Actinic Keratosis (Senile, Solar)

Benign Lichenoid Keratosis (Fig. 18.4) (Lichen Planus-Like Keratosis)

Fig. 18.4.

Benign lichenoid keratosis.

Seborrheic Keratosis

Inverted Follicular Keratosis (Fig. 18.5)

Fig. 18.5.

Inverted follicular keratosis.

Warty Dyskeratoma (Fig. 18.6)

Fig. 18.6.

Warty dyskeratoma.

Linear Epidermal Nevus

Nevus Comedonicus

White Sponge Nevus

Leukoedema

Geographic Tongue (Lingua Geographica )

Clear Cell Acanthoma (Fig. 18.7)

Fig. 18.7.

C lear cell acanthoma (A, B).

Large Cell Acanthoma

Squamous Cell Carcinoma In Situ (Bowen Disease )

Bowenoid Papulosis

Squamous Cell Carcinoma (Fig. 18.8)

Fig. 18.8.

S quamous cell carcinoma.

Verrucous Carcinoma

Keratoacanthoma

Dilated Pore of Winer

Pilar Sheath Acanthoma

Trichofolliculoma (Fig. 18.9)

Fig. 18.9.

Trichofolliculoma.

Tumor of the Follicular Infundibulum (Fig. 18.10)

Fig. 18.10.

Tumor of the follicular infundibulum.

Basaloid Follicular Hamartoma

Trichilemmoma (Fig. 18.11)

Fig. 18.11.

T richilemmoma.

Trichoadenoma (Fig. 18.12)

Fig. 18.12.

Trichoadenoma.

Trichoepithelioma

Trichoblastoma

Trichodiscoma

Perifollicular Fibroma and Fibrofolliculoma

Pilomatricoma (Fig. 18.13) (Calcifying Epithelioma of Malherbe)

Fig. 18.13.

Pilomatricoma.

Basal Cell Carcinoma (Fig. 18.14)

Fig. 18.14.

Ba sal cell carcinoma.

Fibroepithelioma of Pinkus (Fig. 18.15)

Fig. 18.15.

Fibroepithelioma of Pinkus.

Malignant Pilomatricoma

Nevus Sebaceous (Fig. 18.16)

Fig. 18.16.

Nevus sebaceous.

Sebaceous Hyperplasia

Sebaceous Adenoma

Sebaceous Epithelioma

Sebaceous Carcinoma (Fig. 18.17)

Fig. 18.17.

Sebaceous carcinoma.

Syringoma-Like Proliferations Associated with Alopecia

Eccrine Syringofibroadenoma (Fig. 18.18)

Fig. 18.18.

Eccrine syringofibroadenoma.

Syringoma (Fig. 18.19)

Fig. 18.19.

Syringoma.

Chondroid Syringoma (Benign Mixed Tumor, Fig. 18.20)

Fig. 18.20.

Chondroid syringoma.

Malignant Chondroid Syringoma

Papillary Eccrine Adenoma

Aggressive Digital Papillary Adenoma/Adenocarcinoma

Hidradenoma, Solid-Cystic Hidradenoma, and Eccrine Acrospiroma (Fig. 18.21)

Fig. 18.21.

N odular hidradenoma (A, B).

Hidradenocarcinoma (Malignant Nodular Hidradenoma )

Hidroacanthoma Simplex (Intraepidermal Poroma )

Eccrine Poroma (Fig. 18.22)

Fig. 18.22.

Eccrine poroma.

Porocarcinoma (Malignant Eccrine Poroma )

Cylindroma and Malignant Cylindroma (Fig. 18.23)

Fig. 18.23.

Cylindroma.

Eccrine Spiradenoma and Malignant Eccrine Spiradenoma (Fig. 18.24)

Fig. 18.24.

Eccrine spiradenoma (A, B).

Eccrine Duct Carcinoma

Syringoid Eccrine Carcinoma (Eccrine Epithelioma )

Microcystic Adnexal Carcinoma (Fig. 18.25)

Fig. 18.25.

Microcystic adnexal carcinoma (A, B).

Mucinous Eccrine Carcinoma

Adenoid Cystic Carcinoma

Mucoepidermoid Carcinoma

Apocrine Nevus

Syringocystadenoma Papilliferum (Fig. 18.26)

Fig. 18.26.

S yringocystadenoma papilliferum.

Hidradenoma Papilliferum

Tubular Apocrine Adenoma (Fig. 18.27)

Fig. 18.27.

Tubular apocrine adenoma.

Apocrine Carcinoma

Merkel Cell Carcinoma (Fig. 18.28)

Fig. 18.28.

Merkel cell carcinoma (A, B).

Adipocyte-Derived Tumors and Proliferations

Neural-Derived Tumors and Proliferations

Schwannoma (Neurilemmoma, Fig. 18.29)

Fig. 18.29.

Plexiform schwannoma.

Clinical

♦

A peripheral nerve sheath-derived tumor that generally presents as a solitary nodule/mass on the head, neck, or extremities of adults

 

♦

Rarely, multiple tumors may be evident (schwannomatosis), and at least some of these cases are associated with neurofibromatosis type 2

 

♦

In general, schwannomas have little, if any, malignant potential

 

Microscopic

♦

A well-circumscribed, encapsulated tumor within the subcutis or deeper tissues

 

♦

Occasionally, dermal involvement may be evident

 

♦

The tumor is composed of spindle cells with wavy, pointed nuclei embedded in a collagenous and highly vascular stroma

 

♦

Classically, cellular, Antoni A areas with palisading, Verocay bodies are admixed with paucicellular, myxoid, Antoni B areas

 

♦

Degenerative changes are frequent findings and include hyalinization, vascular thrombosis, dystrophic mineralization, and hemorrhage

 

♦

The ancient variants typically show some degree of nuclear pleomorphism and enlargement with a smudgy chromatin pattern

 

♦

Plexiform variants exist and typically present in childhood or adolescence

 

♦

These tumors are composed of multiple, cellular, Antoni A-like, encapsulated nodules that must be differentiated from plexiform neurofibroma and plexiform fibrohistiocytic tumor

 

♦

Cellular variants are moderately to markedly cellular and may have mitotic activity. Nuclear pleomorphism and necrosis, however, are absent. Melanotic variants also exist and must be differentiated from malignant melanoma

 

Special Studies

♦

Schwannomas are derived from the peripheral nerve sheath and, therefore, lack axonal differentiation; that is, they are neurofilament and silver staining negative

 

♦

Schwann cells are S-100 protein positive and are generally surrounded by type IV collagen-rich basement membrane

 

♦

Epithelial membrane antigen typically stains the capsule of schwann omas

 

Palisaded and Encapsulated Neuroma (Solitary Circumscribed Neuroma, Fig. 18.30)

Fig. 18.30.

Palisaded and encapsulated neuroma.

Clinical

♦

Solitary, flesh-colored papule on the face of middle-aged to older adults

 

Microscopic

♦

A nodular to multinodular, often dumbbell-shaped proliferation of spindle cells embedded in a collagenous matrix

 

♦

These lesions are well circumscribed but only partially encapsulated

 

♦

The superficial component generally lacks a true capsule and tends to resemble a neurofibroma, while the deep component is encapsulated and resembles a schwannoma

 

♦

The spindle cells demonstrate wavy, pointed nuclei and lack mitotic activity

 

♦

Contrary to its name, true nuclear palisading is rare in this lesion

 

♦

A nerve may be evident entering the base of the lesion

 

Special Studies

♦

Like neurofibroma, this lesion contains both axons and schwann cells and, hence, is S-100 protein and neurofilament positive

 

Granular Cell Tumor (Fig. 18.31)

Fig. 18.31.

Granular cell tumor.

Clinical

♦

Slowly growing, sometimes painful, flesh-colored nodules with a predilection for the tongue, trunk, and extremities of adults

 

♦

While usually solitary, multiple, and familial variants exist

 

Microscopic

♦

Irregular fascicles and/or sheets of large, round to polygonal cells with eosinophilic, granular cytoplasm

 

♦

Cell borders are indistinct giving this tumor a syncytial appearance

 

♦

Nuclei are generally round to ovoid, central, and monomorphic

 

♦

Nuclear pleomorphism, mitotic activity, necrosis, and large tumor size may be associated with the rare malignant variants

 

♦

Prominent pseudoepitheliomatous hyperplasia of the epidermis is often seen overlying this tumor and must not be mistaken for squamous cell carcinoma

 

Special Studies

♦

While the cell of origin remains to be clarified, most authorities support a schwann cell derivation for these tumors

 

♦

Accordingly, these tumors are usually, but not always, S-100 protein and neuron-specific enolase positive

 

Differential Diagnosis

♦

Secondary granular cell change is not an uncommon finding in other tumor types (dermatofibroma, neurofibroma, etc.) which should be excluded prior to making the diagnosis of granular cell tumor

 

♦

This tumor should also be differentiated from congenital epulis discussed below

 

Nerve Sheath Myxoma (NSM ) and Cellular Neurothekeoma (Fig. 18.32)

Fig. 18.32.

Neurothekeoma.

Clinical

♦

Soft, mobile, flesh-colored papules on the face or upper extremities of young adults

 

♦

These tumors may recur with incomplete excision

 

Microscopic

♦

NSM is a fascicular to lobular dermal tumor composed of spindle and stellate cells embedded in myxoid lobules which in turn are separated by fibrous septae

 

♦

Cellular neurothekeoma is composed of more uniform, epithelioid cells in nests and fascicles with minimal myxoid background material

 

♦

Mitotic activity and mild nuclear pleomorphism may be seen in both lesions

 

Special Studies

♦

NSM is typically S-100 protein+ and is likely derived from the peripheral nerve sheath

 

♦

Cellular neurothekeoma is S-100 protein− and its cell of origin is unclear

 

♦

The lack of S-100 protein positivity in the cellular variants allows these lesions to be readily distinguished from most melanocytic neoplasms

 

Cutaneous Meningothelial Heterotopias/Meningiomas (Fig. 18.33)

Fig. 18.33.

Meningioma.

Clinical

♦

Classic meningocele is typically a transilluminating mass along the lower spine and represents a congenital defect

 

♦

Rudimentary meningocele is thought to be a herniation of the meninges into the superficial tissues of the scalp with a subsequent loss of its intracranial attachment

 

♦

Cutaneous meningioma comes in three forms: type I is congenital lesion involving the head and paravertebral regions of children and is secondary to misplaced arachnoid cells during embryogenesis; type II occurs on the head and neck region of adults and is thought to be secondary to a proliferation of arachnoid cells through a cranial foramina; type III represents a metastasis or direct extension of tumor into skin from an intracranial primary lesion

 

Microscopic

♦

Meningoceles are typically cyst-like structures lined by arachnoid cells and having surrounding dense fibrous tissue with occasional collections of meningothelial cells in whorl-like structures

 

♦

Meningiomas are usually well-circumscribed deep dermal to subcutaneous proliferations composed of spindle cells arranged in fascicles and whorls with or without psammoma body formation

 

♦

Nuclear pleomorphism and mitotic activity may be seen, particularly in the type III variants

 

♦

Special studies

 

♦

Meningothelial proliferations are usually vimentin and EMA+

 

♦

Cytokeratin and S-100 protein may also be expressed by these tumors

 

Smooth Muscle-Derived Tumors and Proliferations

Piloleiomyoma (Pilar leiomyoma, Fig. 18.34)

Fig. 18.34.

Piloleiomyoma.

Clinical

♦

Multiple, somewhat painful papules or nodules on the trunk or extremities of young adults

 

♦

May be inherited in an autosomal dominant fashion

 

Microscopic

♦

A fairly well-circumscribed yet irregular proliferation of smooth muscle fascicles within the dermis

 

♦

The individual cells have elongated eosinophilic cytoplasm and cigar-shaped nuclei

 

♦

No nuclear pleomorphism, mitotic activity, or necrosis is evident

 

Angioleiomyoma (Fig. 18.35)

Fig. 18.35.

Angioleiomyoma.

Clinical

♦

A solitary, sometimes painful nodule on the extremities of adults

 

Microscopic

♦

A nodular, well-circumscribed proliferation of smooth muscle in fascicles admixed with numerous, variably sized vessels

 

♦

Degenerative changes are frequent

 

Leiomyosarcoma (Fig. 18.36)

Fig. 18.36.

Leiomyosar coma.

Clinical

♦

Two clinical variants exist: a superficial or cutaneous variant and a deep or subcutaneous variant

 

♦

The former predominates on the limbs of young adults and is likely derived from the arrector pili muscle

 

♦

This variant may locally recur but generally does not metastasize

 

♦

The subcutaneous variant predominates on the limbs of the elderly and has both local recurrence and metastatic potential

 

Microscopic

♦

The cutaneous variant demonstrates an irregular, infiltrating, and haphazard proliferation of smooth muscle bundles reminiscent of piloleiomyoma

 

♦

However, unlike piloleiomyoma, this tumor has low-grade nuclear pleomorphism, mitotic activity, and, rarely, necrosis

 

♦

The deep or subcutaneous variant is akin to leiomyosarcomas arising elsewhere and consists of a nodular, at least focally infiltrating, proliferation of smooth muscle fibers in well-formed to ill-defined bundles with varying degrees of nuclear pleomorphism, mitotic activity, and necrosis

 

Fibrohistiocytic, Histiocytic, and Langerhans Cell-Derived Proliferations

Fibrous Histiocytoma (Dermatofibroma, Fig. 18.37)

Fig. 18.37.

Dermatofibroma.

Clinical

♦

Usually single, occasionally multiple, slightly elevated, smooth, flesh-colored to hyperpigmented nodules on the extremities or trunk of adults

 

Microscopic

♦

Numerous subtypes have been described, but all are generally made up of a proliferation of histiocytes, fibroblasts, and collagenous tissue in varying proportions

 

♦

The prototypical lesion (dermatofibroma) consists of a fairly well-circumscribed, unencapsulated, middermal proliferation with feathery edges, an overlying Grenz zone, and epidermal hyperplasia with basilar hyperpigmentation

 

♦

The cellular component consists of spindled, fibroblast-like cells admixed with plump histiocytic cells in an irregular fashion

 

♦

Storiform areas may be evident, and there may be focal extension into the subcutis

 

♦

Chronic inflammatory cells, multinucleated giant cells, xanthomatized histiocytes, and hemosiderin-laden histiocytes are also frequently identified within these lesions

 

♦

Important variants include atypical dermatofibroma (dermatofibroma with monster cells), aneurysmal fibrous histiocytoma, and epithelioid cell histiocytoma, all of which may be mistaken for other more aggressive entities

 

♦

Atypical dermatofibroma is a lesion showing large, hyperchromatic, multinucleated giant cells in addition to typical dermatofibroma features and should be distinguished from atypical fibroxanthoma and malignant fibrous histiocytoma

 

♦

Aneurysmal fibrous histiocytoma is a fibrous histiocytoma with prominent intralesional hemorrhage and cystic, pseudovascular spaces

 

♦

This lesion should be distinguished from angiomatoid fibrous histiocytoma, a lesion of intermediate-grade malignancy occurring in the pediatric population

 

♦

Epithelioid cell histiocytoma is composed of a polypoid well-circumscribed proliferation of angulated, epithelioid, histiocytic-appearing cells surrounded by an epidermal collarette

 

♦

This lesion should be distinguished from melanocytic tumors, both Spitz nevus and melanoma

 

Special Studies

♦

Most fibrous histiocytomas express FXIIIa but are negative for CD34

 

♦

Dermatofibroma sarcoma protuberans tends to have the opposite staining pattern, but overlap and divergent staining patterns occasionally occu r

 

Angiomatoid Fibrous Histiocytoma (Fig. 18.38)

Fig. 18.38.

Angiomatoid fibrous histiocytoma (A, B).

Clinical

♦

A fairly deep-seated, usually subcutaneous, nodule or mass within the extremities of children and adolescents

 

♦

This lesion is considered to be of borderline or intermediate malignancy and may recur and, rarely, metastasize

 

Microscopic

♦

A circumscribed, partially cystic and lobular mass usually centered on subcutaneous tissue

 

♦

This tumor is composed of an admixture of cystic, blood-filled pseudovascular spaces, myxoid lobules of histiocytic-appearing cells, and peripheral lymphocytic inflammation and fibrosis

 

♦

The neoplastic cells are somewhat spindled to plump, epithelioid cells with eosinophilic to amphophilic cytoplasm and mildly pleomorphic nuclei

 

♦

Mitotic figures may be evident

 

Special Studies

♦

The histiocytic-appearing cells often show expression of smooth muscle actin, desmin, and CD34, suggesting to som e a myofibroblastic derivation to this tumor

 

Juvenile Xanthogranuloma (Fig. 18.39)

Fig. 18.39.

Juvenile xanthogranuloma.

Clinical

♦

Solitary to multiple, yellow to red papules on the head and neck region of infants are the most common presentation

 

♦

However, adolescents and adults may also be affected, and other body sites may be involved

 

♦

Visceral involvement may be evident with the eye being the most common extracutaneous site of involvement

 

♦

Typically, the cutaneous lesions regress over time

 

Microscopic

♦

Fairly well-circumscribed collection of histiocytes within the dermis admixed with Touton giant cells, xanthomatized histiocytes, and chronic inflammatory cells

 

♦

The epidermis is spared, but periadnexal involvement is common

 

♦

Spindle cell and inflammatory cell-rich variants exist

 

Atypical Fibroxanthoma (Fig. 18.40)

Fig. 18.40.

Atypical fibroxanthoma.

Clinical

♦

Typically a solitary, often ulcerated polypoid nodule on the sun-exposed skin (head and neck) of the elderly

 

♦

A less common variant occurs on the trunk and extremities of young adults

 

♦

These tumors, when limited to superficial tissues, may locally recur but have minimal metastatic potential

 

Microscopic

♦

A nodular, often well-circumscribed, proliferation of very pleomorphic epithelioid to spindle cells with frequent mitoses, often atypical

 

♦

These tumors are usually centered on the dermis and frequently about the dermal–epidermal junction where they stop abruptly

 

♦

Epidermal ulceration is common, but true epidermal involvement with pagetoid spread should raise concerns about malignant melanoma or squamous cell carcinoma

 

♦

Rarely, the tumor is composed of spindle cells in poorly defined fascicles and may be mistaken for leiomyosarcoma

 

♦

While occasional tumors may show superficial involvement of the subcutaneous tissues, extensive subcutaneous involvement and/or prominent vascular invasion and necrosis should lead to an alternate diagnosis (e.g., malignant fibrous histiocytoma)

 

Special Studies

♦

This tumor is a diagnosis of exclusion; therefore, S-100 protein, cytokeratin, and desmin should be negative by immunoperoxidase technique to exclude malignant melanoma, carcinoma, and leiomyosarcoma, respectively

 

♦

Smooth muscle actin may be expressed by a subset of these tumors and is not indicative of smooth muscle differentiation (leiomyosarcoma) in the absence of desmin positiv ity

 

Xanthomas and Xanthelasma (Fig. 18.41)

Fig. 18.41.

Verruciform xanthoma.

Clinical

♦

Numerous clinical and histologic subtypes exist, many of which are related to systemic lipid abnormalities and represent storage disorders

 

♦

Eruptive

• 
  
  Yellow papules on the buttocks and other sites associated with type I hyperlipoproteinemia

 

♦

Tuberous

• 
  
  Yellow papules and nodules on the extensor surfaces associated with hyperlipoproteinemia types II–IV

 

♦

Tendinous

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