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PURPOSE: Despite paramount importance for understanding pathophysiology of lymphedema, post operative changes in the lymphatic system has been poorly studied. One of the reasons is that there has been no standard animal model for investigating these changes after lymph node dissection. Based on our previous studies, a canine revealed to be an ideal animal model for studying lymphatics because of adequate number of lymphatic channels and their reasonable size. The aims of this study were to delineate the entire peripheral lymphatic system in a dog and to investigate postoperative changes of lymphatic architecture.
METHODS: Five mongrel dogs weighing 23-27 kg were used. Indocyanine green (ICG) and infrared fluorescent lymphography was used to identify lymphatic vessels. The individual channels were dilated with hydrogen peroxide, injected with radio-opaque lead oxide mixture with intralymphatic microinjection technique and recorded on radiographs in order to delineate normal lymphatics. One dog underwent unilateral lymph node dissections of lymphatic basin of the forelimb. The dog was scanned with the infrared fluorescent lymphography. Then cannulation was performed at the dorsal paw in the operated forelimb and radio-contrast media was injected with syringe pump (lymphography) one year after the operation. C-arm was used for investigating lymphatic alterations.
RESULTS: Lymphatic vessels picked up the ICG dye even in the post-mortem dog and therefore the ICG lymphography could demonstrate lymphatic channels running in the subcutaneous tissue. The lymphatic vessels originated from near the dorsal and ventral midlines and feet. Eight different sites of lymph node were distinguished in the dog body. Each lymphatic vessel was colour coded retrogradely from each lymphatic basin. Thus the body was divided into eight lymphatic territories (lymphosomes) and lymphatic vessels between territories did not overlap each other. There was no midline crossover. Lymphosomes were uniform between each dog. Lymphatic basin in the forelimb was specified with the ventral superficial cervical node and axillary lymph node. In a dog that underwent unilateral lymph node dissection of the nodes, temporary swelling of the forelimb and torso occurred but it subsided after two weeks. Lymphography revealed that was normal appearance of the lymphatic vessels from the paw to the operated site. However, lymph capillary dilation (dermal backflow sign) was seen in correspondence with the operated area. Abnormal lymphatic channels were found proximal to the dermal backflow and they connected to the ipsilateral dorsal superficial cervical node and the contralateral ventral cervical lymph node. They were regarded as collateral lymph formation after lymph node dissection.
CONCLUSION: We were able to demonstrate, mapping of the lymphatic system (lymphosomes) in a canine model. For the first time, lymphatic collateral formation after lymph node dissection was recorded with lymphography in a living dog. This canine model is useful for investigating post operative changes of the lymphatic system, and may help us to better understand the pathophysiology of lymphedema and lymphatic pathway changes after lymph node dissection.