B16. Primary skin lesions, basics of dermatohistopathology

Flat lesions
- Macule
  - A flat skin lesion < 1 cm in size with discolouration
- Patch
  - A flat skin lesion > 1 cm in size with discolouration
Infiltrative lesions
- Papule
  - An elevated palpable skin lesion < 0,5 cm in size
  - Epidermal
- Plaque
  - An elevated palpable skin lesion > 0,5 cm in size
  - Intradermal
- Tuber
  - An elevated palpable skin lesion whose infiltration involves the entire depth of the dermis
- Nodule
  - A circumscribed elevated lesion > 1 cm
  - In dermis and subcutis
- Tumor
  - Large solid mass of tissue
Fluid-filled lesions
- Vesicle
  - Small fluid-containing lesion
  - Intraepidermal
- Bulla
  - Large fluid-containing lesion
  - Intraepidermal or subepidermal
- Urtica/wheal
  - Transient oedema in the dermis
- Pustule
  - Collection of pus in or below the epidermis
Dermatopathological terms
- Acantholysis
  - Separation of epidermal cells due to dissolution of desmosomes
  - E. g. in pemphigus vulgaris
- Acanthosis
  - Hyperplasia of stratum spinosum
  - E.g. in acanthosis nigricans
- Hypergranulosis
  - Hyperplasia of stratum granulosum
  - E.g. in lichen planus
- Hyperkeratosis
  - Hyperplasia of stratum corneum
  - E.g. in psoriasis
- Papillomatosis
  - Hyperplasia and enlargement of dermal papillae
- Parakeratosis
  - Keratinocytes in stratum corneum retain their nuclei
  - E.g. in
    - Psoriasis
    - Dandruff
- Spongiosis
  - Intraepidermal oedema
  - E.g. in
    - Atopic dermatitis
    - Allergic contact dermatitis