Address for correspondence : Jung-Hae Cho, MD, Department of Otorhinolaryngology Head and Neck Surgery, College of Medicine, The Catholic University of Korea, St. Vincent's Hospital, 93 Jungbu-daero, Paldal-gu, Suwon 442-723, Korea
Tel : +82-31-249-8306, Fax : +82-31-253-3752, E-mail : jhchomd@catholic.ac.kr

Introduction

Trichilemmal cysts usually occur on hair-bearing areas, such as the scalp, trunk, and groin.1) Most patients present with smooth, rounded, intradermal swellings on the scalp. To our knowledge, a trichilemmal cyst involving the submandibular gland has not been previously reported, especially in young boy. Here, we present a trichilemmal cyst invading submandibular gland in a 16-year-old boy that was misdiagnosed as a branchial cleft cyst (BCC) due to its similar clinical and radiological features.

Case

A 16-year-old male presented with a painless swelling in the left submandibular area. The swelling had been present for 6 months and had grown slowly. He had no history of trauma or surgery. The physical examination revealed a soft, well-circumscribed 2×3 cm mass, covered with normal skin, in the left submandibular region. Fine needle aspiration cytology was performed, but it revealed only the presence of some amorphous, eosinophilic material. Contrast-enhanced computed tomography (CT) showed a hypodense mass with a non-enhancing thick rim in the left submandibular triangle (Fig. 1). However, the border between mass and submandibulr gland was not definite. Although we presumptively diagnosed the cystic mass as a second BCC, we considered the possibility of malignant tumor because of its invasiveness. Excision was performed under general anesthesia. At surgery, we saw that the cyst extended to the posterior part of the submandibular gland. As the cyst could not be divided from the submandibular gland and was partially ruptured in binding portion due to severe adhesion, it was excised totally, in continuity with the submandibular gland (Fig. 2A). The cyst was filled with keratin like material. The histopathological examination revealed that the cyst was lined with keratinizing stratified squamous epithelium and had non lamellated keratin, but no atypia or dyskeratotic cells (Fig. 2B). This confirmed the diagnosis of a trichilemmal cyst involving the submandibular gland. The postoperative recovery was uneventful and there has been no evidence of tumor recurrence for 3 years.

Discussion

Approximately 90% of trichilemmal cysts are located on the scalp. They arise from the outer root sheath of the hair follicle. The wall of a trichilemmal cyst is composed of stratified squamous epithelium, consisting of pale, corrugated cells. The epithelial lining cells mature into keratin without formation of a granular layer, and the cyst is filled with keratin.2) Pathologically, a trichilemmal cyst can be distinguished from an epidermal cyst by the non-lamellated keratin in the former. Although trauma is considered a cause of trichilemmal cysts, the definite etiology remains unknown.
There are a few case reports of trichilemmal cysts in unusual sites. Perez, et al.3) reported the case of a trichilemmal cyst presenting intraorally and explained their case as evidence of mild epithelial proliferation and slight foci of metastatic epidermoid keratinization, possibly related to mild trauma. El-Bahy and Ishak4) presented a trichilemmal cyst involving the temporal and infratemporal fossae. They performed a frontotemporal craniotomy with an orbitozygomatic osteotomy and confirmed that the histology was that of a trichilemmal cyst. Recently, a giant trichilemmal cyst in the neck was reported.5) Our case is distinct from this case in that the tumor invaded the submandibular gland and occurred in a young boy.
In rare cases, proliferation of a trichilemmal cyst due to chronic trauma or inflammation leads to formation of a tumor, known as a proliferating trichilemmal cyst. Histologically, it shows mitotic figures, mild-to-moderate cytological atypia, and dyskeratotic cells. In the oncological transformation of a trichilemmal tumor, Saida, et al.6) defined three stages: the adenomatous (trichilemmal cyst), epitheliomatous (proliferating trichilemmal cyst), and carcinomatous (malignant proliferating trichilemmal tumor) stages. Although a trichilemmal cyst can rarely become cancerous, it has malignant potential and needs to be removed when it is found.
The differential diagnosis of cystic swellings in the submandibular triangle includes BCC, cystic hygroma, submandibular gland mucocele, and other cystic cervical metastases. The most common cause of a cystic lesion in the submandibular triangle is a BCC, predominantly in younger patients. It is important to differentiate a submandibular trichilemmal cyst from a BCC because a second BCC does not need to be resected with the submandibular gland in almost all cases. On CT imaging, an uncomplicated BCC has a thin, smooth rim and low-density mucoid contents. An infected cyst has a thick, irregular, enhancing rim, and it may become septated. Meanwhile, a branchiogenic carcinoma, has internal vascularization, intracystic solid components or an irregular outer wall, and infiltration to the surrounding tissues. Thus, a trichilemmal cyst with local infiltration features in the submandibular area is similar to branchigogenic carcinoma on CT and needs to be differentiated prior to surgery.
Trichilemmal cysts have been treated successfully with surgical excision. Theoretically, limited surgical resection is sufficient for a cure. However, the surgical results for a trichilemmal cyst involving submandibular gland have not been reported. Patients with a skin adnexal tumor involving the parotid gland should undergo a subtotal or total parotidectomy, ensuring adequate margin. In our case, because the tumor was strongly adherent to the submandibular gland, we excised the mass and submandibular gland simultaneously. Although it is very rare, long-term surgical result is needed.

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2. McGavran MH, Binnington B. Keratinous cysts of the skin. Identification and differentiation of pilar cysts from epidermal cysts. Arch Dermatol 1966;94(4):499-508.

3. Perez LM, Bruce JW, Murrah VA. Trichilemmal cyst of the upper lip. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;84(1):58-60.

4. El-Bahy K, Ishak E. Trichilemmal cyst involving the skull base. Acta Neurochir (Wien) 2004;146(12):1361-4.

5. Karaman E, Duman C, Yagiz C. Giant trichilemmal cyst at the neck region. J Craniofac Surg 2009;20(3):961-2.

6. Saida T, Oohara K, Hori Y, Tsuchiya S. Development of a malignant proliferating trichilemmal cyst in a patient with multiple trichilemmal cysts. Dermatologica 1983;166(4):203-8.