Excoriation Traumatic lesion breaking the epidermis
and causing a raw linear area (i.e., deep
scratch); often self-induced
Lichenification Thickened and rough skin characterized by
prominent skin markings (as lichen on a
tree trunk); usually the result of repeated
Macule Circumscribed lesion, 5 mm or smaller in
diameter, characterized by flatness and
distinguished by coloration (patch is
greater than 5 mm)
Onycholysis Separation of nail plate from nail bed
Papule Elevated dome-shaped or flat-topped lesion
5 mm or less across (nodule is greater than
Plaque Elevated flat-topped lesion, usually greater
than 5 mm across (may be caused by
Pustule Discrete, pus-filled, raised lesion
Scale Dry, horny, plate like excrescence; usually
the result of imperfect cornification
Vesicle Fluid-filled raised lesion 5 mm or less
across (Bulla is greater than 5
mm. Blister is the common term for either.)
Wheal Itchy, transient, elevated lesion with
Acantholysis Loss of intercellular cohesion between
Acanthosis Diffuse epidermal hyperplasia
Dyskeratosis Abnormal, premature keratinization within cells
below the stratum granulosum
Erosion Discontinuity of the skin showing incomplete
loss of the epidermis
Exocytosis Infiltration of the epidermis by inflammatory
Intracellular edema of keratinocytes, often seen
in viral infections
Hypergranulosis Hyperplasia of the stratum granulosum, often
due to intense rubbing
Lentiginous A linear pattern of melanocyte proliferation within the
epidermal basal cell layer
Papillomatosis Surface elevation caused by hyperplasia and
enlargement of contiguous dermal papillae
Para keratosis Keratinization with retained nuclei in the stratum
corneum. On mucous membranes, Para keratosis is
Spongiosis Intercellular edema of the epidermis
Ulceration Discontinuity of the skin showing complete loss of
the epidermis revealing dermis or subcutis
Vacuolization Formation of vacuoles within or adjacent to cells;
often refers to basal cell-basement membrane zone
• Squamous epithelial cells (keratinocytes), in addition to
producing protective keratin protein, are major sites for
the biosynthesis of soluble molecules (cytokines) that
regulate adjacent epidermal cells as well as cells in the
• Melanocytes within the epidermis are cells responsible
for the production of melanin, a brown pigment that
protects against potentially injurious ultraviolet (UV)
radiation in sunlight.
• Dendritic cells. Skin is constantly battered with
microbial and nonmicrobial antigens that are processed
by intraepidermal dendritic Langerhans cells, which
interact with the systemic immune system by migrating
to regional lymph nodes.
• Specialized dendrocytes within the dermis perform
similar functions there.
Deep dermal and
Blue nevus Non-nested
cells with pink-
Halo nevus Lymphocytic
Melanocytic nevus, junctional type.
A, In clinical appearance, lesions are small, relatively flat, symmetric,
B, On histologic examination, junctional nevi are characterized by
rounded nests of nevus cells originating at the tips of rete ridges
along the dermoepidermal junction.
Melanocytic nevus, compound type.
(A) is more raised and dome-shaped. The symmetry and
uniform pigment distribution suggest a benign process.
(B), compound nevi combine the features of junctional nevi
(intraepidermal nevus cell nests) with nests and cords of nevus
cells in the underlying dermis).
• Dysplastic nevus.
• A, Numerous clinically atypical nevi on the back.
• B, One such lesion (inset A) has a compound nevus
component (left side of scanning field) and an
asymmetric junctional nevus component (right
side of scanning field).
• The former correlates grossly with the more
pigmented and raised central zone and the latter
with the less pigmented, flat peripheral rim.
• C, An important feature is the presence of cytologic
atypia (irregularly shaped, dark-staining nuclei). The
dermis underlying the atypical cells characteristically
shows linear, or lamellar, fibrosis.
• Potential steps of tumour progression in
• A, Lentiginous melanocytic hyperplasia.
• B, Lentiginous junctional nevus.
• C, Lentiginous compound nevus with abnormal
architectural and cytologic features (dysplastic
• D, Early melanoma, or melanoma in radial growth
phase (large dark cells in epidermis).
• E, Advanced melanoma (vertical growth phase)
with malignant spread into the dermis and vessels.
• The risk of malignant transformation of any single
dysplastic nevus is extremely low but can occur.
• Clinical and pathologic features are used to gauge the
probability of metastatic spread and prognosis.
• 1) Tumour Depth (The Breslow Thickness)
• (2) Number Of Mitoses;
• (3) Evidence Of Tumour Regression (Presumably Due To
The Host Immune Response);
• (4) The Presence And Number Of Tumour Infiltrating
• (5) Gender; And
(6) Location (Central Body Or Extremity).
• In a retrospective multivariate study by the American Joint
Committee on Cancer (AJCC), tumour thickness and presence
or absence of ulceration had prognostic significance.
• Because most melanomas initially metastasize to regional
Benign Epithelial Tumours
• Benign epithelial neoplasms are common and usually
biologically inconsequential, although they may cause
significant psychological discomfort for the affected
• These tumours, derived from the keratinizing stratified
squamous epithelium of the epidermis and hair follicles
and the ductular epithelium of cutaneous glands, often
recapitulate the structures from which they arise.
• They are sometimes confused clinically with malignancy,
particularly when they are pigmented or inflamed, and
histologic examination of a biopsy is frequently required
to establish a definitive diagnosis
• A well-demarcated coin like pigmented lesion
containing dark keratin-filled surface
plugs (inset) is composed histologically of benign
basaloid cells associated with prominent keratin-
filled "horn" cysts, some of which communicate
with the surface (pseudo-horn cysts).
• On histologic examination, these neoplasms are
exophytic and sharply demarcated from the
• They are composed of sheets of small cells that
most resemble basal cells of the normal epidermis
• Variable melanin pigmentation is present within
these basaloid cells, accounting for the brown
• Exuberant keratin production (hyperkeratosis)
occurs at the surface, and small keratin-filled cysts
(horn cysts) and invaginations of keratin into the
main mass (invagination cysts) are characteristic
• Acanthosis nigricans is a condition marked by thickened, hyper
pigmented skin with a "velvet-like" texture that most
commonly appears in the flexural areas (axillae, skin folds of
the neck, groin, and anogenital regions).
• It can be an important cutaneous marker of benign and
malignant conditions and, accordingly, is divided into two
• The benign type, which constitutes about 80% of all cases,
develops gradually and usually occurs in childhood or during
• It may occur (1) as an autosomal dominant trait with variable
penetrance, (2) in association with obesity or endocrine
abnormalities (particularly with pituitary or pineal tumors and
diabetes), and (3) as part of several rare congenital syndromes
Fibro epithelial Polyp (skin tag)
• The fibro epithelial polyp has many names
(acrochordon, squamous papilloma, skin tag)
and is one of the most common cutaneous
• It is generally detected as an incidental finding in
middle-aged and older individuals on the neck,
trunk, face, and intertriginous areas as a soft,
flesh- coloured, bag-like tumour often attached
to the surrounding skin by a slender stalk
• Epithelial cysts are divided into several histologic types.
• The epidermal inclusion cyst has a wall resembling
normal epidermis and is filled with laminated strands of
• Pilar or trichilemmal cysts have a wall that resembles
follicular epithelium, without a granular cell layer and
filled by a more homogeneous mixture of keratin and
• The dermoid cyst is similar to the epidermal inclusion
cyst, but also contains multiple appendages (such as
small hair follicles) budding outward from its wall.
• Finally, steatocystoma simplex is a cyst with a wall
resembling the sebaceous gland duct, and from which
numerous compressed sebaceous lobules originate
• The cylindroma is composed of islands of cells
resembling those of the normal epidermal or
adnexal basal cell layer (basaloid cells).
• These islands fit together like pieces of a jigsaw
puzzle within a fibrous dermal matrix .
• Trichoepithelioma is a proliferation of basaloid
cells that forms primitive structures resembling
hair follicles .
• Sebaceous adenoma shows a lobular proliferation of
sebocytes with increased peripheral basaloid cells and
more mature sebocytes in the central portion,
characterized by frothy or bubbly cytoplasm due to
lipid vesicle content (Fig. 25-12A).
• Pilomatrixomas are composed of basaloid cells that
show trichilemmal or hair like differentiation similar
to that seen in the germinal portion of the normal hair
bulb in the anagen growth phase (Fig. 25-12B).
• Apocrine carcinoma shows ductal differentiation with
prominent decapitation secretion similar to that seen
in the normal apocrine gland (Fig. 25-12C). The
infiltrative growth pattern is a hint of malignancy in
this otherwise well-differentiated tumour.
• Actinic keratosis are usually less than 1 cm in
diameter; are tan-brown, red, or skin-
colored; and have a rough, sandpaper-like
consistency. Some lesions may produce so
much keratin that a "cutaneous horn"
• A, Excessive scale formation in this lesion has
produced a "cutaneous horn."
• B, Basal cell layer atypia (dysplasia) is associated
with marked hyperkeratosis and Para keratosis.
• C, Progression to full-thickness nuclear atypia,
with or without the presence of superficial
epidermal maturation, heralds the development
of squamous cell carcinoma in situ.
• ACTINIC (Solar) KERATOSIS, i.e. precursor to SCC
• SQUAMOUS CELL CARCINOMA, squamous
“pearls”, intercellular bridges
• BASAL CELL CARCINOMA, by far, MOST
COMMON, BLUE palisading nests
• MERKEL CELL CARCINOMA (TUMOR), VERY
MALIGNANT AND LETHAL, LOOK LIKE SMALL CELL
CA. OF LUNG
• BOTH SCC and BCC related to SUN (i.e., radiation)
• SCC also related to As, carcinogens, chaw, betel
nut, HPV, familial, etc.
• BOTH SCC and BCC can do local damage but very
• MERKEL CELL tumors metastasize early and
extensively, like melanomas.
SQUAMOUS CELL CARCINOMA
• Squamous cell carcinoma is the second most common
tumour arising on sun-exposed sites in older people,
exceeded only by basal cell carcinoma.
• Except for lesions on the lower legs, these tumours
have a higher incidence in men than in women.
• Invasive squamous cell carcinomas are usually
discovered while they are small and resectable.
• Less than 5% of these tumours metastasize to
regional nodes; these lesions are generally deeply
invasive and involve the sub cutis.
• A.Lesions are often nodular and ulcerated as
seen in this scalp tumour.
• B, Tongues of atypical squamous epithelium
have transgressed the basement membrane,
invading deeply into the dermis.
• C, A magnified image reveals invasive
tumour cells showing enlarged nuclei with
angulated contours and prominent nucleoli.
• Squamous cell carcinomas that have not
invaded through the basement membrane of
the dermoepidermal junction (termed in situ
carcinoma) appear as sharply defined, red,
• More advanced, invasive lesions are nodular,
show variable keratin production
(appreciated grossly as hyperkeratosis scale),
and may ulcerate .
• The most important cause of cutaneous squamous cell
carcinoma is DNA damage induced by exposure to UV
• Tumour incidence is proportional to the degree of
lifetime sun exposure.
• A second common association is with
immunosuppression, most notably chronic
immunosuppression as a result of chemotherapy or
• Immunosuppression may contribute to carcinogenesis by
reducing host surveillance and increasing the
susceptibility of keratinocytes to infection and
transformation by oncogenic viruses, particularly human
papilloma virus (HPV) subtypes 5 and 8.
• Other risk factors for squamous cell carcinoma
include industrial carcinogens (tars and oils),
chronic ulcers and draining osteomyelitis, old
burn scars, ingestion of arsenicals, ionizing
radiation, and (in the oral cavity) tobacco and
betel nut chewing .
• Basal cell carcinoma is the most common invasive
cancer in humans, with nearly 1 million estimated
cases per year .
• These are slow-growing tumours that rarely
metastasize. They have a tendency to occur at
sun-exposed sites and in lightly pigmented people.
• As with squamous cell carcinoma, the incidence of
basal cell carcinoma rises sharply with
immunosuppression and in people with inherited
defects in DNA repair such as xeroderma
Basal cell carcinoma. Pearly, telangiectatic nodules (A) are composed
of nests of uniformly atypical basaloid cells within the dermis (B) that
are often separated from the adjacent stroma by thin clefts (C), an
artefact of sectioning.
• the tumour cells resemble those in the normal basal cell layer of
the epidermis. They arise from the epidermis or follicular
epithelium and do not occur on mucosal surfaces. Two patterns are
• Multifocal growths originating from the epidermis and sometimes
extending over several square centimeters or more of skin surface
(multifocal superficial type) and nodular lesions growing downward
deeply into the dermis as cords and islands of variably basophilic
cells with hyper chromatic nuclei, embedded in a mucinous matrix,
and often surrounded by many fibroblasts and lymphocytes.
• The cells at the periphery of the tumour cell islands tend to be
arranged radially with their long axes in parallel
alignment (palisading). In sections, the stroma retracts away from
• Benign fibrous histiocytoma refers to a
heterogeneous family of morphologically and
histogenetically related benign dermal
neoplasms of uncertain lineage.
• These tumours are usually seen in adults and
often occur on the legs of young to middle-aged
• The most common form of fibrous histiocytoma is
referred to as a dermatofibroma.
• These tumours are formed by benign, spindle-
shaped cells arranged in a well-defined,
nonencapsulated mass within the mid-dermis.
• Extension of these cells into the subcutaneous fat
is sometimes observed.
• Many cases demonstrate a peculiar form of
overlying epidermal hyperplasia, characterized by
downward elongation of hyper pigmented rete
ridges (a pseudo- epitheliomatous pattern).
• Dermatofibrosarcoma protuberans is best
regarded as a well-differentiated, primary fibro
sarcoma of the skin.
• These tumours are slow growing, and although
they are locally aggressive and can recur, they
• Clinically they are firm, solid nodules that arise
most frequently on the trunk. They often develop
as aggregated "protuberant" tumours within a
firm (indurated) plaque or nodule that may
Benign fibrous histiocytoma (dermatofibroma). This firm, tan papule
on the leg (A) shows a localized proliferation of benign-appearing
spindle cells within the dermis (B). C, Note the characteristic
overlying epidermal hyperplasia and the tendency of fibroblasts to
surround individual collagen bundles.
• These neoplasms are cellular, composed of
fibroblasts arranged radially, reminiscent of blades of
a pinwheel, a pattern referred to as storiform.
• Mitoses are rare. In contrast to that in
dermatofibroma, the overlying epidermis is generally
• Deep extension from the dermis into subcutaneous
fat, producing a characteristic "honeycomb" pattern,
is frequently present .
• These tumours may extend down fibrous septae in
the subcutis and thus require wider excision than
would appear to be necessary to prevent local
• Cutaneous T cell lymphoma (CTCL) represents a
spectrum of lymph proliferative disorders
affecting the skin
• Two different clinical types of malignant T-cell
disorders were originally recognized: mycosis
fungoides, a chronic proliferative process; and a
more aggressive nodular eruptive variant, mycosis
• It is now known that a variety of presentations of
T-cell lymphoma occur in the skin, but this section
will focus on mycosis fungoides.
A, Several ill-defined, erythematous, often scaling, and
occasionally ulcerated plaques.
B, Microscopically, there is an infiltrate of atypical
lymphocytes that show a tendency to accumulate beneath
the epidermal layer and to invade the epidermis.
• The histologic hallmark of CTCL of the mycosis fungoides
type is the presence of the Sézary-Lutzner cells.
• These are T-helper cells (CD4+) that characteristically form
band-like aggregates within the superficial dermis (Fig. 25-
19B) and invade the epidermis as single cells and small
clusters (Pautrier micro abscesses).
• These cells have markedly infolded nuclear membranes,
imparting a hyperconvoluted or cerebriform contour.
Although patches and plaques show pronounced
epidermal infiltration by Sézary-Lutzner cells
(epidermotropism), in more advanced nodular lesions the
malignant T cells often lose this epidermotropic tendency,
grow deeply into the dermis, and eventually spread
• The term mastocytosis refers to a spectrum of rare
disorders characterized by increased numbers of mast cells
in the skin and, in some instances, in other organs.
• A localized cutaneous form of the disease that affects
predominantly children and accounts for more than 50% of
all cases is termed urticaria pigmentosa.
• These lesions are multiple, although solitary
mastocytomas may also occur, usually shortly after birth.
• About 10% of individuals with mast cell disease have
systemic disease, with mast cell infiltration of many organs.
These individuals are often adults, and unlike localized
cutaneous disease, the prognosis may be poor.
A, Solitary mastocytoma in a 1-year-old child. B, By routine histology,
numerous ovoid cells with uniform, centrally located nuclei are observed in
the dermis. C, Giemsa staining reveals purple, "metachromatic" granules
within the cytoplasm of the cells.
• The histologic picture in urticaria pigmentosa or
solitary mastocytoma varies from a subtle increase in
the numbers of spindle-shaped and stellate mast cells
around superficial dermal blood vessels, to large
numbers of tightly packed, round to oval mast cells in
the upper to mid-dermis
• Variable fibrosis, edema, and small numbers of
eosinophils may also be present.
• Mast cells may be difficult to differentiate from
lymphocytes in routine, hematoxylin and eosin-
stained sections, and special metachromatic stains
(toluidine blue or Giemsa) must be used to visualize
their granules .