Trichoadenoma (Trichoadenoma of Nikolowski)

Are You Confident of the Diagnosis?

What you should be alert for in the history

The diagnosis of trichoadenoma is considered when a patient presents with an asymptomatic solitary lesion on the face or buttock.

Characteristic findings on physical examination

Trichoadenomas are typically found on either the face or buttocks. They are usually solitary nodules ranging from 0.5 to 1.5cm in size.

Expected results of diagnostic studies

On histology, trichoadenomas consist of multiple keratin-filled horn cysts, lined with stratified squamous epithelium intermingled with solid islands or strands of basaloid or infundibular cells lying within a sclerotic stroma in the dermis.

On immunohistochemistry, the following staining patterns are observed in trichoadenomas:

Cytokeratin 10 staining present in the inner cells of most horn cysts with keratohyaline granules

Cytokeratin 15 staining seen in the outermost cells of the horn cysts and the basaloid epithelium

The above staining pattern observed in trichoadenomas suggest that they differentiate mainly toward the follicular infundibulum (as indicated by cytokeratin 10 staining pattern) and follicular hair bulge of the outer root sheath (as indicated by cytokeratin 15 staining pattern).

Diagnosis confirmation

The differential diagnosis includes other follicular tumors such as trichoepithelioma and its variant, desmoplastic trichoepithelioma, as well as trichofolliculoma. It can also resemble basal cell carcinoma.

Nikolowski originally described trichoadenoma as a distinct entity. Since then, others have regarded it as a variant of desmoplastic trichoepithelioma. However, recent immunohistochemistry studies support the position that desmoplastic trichoepithelioma is indeed a distinct clinical entity from trichoadenoma.

In one study, immunohistochemistry was used to demonstrate expression pattern of cytokeratin 20, Ber-EP4, and androgen receptor in both trichoadenomas and desmoplastic trichoepitheliomas. The study found that cytokeratin 20 was expressed in both trichoadenomas and desmoplastic trichoepitheliomas; however, Ber-EP4 was expressed by desmoplastic trichoepitheliomas, but not expressed by trichoadenomas.

Trichoadenomas are commonly placed in a spectrum of follicular neoplasms, between trichoepithelioma and trichofolliculoma. Trichoadenoma expresses only cytokeratin 10 and 15, while trichofolliculomas do not express cytokeratin 10, but do express cytokeratin 15, 16, and 17. In addition, trichoepitheliomas express only cytokeratin 15.

Clinically, basal cell carcinoma may appear similar to trichoadenoma. The two entities can be easily confused, especially in the elderly. Immunohistochemistry demonstrates expression of the androgen receptors in most basal cell carcinomas, while it is negative in trichoadenomas.

Who is at Risk for Developing this Disease?

While the exact incidence is unknown, trichoadenomas are very rare benign tumors. They may occur at any age and do not have specific predilection to either females or males. There are no associated risk factors for developing trichoadenomas.

One case of congenital trichoadenoma has been reported in the literature.

What is the Cause of the Disease?

The etiology of solitary trichoadenoma remains unclear.


It has been suggested that a trichoadenoma arising within an intradermal nevus can be a result of the local paracrine effect of cytokines or growth factors secreted by nevus cells inducing epithelial proliferation similar to the induction effect seen commonly in dermatofibromas.

Systemic Implications and Complications

Trichoadenomas are benign hamartomas, which appear sporadically. Although there are no systemic implications or complications, trichoadenomas may be cosmetically unappealing in some patients, and may be responsible for psychological concerns. Management of these concerns should be addressed on an individual basis.

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 Erbium:YAG laser alone
Electrosurgery Combination of carbon dioxide laser and erbium:YAG laser
YAG- yttrium aluminum garnet

Optimal Therapeutic Approach for this Disease

Initially, treatment should focus on reassuring the patient about the benign nature of the lesion. If the patient has cosmetic concerns associated with the tumor, surgical options are given. Only surgical excision and deep shave excisions 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 options (i.e. photodynamic therapy or laser), have been reported thus far.

Complete surgical excision with histologic review is the best option for this tumor for several reasons. It is commonly a solitary lesion, and basal cell carcinoma is an important differential diagnosis that needs to be ruled out. With surgical excision, the deeper dermal component can be fully excised. If incompletely treated or excised, adnexal neoplasms such as trichoadenomas can continue to grow and recur.

Deep shave removal of the lesion can be done, but it will not guarantee that the entire tumor is removed, and 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. Although there is no guarantee, 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 has less thermal effect when compared to electrosurgery. Ablative lasers have been attempted in other adnexal neoplasms (such as trichodiscomas and trichoepitheliomas) with success and good cosmetic outcomes; however, recurrence has been reported. Because of their dermal involvement, trichoadenomas and other adnexal tumors treated with laser ablation have a tendency to recur.

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

No recurrence after surgical excision has been documented. Once the diagnosis of trichoadenoma is confirmed pathologically, no further treatment or follow-up is necessary.

Unusual Clinical Scenarios to Consider in Patient Management

Unusual clinical presentations of trichoadenomas have occurred. Although they commonly range between 0.5-1.5cm in size, and usually are smooth nodules, one congenital trichoadenoma has been reported to be 3x4cm in size, and was an irregularly shaped, linear, slightly raised, verrucous plaque clinically resembling nevus sebaceous. The lesion was diagnosed histologically as a trichoadenoma with the presence of numerous epidermoid cysts, some of which contained one or more vellous hairs.

Another case of verrucous trichoadenoma was reported in a 20-month-old infant. In the infant, trichoadenoma appeared as tiny whitish grouped papules. The differential diagnosis included milia, but histology was consistent with trichoadenoma.

Trichoadenomas can present on the eyelids and can be mistaken for basal cell carcinoma.

Rarely, trichoadenomas are combined with intradermal melanocytic nevi, and can be seen together with pigmented lesions, as was seen in one case.

Only one case of trichoadenoma arising from a nevus sebaceous has been reported. Multiple neoplasms, both benign and malignant, can arise from sebaceous nevi. The most common benign neoplasms are trichoblastoma and syringocystadenoma papilliferum, and the most common malignant neoplasm is a basal cell carcinoma.

In this case, five neoplasms: trichoadenoma, trichoblastoma, syringocystadenoma papilliferum, basal cell carcinoma, and sebaceous carcinoma, occurred simultaneously within a nevus sebaceous. It is extremely rare for three or more neoplasms to occurin the same lesion at the same time.

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.)

Kurokawa, I, Mizutani, H, Nishijima, S, Kato, N, Yasui, K, Tsubura, A. “Trichoadenoma: cytokeratin expression suggesting differentiation towards the follicular infundibulum and follicular bulge regions”. Br J Dermatol. vol. 153. 2005. pp. 1084-6. (This is a study that used immunohistochemistry to determine the different cytokeratin staining patterns in a patient with trichoadenoma. It compares and contrasts the different staining patterns observed in trichofolliculomas and trichoepitheliomas, which are common differential diagnoses for trichoadenoma.)

Shimanovich, I, Krahl, D, Rose, C. “Trichoadenoma of Nikolowski is a distinct neoplasm within the spectrum of follicular tumors”. J Am Acad Dermatol. vol. 62. 2010. pp. 277-83. (This study distinguished desmoplastic trichoepithelioma from trichoadenoma using immunohistochemistry. Three different antigens were used, including cytokeratin 20, Ber-EP4, and androgen receptor. Expression patterns in trichoadenoma were compared with desmoplastic trichoepithelioma.)

Lee, WS, Oh, St, Lee, JY, Cho, BK. “Congenital trichoadenoma with an unusual clinical manifestation”. J Am Acad Dermatol. vol. 57. 2007. pp. 905-6. (This was a case report about trichoadenoma, presenting as an unusual verrucous plaque, that was present at birth in a 5-year-old boy. It is the only reported case in literature.)

Gonzalez-Vela, MC, Val-Bernal, JF, Garcia-Alberdi, E, Gonzalez-Lopez, MA, Fernandez-Llaca, JH. “Trichoadenoma associated with an intradermal melanocytic nevus: A combined malformation”. Am J Dermatopathol. vol. 29. 2007. pp. 92-5. (This is the first case of trichoadenoma combined with intradermal melanocytic nevus.)

Lee, JH, Kim, YY, Yoon, SY, Lee, JD, Cho, SH. “Unusual presentation of trichoadenoma in an infant”. Acta Derm Venerol. vol. 88. 2007. pp. 291-2. (Trichoadenomas typically present as solitary papules. This is an unusual case of an infant presenting with multiple grouped papules clinically resembling milia.)

Shields, JA, Shields, CL, Eagle, RC. “Trichoadenoma of the eyelid”. Am J Ophthalmol. vol. 126. 1998. pp. 846-8. (This is an interesting paper about trichoadenoma presenting on the eyelid. It was mistaken for a basal cell carcinoma in an 80-year-old woman.)