Proliferating trichilemmal tumor (proliferating tricholemmal tumor, proliferating pilar cyst)

Are You Confident of the Diagnosis?

What you should be alert for in the history

Proliferating trichilemmal tumor (PTT) typically presents as cystic nodules on the scalp of elderly females, although they can arise at other sites and in males. PTT may be asymptomatic, but can be painful if inflammed or ulcerated. Patients report a long-standing lesion, sometimes with recent growth.

Characteristic findings on physical examination

On physical examination, PTT can be smooth dermal to subcutaneous masses or exophytic to fungating. Ulceration is sometimes present, with foul-smelling drainage of keratinous material (Figure 1). PTT typically range from 1-10 cm, but can achieve sizes up to 25 cm.

Figure 1.

Clinical appearance of PTT – ulcerated.

Expected results of diagnostic studies

Imaging (computed tomography [CT] or magnetic resonance imaging [MRI]) can be helpful if there is concern for deep invasion or malignant transformation, and show solid and cystic areas as well as calcification. Poorly defined margins, invasion of tissue planes, areas or necrosis, and lymphadenopathy can be seen in malignant PTT.

Diagnosis confirmation

The clinical differential for PTT includes pilar cyst, squamous cell carcinoma, cylindroma, and other adnexal neoplasms. Biopsy is necessary to confirm the diagnosis, and demonstrate a well-circumscribed proliferation of lobules of squamous cells showing trichilemmal keratinization (Figure 2, Figure 3) (proceeding to eosinophilic dense keratin without an intervening granular layer). Squamous eddies, focal clear cell change, and calcification are common. Areas of conventional pilar cyst are usually present. Mild cytologic atypia and increased mitotic activity can be seen, making differentiation from malignant proliferating trichilemmal tumor or squamous cell carcinoma sometimes difficult. Infiltrative growth, marked atypia, high mitotic activity, and zones of geographic necrosis may be signs of malignant transformation.

Figure 2.

Low-power view of a proliferating pilar tumor showing a rounded, pushing border. (H&E, X20)

Figure 3.

Trichilemmal keratinization with squamous atypia (H&E, 200X).

Who is at Risk for Developing this Disease?

PTT occur most commonly in women over the age of 60. An autosomal dominant trait has been reported with pilar cysts.

What is the Cause of the Disease?

PTT likely arise from pilar cysts, possibly triggered by local irritation of trauma.

Systemic Implications and Complications

PTT can have locally aggressive growth and rarely undego malignant transformation. In the setting of malignant transformation, metastases to locoregional soft tissue, lymph nodes, and even distant sites can occur.

Treatment Options

Complete surgical excision of the lesion is typically curative.

Optimal Therapeutic Approach for this Disease

Complete surgical removal is typically curative. Mohs micrographic surgery may have a lower recurrence rate compared to simpleexcision.

Patient Management

Complete excision and histologic examination or Mohs micrographic surgery should be performed on suspected PTT. Close clinical follow-up for signs of recurrence or metastatic disease should be considered when lesions show high-risk features such as size larger than 5 cm, rapid growth, significant cytologic atypia, high mitotic rate, or an infiltrative growth pattern.

Unusual Clinical Scenarios to Consider in Patient Management

If malignant PTT is diagnosed, additional work-up including lymph node examination and imaging (CT, MRI, or positron emission tomography [PET] ) may be helpful. There is limited data on optimal treatment of metastatic disease and consultation with an oncologist is recommended.

What is the Evidence?

Folpe, AL, Reisenauer, AK, Mentzel, T, Rutten, A, Solomon, AR. “Proliferating trichilemmal tumors: clinicopathologic evaluation is a guide to biologic behavior”. vol. 30. J Cutan Pathol. pp. 492-8. (A series of five cases of PTT identifying location, recent growth, size, infiltrative pattern, and significant atypia with mitoses as characteristics that favor malignant behavior.)

Kim, HJ, Kim, TS, Lee, KH, Kim, YM, Suh, CH. “Proliferating trichilemmal tumors: CT and MR imaging findings in two cases, one with malignant transformation”. AJNR Am J Neuroradiol. vol. 22. 2001. pp. 180-3. (Case report describing the imaging findings in PTT.)

Sau, P, Graham, JH, Helwig, EG. “Proliferating epithelial cysts. Clinicopathologic analysis of 96 cases”. J Cutan Pathol. vol. 22. 1995. pp. 394-406. (A series of 63 cases of PTT showing an overall good prognosis and low recurrence rate with wide local excision.)

Satyaprakash, AK, Sheehan, DJ, Sangueza, OP. “Proliferating trichilemmal tumors: A review of the literature”. Dermatol Surg. vol. 33. 2007. pp. 1102-8. A consise review of PTT.

Ye, J, Nappi, O, Swanson, PE, Patterson, JW, Wick, MR. “Proliferating pilar tumors: a clinicopathologic study of 76 cases with a proposal for definition of benign and malignant variants”. Am J Clin Pathol. vol. 122. 2004. pp. 566-74. (A large case series in which the authors propose histologic features grouping PTT into benign, low-grade malignant, and high-grade malignant categories.)