Intralymphatic nevus cells in benign nevi.

The histogenesis of nevus cell aggregates in lymph nodes lesion is controversial, and various hypotheses have been used to explain their origin. One of them is the transport of cells from cutaneous nevi or lesions to lymph nodes, called mechanical transport theory. We investigated in our cases of benign nevi to obtain evidence to substantiate this theory. A total of 369 benign cutaneous nevi were prospectively evaluated in excisional biopsy samples. Immunohistochemical stainings for CD31 and podoplanin (D2-40) were performed in the cases with intralymphatic nevus cell aggregate (ILNA), suspected for ILNA, and/or intralymphatic nevus cell protrusion. A total of 13 ILNAs were found in 10 patients. Six ILNA were verified with their histology as well as immunohistochemically with D2-40 and CD31. Protrusions of nevus cells inside the lymphatics (intralymphatic nevus cell protrusion) were seen in all cases of ILNA and also in 27 nevi where an ILNA was not observed. In most nevi, the perilymphatic orientation of nevus cells and their affinity to the lymphatics were observed. We suggested that ILNAs can be dislodged with local minor trauma and be carried inside the lymphatic vessel to the draining lymph node. Besides, whether ILNA or not, nevus cells could also move toward lymphatic spaces with mechanical effects due to their affinity to lymphatics and their localizations that are very close to the endothelium. Our findings might support the mechanical transport theory.