Skin nonmelanocytic tumor

Benign (nonmelanotic) epidermal tumors or tumor-like lesions


Topic Completed: 1 August 2011

Minor changes: 24 September 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Porokeratosis

Mowafak Hamodat, M.B.Ch.B., M.Sc.
Page views in 2020: 7,445
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Cite this page: Hamodat M. Porokeratosis. website. Accessed December 3rd, 2021.
Definition / general
  • Rare disease, consists of an atrophic center bordered by a peripheral grooved keratotic ridge
  • Six major categories: classic, localized, linear, punctuate, disseminated superficial porokeratosis and disseminated superficial actinic porokeratosis
  • May be associated with a slight increase in neoplasia (basal cell and squamous cell carcinoma, Bowen's disease)
  • May develop against a background of solid organ transplantation or blood transfusion, possibly related to hepatitis C infection
Microscopic (histologic) description
  • Recommended to biopsy peripheral grooved ridge to see classic features
  • Keratin-filled epidermal invagination with an angulated, parakeratotic tier (cornoid lamella)
  • Epithelium deep to the tier is vacuolated and devoid of a granular cell layer
  • Adjacent epithelium towards the center is either atrophic, normal thickness or acanthotic
  • Dyskeratotic cells may be seen
  • Liquefactive degeneration of the basal cell layer is present; may be conspicuous cytoid bodies
  • Dermis shows a non-specific inflammatory cell infiltrate with telangiectatic vessels
  • In actinic variant, is often solar elastosis and atrophy of adjacent epidermis
Microscopic (histologic) images

Contributed by Angel Fernandez-Flores, M.D.

Differential diagnosis
  • Cornoid lamella formation: also seen in seborrheic warts, solar keratosis, veruca vulgaris, squamous cell carcinoma and basal cell carcinoma, porokeratotic eccrine nevi
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