Benign melanocytic lymph node deposits in the setting of giant congenital melanocytic nevi: the large congenital nodal nevus.

BACKGROUND

Benign melanocytic rests are a frequent finding in superficial lymph nodes removed during sentinel lymph node biopsies for melanoma. Whereas the histopathology of these deposits is well understood, very little is known regarding melanocytic lymph node deposits in the setting of giant congenital melanocytic nevi.

METHODS

We analyzed lymph nodes removed from the drainage basin of giant congenital melanocytic nevi in three patients who had developed melanoma within their giant congenital nevi.

RESULTS

Two of three patients showed widespread, capsular and parenchymal melanocytic deposits in multiple nodes (9 of 11 nodes in one patient and 6 of 8 in the other). Melanocytes were small, non-mitotically active and resembled those in the associated giant congenital melanocytic nevus. Melanocytes were arranged singly and in small nests ∼0.05 mm in diameter, with some larger sheets up to 1 mm. Nodal melanocytes stained for Melan A and S100 on immunohistochemical evaluation, but showed negative or minimal HMB-45 reactivity.

CONCLUSIONS

Evaluation of lymph nodes in the setting of giant congenital melanocytic nevi is complicated by the presence of often numerous, parenchymal melanocytic nevic deposits. Bland cytology and minimal or absent HMB-45 staining may be helpful in differentiating these nodal melanocytic nevi from metastatic melanoma. We term this phenomena large congenital nodal nevus.