Histopathology: skin pathologyThese presentations are to help you identify, and to test yourself on

identifying, basic histopathological features. They do not contain theadditional factual information that you need to learn about these topics, or

necessarily all the images from resource sessions.

This presentation contains images of basic histopathological features ofcommon skin pathologies.

Before viewing this presentation you are advised to review relevanthistology, sections on inflammation, healing, neoplasia, psoriasis and

dermatitis in a pathology textbook, relevant lecture notes, relevantsections of a histopathology atlas and the histopathology power point

presentations on healing and neoplasia.

Copyright University of Adelaide 2011

Med 3: skin cases semester 1

Skin, solar elastosis. Note the grey-purple discolouration (it should beeosinophilic) of the dermal connectivetissue (black star). This results fromchronic sun damage. Age and sunrelated changes to the dermis,particularly to the elastic tissuecomponent, lead to wrinkling.

Solar/actinic keratosis (epidermal dysplasia caused by sun damage) left side of black line, normal epidermis right side.Note that in the solar keratosis there is disorganization of keratinocytes and some keratinocytes have enlarged nuclei,the stratum granulosum is absent and nuclei are retained in the stratum corneum (parakeratosis). This results frommore rapid proliferation of cells with insufficient time for normal differentiation as they ascend from the basal layer. Theblue line denotes the approx. location of the epidermal basement membrane.

Squamous cell carcinoma (outlined by blue lines) invading through dermis into subcutaneous tissue (verylow power view). Origin from the epidermis is not always readily seen. The tumour comprises invasiveislands of cells that appear eosinophilic on low power due to their relatively low N:C ratios as many aresimilar to cells of the stratum spinosum. The dark discolouration (predominant staining withhaematoxylin) in the dermis at the edges of the lesion is due to a chronic inflammatory cell infiltrate.Black stars: epidermis. (From Australian Cancer Society collection 1991)

Squamous cell carcinoma. High power view of tumour cells (tumour cells only, the invasive nature of the cells cannotbe seen here). The cells show cytological features of malignancy: nuclear enlargement, pleomorphism, prominentnucleoli. These cells are mostly relatively well differentiated being similar to cells of the stratum spinosum withabundant eosinophilic cytoplasm and intercellular bridges (black arrows). However, some cells focally aredifferentiating further (black star), becoming flattened and keratinising and their nuclei are undergoing pyknosis, similarto more superficial squamous cells.

Squamous cell carcinoma. High power view of tumour cells. The cells show cytological features ofmalignancy: nuclear enlargement, pleomorphism, prominent nucleoli. These cells are mostly welldifferentiated being similar to cells of the stratum spinosum with abundant eosinophilic cytoplasm andintercellular bridges (black arrow). However, some cells focally are differentiating further, becomingflattened and fully keratinising, forming a keratin pearl (black star).

Squamous cell carcinoma, medium power view. The cells show cytological features of malignancy:nuclear enlargement, pleomorphism, prominent nucleoli. However, these cells are fairly poorlydifferentiated. It is difficult to tell that they are squamous. They still have some eosinophilic cytoplasm butthere is no keratinisation. Intercellular bridges are difficult to distinguish at this power.

Basal cell carcinoma (outlined by blue lines) invading through dermis into subcutaneous tissue (very lowpower view). The tumour comprises invasive islands of cells that appear basophilic on low power due totheir high N:C ratios as many are similar to cells of the stratum basale. Black stars: epidermis.

(From Australian Cancer Society Collection, 1991)

Basal cell carcinoma (medium power). Islandsof cells (black stars) originating from epidermisinvading into dermis. Cells at the edges of theislands are arranged in a palisade pattern(peripheral palisading) and have high N:Cratios similar to cells of the stratum basale.Epidermis over the tumour is beginning toulcerate (blue star) as is common in theselesions (which are sometimes referred to as‘rodent’ ulcers). A chronic inflammatory cellinfiltrate is seen in the surrounding dermis.

Red star: intact epidermis

Basal cell carcinoma (high power). The cells at the edge of the tumour are arranged in apalisade pattern (peripheral palisading - black arrows) and have high N:C ratios similar to cellsof the stratum basale.

Tumour

Stroma

Normal epidermis and papillary dermis (high power). Scattered melanocytes (black arrows) areeasily seen at the dermo-epidermal junction.

Normal epidermis and papillary dermis (high power). Melanin stains black in this MassonFontana stain. Scattered melanocytes (black arrows) are easily seen. Note how most of themelanin has been transferred to keratinocytes.

Common types of benign melanocyticnaevi generally contain bland naevus cellsthat are arranged as nests at thedermoepidermal junction and/or nests orsheets in the dermis.

The image demonstrates a compoundmelanocytic naevus with both junctional(black arrows) and dermal (red stars)naevus cells. Note the prominentpigmentation which gives these lesionstheir brown colour macroscopically.

Invasive malignant melanomas contain melanocytesthat are generally arranged as nests at thedermoepidermal junction and/or nests or sheets inthe dermis. The cells however are atypical. In situmelanomas contain only a junctional component i.e.no invasive dermal component.

The image demonstrates an invasive malignantmelanoma. Black arrows: junctional nests ofmalignant melanocytes.

Red stars: malignant melanocytes invading thedermis.

In malignant melanoma, malignant cells also invadeupwards into the epidermis (blue arrow), a featureknown as pagetoid spread.

Note the prominent pigmentation (mostly inmacrophages here) which gives these lesions theirbrown colour macroscopically.

Invasive malignant melanoma.

Black arrows: junctional nests of malignant melanocytes.

Blue arrows: malignant melanocytes invading upwards into the epidermis

Red star: malignant melanocytes invading the dermis

In the absence of metastases, the prognosis of melanoma is mainly dependent on the depth ofinvasion into dermis measured in mm from the overlying stratum granulosum (Breslowthickness). The grade and type are not significant in determining prognosis. (From AustralianCancer Society collection 1991)

Seborrhoeic keratoses may be pigmented. They often have a ‘stuck on’ appearance macroscopically.Micrograph (low power): Benign epidermal proliferation. (From Australian Cancer Society collection 1991)

Depending on their likely nature and location, skin lesions may be removed in their entirety and sent to apathology laboratory for assessment. Such excision biopsies are therapeutic as well as diagnostic. (FromAustralian Cancer Society collection 1991)

The specimen is placed in a container of formalin, labelled, and along with a request form, sentto a pathology laboratory.

In the pathology laboratory, the specimen with the lesion is transversely sectioned (black lines). Theslices of tissue are embedded in paraffin, sectioned and stained and the resulting histopathology sectiondemonstrates the excision margins as well as the lesion (inset). A diagnosis is made and the referringdoctor can also be informed as to whether the lesion is completely excised. (From Australian CancerSociety collection 1991)

Psoriasis. Thickened (acanthotic) epidermis with elongated narrow rete pegsBlack arrow: absence of stratum granulosumRed star: parakeratosisBlue star: Nuclear debris and inflammatory cells: microabscess

Acute eczematous dermatitis. Histologically, intercellular edema produces widenedintercellular spaces within the epidermis (spongiosis), eventually resulting in small, fluid-filledintraepidermal vesicles. (From Robbins & Cotran Pathologic Basis of Disease 7E CopyrightElsevier).

Skin: full thickness burn (low power). Burnedtissue undergoes coagulative necrosis - thearchitecture is still discernable (e.g. blackstars indicate sweat glands in deep dermis)but no nuclei are seen.

Skin: partial thickness burn (low power).Cells in the deep dermis are still viable(nuclei are retained) but tissue in thesuperficial and mid dermis showscoagulative necrosis. The epidermis is nolonger present.Black arrow: inflammatory cellsBlue stars: necrotic sweat glands in middermisBlack stars: viable sweat glands in deepdermis

Skin, burn: sweat glands (black star) and hairfollicle (red star) showing coagulative necrosis.The architecture is still discernable but nonuclei are seen. The nuclei (black arrows) inthe interstitial tissues are of inflammatory cells(probably neutrophils).

Skin, recent wound extending intosubcutaneous adipose tissue.Blood clot fills the wound (bluestar).Yellow star: surface scabBlack star: adjacent dermis.Such a wound with closelyopposed edges, especially ifsutured, will undergo healing byprimary intention.

Skin, recently healed woundextending into subcutaneousadipose tissue (very low power).Yellow star: epidermis hasregenerated across the wound.Blue star: recently formed scar.Black star: adjacent dermis.

Skin, early fibrous scar (S) withnormal dermis (D) on either side,low power. This represents the endresult of healing by primaryintention as healing followed asimple incision for removal of askin lesion. The scar here stillcontains quite a few fibroblasts.(From Wheater’s BasicHistopathology, a Colour Atlas andText, 4th ed. by Stevens, Lowe andYoung, Churchill Livingstone.)

Tissue taken from an ulcer of the skinshowing granulation tissue. This largerarea of damage will heal by secondaryintention. Healing by secondaryintention also occurs in chronic pepticulcers and following infarction inorgans (except in the brain)

In certain situations wound healing canbe complicated by excessive formationof the components of repair. In keloids,thick bundles of collagen (black star)are formed that do not regress.