Bulla (definition)

(bul'ah) (Latin. Bulla - a round swelling, a bubble)



A bulla is a circumscribed elevation of skin of 0.5 cm or more in diameter containing a liquid. The distinction between vesicle and bulla is arbitrary and depends only on size (vesicles are less than 0.5 cm).

Examples of bullae:

Dermal bulla

A bulla caused by separation of tissue components of the dermis with collection of serous fluid.
Example: dystrophic epidermolysis bullosa

Epidermal vesicle or epidermal bulla

A blister formed within the epidermis by pathologic change in epidermal cells or cellular cohesion.
Example: miliaria crystallina

Spongiotic vesicle or spongiotic bulla

An intraepidermal multilocular vesicle or blister formed by separation of epidermal cells by edema. Lymphocytes predominate in allergic contact dermatitis and neutrophilic leukocytes predominate in irritant dermatitis.

Subcorneal bulla

A bulla formed by exudate beneath the stratum corneum, and above the stratum spinosum.
Example: bullous impetigo

Subepidermal vesicle or subepidermal bulla

A vesicle or bulla formed by cleavage of the dermal-epidermal interface and with the roof of the bulla composed of the epidermis.
Example: bullous pemphigoid


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