INTRODUCTION

ACBN is an uncommon entity newly described in the literature [1]. It is an intermediate form between typical cellular blue nevus and malignant blue nevus; it also presents as a differential diagnosis for deep penetrating blue nevus [2]. ACBN has an unpredictable evolution that may exceptionally undergo a malignant transformation to become a malignant blue nevus characterized by lymph node metastases present in 80% to 90% of cases [3,4]. It is usually manifested histologically by the presence of cells lacking atypical mitoses and necrosis [5].

CASE REPORT

A 37-year-old female without any particular pathological history, especially melanoma, consulted for a blackish intergluteal lesion evolving for eighteen months. A general examination revealed a patient in good general condition. A dermatological examination found a pedunculated bluish-black mass of 3,5 cm along the long axis of firm consistency and with a non-infiltrated base (Fig. 1a). Dermoscopy showed a bluish-white veil, a chrysalis, and a red background (Fig. 1b). The lymph nodes were free. An excisional biopsy was performed.

Figure 1: (a) Bluish-black, 3.5 x 2.5 x 1.0 cm, pedunculated, single mass in a intergluteal location. (b) Dermoscopy: Bluish-white veil, chrysalis, and a red background.

Histologically, the lesion was polypoid, with considerable dermal and partly hypodermal cellularity made of intensely pigmented dendritic cells and epithelioid cells. Some mitoses without atypia were observed without epidermal invasion or necrosis. Proliferation encompassed eccrine pletons and adipocyte lobules in depth, with images of nerve pseudoinvasion. Immunohistochemistry reavealed intense and diffuse expression of P16 by the tumor cells, as well as diffuse and homogeneous expression of HMB45, with an estimated KI67 of 5–10% (Figs. 2a – 2c). On the basis of clinical and histopathological data, the diagnosis of pedunculated NBCA was retained.

Figure 2: (a) Presence of a tumor proliferation made of spindle-shaped melanocytic cells, sometimes epithelial, with enlarged nuclei, heterogeneous chromatin, and one or more basophilic nucleoli. The cytoplasm was abundantly loaded with melanin pigments. (H&E, 100×). (b) Edematous papillary dermis with the Grenz zone preserved (H&E, 100×). (c) Immunostaining of melanocytic cells with HMB-45.

DISCUSSION

The term ACBN has been used to label lesions that have the characteristics of the associated blue cell nevus of cellular atypia, prominent nucleoli, and a mitotic index of less than 2 digits/mm [6]. The true nature of ACBN is not fully revealed due to the lack of data in the literature, however reported cases have suggested its benign nature [3,7].

Epidemiologic elements are important to consider in the diagnostic orientation as well as the therapeutic management [8]. NBCA usually affects young females, with a sex ratio of 9/6, and the clinical diagnosis is usually made at the age of twenty years [4,9], which was our case.

The localizations of ACBN described in the literature are, by order of frequency, the sacral region, which was the case of our patient, the scalp, and the limbs [10]. Concerning the tumor size of ACBN, it varies from 1 to 4 cm according to the authors, yet beyond these dimensions, malignancy is suspected [4,6,10].

In our case, histologically, the lesion showed low mitotic activity in the absence of necrosis without any evidence of recurrence or metastasis after twelve months post-surgery.

In contrast to ACBN, malignant blue nevus has more malignant cytologic features, including atypical mitoses and necrosis [11], as well as high aggressiveness: 80% of patients have metastasis at the time of diagnosis, and the five-year mortality rate is high [4,6,12].

Unlike ACBN, deep penetrating nevus occurs in a slightly older population and is more common in the head and neck regions. It has some of the characteristics of ACBN, with extension to the papillary dermis and subcutaneous fat as well as to the periphery of blood vessels, nerves, and skin appendages, which is unusual in ACBN [9,13], yet not impossible, which was the case in our patient.

CONCLUSION

Atypical blue-cell nevus is a particular and borderline histological form. Its pedunculated form is rare, with only two cases cited in the literature [1]. Its evolution and prognosis are difficult to determine. Surgical removal and long-term clinical monitoring are always recommended.

REFERENCES

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9. Krishnan S, Yesudian DP, Jayaraman M, Janaki VR, Yesudian P. Malignant blue nevus. Indian J Dermatol Venereol Leprol. 1997;633:183-5.

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11. Aloi F, Pich A, Pippione M. Malignant cellular blue nevus:A clinicopathological study of 6 cases. Dermatology. 1996;1921:36-40.

12. Rodriguez HA, Ackerman LV. Cellular blue nevus:Clinicopathologic study of forty-five cases. Cancer. 1968;213:393-405.

13. Mehregan DA, Mehregan AH. Deep penetrating nevus. Arch Dermatol. 1993;1293:328-31.