Pathology of Trichoblastoma - Dr Sampurna Roy MD

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Pathology of Trichoblastoma

Dr Sampurna Roy MD 2022

Answer - Trichoblastoma

As originally described by Headington in 1970, these are very rare tumours that tend to be larger and more deeply located than trichoepithelioma.

They 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.

Clinical presentation: Presents as a well circumscribed, solitary lesion (more than 1 cm in diameter).The incidence in males is approximately 30% higher than that in females.

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

Microscopic features:

- Large well-circumscribed basaloid tumour ;

- No epidermal connection ;

- Located in mid and lower dermis ;

- May extend to the subcutis ;

- Nests of basaloid cells ;

- Variable stromal condensation & pilar differentiation ;

- Associated fibrotic stroma with increased numbers of fibroblasts

- Primitive hair bulbs (stromal induction) ;

- Apocrine and sebaceous differentiation ;

- Stromal amyloid and merkel cells.

Variants:

- Clear cell ;

- Pigmented ;

- Adamantinoid ;

- 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. No sebaceous differentiation. Differential diagnosis: Rippled-pattern sebaceoma.

- Cutaneous lymphadenoma is an adamantinoid variant of trichoblastoma.

Depending on the degree of differentiation toward other follicular components and the relative prominence of stromal and epithelial elements this group was classically subdivided into trichoblastoma nos, trichoblastic fibroma and trichogenic trichoblastoma.

- Trichoblastic fibroma include both germ and fibrous stroma.

- Trichogenic trichoblastoma is the most mature form and include complete hair follicle.

- Cystic trichoblastoma - Cystic trichoblastoma (so-called trichoblastic infundibular cyst): a report of three new cases.

Differential diagnosis:

Basal cell carcinoma: It is a basaloid neoplasm that originates from the epidermis. As opposed to trichoblastoma, it is characterized by basaloid nodules, with prominent peripheral palisading and clefting between the neoplasm and surrounding stroma.

Classic trichoepithelioma (more keratocysts are present and distinction is very difficult).

Trichoblastic carcinoma (or malignant trichoblastoma) is a rare malignant cancer of adnexal structures with morphological features that in some cases are reminiscent of a trichoblastoma.

Further reading:
False-negative tumor-free margins following mohs surgery for aggressive trichoblastoma.

Trichoblastoma: management of a rare skin lesion.

Trichoblastoma shares cytokeratin 15-positive cells with seborrheic keratosis in a composite tumor--novel immunohistochemical findings.

Vulvar Trichoblastoma: Case Report and Literature Review.

Pigmented trichoblastoma with sebaceous hyperplasia

Rippled-pattern trichoblastoma with apocrine differentiation arising in a nevus sebaceus: report of a case and review of the literature.

Multiple clear cell trichoblastoma.

Solitary trichoblastoma.

High-grade trichoblastic carcinoma arising in trichoblastoma : a rare adnexal neoplasm often showing metastatic spread.

Trichoblastoma with apocrine and sebaceous differentiation.

A rippled-pattern trichoblastoma: an immunohistochemical study.

Trichoblastoma is the most common neoplasm developed in nevus sebaceus of Jadassohn:a clinicopathologic study of a series of 155 cases.