Epidermoid & Dermoid Cyst

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Epidermoid & Dermoid Cyst

Introduction

The epidermoid cyst, often mistakenly called a sebaceous cyst or wen, is a very common skin lesion which arises from traumatic entrapment of surface epithelium (epidermal inclusion cyst) or, more often, from aberrant healing of the infundibular epithelium during an episode of follicular inflammation or folliculitis. Oral and pharyngeal epidermoid cysts of the inclusion cyst variety also occur, but are rare in adults and are frequently so small that they are not biopsied. Syndromes associated with multiple cutaneous epidermoid cysts, such as Gardner syndrome, Gorlin syndrome and pachyonychia congenita, do not demonstrate cysts of the oral mucosa, but facial cysts may occur. Epidemiologic investigation has determined a prevalence rate of 1 cyst per 2,000 adults (Table 1).

The epidermoid cyst of the oral floor midline has a much greater growth potential than epidermoid cysts occurring at other oral/pharyngeal sites. These large cysts are often given the label dermoid cyst by authorities who believe it to be a forme fruste of benign, cystic teratoma. Since its first description in 1852 as a sublingual cyst or wen, the distinction between the oral floor epidermoid and dermoid cyst has been rather confused. As it is likely that most examples represent cystic degeneration of embryonically entrapped epidermis, and as the microscopic features of this cyst are almost always identical to those of the epidermoid cyst of the skin or other oral locations, the present author suggests that the use of the term dermoid cyst be reserved only for those cysts with epidermal adnexa beneath the lining epithelium. Congenital teratoid cyst contains elements derived from all three germ layers, ectoderm, mesoderm and endoderm.

Clinical Features

The epidermoid cyst of the oral/pharyngeal mucosa is usually located on the attached gingiva, where it has traditionally been called gingival cyst of adult. At this site the lesion is presumably secondary to cystic degeneration of odontogenic embryonic rests or traumatic inclusions of surface epithelium. Other common locations are the lateral tongue, oral floor, lateral pharyngeal wall, and soft palate. Most cases are diagnosed during the teen or young adult years.

The epidermoid cyst typically remains less than 1 cm. in diameter and may be somewhat movable beneath the surface, except on bone-bound mucosa. The cyst is almost always superficial, producing a sessile nodule with a white or yellow-white discoloration (Figures 1 & 2); the occasional deeper lesions may show a normal color. The larger "dermoid cyst" is usually found in the oral floor midline above the mylohyoid muscle, although the occasional dumbbell-shaped cyst will penetrate through a hiatus in the muscle and extend into the submental area, possibly imparting a double chin appearance (Figure 3). In this location the cyst may reach 6-7 cm. in greatest diameter, may become infected, and may interfere with swallowing or the proper function of the tongue.

Pathology and Differential Diagnosis

The epidermoid cyst is lined by a thin stratified squamous epithelium with few rete processes (Figures 3 & 4). Quite often, there is no granular cell layer and keratin from the surface of the epithelium can be seen to be sloughing into the cystic lumen, which is usually filled with degenerated and necrotic keratinaceous detritus. Areas of epithelial degeneration or ulceration may be seen, usually associated with a mild to moderately intense chronic inflammatory cell reaction. Inflammation may extend deeply into subepithelial fibrovascular stroma. Occasional cysts have contained fungi, bacteria or necrotic food debris in their lumina, and darkly hematoxylophilic precipitated salts (dystrophic calcification) may be seen within the necrosed keratin.

When keratin degenerates within an ulcer bed of the cyst wall, cholesterol crystals form elongated, sharp-ended clefts (cholesterol clefts) which are clear spaces in stained tissue sections because of the dissolution of the associated fats by laboratory processing. Foreign-body multinucleated giant cells are frequently seen adjacent to or surrounding such clefts. This cholesterol granuloma will occasionally proliferate into the lumen of the cyst from an area of ulceration (Figure 5).

The dermoid cyst differs from epidermoid cyst only in the presence within its walls of normal or dysmorphic adnexal appendages, usually sebaceous glands or abortive hair follicles (Figure 6). If the cyst wall contains other elements, such as muscle (other than pilar arrector smooth muscle) or bone, the term teratoid cyst is preferred.

Treatment and Prognosis

Treatment consists of conservative surgical removal, trying not to rupture the cyst, as the luminal contents may act as irritants to fibrovascular tissues, producing postoperative inflammation. Recurrence is unlikely after treatment. Malignant transformation of oral cysts has not been reported.