Aberrant neural crest cells migration leads to melanocyte presence in the umbilical cord

Systematic evaluation of the umbilical cord is an integral part of placental examination. Among the important parameters of this exam is the assessment of visible lesions such as knots and discoloration. The latter can be due to funisitis (yellow-white), meconium staining (green), vascular congestion (red-blue), or maternal hyperbilirubinemia (yellow). This case series presents fifteen examples of umbilical cord lesions characterized by foci of brown-black discoloration caused by melanin deposition.

Placental pathology reports from our institutions mentioning melanocytes or melanin in the umbilical cord were reviewed, and the slides pulled for histologic analysis by members of the pathology team. Immunohistochemical (SOX10, Melan-A, PHOX2B, and CD56) and histochemical (Fontana-Masson) staining was performed retrospectively on the umbilical cord sections.

Fifteen cases of umbilical cord with grossly visible brown linear stippling or punctate discoloration were confirmed. Microscopic examination showed scattered SOX10-positive melanocytes in the amnion layer with melanin deposition and uptake by the amniocytes. Nine of the fifteen infants and none of the mothers had congenital melanocytic lesions, 7 with "congenital dermal melanocytosis" (CDM), and 2 with congenital melanocytic nevi (CMN).

To the best of our knowledge, this is the first description of melanocytes and melanin pigment in the umbilical cord. We propose that an aberrant migration of neural crest cells into the umbilical cord, with subsequent differentiation into melanocytes, is the most likely pathogenesis.