Skin nontumor

Topic Completed: 1 June 2012

Minor changes: 13 July 2020

Copyright: 2002-2020,, Inc.

PubMed Search: cutaneous horn, pseudoepitheliomatous hyperplasia

Hillary Rose Elwood, M.D.
Christopher S. Hale, M.D.
Page views in 2019: 20,046
Page views in 2020 to date: 11,301
Cite this page: Elwood HR, Hale CS. Patterns. website. Accessed September 29th, 2020.
See Abscess under Skin nontumor > Infectious Disorders
Cutaneous horn
Definition / general

Clinical features
  • Usually solitary
  • Predilection for the head and neck and hands of older persons
  • Hard yellow to brown skin excrescence composed of compact keratin resembling a horn
  • Can be straight or curved and can measure up to several centimeters in length

Case reports

Clinical images

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Cutaneous horn

Microscopic (histologic) description
  • Usually epidermal type keratin (with granular layer)
  • Occasionally has trichilemmal-like features (no granular layer but deep red granules) - termed trichilemmal horn
  • Examination of the base of the lesion is needed to determine the underlying etiology
  • Sometimes base contains epidermal hyperplasia without atypia

Microscopic (histologic) images

Contributed by Hillary Rose Elwood, M.D.

Low power

Verruca vulgaris

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Actinic keratosis with cutaneous horn

Exfoliative dermatitis / erythroderma
Clinical features
  • Total body erythema (> 90% of cutaneous surface) and scaling, due to drug reaction, allergic contact dermatitis, psoriasis, pityriasis rubra pilaris, malignancy
  • Associated with dermatopathic lymphadenitis
  • May clinically resemble chronic graft versus host disease (Ann Dermatol 2009;21:319)

Clinical images

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Various images

Microscopic (histologic) description
  • Nonspecific changes
  • May have lichenoid dermatitis

Differential diagnosis
Lichenoid dermatitis
  • A histological pattern, not a distinct clinical entity
  • Due to drug eruption, actinic keratosis, lupus erythematosus, acute graft versus host disease, regressing melanoma and dermatofibroma
  • May be a delayed hypersensitivity reaction
  • May present as a neoplasm
  • Micro description:
    • Dense, band-like lymphocytic infiltrate in dermis that obscures dermoepidermal junction
    • Cytoplasmic vacuolization of basal keratinocytes with a brightly eosinophilic cytoplasm; the nucleus becomes extruded to become round / oval eosinophilic bodies (colloid bodies)
    • Regenerated epithelium has a disorderly basement membrane
    • May have large cell acanthoma or solar lentigo within the lesion
Pseudoepitheliomatous hyperplasia
Definition / general
  • Pseudoepitheliomatous (pseudocarcinomatous) hyperplasia (PEH) is a histologic pattern, not a specific diagnosis
  • Histologic mimic of squamous cell carcinoma
  • PEH occurs in a wide range of settings such as:
    • Chronic irritation, including borders of ulcers and healing wounds, urostomy / colostomy sites, prior biopsy site, stasis ulcer, pyoderma gangrenosum, prurigo nodularis, lichen simplex chronicus, halogenoderma
    • Inflammatory dermatoses such as hypertrophic lichen planus, pemphigus vegetans, chronic arthropod bite
    • Infectious dermatoses such as tuberculosis verrucosa cutis, pyoderma vegetans, atypical mycobacterial infection, deep fungal infection
    • Overlying tumors such as granular cell tumor, cutaneous T cell lymphoma, CD30+ lymphoproliferative disorders, Spitz nevi, melanoma
  • Differential for PEH with intraepidermal neutrophilic microabscesses includes:

Case reports

Microscopic (histologic) description
  • Prominent acanthosis of epidermis and adnexal epithelium with deep, somewhat bulbous, downgrowths of epithelial cells that may appear invasive
  • Dermal fibrosis and reactive vascular proliferation may be present
  • In cases associated with an inflammatory or infectious process, there may be intraepidermal microabscesses
  • Often associated with trapping of elastic fibers within epidermis
  • Absent or minimal atypia, rare mitoses

Microscopic (histologic) images:

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Inflammatory infiltrate in dermis

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Surface epithelium

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Acanthotic squamous epithelium

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Mild chronic inflammation

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Pseudoepitheliomatous hyperplasia

Differential diagnosis
  • Pseudoepitheliomatous hyperplasia can be seen in a number of settings, as outlined above, and its presence should prompt a search for an underlying infectious process, inflammatory process or tumor as appropriate
  • Well differentiated squamous cell carcinoma:
    • Can be extremely difficult to impossible to distinguish PEH from squamous cell carcinoma (SCC), especially on superficial shave biopsies
    • PEH is mainly differentiated by clinical findings and / or the discovery of an underlying reason for its presence
    • Findings that favor SCC include increased mitoses particularly atypical mitoses, more pronounced cytologic atypia, perineural / lymphovascular invasion
Spongiotic dermatitis
  • Clinically correlates with eczematous dermatitis
  • Encompasses a large number of diseases, including allergic contact dermatitis and irritant contact dermatitis
  • Microscopic description: intraepidermal edema with clear spaces separating keratinocytes
    • Acute: also perivascular lymphocytic infiltrates in upper dermis, lymphocyte exocytosis
    • Subacute: focal parakeratosis, acanthosis, papillomatosis, eosinophils
    • Chronic: prominent parakeratosis, acanthosis, papillomatosis; may have minimal spongiosis; fibroplasia of papillary and upper reticular dermis; variable inflammatory infiltrate
    • May resemble early cutaneous T cell lymphoma, which has large numbers of cerebriform nuclei, Pautrier microabscesses, epidermotropism

      Contributed by Dr. Asmaa Gaber

      Spongiotic dermatitis

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