David Cassarino, MD, PhD

Scanning magnification of a trichoblastoma shows a nodular basaloid proliferation associated with a fibrotic stroma. Note the presence of scattered folliculocystic structures image.

High magnification of a trichoblastoma shows a lobular basaloid proliferation associated with a cellular, fibrotic stroma image. Note the prominent stromal-stromal retraction artifact image.



  • Trichoblastoma (TB)


  • Giant trichoepithelioma (TE)

  • Trichogerminoma

  • Rippled pattern trichomatricoma

  • Trichoblastic fibroma

  • Cutaneous lymphadenoma


  • Benign dermal-based adnexal tumor showing primitive follicular differentiation



  • Incidence

    • Uncommon tumors

  • Age

    • Usually occur in adults


  • Head and neck area, especially the scalp


  • Dermal nodule/mass lesion

    • Usually single but may rarely be multiple

  • Usually asymptomatic


  • Surgical approaches

    • Complete excision is curative

    • Should be recommended in cases of partial biopsy in order to exclude basal cell carcinoma (BCC)


  • Excellent in most cases

  • Rare recurrences and association with, or progression to, malignancy (BCC)


General Features

  • Nodular lesion involving the deep dermis and subcutis


  • Large, typically > 1 cm in diameter


Histologic Features

  • Large, basaloid-appearing deep dermal-based nodule

    • Usually symmetric and shows well-circumscribed borders

    • Composed of irregular lobules and nests of basaloid cells

    • No epidermal connections

    • May extend into superficial subcutis

  • Associated fibrotic stroma with increased numbers of fibroblasts

    • Stromal amyloid may be present

    • Calcifications and granulomatous inflammation occasionally seen but less common than in TE

  • Papillary mesenchymal bodies classically present, similar to TE

    • Invagination of fibroblastic stroma into primitive follicular structures

    • Represents abortive follicular induction


  • Trichogerminoma

    • Tightly packed lobules of primitive basaloid cells with minimal stroma

  • Rippled pattern trichomatricoma

    • Palisading ribbons of basaloid cells; may resemble Verocay bodies

  • Trichoblastic fibroma

    • Less epithelial structures, more prominent stroma, which may appear desmoplastic

  • Cutaneous lymphadenoma

    • Rare variant with a prominent lymphocytic infiltrate and clear cell features


Basal Cell Carcinoma

  • BCC usually shows multiple attachments to the overlying epidermis (focal or absent in TB)

  • BCC also shows the following features (which are not seen in TB)

    • Prominent peripheral palisading

    • Mucinous stroma

    • Tumor-stromal retraction artifact (stromal-stromal retraction seen in TB)

    • Numerous mitotic and apoptotic figures

  • Immunohistochemistry may be useful in some cases (particularly small, partial biopsies)

    • Bcl-2, p53, and Ki-67 all elevated in BCC (should be low in TB)

    • CK20 highlights Merkel cells in TB (absent in BCC)


  • Small, papular lesion clinically

  • Overlapping histologic features, but TE is smaller, more superficial than TB

  • Usually shows more prominent folliculocysts, calcifications, and granulomatous inflammation


  • More superficial, epidermal- or follicular-based adnexal neoplasm

  • Composed of lobules and nests of predominantly basaloid cells with minor population of clear cells

  • May show rippled pattern with nuclear palisading, similar to rippled pattern trichomatricoma

  • Scattered mature sebaceous cells with multivacuolated cytoplasm


  • Dermal-based neoplasm composed of basaloid cells with ductal differentiation

  • Irregular, “jigsaw puzzle” pattern of variably shaped lobules and nests

    • Surrounded by hyalinized basement membrane, and nests contain hyalinized globules

  • Focal ductal lumina present (may be highlighted by EMA &/or CEA)

Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Trichoblastoma

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