live post-adolescent, female, nonlactating pig (30 kg). We insufflated the subcutaneous tissue over the groin and inserted three ports (1 x 10 mm and 2 x 5 mm) for dissection. We injected the Cy5-cobalamin bioconjugate in a dermal location on the hind limb. A HeNe laser stimulated the CobalaFluor in the lymphatics and the emitted fluorescence passed through a holographic notch filter to a three-chip camera.

Under white light, the lymphatic trunks and the sentinel node were visualized within minutes of injection. Both the lymphatic trunks and the node fluoresced bright red under stimulation with red laser light.

These preliminary studies establish the potential usefulness of this new agent in lymphatic mapping. This novel technology might be useful in visualizing cancers that spread to regional lymph nodes. This technique has the potential to map the lymphatic drainage and to identify the presence of malignant cells in that drainage with currently available minimally invasive technology.