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Amelanotic Cellullar Blue Nevus - Submitted on: Monday November, 17, 2003
Contributed by:Artur Zembowitz, MD, N/A
We have recently described a series of 20 cellular blue nevi devoid of pigmentation.1 Recognition of this variant of blue nevus is particularly important as it often confused with other entities. In our series, clinical diagnosis of a melanocytic lesion was considered in only 4 cases. Diagnosis of a blue nevus was not suspected at all. Amelanocytic CBN has similar age, sex and site distribution to common CBN. Histological diagnosis of amelanotic CBN may be very challenging on a small biopsy. In our series only 8 out of 19 cases submitted for the second opinion were correctly diagnosed as CBN.


Definition:
Amelanotic cellular blue nevus is a cellular blue nevus with minimal or without melanin pigmentation.

Clinical Features:
Our series showed clinical demographics similar to pigmented counterparts with predilection to young people. The mean age at the time of occurrence was 24 years with a range 6-74 years. Females were more commonly involved with female-to-male ratio of approximately 2:1. The lower back, distal extremities, and scalp were the most common sites of occurrence. Importantly, the lack of pigmentation resulted in an atypical clinical appearance. The lesions were amelanotic cutaneous and/or subcutaneous nodules.

Histology:
Figures
(Click on an image for a larger view)
Figure 1:Low magnification view of amelanotic cellular blue nevus
Figure 2: High magnification of amelanotic cellular blue nevus
The key to diagnosis of ACBN is recognition of blue nevus features in spit of the lack of expected pigmentation. These lesions are biphasic with classic BN-like spindle and dendritic cell proliferation in the superficial dermis. Characteristic cellular expansive nodules or sheets of round to oval cells with oval nuclei inconspicuous nucleoli and clear to lightly eosinophilic cytoplasm in the dermal component are present in deep reticular dermis or within a classic blue nevus areas (Figures 1, 2). In some cases, all with alveolar architectural pattern, the cellular nodules contain multinucleated wreath-like cells. Mitotic activity of up to 3 mitoses per mm2 can be present.


Treatment:
Complete excision is curative, as none of the completely excised lesions recurred.

Differential Diagnosis: Histological differential diagnosis of ACBN include amelanotic melanoma, desmoplastic melanoma, malignant cellular blue nevus, clear cell sarcoma, dermatofibroma, cellular neurothekeoma, myoepithelioma


Bibliography:
  • Zembowicz,A, Granter,SR, McKee,PH, Mihm,MC. Amelanotic cellular blue nevus: a hypopigmented variant of the cellular blue nevus: clinicopathologic analysis of 20 cases. Am.J.Surg.Pathol. 2002;26:1493-1500.
     

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