Ⅰ. INTRODUCTION
The Odontogenic Keratocyst (OKC) is a developmental odontogenic cyst arising from the cell rests of the dental lamina, occupying a significant clinical position in the maxillofacial region due to its unique histological features and high recurrence rate1. While historically categorized as odontogenic keratocyst (OKC) regardless of keratinization patterns, the diagnostic criteria have been redefined as the correlation between keratinization type and prognosis became evident. Notably, according to the 5th edition of the WHO Classification of Head and Neck Tumours (2022; published 2024), the orthokeratinized variant, previously considered a subtype of OKC, is now recognized as a distinct entity termed orthokeratinized odontogenic cyst (OOC)2.
This reclassification is grounded in the disparate biological behaviors of the two entities. The orthokeratinized odontogenic cyst (OOC) is histologically characterized by a prominent granular layer and a flat basal cell interface, clinically exhibiting less aggressive behavior and a low recurrence rate3,4. In contrast, odontogenic keratocyst (OKC) as currently defined, refer specifically to lesions with a parakeratinized, corrugated epithelial lining and a palisaded basal cell layer5. These parakeratinized lesions demonstrate aggressive growth potential, often expanding through the medullary bone via the formation of daughter cysts or high epithelial proliferation, and are associated with a high recurrence rate ranging from 25% to 60% following enucleation6,7. Accordingly, accurate histological differentiation is essential for predicting prognosis and determining the treatment modality.
Clinically, the vast majority of OKCs present as intraosseous lesions, most commonly involving the posterior mandible and ascending ramus6. However, rare cases of peripheral odontogenic keratocyst (POKC) occurring in the gingiva or adjacent soft tissues without intraosseous involvement, have been reported8. POKCs account for less than 1% of all OKC cases and are predominantly found in the gingiva9. Given that cystic lesions in soft tissues are more commonly benign entities such as OOCs or epidermoid cysts10, the identification of a parakeratinized OKC within soft tissue represents an exceptionally rare finding with potential clinical significance, necessitating careful differential diagnosis and long-term follow-up.
Notably, the occurrence of a parakeratinized OKC in the buccal mucosa, as seen in this case, is extremely rare in the literature11. We report a rare case of a parakeratinized odontogenic keratocyst arising in the buccal mucosa of a 71-year-old male, presenting as a soft tissue mass without bony involvement on radiography. The clinical and histopathological features of this case are described, along with a review of the relevant literature, to highlight its diagnostic considerations and therapeutic implications.
Ⅱ. CASE REPORT
The study protocol was exempted from review by the Institutional Review Board of Jeonbuk National University Hospital (IRB No. CUH 2026-04-052). This study was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from the patient for the publication of this case report.
A 71-year-old male patient visited the Department of Oral and Maxillofacial Surgery with a chief complaint of a progressively enlarging mass in the right buccal cheek accompanied by dull pain during mastication and mouth opening. The patient stated that he had been aware of a painless swelling in the same area for approximately 20 years, during which time it caused no functional impairment. However, the symptoms exacerbated two months prior to presentation, reportedly following alcohol consumption. Initial management at a local otolaryngology clinic, consisting of incision and drainage with antibiotic therapy, resulted in no significant improvement, and the patient was subsequently referred to our department.
Clinical examination revealed a swelling measuring approximately 2.5 cm in diameter in the right buccal region. The overlying mucosa showed no signs of inflammation, ulceration, or fistula formation. On palpation, the lesion was firm, non-tender, and freely mobile. Needle aspiration yielded a brownish, turbid fluid (Fig. 1).
Radiographic evaluation was performed. Panoramic radiography revealed no significant bony changes or radiolucent defects in the maxilla or mandible (Fig. 2). Contrast-enhanced facial computed tomography (CT) scans showed a benign cystic lesion or small abscess measuring approximately 18 mm in diameter, located in the soft tissue anterior to the right mandibular coronoid process, without evidence of bony involvement (Fig. 3).
Under the clinical impression of a benign soft tissue cyst, surgical excision was performed under local anesthesia. The cystic lesion was carefully dissected and ensured complete enucleation without rupture. Although the lesion was successfully enucleated, its interface with the surrounding buccinator muscle and connective tissues was not clearly defined, requiring careful and meticulous dissection. The excised cystic mass measured approximately 2.0 cm in diameter. The specimen was submitted for histopathological examination.
Histopathological examination revealed a cystic cavity lined by a uniform parakeratinized stratified squamous epithelium, 6–8 cell layers in thickness. The basal cell layer exhibited a prominent palisaded arrangement of cuboidal to columnar cells with hyperchromatic nuclei. The luminal surface showed a characteristic corrugated appearance and rete ridges were absent. Based on these histological features, a definitive diagnosis of a parakeratinized odontogenic keratocyst was established (Figs. 4 and 5).
The postoperative course was uneventful. At the 6-month and 2-year follow-up visits, no clinical evidence of recurrence was observed, and the patient remained asymptomatic (Fig. 6).
Ⅲ. DISCUSSION
Odontogenic keratocysts (OKCs) are derived from remnants of the dental lamina and most commonly present as intraosseous lesions1. However, epithelial remnants of the dental lamina, known as the Rest of Serres, may persist within the soft tissues, from which cystic lesions can arise. Cysts arising from these extraosseous remnants are termed peripheral odontogenic keratocyst (POKC)8. POKCs are exceedingly rare, accounting for less than 1% of all OKCs9, and although they predominantly occur in the gingiva, involvement of the buccal mucosa is particularly uncommon11. Although the exact origin remains uncertain, it has been suggested that remnants of the dental lamina may become ectopically displaced into the buccal mucosa during embryogenesis. These extraosseous remnants subsequently undergo cystic degeneration to form a POKC15.
Clinical diagnosis of POKC in the buccal mucosa is challenging due to its non-specific features. In the present case, the lesion appeared as a firm, mobile soft tissue mass without bony involvement, clinically mimicking common benign soft tissue lesions such as epidermoid cysts or sebaceous cysts10. Furthermore, the buccal mucosa is anatomically remote from the dental arch, making odontogenic lesions less likely to be considered in the initial differential diagnosis. Therefore, histopathological evaluation is essential for definitive diagnosis.
Consistent with previously reported cases of buccal POKCs11,14,15, the present case manifested as a mobile, circumscribed soft tissue mass lacking bony involvement, which frequently leads to an initial misdiagnosis of benign non-odontogenic cysts. However, compared to most documented cases that were identified and excised relatively early upon discovery14,15, a uniquely distinctive feature of our case is the exceptionally prolonged clinical course; the patient reported the presence of an asymptomatic swelling for approximately 20 years prior to a recent acute exacerbation. Furthermore, similar to previous reports noting the close adherence of buccal POKCs to adjacent structures like the buccinator muscle13,14, our surgical findings also demonstrated close adherence to surrounding connective tissues, highlighting the necessity of meticulous dissection to ensure complete extraosseous enucleation.
As highlighted in the introduction, distinguishing orthokeratinized odontogenic cyst (OOC) from OKC is critical under the 5th edition of the WHO Classification of Head and Neck Tumours2. While OOCs generally follow an indolent clinical course, OKCs characterized by a parakeratinized epithelial lining are associated with inactivation of the PTCH1 gene, which is thought to contribute to their increased intrinsic growth potential relative to orthokeratinized lesions6,7.
Despite this aggressive biological potential, peripheral OKCs generally exhibit a lower recurrence rate than intraosseous OKCs. This may be related to the confinement within soft tissues and the absence of medullary bone spaces that facilitate extensive spread12. Nevertheless, recurrence has been reported, particularly in cases where complete removal is challenging due to close adherence to surrounding structures, including the buccinator muscle13,14. Consequently, although conservative surgical enucleation remains the treatment of choice, the diagnosis of a parakeratinized OKC necessitates a more rigorous long-term follow-up.
In conclusion, although peripheral odontogenic keratocysts (POKCs) in the buccal mucosa are exceedingly rare and may be clinically misdiagnosed as benign non-odontogenic cysts, they must be included in the differential diagnosis of solitary soft tissue masses in this region. Because clinical features alone are non-specific and insufficient for accurate diagnosis, definitive histopathological confirmation of the parakeratinized epithelial lining is essential. Furthermore, rigorous long-term follow-up is highly recommended due to the lesion's intrinsic potential for recurrence.
