REVIEW – BAKER (2014)
Lymphatic Function is Impaired Following Irradiation of a Single Lymph Node

Patients are frequently told by their oncologists that performance of sentinel lymph node biopsy does not result in a significant risk of lymphedema. Patient experience very often shows that this is not true. Common practice today is for conservative breast surgery to be followed by irradiation for local control of recurrence. When lymphedema occurs after the combination of sentinel lymph node biopsy, lumpectomy and radiotherapy, it is puzzling to both the oncologist and the patient, since this was not the expectation.

An interesting study just documented investigates, using a rabbit model, the effect of the irradiation of a single lymph node on lymphatic transport. This study resulted in the conclusion that irradiation of a single lymph node caused impaired lymph transport and increased the pressure required to maintain flow through the lymphatic system. New lymph vessel formation and growth of lympho-venous anastomoses indicated the development of alternative drainage pathways as a compensatory response.

The human analog of this animal study might be the removal or irradiation of one or more lymph nodes in pathways responsible for drainage of the breast or arm. In the animal test radiation of intact nodes decreased lymph transport significantly at one week, one month, and 6 months post treatment in comparison to controls. Surprisingly, this functional decline was similar to that detected with a combination of node removal and irradiation of the excision site. The pressure–flow relationships were significantly different from controls. This may be due in part to fibrosis and thickening of the nodal capsules and trabeculae observed at 1 and 6 months. Imaging studies revealed a vigorous new lymphatic vessel growth and occasionally, vessels anastomosed with local veins.

The authors conclude that the fact that the magnitude of functional suppression following lymph node excision plus radiation is similar to irradiation alone, suggests that a major portion of the injury to the system was caused by the radiation itself. Collagen deposition in the node resulting in a thickened nodal capsule may have contributed to this functional deficit. The edema associated with lymph node removal or irradiation in the rabbit model appears to be largely sub clinical. However, there was a tendency for tissue water to decrease in the irradiated limbs. This was likely due to fibrosis in the affected tissues. The development of new lymphatic vessels and lympho-venous anastomoses indicated a vigorous attempt by the host to compensate for the lymph flow impediments by establishing collateral pathways for drainage.

This paper by Baker, et al. (2014) together with the paper by Johansson et al. (2014) go a long way to explaining the etiology of breast and upper extremity lymphedema after conservative breast surgery and sentinel lymph node dissection and radiotherapy.

REFERENCES:

Baker A, Semple JL, Moore S & Johnston M: "Lymphatic function is impaired following irradiation of a single lymph node" Lymphatic Res Biol. 2014; 12 (2): 76–88.

Johansson K, Lathinen T & Björk-Eriksson: "Breast edema following breast conserving surgery and radiotherapy" Euro J Lymphology 2014;25(70): 1-5.

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© 2002 Robert Weiss, Porter Ranch, CA