Seborrheic keratosis

Seborrheic keratosis
Diagnosis in short
Seborrheic keratosis. H&E stain.
LM	horn cysts, pigmented basal layer, hyperkeratosis
Subtypes	acanthotic seborrheic keratosis, reticulated seborrheic keratosis, irritated seborrheic keratosis, digitated seborrheic keratosis, stucco keratosis
LM DDx	actinic keratosis, verruca vulgaris, basal cell carcinoma (fibroepitheliomatous pattern) - for reticulated SK, melanocytic nevus, condyloma acuminatum, inverted follicular keratosis, fibroepithelial polyp
Gross	raised lesion
Site	skin
Associated Dx	internal malignancy - if very many
Clinical history	old age
Prevalence	very common
Prognosis	benign
Clin. DDx	melanocytic lesion

Seborrheic keratosis, abbreviated SK, is a very common diagnosis is dermatopathology.

General

• Benign.
• Most common tumour in older people.
• "Large number" of SKs = paraneoplastic syndrome (Leser–Trélat sign).

Epidemiology:

• Old people.
• Usually in sun exposed area.

Gross

Clinical image showing a large number of SKs (Leser–Trélat sign). (WC/Heilman)

• "Stuck-on" appearance - raised lesion.

Microscopic

Features:

• Raised above skin surface.
• Border sharply demarcated.
• Hyperkeratosis - stratum corneum extra thick.
  • May be minimal.
  • Usually predominantly basketweave pattern.
• Horn cysts - intraepidermal collections of keratin - key feature.
  • Actually invaginations - not true cysts; thus, they may more accurately be called pseudohorn cysts.
• Clusters of cells with brown granular material in the superficial dermis/dermoepidermal junction - pigmented melanocytes.

DDx:

• Actinic keratosis - especially, irritated SKs; have nuclear atypia and parakeratosis.
• Verruca vulgaris - koilocytes, compact hyperkeratosis and parakeratosis.
  • SKs typically have prominent basketweave hyperkeratosis.
  • SKs may have papillomatous projections.
• Basal cell carcinoma, fibroepitheliomatous pattern - esp. reticulated SK.
• Melanocytic nevus.
• Condyloma acuminatum - may have horn cysts, more probable than SK in the genital area.
• Inverted follicular keratosis - predominantly endophytic growth pattern, may be considered a variant of seborrheic keratosis.
• Collision with another lesion.
  • In one series, 85 of 639 SK were associated with other lesions.
  • It is postulated that melanocytic lesions are associated with SKs.
• Papillomatous compound nevus - a beign nevus with seborrheic keratosis-like features.
• Acanthosis nigricans - site important.
• Fibroepithelial polyp, epithelial type - may have abundant compact keratin, lack horn cysts.
• Eccrine poroma - lack horn cysts.

Images

• 

  Seborrheic keratosis. (WC)

• 

  Seborrheic keratosis - low mag. (WC)

• 

  Seborrheic keratosis - high mag. (WC)

• 

  SK - low mag. (WC)

• 

  SK - intermed. mag. (WC)

• 

  SK - high mag. (WC)

www

• Seborrheic keratosis - high mag. (dermatlas.org).
• Seborrheic keratosis - low mag. (dermatlas.org).
• Gallery of SK variants (ispub.com).
• Acantholytic SK (ispub.com).

Histologic subtypes

Like very common lesion, there are subtypes:

• Acanthotic seborrheic keratosis - thickened stratum spinosum; thick epidermis.
• Reticulated seborrheic keratosis - vaguely resembles fibroepithelioma of Pinkus (BCC, fibroepitheliomatous pattern).
• Irritated seborrheic keratosis - spongiosis (epidermal intercellular edema) and inflammation.
• Digitated seborrheic keratosis - papillomatous projections, architecture mimics a verruca.
• Stucco keratosis - pointed papillomatous projections.

Sign out

Skin Lesion, Left Lower Leg, Excision:
- Seborrheic keratosis, completely excised.
- Solar elastosis.

Skin Lesion (Submitted "Seborrheic Keratosis"), Right Back, Excision:
     - Extensively fragmented bland superficial squamous epithelium with 
       horn cysts and keratineous material, compatible with impression of 
       seborrheic keratosis; deeper lesion cannot be excluded.

Block letters

SKIN LESION, MID BACK, BIOPSY:
- SEBORRHEIC KERATOSIS.

SKIN LESION, RIGHT SCAPULA, PUNCH BIOPSY:
- RETICULATED SEBORRHEIC KERATOSIS.

SKIN LESION ("NEVUS"), RIGHT TRUNK AT BRA LINE, SHAVE BIOPSY:
- IRRITATED SEBORRHEIC KERATOSIS (HYPERKERATOTIC TYPE).

SKIN LESION, LEFT POSTERIOR SHOULDER, EXCISION:
- SEBORRHEIC KERATOSIS (ACANTHOTIC TYPE), COMPLETELY EXCISED.

SKIN LESION, LEFT POSTERIOR SHOULDER, EXCISION:
- SEBORRHEIC KERATOSIS WITH PIGMENTATION (ACANTHOTIC TYPE), COMPLETELY EXCISED
  IN THE PLANE OF SECTION.
- NEGATIVE FOR MELANOCYTIC LESION.

Micro

The sections show skin with acanthosis, pseudohorn cysts, hyperkeratosis and focal basal epidermal pigmentation. There is no basal nuclear atypia, and there are no melanocytic nests. Mitotic activity is not apparent. There is minimal dermal inflammation. There is no apparent solar elastosis.

Without horn pseudocysts

The sections show skin with acanthosis, a thin layer of compact keratin and focal basal epidermal pigmentation. Dilated blood vessels surrounded by collagen are seen in the superficial dermis. No pseudohorn cysts are identified. A granular layer is present.

There is no basal nuclear atypia. There is no mitotic activity and no melanocytic nests. There is no solar elastosis. No koilocytes are apparent.

Minimal hyperkeratosis

The sections show skin with acanthosis, pseudohorn cysts, rare parakeratosis, minimal hyperkeratosis and focal basal epidermal pigmentation. There is no basal nuclear atypia, no appreciable mitotic activity and there are no melanocytic nests. There is minimal dermal inflammation. Solar elastosis is present.

Reticulated seborrheic keratosis

The sections show hair-bearing skin with fine strands of benign basaloid epidermal cells extending from the epidermis. The superficial dermis has dense collagen. No significant inflammation is present. Pseudohorn cysts are present focally.

There is no hyperkeratosis or acanthosis. No pigmentation is apparent. No large blood vessels are identified. No nuclear atypia is seen.

Irritated SK

The sections show skin with acanthosis, pseudohorn cysts, hyperkeratosis and basal epidermal pigmentation. There are no melanocytic nests. Mitotic activity is not readily apparent. A dermal lymphohistiocytic infiltrate is present. Reactive basal cell changes are present. There is no apparent solar elastosis. The lesion is incompletely excised.

Wart-like SK

The sections show skin with papillomatous acanthosis and, predominantly, basketweave hyperkeratosis. A lesser amount of compact hyperkeratosis and parakeratosis is present. Koilocytes are not identified. Blood vessels close to the dermal-epidermal junction are not prominent. Pseudohorn cysts are not apparent.

There are no melanocytic nests. There is no apparent solar elastosis. There is a moderate lymphohistiocytic dermal infiltrate. There is minimal basal atypia. Mitotic activity is not readily apparent.

Stucco keratosis

The sections show skin with pointed papillomatous projections and hyperkeratosis. There is no basal nuclear atypia, and there are no melanocytic nests. Mitotic activity is not apparent. There is minimal dermal inflammation. Solar elastosis is present. The lesion is excised in the plane of section.

Note:

• Signed out as seborrheic keratosis, early.

See also

• Non-malignant skin disease.
• Dermatopathology.