Solar elastotic material in dermal lymphatics and lymph nodes.

The movement of material via passive mechanical transport through lymphatic channels (also known as benign mechanical transport) is a physiologic mechanism invoked to explain the occasional presence of benign heterotopic tissues within lymph nodes. However, historically, the concept of benign mechanical transport has provoked controversy. The proof of this concept is of fundamental importance to the claim that foreign cells or cellular aggregates found within a sentinel lymph node do not necessarily represent clinically relevant metastatic disease. Herein we present the previously undescribed finding of solar elastotic material within the dermal lymphatics, and/or capsules, subcapsular sinuses, and parenchyma of lymph nodes of 9 patients. Eight of the patients were treated and/or staged for cutaneous melanoma; one had Merkel cell carcinoma. Solar elastotic material was found in lymph nodes in association with metastatic melanoma, nodal melanocytic nevi, and in otherwise unremarkable lymph nodes lacking extrinsic cells. These findings support the concept of the mechanical transport of both benign and malignant tissues through lymphatics and document that passively transported material can appear in any compartment of the lymph node; an important concept to give evidence for, as it offers a sound explanation for the presence of some cellular deposits within lymphoid tissue and supports the assertion that some of these deposits are benign.