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Thursday 3 June 2010


Definition: Trichoblastomas are a cutaneous condition characterized by benign neoplasms of follicular germinative cells. Trichoblastomas are epithelial tumors consisting mostly of follicular germinative cells. There are rare cases of malignant degeneration.

Trichoblastomas are very rare tumours that tend to be larger and more deeply located than trichoepithelioma.

Trichoblastomas are formed of varying combinations of basaloid germ cells and follicular mesenchyme with varying degrees of primitive hair bulb formation (stromal induction).

Trichoblastomas are not aggressive unless they contain an element of basal cell carcinoma.


- Trichoblastoma

- Trichoblastoma w/ pale micronodules (Zellballen) aka trichogerminoma

- Trichoblastoma and lymphocytes in tumor nests

- syringocystadenocarcinoma papilliferum with trichoblastoma in nevus sebaceus

- Trichoblastoma, small nodular type

- "Ripple pattern" trichoblastoma with Verocay-like arrangement of cells. (sebaceoma can have similar pattern).

- Digital slide :

Clinical presentation

Presents as a well circumscribed, solitary lesion (more than 1cm in diameter).

Site: Head, particularly the scalp is a common site.


TB can arise practically at any age, but are more common in adults. Women are equally often affected as men. The preferred anatomical sites are head and neck region, especially face and scalp.

They are extremely rare on distal extremities. The majority of trichoblastomas are less then 2 cm in size with occasional examples of giant trichoblastomas sometimes reaching several centimeters.

Giant trichoblastomas are also sometimes referred to as solitary or giant trichoepitheliomas have special predilection for the face and perianal area.


- Large circumscribed basaloid tumour
- No epidermal connection
- Located in mid & lower dermis
- May extend to the subcutis
- Nests of basaloid cells
- Variable stromal condensation & pilar differentiation
- Primitive hair bulbs (stromal induction)
- Apocrine & sebaceous differentiation
- Stromal amyloid & merkel cells
- Possible ripple pattern


- Clear cell
- Pigmented
- Adamantinoid

  • Cutaneous lymadenoma is an adamantinoid variant of trichoblastoma.
    - Rippled-pattern
  • Rippled-pattern trichoblastoma is characterized by peculiar arrangement of the basaloid cells in linear rows parallel to one another similar to the palisading of nuclei of Verocay bodies seen in schwannomas.
    - desmoplastic
    - giant trichoblastoma

Trichoblastic fibroma is a designation used to characterize small nodular trichoblastomas with conspicuous fibrocytic stroma, sometimes constituting over 50% of the lesion. Trichoblastic fibroma include both germ and fibrous stroma.

Trichogenic trichoblastoma most mature form and include complete hair follicle.


Trichoblastoma is the most common neoplasm developed in nevus sebaceus of Jadassohn.

Differential diagnosis

- basal cell carcinoma
- classic trichoepithelioma (more keratocysts are present; distinction is very difficult)

Molecular biology

- PTCH mutations are not mainly involved in the pathogenesis of sporadic trichoblastomas.

- Activating mutations in the RAS/mitogen-activated protein kinase signaling pathway in sporadic trichoblastoma and syringocystadenoma papilliferum.

Differential diagnosis

- basal cell carcinoma
- trichoadenoma


- Wikipedia

See also

- cutaneous tumors


- High-grade trichoblastic carcinoma arising in trichoblastoma : a rare adnexal neoplasm often showing metastatic spread. Am J Dermatopathol. 2005; 27(1):9-16.
Fibroepithelioma of pinkus is a fenestrated trichoblastoma.Am J Dermatopathol. 2005 Apr;27(2):149-54.

- Trichoblastoma with apocrine and sebaceous differentiation.Am J Dermatopathol. 2005;27(1):6-8.

- Androgen receptor expression helps to differentiate basal cell carcinoma from benign trichoblastic tumors.Am J Dermatopathol. 2005;27(2):91-5

- Vulvar Trichogenic Tumors: A Comparative Study With Vulvar Basal Cell Carcinoma. Am J Surg Pathol. 2005 ;29 (4):479-484.

- Low-grade trichoblastic carcinosarcoma of the skin. Am J Dermatopathol. 2004;26(4):304-9

- Trichoblastic neoplasm with apocrine differentiation.Am J Dermatopathol 2002;24(4):358-60

- Melanotrichoblastoma: immunohistochemical study of a variant of pigmented trichoblastoma. Am J Dermatopathol 2002 Dec;24(6):498-501

- Trichoblastoma arising within an apocrine poroma.Am J Dermatopathol 2002 Feb;24(1):59-62

- Clear Cell Trichoblastoma in Association With A Nevus Sebaceus . Am J Dermatopathol 2001;23:143-145

- Sebaceous carcinoma, trichoblastoma, and sebaceoma with features of trichoblastoma in nevus sebaceus.Am J Dermatopathol. 2001 Oct;23(5):456-62.

- Cytokeratins as Markers of Follicular Differentiation. An Immunohistochemical Study of Trichoblastoma and Basal Cell Carcinoma . Am J Dermatopathol 2001;23:501-509

- Trichoblastoma of the skin occurring in the breast. A case report.Acta Cytol. 2001 May-Jun;45(3):435-40.

- Rippled-pattern sebaceous trichoblastoma. J Cutan Pathol 2000;27(9):455-9

- A rippled-pattern trichoblastoma: an immunohistochemical study. J Cutan Pathol 2000;27(9):460-5

- Trichoblastic carcinoma ("malignant trichoblastoma") with lymphatic and hematogenous metastases. Mod Pathol 2000 ;13(6):673-8

- Trichoblastoma is the most common neoplasm developed in nevus sebaceus of Jadassohn:a clinicopathologic study of a series of 155 cases. Am J Dermatopathol 2000;22(2) :108-18

- Cytokeratin expression in trichoblastic fibroma (small nodular type trichoblastoma), trichoepithelioma and basal cell carcinoma. Br J Dermatol 1999;140(1):8-16

- Immunohistochemical comparison of cutaneous lymphadenoma, trichoblastoma, and basal cell carcinoma: support for classification of lymphadenoma as a variant of trichoblastoma. J Cutan Pathol 1999 Mar;26(3):119-24.

- Nodular desmoplastic variant of trichoblastoma. Am J Surg Pathol 1994;18(5):495-500

- Giant trichoblastoma on the scalp. Am J Dermatopathol 1993;15(5):497-502

- Pigmented trichoblastoma. Am J Dermatopathol 1992;14(4) : 345-9