Digital Myxoid Cyst

■ Most common on the dorsal surface of the index or middle finger, overlying the distal interphalangeal joint, just above the proximal nail fold (Fig. 20C)

■ Ill-defined collection of mucin in superficial dermis, may have overlying collarette of epidermis (Fig. 20D)

■ Mild inflammation at the periphery

Figure 1 (A) Multiple well circumscribed, hyperplgmented, verrucous plaques with a "stuck-on" appearance. (B) Well circumscribed and symmetric lesion demonstrating papillomatosis and acanthosis of the epidermis. Predominantly exophytic. (C) Scattered pseudohorn cysts created by cross-sectioning the keratin-filled crypts. (D) Proliferation of small, relatively uniform basaloid keratino-cytes with an approximately 1:1 nuclear to cytoplasmic ratio. No significant nuclear atypia.

Figure 1 (A) Multiple well circumscribed, hyperplgmented, verrucous plaques with a "stuck-on" appearance. (B) Well circumscribed and symmetric lesion demonstrating papillomatosis and acanthosis of the epidermis. Predominantly exophytic. (C) Scattered pseudohorn cysts created by cross-sectioning the keratin-filled crypts. (D) Proliferation of small, relatively uniform basaloid keratino-cytes with an approximately 1:1 nuclear to cytoplasmic ratio. No significant nuclear atypia.

(B>

Figure 2 (A) Well circumscribed, light tan patch with slightly raised border, progressing to a plaque. (B) Hyperpigmented basalar kera-tinocytes of a solar lentigo with proliferation of small basaloid cells in strands and development of pseudohorn cysts. (C) Well circumscribed, dark brown to black plaque with pebbly surface. No extension of pigment into surrounding skin. (D) Proliferation of small basaloid keratinocytes with abundant melanin in their cytoplasms, no significant increase in melanocytes.

Figure 2 (A) Well circumscribed, light tan patch with slightly raised border, progressing to a plaque. (B) Hyperpigmented basalar kera-tinocytes of a solar lentigo with proliferation of small basaloid cells in strands and development of pseudohorn cysts. (C) Well circumscribed, dark brown to black plaque with pebbly surface. No extension of pigment into surrounding skin. (D) Proliferation of small basaloid keratinocytes with abundant melanin in their cytoplasms, no significant increase in melanocytes.

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Figure 3 (A) Circumscribed reddish-brown papule with an erythematous base. (B) Seborrheic keratosis with a dense superficial perivascular and lichenoid, predominantly lymphocytic inflammatory infiltrate. (C) Gradual change from small basaloid keratinocytes to large keratinocytes with abundant keratin (squamous differentiation). (D) Individual keratinocytes may demonstrate mild to moderate nuclear atypia.

Figure 3 (A) Circumscribed reddish-brown papule with an erythematous base. (B) Seborrheic keratosis with a dense superficial perivascular and lichenoid, predominantly lymphocytic inflammatory infiltrate. (C) Gradual change from small basaloid keratinocytes to large keratinocytes with abundant keratin (squamous differentiation). (D) Individual keratinocytes may demonstrate mild to moderate nuclear atypia.

Figure 4 (A) Thin anastomosing strands of small, uniform basaloid cells extending into the dermis. (B) Round or nested aggregates of uniform basaloid cells separated by larger keratinocytes with squamous differentiation. (C) Acanthotic proliferation of small basaloid keratinocytes. (D) Dendritic melanocytes sprinkled at all levels of the epidermis.

Figure 4 (A) Thin anastomosing strands of small, uniform basaloid cells extending into the dermis. (B) Round or nested aggregates of uniform basaloid cells separated by larger keratinocytes with squamous differentiation. (C) Acanthotic proliferation of small basaloid keratinocytes. (D) Dendritic melanocytes sprinkled at all levels of the epidermis.

Figure 5 (A) Papillated epidermal hyperplasia simulating a seborrheic keratosis. (B) Atypical keratinocytes with large hyperchro-matic and pleomorphic nuclei, along with scattered mitotic figures. (C) Well circumscribed and symmetric melanocytic proliferation simulating a seborrheic keratosis. (D) Single and nested atypical melanocytes at all levels of the epidermis.

Figure 5 (A) Papillated epidermal hyperplasia simulating a seborrheic keratosis. (B) Atypical keratinocytes with large hyperchro-matic and pleomorphic nuclei, along with scattered mitotic figures. (C) Well circumscribed and symmetric melanocytic proliferation simulating a seborrheic keratosis. (D) Single and nested atypical melanocytes at all levels of the epidermis.

Figure 6 (A) Multiple small, hyperpigmented, smooth papules on face. (B) Dome-shaped papule with epidermal hyperplasia and a central collagenous core. (C) Multiple small hyperkeratotic papules on the lower leg and dorsal foot. (D) Digitated epidermal hyperplasia with overlying compact orthokeratosis.

Figure 6 (A) Multiple small, hyperpigmented, smooth papules on face. (B) Dome-shaped papule with epidermal hyperplasia and a central collagenous core. (C) Multiple small hyperkeratotic papules on the lower leg and dorsal foot. (D) Digitated epidermal hyperplasia with overlying compact orthokeratosis.

Figure 7 (A) Dome-shaped papule with rough, scaly surface. (B) Exo-endophytic proliferation of small basaloid and larger keratinocytes with a digitated and bulbous architectural pattern. (C) Numerous squamous eddies in the endophytic portion of this lesion. (D) Squamous eddy with mild nuclear atypia and no keratin pearl.

Figure 7 (A) Dome-shaped papule with rough, scaly surface. (B) Exo-endophytic proliferation of small basaloid and larger keratinocytes with a digitated and bulbous architectural pattern. (C) Numerous squamous eddies in the endophytic portion of this lesion. (D) Squamous eddy with mild nuclear atypia and no keratin pearl.

Figure 8 (A) Well circumscribed, hyperkeratotic tan papule on the arm. (B) Digitated epidermal hyperplasia with a prominent granular layer and koilocytes. (C) Verrucous epidermal hyperplasia and acanthosis with a proliferation of both basaloid and large keratinocytes. (D) Horn cyst with mild atypia of the surrounding keratinocytes and associated inflammation.

Figure 8 (A) Well circumscribed, hyperkeratotic tan papule on the arm. (B) Digitated epidermal hyperplasia with a prominent granular layer and koilocytes. (C) Verrucous epidermal hyperplasia and acanthosis with a proliferation of both basaloid and large keratinocytes. (D) Horn cyst with mild atypia of the surrounding keratinocytes and associated inflammation.

Figure 9 (A) Small tan papules with a linear distribution coalescing into a plaque. (B) Papillated epidermal hyperplasia without pseudohorn cysts. (C) Hyperpigmented verrucous papules in a linear distribution on the lower leg and dorsal foot. (D) Alternating zones of hypergranulosis with overlying orthokeratosis and hypogranulosis with overlying parakeratosis.

Figure 9 (A) Small tan papules with a linear distribution coalescing into a plaque. (B) Papillated epidermal hyperplasia without pseudohorn cysts. (C) Hyperpigmented verrucous papules in a linear distribution on the lower leg and dorsal foot. (D) Alternating zones of hypergranulosis with overlying orthokeratosis and hypogranulosis with overlying parakeratosis.

Figure 10 (A) Well circumscribed, dome-shaped, erythematous plaques with a glistening surface on the lower leg. (B) Proliferation of keratinocytes with normal nuclei and clear or pale-staining cytoplasms. (C) Zone of pale-staining keratinocytes with sharp separation from the surrounding basaloid keratinocytes. (D) Neutrophils and neutrophilic particles scattered throughout the zones of clear cells.

Figure 10 (A) Well circumscribed, dome-shaped, erythematous plaques with a glistening surface on the lower leg. (B) Proliferation of keratinocytes with normal nuclei and clear or pale-staining cytoplasms. (C) Zone of pale-staining keratinocytes with sharp separation from the surrounding basaloid keratinocytes. (D) Neutrophils and neutrophilic particles scattered throughout the zones of clear cells.

(B)

Figure 11 (A) Papillated epidermal hyperplasia and acanthosis with focal granular degeneration. (B) Granular or epidermolytic change with edema, pale-staining cytoplasms, coarse keratohyaline-like granules, and eosinophilic trichohyaline-like granules.

(C) Architecture of a seborrheic keratosis with extensive acantholysis of keratinocytes.

(D) Acantholysis and dyskeratosis of keratinocytes with the architecture of a seborrheic keratosis.

Figure 11 (A) Papillated epidermal hyperplasia and acanthosis with focal granular degeneration. (B) Granular or epidermolytic change with edema, pale-staining cytoplasms, coarse keratohyaline-like granules, and eosinophilic trichohyaline-like granules.

(C) Architecture of a seborrheic keratosis with extensive acantholysis of keratinocytes.

(D) Acantholysis and dyskeratosis of keratinocytes with the architecture of a seborrheic keratosis.

Figure 12 (A) Papillomas in the axilla. (B) Polypoid papules with smooth surface and flattened rete ridges. (C) Well circumscribed, slightly raised erythematous plaque with scale. (D) Dense lichenoid mononuclear cell infiltrate which obscures the dermal-epidermal junction and is seen in association with necrotic keratinocytes. There is minimal atypia of the keratinocytes.

Figure 12 (A) Papillomas in the axilla. (B) Polypoid papules with smooth surface and flattened rete ridges. (C) Well circumscribed, slightly raised erythematous plaque with scale. (D) Dense lichenoid mononuclear cell infiltrate which obscures the dermal-epidermal junction and is seen in association with necrotic keratinocytes. There is minimal atypia of the keratinocytes.

Figure 13 (A) Large nodule with raised borders and a central keratin-filled plug.

(B) Exo-endophytic proliferation of large keratinocytes with a central keratin-filled plug and overhanging lips of epidermis.

(C) Exo-endophytic proliferation of keratinocytes with a central cystic cavity.

(D) Acantholytic and dyskeratotic keratinocytes filling the central invagination.

Figure 13 (A) Large nodule with raised borders and a central keratin-filled plug.

(B) Exo-endophytic proliferation of large keratinocytes with a central keratin-filled plug and overhanging lips of epidermis.

(C) Exo-endophytic proliferation of keratinocytes with a central cystic cavity.

(D) Acantholytic and dyskeratotic keratinocytes filling the central invagination.

Figure 14 (A) Exo-endophytic round, firm, well circumscribed cystic nodule. (B) Well circumscribed dermal and subcutaneous nodule with epithelial lining and central keratin. (C) Epithelial wall simulating normal epidermis with a prominent granular layer. Laminated keratin centrally. (D) Dense granulomatous inflammation adjacent to a rupture of the cyst wall.

Figure 14 (A) Exo-endophytic round, firm, well circumscribed cystic nodule. (B) Well circumscribed dermal and subcutaneous nodule with epithelial lining and central keratin. (C) Epithelial wall simulating normal epidermis with a prominent granular layer. Laminated keratin centrally. (D) Dense granulomatous inflammation adjacent to a rupture of the cyst wall.

Figure 15 (A) Firm, round, well circumscribed nodule on the forehead. (B) Round dermal nodule with an epithelial lining and dense central keratin. (C) Epithelial lining with no granular layer and central homogeneous, pink staining keratin core. (D) Pale-staining, swollen keratinocytes next to homogeneous keratin.

Figure 15 (A) Firm, round, well circumscribed nodule on the forehead. (B) Round dermal nodule with an epithelial lining and dense central keratin. (C) Epithelial lining with no granular layer and central homogeneous, pink staining keratin core. (D) Pale-staining, swollen keratinocytes next to homogeneous keratin.

Figure 16 (A) Large, firm, cystic structure on scalp. (B) Relatively well circumscribed dermal cystic structure, appears multinodular. (C) Folded and layered cross-sections of epithelial wall similar to a pilar cyst. (D) Multiple layers of well differentiated squamous cells, swollen appearing keratinocytes adjacent to homogeneous keratin core.

Figure 16 (A) Large, firm, cystic structure on scalp. (B) Relatively well circumscribed dermal cystic structure, appears multinodular. (C) Folded and layered cross-sections of epithelial wall similar to a pilar cyst. (D) Multiple layers of well differentiated squamous cells, swollen appearing keratinocytes adjacent to homogeneous keratin core.

Figure 17 (A) Multiple nodular cystic, tan to yellow lesions on the chest. (B) Sebaceous lobules entering cyst in association with a crenulated epithelial lining of two to three layers of keratinocytes. (C) Tan to bluish cystic papules on the chest. (D) Dermal cyst with numerous vellus hairs in contents.

Figure 17 (A) Multiple nodular cystic, tan to yellow lesions on the chest. (B) Sebaceous lobules entering cyst in association with a crenulated epithelial lining of two to three layers of keratinocytes. (C) Tan to bluish cystic papules on the chest. (D) Dermal cyst with numerous vellus hairs in contents.

Figure 18 (A) Epidermoid cyst with amorphous pigmented keratin in center. (B) Multiple epidermal appendages arising from or entering the cyst wall. Hair shafts are seen in the lumen. (C) Epithelial lining with simple cuboidal and columnal epithelium with cilia. (D) Epithelial lining with pseudostratified columnal epithelium. Smooth muscle bundles seen in the surrounding stroma.

Figure 18 (A) Epidermoid cyst with amorphous pigmented keratin in center. (B) Multiple epidermal appendages arising from or entering the cyst wall. Hair shafts are seen in the lumen. (C) Epithelial lining with simple cuboidal and columnal epithelium with cilia. (D) Epithelial lining with pseudostratified columnal epithelium. Smooth muscle bundles seen in the surrounding stroma.

(C)

Figure 19 (A) Epithelial lining with pseudo-stratified columnal epithelium, cilia, and goblet cells. (B) Epithelial lining with stratified squamous and ciliated columnal epithelium. Dense lymphoid aggregates in surrounding stroma. (C) Multiple dermal cystic structures with epithelial linings. (D) Columnal epithelial lining with hemorrhage and fibrosis in the stroma.

Figure 19 (A) Epithelial lining with pseudo-stratified columnal epithelium, cilia, and goblet cells. (B) Epithelial lining with stratified squamous and ciliated columnal epithelium. Dense lymphoid aggregates in surrounding stroma. (C) Multiple dermal cystic structures with epithelial linings. (D) Columnal epithelial lining with hemorrhage and fibrosis in the stroma.

Figure 20 (A) Cystic swelling on the lower lip. (B) Amorphous zone of mucinous material with lymphocytes and neutrophils, but no epithelial lining. (C) Compressible cystic lesion on the dorsal finger. (D) Ill-defined collection of mucin in the superficial dermis with a surrounding epidermal collarette. No epithelial lining is present.

Figure 20 (A) Cystic swelling on the lower lip. (B) Amorphous zone of mucinous material with lymphocytes and neutrophils, but no epithelial lining. (C) Compressible cystic lesion on the dorsal finger. (D) Ill-defined collection of mucin in the superficial dermis with a surrounding epidermal collarette. No epithelial lining is present.

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