Year : 2007 | Volume
: 52 | Issue : 2 | Page : 109--110
Genital and perianal melanoacanthomas
Manjunath M Shenoy1, S Teerthanath2, KR Bhagavan3,
1 Department of Skin and VD, KS Hegde Medical Academy, Deralakatte., Mangalore - 574 160, India
2 Department of Pathology, KS Hegde Medical Academy, Deralakatte., Mangalore - 574 160, India
3 Department of General Surgery, KS Hegde Medical Academy, Deralakatte., Mangalore - 574 160, India
Manjunath M Shenoy
Department of Skin and VD, KS Hegde Medical Academy, Deralakatte., Mangalore - 574 160
Melanoacanthoma is a benign mixed tumor of melanocytes and keratinocytes. It has been regarded as a rare variety of Seborrheic keratosis. A 50-year-old male presented with multiple asymptomatic pigmented growths on the lower abdomen, inner thighs, external genitals and perianal areas. Histopathology revealed features of melanoacanthoma. The case is being reported for unusual sites of occurrence of an uncommon cutaneous tumor.
|How to cite this article:|
Shenoy MM, Teerthanath S, Bhagavan K R. Genital and perianal melanoacanthomas.Indian J Dermatol 2007;52:109-110
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Shenoy MM, Teerthanath S, Bhagavan K R. Genital and perianal melanoacanthomas. Indian J Dermatol [serial online] 2007 [cited 2020 May 25 ];52:109-110
Available from: http://www.e-ijd.org/text.asp?2007/52/2/109/33292
Melanoacanthomas are among the rare cutaneous tumors. Although melanoacanthoma can be found both on the skin and oral mucosa, oral melanoacanthomas are rare reactive mucosal lesions which demonstrate hyperplasia of spinous keratinocytes and melanocytes and are unrelated to seborrheic keratosis.  Cutaneous Melanoacanthomas manifest as pigmented papules, plaques, cutaneous horns or nodules.  They are commonly found on the head and trunk areas. Patients are generally asymptomatic and may wait for decades before they seek treatment. Microscopic examination of cutaneous melanoacanthoma reveals a proliferation of keratinocytes and melanocytes localized to the epidermis. Many melanocytes are scattered throughout the tumor lobules rather than localized to the basal layer, a feature that distinguishes melanoacanthomas from other cutaneous tumors.
A 50-year-old male presented with multiple asymptomatic pigmented growths on the lower abdomen, inner thighs, external genitals and perianal areas for the past 10 years. To begin with they were flat brownish lesions, which later got elevated. There were no significant medical or surgical problems in the past. On examination there were multiple pigmented verrucous papules, plaques and nodules measuring 0.5 to 6 cm on the lower abdominal wall, root and shaft of penis, left inner thigh and perianal skin [Figure 1],[Figure 2]. Lesions in the perianal areas were pedunculated. There were a few slightly elevated flat-topped papular lesions on the penile shaft and scrotum giving a stuck-on appearance. Mucous membranes were devoid of any lesions and there was no lymphadenopathy. Apart from these findings, dermatological and systemic examinations were normal. Keeping the clinical features in view, Seborrheic keratosis and genital warts were considered for differential diagnosis. He was investigated and his complete blood count, renal function test and blood sugar levels were with in normal limits. VDRL and human immunodeficiency virus enzyme-linked immunosorbent assay were non reactive. One of the cutaneous lesions was excised and histopathological examination was carried out. There were hyperkeratosis, acanthosis and papillomatosis with the base of the tumor lying in a straight line with the surrounding normal epidermis [Figure 3]. These features were suggestive of diagnosis of seborrheic keratosis. The tumor lobule was composed of keratinocytes along with scattered melanocytes a feature that was characteristic of melanoacanthoma.
Mishima and Pinkus coined the term melanoacanthoma in 1960 to describe a pigmented, benign proliferation of both keratinocytes and dendritic melanocytes.  They are generally regarded as a type of Seborrheic keratosis; however it needs to be distinguished from ordinary pigmented seborrheic keratosis. Melanoacanthomas are rare and have been described more frequently in white patients.  They develop in the middle-aged and the elderly like any other type of seborrheic keratosis. They are found mainly on the trunk or head, often on the lip or eyelid.
Microscopically melanoacanthoma are characterized by epidermal proliferation of keratinocytes and melanocytes. Acanthosis, hyperkeratosis, papillomatosis and small horn pearls may also be seen.  Many melanocytes are scattered throughout the tumor lobules of a melanoacanthoma rather than localized to the basal layer. These melanocytes are large and highly dendritic and they contain varying amounts of melanin. Two histologic types of melanoacanthomas are described: a diffuse type in which melanocytes are unevenly scattered throughout the lesion and a clonal type in which melanocytes and keratinocytes are clustered in small nests.  There was partial or complete disturbance of transfer of melanin from these highly dendritic melanocytes to neighboring keratinocytes.  Immunofluorescent studies and a immunoprecipitin assay have shown that melanoacanthomas are not related to malignant melanoma, and hence removal by simple excision, curettage or cryotherapy should be curative.
In our case the lesions were up to 6 cm in size and were located in unusual sites like penile shaft and perianal region. Prior to this there is one case report of lesion on penile shaft.  We also observed several types of cutaneous lesions like papules, plaques, sessile and pedunculated nodules in the same patients. Surgical excision of bigger lesions was done, and the specimens were sent for histopathologic examination. They also showed features of melanoacanthoma. This case is reported for the unusual sites of occurrence of an uncommon cutaneous tumor.
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