5
Color – Blue

  • Blue tumor, 281
  • Mucin and glands or ducts, 291
  • Mucin, 295

    Basal cell carcinoma

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  • Blue tumor
  • Peripheral palisading
  • Retraction of stroma around individual islands
  • Stroma often mucinous
  • Islands may contain mitoses and individually necrotic cells

    Glomus tumor

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  • Blue tumor
  • Tumor composed of cells with monomorphous, centrally-located, round nuclei (arrows)
  • Cells surround vascular spaces

    Merkel cell carcinoma

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  • Blue tumor
  • Trabecular or nodular pattern on low power
  • Tumor composed of cells with pale nuclei and scant cytoplasm on high power
  • Nuclei have a “salt and pepper” look
  • Numerous scattered mitoses and necrotic cells
  • Cells often overlapping/pushing into each other

    Sebaceoma (sebaceous epithelioma)

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  • Blue tumor
  • Scattered sebocytes among smaller, blue cells
  • Presence of sebaceous ducts
  • Tends to be localized to the upper dermis below the epidermis

    Sebaceous carcinoma

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  • Blue tumor
  • Sebocytes (arrows) among atypical blue cells; sebaceous ducts may be evident
  • Necrosis and atypical cells
  • Infiltrative pattern and/or situated in reticular dermis/subcutaneous tissue

Spiradenoma

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  • Blue tumor
  • “Blue balls” in the dermis
  • Islands of tumor may be peppered by lymphocytes and hyaline pink droplets
  • Tumor composed of more peripheral blue cells and more central pale/clear cells that may be arranged in a trabeculated pattern
  • Occasional ductal components

    Trichoblastoma

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  • Blue tumor
  • Peripheral palisading
  • Generally no epidermal connection
  • Well-circumscribed with clefts between the tumor as a whole and the normal dermis
  • Less differentiation to basaloid islands compared to trichoepithelioma
  • Papillary mesenchymal bodies (small finger-like invagination of dermis pushing into a small basaloid island) may be seen

    Trichoepithelioma

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  • Blue tumor
  • Often an epidermal connection
  • Grape-like fronds of cells or reticulated islands of basaloid cells with peripheral palisading
  • Fibrotic stroma
  • Clefting between the fibrotic stroma and bordering normal dermis
  • Papillary mesenchymal bodies may be seen

Tufted angioma

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  • Blue tumor
  • Groups of cells in dermis (cannon balls) forming small vascular spaces with erythrocytes
  • Clefts (lymphatic space) may be seen around the groups of cells
  • May resemble Kaposiform hemangioendothelioma (usually a deeper, larger tumor)

    Key differences

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    (a)

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    (b)

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    (c)

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    (d)

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    (e)

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    (f)

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    (g)

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    (h)

    1. Basal cell carcinoma: peripheral palisading, clefts between blue islands and stroma
    2. Glomus tumor: round monomorphous cells
    3. Merkel cell carcinoma: pale salt and pepper nuclei
    4. Sebaceoma (sebaceous epithelioma): blue cells with occasional interspersed sebocytes
    5. Spiradenoma: two cell types – pale and blue
    6. Trichoblastoma: peripheral palisading, papillary mesenchymal bodies
    7. Trichoepithelioma: grape-like fronds of cells with peripheral palisading, fibrotic stroma

    8. Tufted angioma: “Cannonballs” of blue cells forming vascular spaces

      Note Some pathologists consider trichoepithelioma to be a variant of trichoblastoma.

    Chondroid syringoma (mixed tumor of skin)

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  • Bluish-pink chondroid areas (long arrows) and duct-like spaces (short arrows)
  • Well-circumscribed

    Mucinous carcinoma

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  • Mucin in pools
  • In center of pools, there are epithelial islands with variable ductal differentiation

    Mucocele

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  • Mucin
  • Mucin often surrounded by giant cells
  • May see mucosal epithelium and/or minor salivary glands

    Key differences

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    (a)

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    (b)

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    (c)

    1. Chondroid syringoma: well-circumscribed blue-pink cartilaginous area containing duct-like spaces
    2. Mucinous carcinoma: pools of mucin containing epithelial islands
    3. Mucocele: pool of mucin with surrounding fibrosis/inflammation; adjacent salivary glands

    Digital mucous cyst

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  • Well-circumscribed mucin (blue, lacy appearance)
  • Acral skin
  • Not a true cyst (no epithelial lining)

    Focal cutaneous mucinosis

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  • Well-circumscribed mucin and stellate fibroblasts
  • Non-acral location

    Follicular mucinosis

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  • Mucin within a distorted hair follicle

    Lupus tumidus

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  • Mucin between collagen bundles
  • Perivascular lymphocytes

  • Mucin can be highlighted by colloidal iron (or other mucin stains) as in the bottom right image

    Source: Case courtesy of Whitney High, MD, JD.

    Neurothekeoma

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  • Variable mucin in nodular collections with spindle cells

  • Nodules separated by fibrosis

    Note Lesions with abundant mucin are probably best-termed nerve sheath myxomas.

    Pretibial myxedema

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  • Mucin filling the dermis (spares papillary dermis)

    Key differences

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    (a)

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    (b)

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    (c)

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    (d)

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    (e)

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    (f)

    1. Digital mucous cyst: acral location
    2. Focal cutaneous mucinosis: non-acral location
    3. Follicular mucinosis: mucin within follicle
    4. Neurothekeoma: nodules of spindle or epithelioid cells in variable myxoid background
    5. Nodular fasciitis: elongated “tissue culture” cells in myxoid background (see page 170)
    6. Pretibial myxedema: mucin filling reticular dermis