Are You Confident of the Diagnosis?

What you should be alert for in the history

The diagnosis of trichoblastoma is considered when an asymptomatic raised skin-colored lesion appears on the scalp or the face of an individual. Cosmesis regarding the size or location of the lesion is a major patient concern associated with trichoblastomas.

Characteristic findings on physical examination

Trichoblastomas are typically found on the face and scalp and range in size from 5mm to 8cm. They are generally nonulcerated skin-colored to brown papules or nodules. Very rarely, pigmented trichoblastomas have been reported.

Expected results of diagnostic studies

On histology, trichoblastomas are large circumscribed basaloid tumors, located in the middle to lower dermis, without epidermal connection. Subcutaneous and superficial variants are exceptions, with the former being located deeper in the subcutaneous tissue, and the latter demonstrating epidermal connection.

Trichoblastomas also have palisading of basaloid cells, focal hair germ-like papillary mesenchymal bodies, and variable amounts of fibrous stroma. There is a spectrum of differentiation ranging from primitive to mature follicular structures.

In 1993, Ackerman proposed a new classification and suggested that the term trichoblastoma encompass all adnexal neoplasms of follicular germinative cells that show benign features, including sharp circumscription, smooth borders, and symmetrical growth patterns. He classified trichoblastomas into the following histopathologic types: adamantoid (cutaneous lymphadenoma), columnar (desmoplastic trichoepithelioma), cribiform (trichoepithelioma), large nodular, small nodular, racemiform-retiform, rippled-pattern, subcutaneous, and superficial (common in nevus sebaceous).

At present, there is no standardized classification system for trichogenic tumors, and several diagnostic terms have been proposed, but one should regard them as distinct entities until a universal classification system is established.

On immunohistochemistry, trichoblastomas express the following staining patterns:

– Trichoblastomas stain positive for cytokeratin 20. This staining is present in the basal layer of the epidermis and within hair follicles. Cytokeratin 20 stains for Merkel cells; hence, these cells are found in the basal layer and hair follicles of trichoblastomas.

– Trichoblastomas also stain positive for CD34 in the tumor stroma.

– Bcl-2 expression is only found at the periphery of the tumor.

Diagnosis confirmation

Basal cell carcinoma is an important differential diagnosis for trichoblastomas. Since basal cell carcinomas are malignant, proper diagnosis and management is important. While basal cell carcinomas may resemble trichoblastomas clinically, histologically there are retraction spaces, atypia, and single cell necrosis in basal cell carcinoma. In addition, basal cell carcinomas do not stain for cytokeratin 20 and CD34 antigens. They also have diffuse staining of bcl-2 compared to peripheral staining seen in trichoblastomas.

Other clinical differential diagnoses include dermal nevus, adnexal tumors such as cylindromas and pilomatricoma, fibrous tumor, and epidermoid cysts. However, these lesions can be differentiated using histology.

Trichoblastic carcinoma may appear similar to trichoblastomas clinically. However, on histology, there is significant asymmetry of the architecture, atypical mitotic figures, necrosis, and substantial infiltration of the tumor into the subcutaneous fat and muscle evident in trichoblastic carcinoma.

Who is at Risk for Developing this Disease?

While the exact incidence is unknown, trichoblastomas are rare benign tumors. They may occur at any age and do not have specific predilection to either females or males. There is no race predominance reported.

Patients with nevus sebaceous are at risk of developing trichoblastomas. Multiple neoplasms, both benign and malignant, can arise from nevus sebaceous. The most common benign neoplams associated with nevus sebaceous are trichoblastoma and syringocystadenoma papilliferum, and the most common malignant neoplasm is basal cell carcinoma. The youngest patient seen with trichoblastoma was a 4-year-old with nevus sebaceous.

The youngest patient seen with solitary trichoblastoma was an 11-year-old girl.

According to one retrospective study, several cases of trichoblastoma, basal cell carcinoma, and trichoblastic carcinoma were identified in individuals treated with low dose x-ray as a depilatory treatment for tinea capitis (prior to the advent of antifungals). This suggests that radiotherapy may be a risk factor for developing trichoblastomas.

What is the Cause of the Disease?

The etiology of solitary trichoblastoma remains unclear.

Systemic Implications and Complications

Trichoblastomas are benign tumors with no systemic involvement. They can be locally aggressive, but malignant potential is very rare. However, there is one rare case of a patient who had malignant transformation of a long-standing trichoblastoma with lymphatic and hematogenous metastases.

Treatment Options

Treatment options are summarized in Table I.

Table I.
Medical Treatment Surgical Procedures Physical Modalities
None Deep shave removal Laser ablation
Punch excision • Carbon dioxide laser alone
Excisional surgery • Er:YAG (erbium:yttrium aluminum garnet) laser alone
Electrosurgery • Combination of carbon dioxide and Er:YAG laser

Optimal Therapeutic Approach for this Disease

Only surgical excision and deep shave excision have been reported as treatment options in the published literature to date. No other treatment modalities, whether medical treatment (i.e. topical or intralesional) or physical treatment options (i.e. photodynamic therapy or laser) have been reported thus far.

Complete excision is the best surgical option for patients with trichoblastomas for several reasons. Trichoblastoma is commonly a solitary lesion and basal cell carcinoma is an important differential diagnosis that needs to be ruled out. In addition, all adnexal tumors can extend deep into the dermis.

With surgical excision, tissue can be sent for pathology to confirm the benign nature of the tumor and the deeper dermal component can be fully excised. Deep shave of the lesion can be performed, but it will not guarantee that the entire tumor is removed so there will be a chance of recurrence. In addition, if the tumor is small, a punch excision around the visible tumor margins can be attempted. This method may reduce the chance of recurrence, and the defect size may be smaller than a complete surgical excision.

Other modalities such as carbon dioxide laser and Er:YAG (erbium:yttrium aluminum garnet) laser alone or in combination can also be used. Laser ablation provides good precision and fewer thermal effects compared to electrosurgery. It has been reported in other adnexal neoplasms such as trichodiscomas and trichoepitheliomas with success and good cosmetic outcomes; however, recurrence has been reported in these cases.

Because of their dermal location, trichoblastomas treated with laser ablation have a tendency to recur. If laser treatment is attempted with deeper and multiple passes, recurrence can be prevented, but there is an increased risk of scarring.

Electrosurgery can also be used, but hypopigmented scars may replace the lesions because of thermal effects. A limited depth of treatment with electrosurgery also increases the risk of recurrence.

Patient Management

It is important to inform patients that all treatment options can result in recurrence of the lesions.

Once the diagnosis of trichoblastoma is confirmed pathologically, no further treatment or follow-up is necessary.

Unusual Clinical Scenarios to Consider in Patient Management

The eyelid is an unusual location for a trichoblastoma, but this location has been reported in the literature.

It is important to keep in mind that, rarely, long-standing trichoblastomas can transform into malignant trichoblastic carcinoma. In one case, a nodule present for 40 years suddenly began to increase in size and became symptomatic with pain and redness on the overlying skin, which histology showed was a transformation of trichoblastoma into trichoblastic carcinoma. Therefore, either a complete excision should be offered to the patient at the time of diagnosis or the lesion should be observed at regular intervals.

What is the Evidence?

Miller, CJ, Iofreda, MD, Billingsley, EM. “Sebaceous carcinoma, basal cell carcinoma, trichoadenoma, trichoblastoma, and syringocystadenoma papilliferum arising within a nevus sebaceous”. Dermatol Surg. vol. 30. 2004. pp. 1546-9. (This was a case report of five neoplastic transformations occurring in a nevus sebaceous simultaneously. It is the first report to publish trichoadenoma arising from nevus sebaceous.)

Swick, B, Baum, CL, Walling, HW. “Rippled-pattern trichoblastoma with apocrine differentiation arising in a nevus sebaceous: report of a case and review of the literature”. J Cutan Pathol. vol. 36. 2009. pp. 1200-5. (This was a good article that discusses the different histologic variants of trichoblastomas as well as different immunohistochemistry expression patterns of CD34, bcl-2, and cytokeratin 20 for both trichoblastomas and basal cell carcinoma.)

Kaddu, S, Schaeppi, H, Kerl, H, Soyer, P. “Subcutaneous trichoblastoma”. J Cutan Pathol. vol. 26. 1999. pp. 490-6. (This was another article that discusses the subcutaneous variant of trichoblastoma as well as other histologic variants of trichoblastomas.)

Mencia-Gutierrez, E, Gutierrez-Diaz, E, Ricoy, J, Rodriguez-Peralto, J. “Eyelid trichoblastoma: an unusual localization”. Int J Dermatol. vol. 42. 2003. pp. 201-2. (A rare case of eyelid trichoblastoma is reported and treatment and histology is also discussed.)

Rofagha, R, Usmani, A, Vadmal, M, Hessel, A, Pellegrini, A. “Trichoblastic carcinoma: a report of two cases of a deeply infiltrative trichoblastic neoplasm”. Dermatol Surg. vol. 27. 2001. pp. 663-6. (This is an article that discusses the histologic difference between trichoblastoma and trichoblastic carcinoma.)

Kang, TW, Kang, H, Kim, HO, Song, KY, Park, YM. “Trichoblastoma in a child”. Pediatr Dermatol. vol. 26. 2009. pp. 476-7. (The youngest patient presenting with trichoblastoma is reported in this case.)

Regauer, S, Beham-Schmid, C, Okcu, M, Hartner, E, Mannweiler, S. “Trichoblastic carcinoma (“malignant trichoblastoma”) with lymphatic and hematogenous metastases”. Mod Pathol. vol. 12. 2000. pp. 673-8. (This is a case report that discusses a rare case of trichoblastoma transforming into malignant trichoblastic carcinoma. Histological differences between benign trichoblastoma and the malignant trichoblastic carcinoma are also discussed.)

Graham, B, Barr, R. “Rippled-pattern sebaceous trichoblastoma”. J Cutan Pathol. vol. 27. 2000. pp. 455-9. (This is another report that discusses the rippled-pattern histological variant of trichoblastoma. It also discusses other histological variants and the differential diagnosis of trichoblastoma.)