Cavitary Primary Morphologic Elements of the Skin: Classification, Clinical Manifestations

Primary morphologic elements are represented by changes in the skin and mucous membranes, which appeared as a result of various pathologic processes in the unchanged skin and mucous membranes.

Three primary cavity morphologic elements are distinguished:

• Vesicle (vesicula);
• Bubble (bulla);
• Pustule (pustula).

Vesicle (vesicula)

A vesicle is a hollow primary exudative morphologic element, which is a small (up to 0.5 cm) fluid-filled mass located in the upper layers of the epidermis. It has a hemispherical shape with clear boundaries and consists of a cover, cavity with contents and bottom. Vesicles can be located in isolation or in groups.

In the process of development of vesicles can open and form erosions and wetting, which are covered with crusts and later fall off, sometimes leaving behind a hyperpigmented spot, which then passes without trace.

Classification of bubbles

By depth of location:

• Subepidermal;
• Intraepidermal;
• Borderline (at the border of the epidermis and dermis).

By the nature of the contents:

• Serous;
• Serous hemorrhagic;
• Hemorrhagic;
• Purulent.

Vesicles are characteristic of herpes skin lesions (herpes simplex and shingles), allergic and contact dermatitis, eczema, impetigo, dyshidrosis, burns, and some autoimmune processes (e.g., Duhring’s dermatitis herpetiformis).

Bubble (bulla)

Vesicle is a cavitary primary exudative morphologic element, which is a mass more than 0.5 cm in diameter, filled with fluid (serous, hemorrhagic or purulent). It is located in the epidermis, on the border with the dermis or in the subcutaneous tissue. It has a dense cover, clear boundaries and consists of:

• Tires (top layer, can be thin or thick);
• Cavities (contains exudate);
• Bottom (depth of occurrence depends on the cause of formation).

The bubbles may be single-chambered or multi-chambered, arranged in isolation or in groups.

In the process of development, blisters may shrink when the contents are resorbed, open with the formation of erosions or ulcers covered with crusts, and in case of deep location – to leave behind scars or areas of hyperpigmentation.

Classification of bubbles

By depth of location:

• Subcorneal (under the stratum corneum) – impetigo, sheet vesicles;
• Intraepidermal (within the epidermis) – herpes, erythema bullosa;
• Subepidermal (at the border of epidermis and dermis) – bullous pemphigoid, porphyria;
• Deep (in the dermis or deeper) – burns, trauma.

By the nature of the contents:

• Serous (clear) – burns, allergic reactions;
• Hemorrhagic (with blood) – vasculitis, trauma;
• Purulent – with secondary infection.

Blisters are characteristic of autoimmune diseases (vesicles, pemphigoid), infections (bullous impetigo, herpes), toxic-allergic reactions, trauma and burns.

Pustule

A pustule is a cavitary primary morphologic element that is a mass of up to 0.5-1 cm filled with purulent contents (leukocytes, bacteria, detritus). It is located in the epidermis, dermis, or around the hair follicle. It has clear boundaries, inflammatory corolla and consists of:

• Covers (thinning epidermis);
• Cavities (purulent exudate);
• Bottom (inflamed dermis).

Pustules can be superficial (heal without scarring) or deep (leave scarring).

In the process of development, pustules open with the release of pus, after which erosions are formed, covered with a crust. In case of deep lesions, they may form ulcers, which subsequently scar.

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Classification of pustules

By localization:

• Follicular (related to the hair follicle) – folliculitis, acne;
• Nonfollicular (not associated with follicles) – pustular psoriasis, impetigo.

Depth:

• Superficial (in the epidermis) – heal without trace;
• Deep (in the dermis) – leads to scarring.

Pustules are characteristic of bacterial infections (staphylococcal, streptococcal pyoderma), inflammatory dermatoses (acne, rosacea), autoimmune processes (pustular psoriasis), fungal and viral infections (herpes, candidiasis).