Invited commentary on “Decorative sentinel lymph node – a new entity?” by Vandeweyer and Van De Casseye

Abstract

In an age of super-specialization we are all most comfortable in our own areas of expertise. To the operating surgeon an unexpected black-hued lymph node is a surprising and disturbing finding that appropriately raises concern that the node may harbor melanoma, even in the absence of a history of prior melanoma. To pathologists pigments in tissues are relatively commonplace, but can be challenging. A dark-colored node may contain melanin pigment, in melanoma cells or in macrophages, hemosiderin or, as in the case reported in this issue, particulate carbon. Rarer possibilities include lipofuscin or homogentisic acid in patients with alkaptonuria. In interpreting the nature and significance of tissue pigmentation pathologists follow wellestablished algorithms. Iron-based pigments, such as hemosiderin react precisely in the Prussian blue histochemical reaction and turn a striking blue color. Melanins turn darker with silver stains and are removed by bleaching agents such as potassium permanganate (iron and carbon are not bleachable). The cytology and histology of a melanized lymph node are remarkably easier to interpret in a hematoxylin and eosin-stained section after removal of the masking melanin by bleaching. Nodal carbon is relatively common: deriving from the tattoo artist in the case of peripheral nodes and cigarette smoke, the coal mine and the polluted urban environment in the case of pulmonary and mediastinal nodes. Carbon pigment is now used to confirm the ‘‘sentinel’’ status of a lymph node [1]. Thus, the intriguing clinical dilemma presented by Vandeweyer et al. in this issue is readily resolved by careful pathologic evaluation of the tissues. Note that this requires fixed tissues and special stains and is thus not a matter that can readily or certainly be resolved by intraoperative frozen-section analysis. A node that is dark-colored on clinical inspection may be the site of metastatic melanoma, but it would seem inappropriate to undertake further and substantial surgery purely on the basis of gross inspection, without detailed and thoughtful histological analysis. Close consultation between the operating room and the surgical pathology laboratory provides a solid basis for optimal clinical management.