Proliferating Trichilemmal Tumor of the Auricula: A Very Rare Locus

Abstract

Proliferating trichilemmal tumor (PTT) is a rare but morphologically characteristic tumor, derived from the external root sheath. They are commonly localized as a solitary lesion on the scalp. They rarely occur in other regions. PTTs generally behave in a benign fashion, up to 20% of the lesions may undergo malignant transformation into squamous carcinoma. We present an elderly woman with a cystic swelling on the crus of auricular helix diagnosed as PTT. To our knowledge, this is the first case in the English literature, of PTT of the auricula.

Introduction

Proliferating trichilemmal tumor (PTT) is a rare but morphologically characteristic tumor, derived from the external root sheath [1]. In 1966, Wilson-Jones described this special type of cyst [2]. PTT was distinguished from proliferating epidermoid cyst in 1995 [3]. More than 80% of the patients are women over the age of 60 [2, 3]. PTTs are commonly (more than 90%) localized as a solitary lesion on the scalp [1, 2]. They rarely occur in other regions [2]. The major histopathological features of this tumor are “prominent epithelial infoldings into the cyst lumen” and ‘trichilemmal keratinization’ [2, 4]. We present an elderly woman with a cystic swelling on the upper auricular region diagnosed as PTT and aim to review the literature regarding this pathology.

Case Report

A 76 years old female visited our department with a 1-month history of a painless, gradually enlarging mass on the left ear. There was no history of trauma, chronic irritation or insect bite. She had been under medical therapies for Diabetes Mellitus (DM) and mild asthma for years. The otorhinolaryngologic examination was within normal limits, except a 2 × 1.5 × 1.2 cm non-tender, smooth surface multicolor cystic mass located on the left auricular helix, proximal to the radix (Fig. 1). The ultrasonographic imaging revealed a 16 mm well demarcated thin-walled cystic mass with milimetric calcifications. Complete excision of the mass with 0.5 mm surgical margins was performed. Macroscopically, the lesion was 2 × 1.5 × 1.2 cm in dimensions and had a well circumscribed cystic appearance (Fig. 2). Microscopically, the lesion was located in the dermis (Fig. 3). Cystic areas of the lesion are layered with a characteristic non-proliferating trichilemmal type keratinizing epithelium, but in some areas, it consists of proliferating epithelial infoldings into the cyst lumen. In proliferating areas, neoplastic epithelium shows trichilemmal keratinization, characterized by peripheral palisading of small basaloid cells and large keratinocytes with ample eosinophilic cytoplasm, that develop abrupt keratinization without granular layer, resulting in compact orhokeratotic eosinophilic keratin. Foreign body giant cell reaction and calcification were observed at the periphery of the lesion. There was no evidence of significant cytological atypia and atypic mitosis. According to the histopathological findings, like as trichilemmal type keratinizing epithelium and proliferating epithelial infoldings into the cyst lumen, it is diagnosed as proliferating trichilemmal cyst/ tumor (Fig. 4). Surgical margins were clean. Two months following the surgery, the patient had no recurrence (Fig. 5). The patient is still in close follow-up.

Fig. 1.

Proliferating trichilemmal tumor on the crus of the auricular helix

Fig. 2.

Macroscopic appearance of the excised tumor

Fig. 3.

Proliferating trichilemmal tumor as a well circumscribed cystic neoplasm involving deeper dermis (H–E stain × 25)

Fig. 4.

The lobules of the neoplastic epithelium show trichilemmal keratinization, characterized by peripheral palisading of small basaloid cells and large keratinocytes with ample eosinophilic cytoplasm that develop abrupt keratinization without previous granular layer, resulting in compact orthokeratotic eosinophilic keratin (H–E stain, × 100)

Fig. 5.

Post-operative 2 months look of the patients auricula

The informed consent was obtained from the patient included in the study.

Discussion

PTT was defined as a solid-cystic neoplasm that shows trichilemmal differentiation similar to that of the isthmus of the hair follicle in WHO Classification of Skin Tumours book. The pathogenesis remains unknown, but in some cases, human papilloma virus, chronic inflammation or trauma may be related to this lesion [4].

Although it is postulated that many PTT cases arise in pre-existing pilar (trichilemmal) cyst, it is still unclear if trichilemmal tumors arise de novo or from a pre-existing trichilemmal cyst. Our patient had a dominant cystic lesion but in some foci, there were prominent epithelial infoldings into the cyst lumen, which is a histomorphological appearance, that may support the emergence of a proliferating trichilemmal tumor from pre-existing tricilemmal cyst. Our patient neither had a history of chronic irritation or trauma nor cytopathic effects of HPV infection (coilocytosis).

Proliferating trichilemmal tumors without atypical features, generally behave in a benign fashion, up to 20% of the lesions may undergo malignant transformation into squamous carcinoma. Tumors with invasive growth pattern or cytologic atypia have an unpredictable course. They may be locally aggressive, recur, or metastasize and can be mortal [3, 4]. Histopathological differentiation from squamous cell carcinoma may be difficult. Even, uncommon benign PTTs may be misdiagnosed as squamous cell carcinoma. in our case, the lesion was benign, there was no evidence of invasive growth pattern, cytologic atypia, increased mitotic activity, atypical mitosis and necrosis. Differential diagnosis should involve, trichilemmal/pilar cyst, proliferating epidermoid cyst, malign PTT, squamous cell carcinoma, keratoacanthoma, pilomatrixoma, sweat gland tumor, cylindroma, basal cell carcinoma.

Our patient had a benign lesion, however in some cases benign and malign foci can be observed in one tumor [2]. A nonscalp location, recent rapid growth, size larger than 5 cm, infiltrative growth, remarkable cytologic atypia and mitotic activity should be considered as malignancy [5].

The majority of these tumors are seen on the scalp, but rarely, they can be observed on the forehead, nose, back, chest, abdomen, buttocks, elbow, wrist, mons pubis and vulva [3]. Mostly, the patients are elderly women as in our case however, to our knowledge up to date, there are no PTT cases in the literature localized on the auricula. Auricula is relatively a less trichous area. Our case is the first PTT observed in the ear. Jung et al. analyzed the auricular benign masses in their research and found that, epidermal cyst was the most commonly (25.3%) observed lesion. The most common locus was ear lobule. The 11.1% of the lesions were on the crus of helix. They did not observe any PTTs in their study [6].

Total excision with a 0.5 cm margin of normal tissue and a long-term follow-up is the best therapeutic approach [5]. We did not perform pre-operative fine needle aspiration which is consistent with the literature regarding this issue. Adequate surgical excision is the mainstay of the treatment [3, 5]. However since, both benign and malign PTTs, are rarely seen, there are no guidelines for the management of these tumors.

Conclusion

This is the first case of PTT mentioned in the English literature which was localized on the ear. Auricular skin is relatively thin, very adhesive to the underlying cartilage, and hair follicules are relatively rare, thus not an expected locus for trichilemmal tumors. Due to their malignancy potential, and, risk of recurrence, all PTTs require a complete excision, thorough histopathological examination, and a close follow-up.

Compliance with Ethical Standards

Conflict of interest

The authors of this study declare that they have no conflict of interest.