This document summarizes the histology of normal skin and various skin diseases. It describes the five layers of normal skin (stratum basale, spinosum, granulosum, corneum, lucidum) and cell types in each layer. Definitions are provided for terms like hyperkeratosis and acanthosis. Histological features of actinic keratosis, keratoacanthoma, basal cell carcinoma, squamous cell carcinoma, malignant melanoma, and Kaposi sarcoma are outlined. Special histological subtypes and staining characteristics are also noted.

3. Normal Skin Histology
 Stratum Corneum
 Stratum Lucidum
 Stratum Granulosum
 Stratum Spinosum
 Stratum Basale
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4.  Stratum basale/germinativum (“basal or “forming”
layer)
 One layer thick mitotic cells
 10-25% melanocytes with processes into next layer
 Merkel cells with sensory neurons
 Stratum spinosum (“prickly” layer)
 Cells appear spiny due to numerous desmosomes
 Many Langerhans cells
 Stratum granulosum (“grainy” layer)
 Cells flatten
 Organelles/nuclei begin to disintegrate
 Keratin precursor granules begin to form
 Stratum corneum + Lucidum(“horny” layer)
 Cells are dead—too far from underlying capillaries to live
 20-30 cells thick up to ¾ of dermal thickness

6. Definitions
 Hyperkeratosis
 Thickening of the stratum corneum, often associated
with a qualitative abnormality of the keratin.
 Parakeratosis
 Modes of keratinization characterized by the retention
of the nuclei in the stratum corneum.
 Dyskeratosis
 Abnormal keratinization occurring prematurely within
individual cells or groups of cells below the stratum
granulosum

7.  Acanthosis
 Diffuse epidermal hyperplasia
 Acantholysis
 Loss of intercellular connections resulting in loss of
cohesion between keratinocytes.

8. keratocanthoma
Dome-shaped
nodule with central
keratin plug; 1-5 cm.
diameter
Cup-shaped lesion with
central crater of keratin;
downward pushing rounded
border
Higher power
keratoacanthomalarge, glassy
squamous cells with
islands of
eosinophilic keratin.

9. Actinic keratosis
Nuclear abnormalities in basal keratinocytes;
dysplasia does not involve full thickness of
epidermis.

10. Histology - SCC
 Irregular masses of epidermal cells proliferating
into dermis
 Keratinization in well-differentiated tumors
 Range in degree of anaplasia

11. In Situ SCC
 In situ SCC-type II (moderate) with atypical
keratinocytes extending to the lower two thirds of the
epidermis

12. In situ SCC
 In situ SCC-type III (severe) with atypical
 keratinocytes extending more than two thirds to full
thickness
 of the epidermis

13. SCC
Irregular tongues of dysplastic
squamous epithelium invading the
dermis
Epithelial cells exhibit glassy
eosinophilic cytoplasm. Dyskeratotic
cells, parakeratosis and horn pearl
formation are also observed.

14.  Verrucous
 Minimal atypia
 Individual cell keratinization

15.  Spindle-Pleomorphic
 Anaplastic
 Little keratinization

16.  Adenoid Squamous
 Anaplasia
 Acantholysis
 Tubular &adenoid appearance

17. Basal Cell Carcinoma
HISTOLOGY
•Large oval
nuclei with
little cytoplasm
•Nuclei are
uniform
•Connective
tissue stroma
causes
palisading
 Nests of basaloid cells within the dermis

18.  Histologic Subtypes
 Solid
 Cystic
 Adenoid
 Keratotic (Basosquamous)

19.  Solid – no cellular
differentiation
 Cystic Differentiation
towards sebaceous glands
Cystic spaces within tumor
lobules

20. Adenoid variety
Glandular pattern

21.  Baso Squamous
 Shows feature of both basal
cell and squamous cell carcinomas
 More aggressive clinically
 Undifferentiated cells in
combination with
parakeratotic cells and
horn cysts

22. Evolution of dysplastic nevus into malignant melanoma over time
(not inevitable, but the potential always exists)
Lentigo
Junctional
Nevus
Advanced MM:
vertical growth
into dermis
Dysplastic
compound
nevus
Early MM: radial
growth in
epidermis,
superficial dermis

23. Malignant melanoma
Dysplastic melanocytes
involve epidermis and
invade the dermis

24. Malignant melanoma, radial & vertical growth phases
Vertical downward growth into derm
Radial growth
Radial: proliferation of atypical melanocytes laterally within epidermis;
Vertical: growth of melanocytes downward, invading into dermis

25. Superficial spreading
Cell spread along
Dermoepidermal jn

26.  Desmoplatic variety
 Atypical melanocyte in desmoplastic stroma

27.  Staining with S-100
in desmoplastic melanoma

28. Nests of small blue
cells, with minimal
cytoplasm
Electron Microscopy: membrane-bound dense
core neurosecretory granules (blue arrows) and
stacks of perinuclear cytokeratin filaments
(black arrows)

29. Kaposi sarcoma
 Numerous atypical, irregular
angulated vascular channels
 Promontory sign- irregular
vascular channels that
partially surround preexisting
blood vessels.
 Plasma cells in surrounding
Stroma - classic finding

30.  Staining for HHV-8 in KS
 IHC for HHV-8- been shown
99% sensitive
100% specific

31. Densely cellular spindle cells in radially arranged fascicles,
invading into subcutis and muscle fibers.
Main portion shows a storiform arrangement with extension into
the subcutaneous fat, with fat entrapment creating a honeycomb
pattern