Perforating lymph vessels in the canine torso: Direct lymph pathway from skin to the deep lymphatics

BACKGROUND: Classic anatomical lymphatic mapping in humans is represented by four territories in the torso divided by the midline and horizontal line at the L2 level. Each territory drains into the ipsilateral axillary or inguinal lymph nodes. Recently, preoperative lymphoscintigraphy for staging breast cancer and malignant melanoma has become common in the clinical arena. It reveals an undescribed direct pathway from the skin of the loin to intraabdominal lymph nodes. The authors investigated the presence of such a lymphatic route using a dog model. METHODS: The authors used seven greyhound dogs for this study. The caliber of their lymph vessels was similar to those of humans, and because of a lack of fat tissue under the integument, the vessels were identified easily. The authors applied their original radiographic technique using hydrogen peroxide and lead oxide for delineating the superficial lymphatic system. RESULTS: Lymphatic territories of the torso were classified with relation to their regional lymph nodes. The authors found perforating lymph vessels in the lumbar and gluteal regions. They originated from the skin, penetrated the abdominal wall, and then drained into paraaortic lymph nodes instead of the axillary and inguinal lymph nodes. They were always accompanied by blood vessels, especially perforating veins. CONCLUSIONS: The authors found perforating lymph vessels in a canine torso. They seem to be equivalent to the unexpected lymph pathways found in humans using lymphoscintigraphy.