Ⅰ. INTRODUCTION
Orthokeratinized odontogenic cyst (OOC) is a distinct entity arising from odontogenic epithelium. It is rare, making up approximately 1% of developmental odontogenic cysts, and represents 7%-17% of all keratinizing jaw cysts1,2. It is commonly represented in individuals in the second to the fifth decades of life, and occurs more commonly in males3. Radiographically, the cyst appears as a well-defined and unilocular or multilocular radiolucency commonly present in association with an unerupted tooth4-6. Histopathologically, an epithelial lining with orthokeratinization is microscopically observed around the cystic lesion1-4. Surgical enucleation is the treatment of choice for OOC, and its recurrence is uncommon1,7-9. Epidermoid cyst (EDC) is a benign cystic lesion that is slow-growing and has a well-defined margin. It tends to occur in areas of embryonic midline fusion, and represents approximately 1.6%-6.9% of all cysts in the head and neck region9,10. It is commonly represented in young and old, but rarely in childhood11. Ultrasonography offers an overall assessment of the EDC. It has a round to oval shape, well-circumscribed margins and hypoechoic a vascular mass located in subcutaneous tissue12. Histopathologically, EDC has stratified squamous epithelial lining and includes a granular layer and keratin lamellae in the lumen9-12. Furthermore, complete surgical removal including the entire cyst wall is required to prevent recurrence9-13. These two types of keratinized cysts present similar histopathological features6,14. Thus, this case report presents an uncommon case that arises simultaneously with OOC in the mandible and EDC around the areas of both ears in a patient who had no history of genetic syndrome. Additionally, the differential diagnosis with unique histopathological features and postoperative closed follow-ups are accentuated for OOCs and EDCs despite their low recurrence rates.
Ⅱ. CASE REPORT
A 21-year-old male patient represented to the Department of Oral and Maxillofacial Surgery, Kyungpook National University Dental Hospital, Korea, with a chief complaint of a slight asymptomatic swelling on the right mandibular body area for a month. The covering gingiva was intact, and no tenderness was noted on palpation. Orthopantomogram showed a well-defined radiolucent lesion with sclerotic margins extending from the periapical region of the right mandibular second premolar to the second molar of the same quadrant. However, the impacted right mandibular third molar was apart from the cystic lesion (Fig. 1A). On the cone-beam computed tomography (CBCT) images, lingual cortical thinning and expansion of the mentioned region were noticeable. Also, the right mandibular canal was displaced to the inferobuccal side of the cyst and was partially included in the lesion (Fig. 1B, C). Under general anesthesia, the lesion was enucleated with curettage and sent for histopathological examination. The gross specimen showed a cystic lesion with a firm consistency and pearl brown color, measuring 2.4 × 2.0 × 0.2 cm in size (Fig. 2A). Microscopically, the cyst lining consisted of strati- fied squamous epithelium which exhibits an orthokeratotic surface of varying thickness. Keratohyalin granules were prominent in the superficial epithelial layer, and the basal cell layer was relatively palisaded (Fig. 2A, B). Finally, the lesion was diagnosed as OOC, based on these features. After that, the patient had lost follow-up, and he presented to our department after two years with discomfort on the right mandibular posterior area. CBCT showed buccolingual thinning and expansion of the cortical bone of the mandibular body again (Fig. 1E, F). Furthermore, swellings were observed on the right ear lobule area and left preauricular region. These swellings were smooth, round, and freely mobile with defined margins (Fig. 1G, H). Under general anesthesia, apicoectomy was performed to enucleate the recurrent cystic lesion on the right mandibular second premolar, and the first and second molar, and then the third molar was extracted. The gross specimen of the recurred lesion was similar to the previous one, measuring 2.0 × 1.5 × 0.2 cm in size (Fig. 2C). The postoperative histopathology report was suggestive of OOC (Fig. 2C, D). Concurrently, masses around both ears were completely removed (Fig. 2E, G). Histopathological examination revealed a cavity that was lined by stratified squamous epithelium resembling epidermis. The lumen was filled with degenerating orthokeratin (Fig. 2 E, F, G and H). These lesions were diagnosed as EDCs. To date, no symptoms and recurrence occurred. To keep an eye on its recurrence, the close follow- up observation was continued.
Ⅲ. DISCUSSION
The OOC is a relatively uncommon developmental odontogenic cyst. In 1992, it had been defined by the World Health Organization (WHO) as a type of odontogenic keratocyst (OKC). Currently, OOC is considered a distinct entity and separated from the OKC1. Histopathological examination demonstrated that OOC has orthokeratinized stratified squamous epithelium lining, prominent granular cell layer and low cuboidal or flattened basal cell layer with a low tendency to nuclear palisading. However, the typical OKC presents a highly cellular parakeratinized epithelial lining with a palisaded layer of basal cells. OOC is different from OKC as it recurs less significantly following surgery, with a recurrence rate of < 2%1-4. Comparatively, OKC has a recurrence rate as high as 28%1,4,9. In this case, the lesion recurred after 2 years despite the complete enucleation with curettage. Although the statically low recurrence rate is reported, close observation is essential following surgery.
EDC is defined as a cystic mass filled with keratin squames and surrounded by stratified squamous epithelium 7,10-12. It can occur at any age, but it is rare to find before puberty. Zito et al reported that it arises most commonly in the third and fourth decades of life15. EDC can be found anywhere on the skin but it is typically found on the face, neck, chest, upper back, scrotum and genitals12. The physical examination generally shows a few millimeters to several centimeters in maximum dimension of nonfluctuant, firm mass. Although EDC usually has no symptoms, it can become tender and swollen because of inflamed rupture of the cyst lining. Histologically EDC is lined by keratinized and stratified squamous epithelium and includes eosinophilic, laminated keratin material within the thin wall10-16. If the cyst wall is ruptured and the inside keratin squames are spilled out into the surrounding tissue, then an acute foreign body reaction will develop in response to the keratin squames12. A ruptured EDC can be red, swollen, and painful15. EDC is etiologically classified as congenital versus acquired. Congenital type of EDC may occur due to the ectodermal implantation into the epidermal rest during the embryonic period. On the other hand, the acquired type commonly results from infection around the pilosebaceous follicle, and the implantation of the epithelium due to injury, such as body piercing, is considered an etiologic factor 14. Most cases of EDC are sporadic, and multiple EDCs can be found in autosomal dominant Gardner syndrome and Gorlin syndrome (basal cell nevus syndrome). Although multiple EDCs may also occur due to the disruption of the follicular orifice as seen in individuals with acne vulgaris, obstruction of the follicle is prominent in the pathogenesis as those with acne vulgaris may have multiple EDCs originating from comedones12. The complete excision of the cyst with the intact cyst wall is the treatment of choice for EDC. In this case, the patient had multiple EDCs on the right earlobe and left preauricular regions. Although he had no history of genetic disorder, as evidence of acne vulgaris on his face, EDCs in both ears appear to be an acquired type.
OOC is histologically very similar to EDC6,14. OOC epithelium was a stratified squamous epithelium that is similar to epidermis. Hyperkeratosis with a prominent granular cell layer was represented in the cyst-lining epithelium. The basal layer consisted of cuboidal cells, and there was no evidence of polarization or palisading of the nuclei of the basal cell8. EDC was lined by epidermis-like stratified squamous epithelium with a well-developed granular cell layer, without rete ridge formation. The lumen was filled with fallen orthokeratin debris. Immunohistochemically, cytokeratins (CK7, 10, 20/13, 17, 18, 19, and 20) and apoptosis-related factor (bcl-2) expression patterns in OKC were quite distinct from OOC and EDC, while both OOC and EDC presented similar reactivity with CKs and bcl-29.These findings suggest that OKC had high cellular proliferation and low differentiation compared to OOC and EDC1,8,9. The character of OOC was positioned intermediately between OKC and EDC. Typically, EDC had the lowest cellular activity in the three cysts and it was a comparatively maturated lesion9.
Ⅳ. CONCLUSION
We represented a case report of combined OOC and EDC in a patient without genetic disorder. Since these two types of keratinized cysts show similar histopathological characteristics, the clinical correlation with the site of occurrence should be considered in diagnosis.
