Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Benign tumors and cysts of the epidermis


Benign acanthomas

Acanthomas are benign cutaneous neoplasms characterized by an expansion of the epidermis. The acanthoma may be composed of clones of cells that displace or compress the preexisting epidermis. In contrast to the reactive acanthosis seen in inflammatory disorders, the rete ridge pattern is commonly ablated by the neoplastic tissue of an acanthoma.

Seborrheic keratoses

Seborrheic keratoses are acanthomas composed of small polygonal keratinocytes about the size of acrosyringeal keratinocytes (the cells that make up the intraepidermal portion of the eccrine duct). The cells are typically smaller than the cells of the surrounding epidermis, and they are commonly pigmented. Architectural subtypes of seborrheic keratoses include acanthotic, hyperkeratotic, reticulated, and clonal. Any of these subtypes may be pigmented, irritated (spindling of cells and squamous eddy formation), or inflamed (usually lymphoid inflammation). Melanoacanthoma is a distinct subtype of seborrheic keratosis composed of small keratinocytes and dendritic melanocytes.

Seborrheic keratoses produce a characteristic loose lamellar “shredded-wheat” stratum corneum. Exceptions include irritated or inflamed seborrheic keratosis. Instead of the characteristic loose lamellar horn, irritated or inflamed seborrheic keratoses produce a compact, brightly eosinophilic, parakeratotic stratum corneum. Adjacent unaffected areas of the seborrheic keratosis still produce the characteristic loose lamellar stratum corneum, and it is common to see remnants of loose stratum corneum above areas of compact stratum corneum. Melanoacanthomas produce a deeply eosinophilic, compact, parakeratotic stratum corneum, even when they are not irritated or inflamed.

Seborrheic keratoses may express BCL-2, a marker associated with resistance to programmed cell death (apoptosis). Activating point mutations in the gene encoding fibroblast growth factor receptor 3, a tyrosine kinase receptor, are also common in seborrheic keratoses.

Acanthotic seborrheic keratosis

Key Features

  • Broad sheets of small polygonal keratinocytes with intervening horn cysts

  • Loose lamellar “shredded-wheat” or “onion-skin” keratin

  • Commonly pigmented

Acanthotic seborrheic keratoses are composed of broad sheets of cells with intervening horn cysts or pseudohorn cysts. Horn cysts are completely encased within the acanthoma, whereas pseudohorn cysts open to the surface. Like other seborrheic keratoses, they may become irritated or inflamed.

Fig. 2.1, Acanthotic seborrheic keratosis

Fig. 2.2, Pigmented acanthotic seborrheic keratosis

Fig. 2.3, Irritated acanthotic seborrheic keratosis

Fig. 2.4, Inflamed acanthotic seborrheic keratosis

Hyperkeratotic seborrheic keratosis

Key Features

  • Tall stacks of loose lamellar “shredded-wheat” keratin

  • Papillomatosis: hills and dales that may produce a “church-spire” appearance

The tall, stacked stratum corneum is typically much thicker than the epidermis. As in other forms of seborrheic keratosis, the keratin has a loose lamellar “shredded-wheat” appearance unless the lesion has become irritated or inflamed. Papillomatosis is characteristic, but variable in degree. Horn cysts are inconspicuous or absent.

Fig. 2.5, Hyperkeratotic seborrheic keratosis

Fig. 2.6, Inflamed hyperkeratotic seborrheic keratosis

Reticulated seborrheic keratosis (adenoid seborrheic keratosis)

Key Features

  • Thin, pigmented, interlacing, downward extensions of the epidermis

  • Reticular (lacelike) configuration of epidermis interspersed with horn cysts

The lesion is composed of thin, interlacing strands of epidermis, typically two cells thick. These strands are generally pigmented.

Differential Diagnosis

Fig. 2.7, Reticulated seborrheic keratosis. (For the differential diagnosis of Dowling–Degos disease, see Fig. 12.15 . For the differential diagnosis of solar lentigo, see Fig. 6.1 )

Solar lentigo

Key Features

  • Shares thin, pigmented, interlacing extension of the epidermis

  • These are shorter and more bulbous than those in reticulated seborrheic keratosis

  • Lacks horn cysts

Clonal seborrheic keratosis

Key Features

  • Clonal islands of small keratinocytes within the epidermis

  • Bland uniform nuclei

  • Absence of duct differentiation within clonal nests

Clonal seborrheic keratosis is characterized by islands of small keratinocytes with uniform bland nuclei. The nests are embedded within the epidermis. Sometimes, the nests are large enough that the normal epidermis is reduced to thin strands separating the large nests. Horn cysts are usually absent. The nests may demonstrate pigment. There may be squamous eddies (irritated seborrheic keratosis), lymphocytes (inflamed seborrheic keratosis), or both. In contrast to Bowen disease, the cells are uniform and atypia is absent. In contrast to hidroacanthoma simplex, no ducts are present within the clones.

Differential Diagnosis

Fig. 2.8, Clonal seborrheic keratosis

Fig. 2.9, Pigmented clonal seborrheic keratosis

Fig. 2.10, Irritated clonal seborrheic keratosis

Fig. 2.11, Irritated and inflamed clonal seborrheic keratosis

Hidroacanthoma simplex

Key Features

  • Clonal islands of small keratinocytes similar in appearance to those of clonal seborrheic keratosis

  • Ducts present focally within the clonal islands

Bowen’s disease

Key Features

  • Clonal islands of atypical keratinocytes within the epidermis

  • Cells may be anaplastic or glassy and eosinophilic

  • Buckshot scatter of cells may be present focally

  • Apoptotic keratinocytes commonly scattered within nests

  • Overlying stratum corneum becomes compact and parakeratotic where clones touch the surface

  • More typical Bowen disease may be present in the adjacent skin

Fig. 2.12, Hidroacanthoma simplex

Fig. 2.13, Clonal Bowen disease

Pigmented seborrheic keratosis

Key Features

  • Pigment within keratinocytes

  • May be acanthotic, hyperkeratotic, reticulated, or clonal

  • When clonal, the pigment is restricted to the clonal islands

Fig. 2.14, Pigmented seborrheic keratosis

Irritated seborrheic keratosis

Key Features

  • Squamous eddies

  • Spindled keratinocytes

  • Horn cysts common

  • Keratin commonly becomes compact, eosinophilic, and parakeratotic

  • Keratin often retains a loose lamellar pattern in some areas

Irritated seborrheic keratosis is characterized by the formation of squamous eddies within the epidermis and the presence of spindled keratinocytes. Some areas of the tumor typically still produce a loose lamellar “shredded-wheat” pattern of keratin, and horn cysts composed of loose lamellar keratin are often present. In areas, the keratin becomes compact, eosinophilic, and parakeratotic. A zone of loose lamellar keratin may be seen above the dense eosinophilic keratin. This was produced before the lesion became irritated. It has since been pushed upward.

Fig. 2.15, Irritated seborrheic keratosis with prominent squamous eddies

Fig. 2.16, Irritated seborrheic keratosis with prominent spindling of keratinocytes

Inflamed seborrheic keratosis

Key Features

  • Lymphocytes and spongiosis

  • In areas, the stratum corneum becomes compact, eosinophilic, and parakeratotic

  • Loose lamellar keratin is commonly retained in other areas

  • Horn cysts are common

  • Lichenoid interface dermatitis may be present

  • An overlying crust may be present

Inflamed seborrheic keratosis is characterized by lymphocytes and spongiosis within the epidermis or the presence of lichenoid interface dermatitis. Some areas of the tumor typically still produce a loose lamellar “shredded-wheat” pattern of keratin, and horn cysts composed of loose lamellar keratin are often present. As in irritated seborrheic keratoses, a zone of loose lamellar keratin may sometimes be seen above a zone of dense eosinophilic keratin. When clonal, the spongiosis and lymphoid infiltrate are typically restricted to the clonal islands.

Fig. 2.17, Inflamed seborrheic keratosis with lymphocytes and spongiosis

Fig. 2.18, Inflamed seborrheic keratosis with lichenoid interface dermatitis

Melanoacanthoma

Key Features

  • Acanthoma composed of both small keratinocytes and pigmented dendritic melanocytes

  • Most pigment is within dendrites

  • Overlying stratum corneum is almost always compact eosinophilic and parakeratotic

Cutaneous melanoacanthomas are a type of seborrheic keratosis, composed of both small cuboidal keratinocytes and pigmented dendritic melanocytes. Most melanin pigment is contained within the melanocytic dendrites, with little visible pigment within the keratinocytes. Unlike most seborrheic keratoses, horn cysts and loose lamellar horn are typically absent. Instead, the overlying stratum corneum is almost always compact, eosinophilic, and parakeratotic. Cutaneous melanoacanthomas may be clonal. Oral melanoacanthomas are reactive proliferations unrelated to seborrheic keratosis.

Fig. 2.19, Melanoacanthoma

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

Related Posts