Skin nonmelanocytic tumor
Benign (nonmelanotic) epidermal tumors or tumor-like lesions
Melanoacanthoma
Author: Hillary Rose Elwood, M.D.
Last author update: 1 January 2016
Last staff update: 1 November 2023
Copyright: 2003-2024, PathologyOutlines.com, Inc.
PubMed Search: Cutaneous melanoacanthoma [title]
Table of Contents
Definition / general | Case reports | Clinical images | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Electron microscopy description | Differential diagnosisCite this page: Elwood H. Melanoacanthoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocyticmelanoacanthoma.html. Accessed April 20th, 2024.
Definition / general
- Benign pigmented lesion composed of melanocytes and keratinocytes
- Best regarded as a variant of seborrheic keratosis
- Oral melanoacanthoma or melanoacanthosis is clinically distinct from cutaneous melanoacanthoma
- Oral melanoacanthoma is likely reactive, possibly a form of postinflammatory hypermelanosis, and not a tumor-like proliferation
- It is not discussed as part of this topic
Case reports
- 58 year old woman with multifocal cutaneous melanoacanthoma with ulceration (Indian J Dermatol Venereol Leprol 2011;77:699)
- 65 year old man with giant melanoacanthoma mimicking melanoma (Indian J Dermatol 2011;56:79)
Clinical images
Images hosted on other servers:
Oval lesion of maximum transverse diameter 10 cm
Ulcerated plaque
Gross description
- Pigmented plaque, papule or nodule with dull surface
- Usually solitary and slow growing lesion on head and neck or trunk of older individuals
- Can clinically mimic a seborrheic keratosis or melanoma
- Large variants have been described, up to 3 cm or more
Microscopic (histologic) description
- Resembles a seborrheic keratosis with acanthotic or slightly verrucous epidermis containing small cuboidal keratinocytes and numerous dendritic melanocytes
- The dendritic melanocytes are heavily pigmented with abundant melanin granules
- Most melanin pigment is contained within the dendritic melanocytes with little transfer to adjacent keratinocytes
- Dendritic melanocytes express usual markers of melanocytic differentiation (i.e. S100, HMB45, MelanA)
- Often has overlying compact eosinophilic parakeratosis even when not irritated
- No significant cytologic atypia present
Microscopic (histologic) images
Images hosted on other servers:
Hyperkeratosis and papillomatosis
Hyperkeratosis and acanthosis
Basaloid cells
Masson-Fontana
Electron microscopy description
- Composed of benign keratinocytes and dendritic melanocytes
- Incomplete transfer of pigment from melanocytes to keratinocytes, normal population of Langerhan cells (J Cutan Pathol 1978;5:127)
Differential diagnosis
- Melanoma:
- While the dendritic melanocytes in melanoacanthoma might be confused for intraepidermal spread of melanocytes, the melanocytes lack atypia and are part of a background keratinocytic proliferation
- Pigmented hidroacanthoma / poroma:
- Contains discrete smooth bordered intraepidermal cellular aggregates with ductal differentiation
- Melanin pigmentation not restricted to pigmented melanocytes
- Pigmented squamous cell carcinoma in situ:
- Full thickness intraepidermal keratinocytic atypia with mitoses and pigment in keratinocytes
- Seborrheic keratosis:
- Melanoacanthoma is a variant of seborrheic keratosis so the distinction is not critical
- Some might sign out melanoacanthoma as seborrheic keratosis, or might use melanoacanthoma with the additional descriptor of 'benign variant of seborrheic keratosis with prominent dendritic melanocytes'
