The normal histologic appearance of the skin
At the top is the epidermis. A thin layer of keratin overlies the
epidermis. This layer of keratinization is thicker on the palms and soles
and in areas where skin is rubbed or irritated. Beneath the epidermis is
the dermis containing connective tissue with collagen and elastic fibers.
At the center can be seen a hair follicle with surrounding sebaceous
Here are normal adnexal structures of the skin. A hair
follicle is seen at the center, with sebaceous glands
above and sweat glands and ducts near the base of the
hair follicle.
This is psoriasis. The thick, silvery, scaling lesions are most
often found over bony prominences, scalp, genitalia, and
hands. It occurs when there is abnormal proliferation and
turnover of epidermis (reduced from a month to only 4 days
for a cell to transit from basal layer to surface).
Microscopically, psoriasis is characterized by downward
elongation of the rete ridges with thinning of overlying
stratum granulosum, with parakeratosis above this. Small
aggregates of neutrophils with surrounding spongiform
change are seen in the superficial epidermis. Capillaries within
dermal papillae are brought close to the surface.
Clinical appearance of lichen planus affecting the
dorsum of the hand. One of the lesions has been
Biopsy of lichen planus showing hyperkeratosis and
infiltrate that hugs irregularly acanthotic epidermis
Clinical appearance of bullous pemphigoid. Large
bullae are present, some of which have ruptured.
Pemphigus vulgaris in which characteristic
suprabasal bulla and dark acantholytic cells can
be seen.
Pemphigus foliaceus with its high
intraepidermal cleavage plane
seborrheic keratosis (SK)
a very common lesion of older adults. SK's are common
over the face, neck, and upper trunk. They are roughsurfaced and brown coin-like plaques that vary from a
few millimeters in size to several centimeters.
This is the microscopic appearance of a seborrheic keratosis
(SK). Broad bands of normal-appearing epidermal cells have
large keratin-filled "horn cysts" within them.
The cells of a basal cell carcinoma are dark blue and
oblong with scant cytoplasm. They resemble the cells
along the basal layer of normal epidermis.
Basal cell carcinoma of the skin
Nests of basaloid cells are dropping off into the upper dermis.
These neoplasms can be multifocal. They are slow growing .
The problems they cause are related to local invasion.
Metastases are quite rare.
squamous cell carcinoma arising on the dorsum of the
Besides sun exposure, risk factors for squamous cell carcinoma arising in
skin include carcinogens such as tars, chronic ulcers, burn scars, arsenic
poisoning, and radiation exposure. In this case there was a history of both
sun exposure as well as exposure to carcinogens.
squamous cell carcinoma is seen at medium power
Note the pleomorphism of the cells. A "squamous
eddy" is seen at the upper left, but some of the cells at
the right show little keratinization.
Melanocytic nevus
Small brown flat to slightly raised nevi are quite common in
Caucasians. They are usually less than a centimeter in
Intradermal nevus
the benign nature of the nevus cells are seen below the
epidermis. The cells are small and round and blue
melanocytes that are in aggregates or sheets.
junctional nevus
there are nevus cells in nests in the lower epidermis as well as
nests appearing to "drop off" into the upper dermis. Unlike a
melanoma, there is no significant atypia and no inflammation.
malignant melanoma of the skin
The lesion is larger than a centimeter, has irregular borders, and
irregular pigmentation, with one very dark area on the left. The
prognosis of a melanoma correlates best with the depth of invasion.
Sun exposure in light-skinned persons leads to melanoma formation.
microscopic appearance of melanoma
Large polygonal cells (or spindle cells in some cases) have very pleomorphic
nuclei with prominent nucleoli. The neoplasm is making brown melanin
pigment. A Fontana-Masson stain for melanin may help to detect small
amounts of cytoplasmic melanin.
A Fontana-Masson silver stain (melanin stain) will demonstrate
a fine dusting of melanin pigment within the cytoplasm of the
neoplastic cells of this malignant melanoma.
The neoplastic cells shown here stain positively with HMB-45,
suggesting that the primary neoplasm is a melanoma