Large plaque type blue nevus with subcutaneous cellular nodules

ARTICLE

Auteur(s) : Edoardo Zattra¹, Roberto Salmaso², Maria Cristina Montesco², Barbara Pigozzi³, Giulia Forchetti¹, Mauro Alaibac¹

¹Unit of Dermatology, University of Padua, Via C. Battisti 206, 35128. Padova, Italy
²Unit of Pathology, University of Padua, Via C. Battisti 206, 35128. Padova, Italy
³Melanoma Unit, Veneto Institute of Oncology, IOV, Padua

Blue nevus is a benign dermal melanocytosis that includes a large spectrum of melanocytic proliferation. There are different varieties of blue nevus (BN) [1]. Among the less frequent there is the “large plaque blue nevus”. We describe a case of large plaque blue nevus with subcutaneous cellular nodules.

A 31-year-old Caucasian male presented with blue-grey, non-palpable patches, darker than the surrounding skin, diffusely involving the left side of the back, the left shoulder, and the elbow (figure 1A). At age 18, a cystic nodule within the lesion was biopsied, and histology showed a neurofibroma-like aspect associated with a dendritic melanocyte population. Immunohistochemistry revealed a diffuse positivity to HMB45 (gp100), NKI C3 and a focal positivity to S-100 and GFAP. An “atypical” blue nevus diagnosed. At age 19, an axillary nodule was biopsied and the pathologist diagnosed a melanocytic schwannoma. At age 25, a nodule on the arm was excised and the diagnosis was “dermal melanocytosis”. Immunohistochemically, neoplastic cells expressed a strong positivity for HMB45, NKI C3, S-100 whereas CD34, neurofilaments and EMA resulted negative. At age 29, a pigmented nodule rapidly increased in size within the lesion. This nodule was surgically removed with the underlying muscular tissue. The lesion showed large nests of pale ovoid small cells containing scant melanin and areas of dendritic pigmented cells, along with many pigmented melanophages. This nodule had a zone of striking nuclear atypia: with vescicular, large, fusiform nuclei containing a prominent nucleolus; cellular and nuclear pleomorphism was also present (figures 1B and C). Immunohistochemistry showed a strong reactivity of neoplastic cells for S100, CD63, MTF-1, Melan A (A103), Tyrosinase and non-reactivity for CD57 and neurofilaments. The mitotic index was 2/10HPF. Histologically the lesion was suggestive for malignant melanoma but considering the evolution of the lesion and the previous biopsies, the pathologist confirmed the diagnosis of atypical blue nevus. As the nodular lesion was not totally resected, a wide re-excision was performed.

The clinical, histological and immunohistochemical features of the lesion we describe are strikingly similar to the “large plaque-type blue nevus with subcutaneous cellular nodules” described by Busam et al. in 2000 [2]. The histopathological features of large plaque blue nevus are similar to ordinary blue nevus; the lesion involves the reticular dermis and subcutis. There is no melanocytic proliferation at the dermo-epidermal junction and in the papillary dermis. The reticular dermal component is characterized by some heterogeneity of melanocytes, including slender dendritic cells, fascicles of spindle cells, aggregated epithelioid melanocytes, and, occasionally, clear melanocytes. Most of them are located in the deep dermis near the subcutis and are, often, predominantly arranged in a periappendageal distribution around blood vessels and nerves. The foci of ordinary blue nevus are separated by Mongolian spot-like areas, in which pigmented or fusiform melanocytes and melanophages are widely spaced from each other as single cells without the formation of cellular aggregates. Hypercellularity areas are present in the subcutis and contain nests and fascicles of melanocytes with clear cytoplasm. Their nuclei are oval in shape with inconspicuous single nucleoli. The cellular nests are surrounded by a population of slender spindle cells, distributed loosely in a fibrous stroma, with variable numbers of heavily pigmented dendritic melanocytes or melanophages.

In conclusion, we describe a case of “large plaque-type blue nevus with subcutaneous cellular nodules”. In our opinion, this lesion is characterized by an uncertain biological behaviour, thus needing close follow up.

Acknowledgements

Références

2 Busam KJ, Woodruff JM, Erlandson RA, Brady MS. Large plaque-type blue nevus with subcutaneous cellular nodules. Am J Surg Pathol 2000; 24: 92-9.