The Dermis is the thickest part of the skin, in two sections:
- The upper Papillary dermis
- The lower Reticular Dermis.
The dermis is very thick on the back eg 7-8mm, and thin on the eyebrow eg 1mm.
Dermal Papillae: finger-like projections upwards of the dermis into the epidermis that also contains superficial dermal blood vessels
Merkel Cells: Found in groups in the Basal Layer of the epidermis. They connect with nerves from the dermis and help transmit touch sensation. Rarely develop into Merkel Cell Cancer.
Langerhans Cells: Found mainly in the Epidermis (also the upper part of the dermis) and are cells involved in immune function. They detect foreign cells such as bacteria and other antigens.
Pigment is normally caused by melanin.
Increased melanin in the keratinocytes & in the melanocytes is found in:
- lentigo (age spot or simple freckle)
- freckle on the lip
- pigmented solar keratosis,
- cancers (pigmented bowens, pigmented BCC)
- Ink spot lentigo
- Seborrhoeic Keratosis
Melanin taken up by melanophages in the dermis is found in Lichen planus like keratosis (LPLK) – these lesions look like flat pink or grey lesions.
Increase number of the melanocytes themselves is found in naevi (moles) & melanoma.
Some other Terms used in skin cancer pathology reports
Acanthosis describes thickened Epidermis eg. Clear Cell Acanthoma / Large Cell Acanthoma.
Full thickness atypia = abnormal keratinocytes that fill the whole epidermis (eg. Intraepithelial carcinoma).
Parakeratosis describes nuclei that are retained in the keratinocytes of the Stratum Corneum.
Melanocytic Proliferation describes the situation where there are more Melanocytes than normal – for example, moles & melanoma.