Case of the month - November 2007 - discussion

The following features are seen:

• Aggregates of epithelioid/spindle type cells within the capsule of the lymph node



• Morphologically these cells are typical of naevus cells



• The s100 positive phenotype is characteristic of naevus cells

Background information:

• Such rests may be found in any lymph node draining a cutaneous site



• In axillary dissections for breast carcinoma they are found in 0.33% of patients and in 0.017% to 0.1% of lymph nodes



• The rests are usually found within the capsule or trabeculae of lymph nodes but may occur adjacent to blood vessels



• Cellular blue naevi may also be found in lymph nodes and are usually seen in sinuses or within the parenchyma



• It is important to be aware of this phenomenon and not mistake the lesion for metastatic carcinoma

Additional information:

• Two theories explaining how the rests reached the lymph nodes:



1. Arrested migration of neural crest progenitor cells during emryogenesis



2. Transport of cells from cutaneous lesions to lymph nodes



• Evidence favouring the first theory:



• Commonly a capsular location sparing sinuses



• Known concurrence of embryogenic migration of melanocytic precursors and development of the lymphatic system



• The presence of blue nevus cells in other sites such as prostate, cervix and vagina



• Lack of cutaneous melanocytic naevi in catchmnet areas of involved lymph nodes in some cases



• The rarity of finding naevus cells and metastatic melanoma in the same node



• Evidence favouring the second theory:



• Naevus cells sometimes found in nodal sinuses or parenchyma



• Intranodal deposits of other tissues are seen e.g. endometrium



• Naevus cells are not found in nodes draining non-cutaneous sites



• Naevus cell clusters are found within cutaneous lymphatics

Reference:

Patterson JW. Nevus cell aggregates in lymph nodes. Am J Clin Pathol 2004: 121: 13-15.

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