Dermatopathology is both exciting and exasperating. tum corneum cells. This occurs in disorders of keratiniza­ Skin has an elegant simplicity in its functions yet a tion because the process of desquamation is disturbed (Figure 1. 1). ferocious complexity in its structure. This is one of the paradoxes that underly the pathology of skin disease Parakeratosis. The presence of nucleated horn cells in and may go some way in explaining the multitudinous the stratum corneum. Normally the horn cells (corneocy­ disorders to which the skin is subject. The ready visibility tes) are thin lamellae of less than 1 f. lm thickness. They of the skin may also help explain why straightforward contain no detectable cytoplasmic contents as these are histological examination cannot always provide an lost in the granular cell layer. Parakeratosis occurs when answer to a clinicians's question. Quite dramatic appear­ the process of keratinization is disturbed such as when ances may be due to alterations of the relative rates of the rate of epidermal cell production is increased (as in blood flow, with or without oedema, in the different psoriasis) so that nuclei are not broken down before the vascular plexuses or around different structures in the stratum corneum is reached and when damage occurs horizontal dimension, neither of which may result in to the upper epidermis (Figure 1. 2). 'much to see' histologically. The inherent sampling error Porokeratosis.

Inhalt

I.- 1 Normal skin.- 2 Reactions to trauma and vascular injury.- II.- 3 Infections.- 4 Disorders of keratinization.- 5 Bullous and vesicular skin disorders.- 6 Eczema, psoriasis, lichen planus.- 7 Other inflammatory diseases.- 8 Connective tissue disease, vasculitis and erythemas.- 9 Acne, rosacea, perioral dermatitis and related disorders.- 10 Miscellaneous disorders of connective tissue.- 11 Scalp and hair disorders.- 12 Cutaneous deposits in metabolic disorders.- III.- 13 Melanocytic naevi and malignant melanoma.- 14 Benign epidermal tumours and cysts.- 15 Premalignant and malignant lesions of epidermis.- 16 Tumours of the dermis.- 17 Lymphocytic, mast-cell and atypical histiocytic skin tumours and dermal leukaemia.