Zhong Zhen Goh¹, Dona Horadagoda¹

¹Department of Anatomical Pathology, Nepean Hospital, Kingswood, NSW 

 

Congenital melanocytic naevus (CMN) is a rare condition with an incidence of 1% of neonates. The naevi can involve anywhere on the skin and does not typically involve the placenta. We present a case of an infant with CMN with benign melanocyte infiltration of the placenta. 

 

A term male infant was born to a 33-year-old woman who had no unusual, pigmented lesions or personal history of melanoma. Examination of the infant showed hyperpigmented and flat skin lesions that covered 70% of the total body surface area. 

 

Gross examination of the placenta showed normal parenchyma with no visible macroscopic pigmented areas or nodules. Microscopic examination of the placenta revealed an incidental finding of pigmented naevus cell population in the villi along with melanin pigment. There was no intervillous space involvement or cytological atypia. These cells were positive with SOX10 and S100 staining. The infant remains healthy at 6 months.

 

Benign melanocyte infiltration of placenta in CMN is rare. To date, there are only 11 published cases, including our own patient.^1-3 This entity appears to have an association with a naevus size of greater than 20cm and presence of satellite nevi.³ Recognition of this entity is important to avoid erroneous misdiagnosis with malignant melanoma.

 

1.     Carroll CB, Ceballos P, Perry AE, Mihm MC Jr, Spencer SK. Severely atypical medium-sized congenital nevus with widespread satellitosis and placental deposits in a neonate: the problem of congenital melanoma and its simulants. J Am Acad Dermatol. 1994 May;30(5 Pt 2):825-8. doi: 10.1016/s0190-9622(94)70088-5. PMID: 8169253.

2.     Antaya RJ, Keller RA, Wilkerson JA. Placental nevus cells associated with giant congenital pigmented nevi.  Pediatr Dermatol. 1995;12260- 262

3.     Ball RA, Genest D, Sander M, Schmidt B, Barnhill RL. Congenital melanocytic nevi with placental infiltration by melanocytes: a benign condition that mimics metastatic melanoma. Arch Dermatol. 1998 Jun;134(6):711-4. doi: 10.1001/archderm.134.6.711. PMID: 9645640.

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