Ⅰ. INTRODUCTION
Odontogenic keratocyst (OKC) and ameloblastoma are representative odontogenic lesions of the jaw, characterized by locally destructive growth and high recurrence rates. In the 2017 WHO classification, OKC was reclassified from keratocystic odontogenic tumor back to a cyst, reflecting advances in understanding the biological characteristics of the lesion1.
OKC accounts for approximately 11-19% of all jaw cysts, most commonly occurs in the 20-40 age group, and is most frequently found in the posterior mandible. Histopathologically, it is characterized by parakeratinized stratified squamous epithelium and palisading arrangement of the basal layer, with high epithelial proliferative activity leading to recurrence rates of 25-60%2,3. Ameloblastoma is the most common be- nign odontogenic tumor, with the unicystic subtype accounting for 10-15% of all ameloblastomas and showing relatively low recurrence rates (10-15%)4,5.
Clinically, both lesions present with similar features including painless swelling, bony expansion, and displacement of adjacent teeth, and radiographically appear as well-defined radiolucent lesions, making differential diagnosis difficult6,7. Traditionally, enucleation or resection has been considered standard treatment; however, in large lesions, there is a high risk of complications such as inferior alveolar nerve damage, pathologic fracture, and loss of adjacent teeth.
Decompression or marsupialization is a conservative treatment method that connects the cyst cavity to the oral cavity, reducing internal pressure and inducing gradual size reduction. Nakamura et al.8 reported that the epithelium of OKC undergoes histological changes after marsupialization, reducing recurrence potential, and recent studies have demonstrated the effectiveness of decompression in reducing OKC volume9. The effectiveness of marsupialization has also been reported for unicystic ameloblastoma, showing particularly excellent results in young patients5,10.
The authors experienced two cases of large odontogenic lesions in the mandible treated with decompression followed by enucleation, where initial clinical and radiographic findings were similar but final pathological diagnoses were confirmed differently as OKC and ameloblastoma. We report a comparative analysis of the clinical, radiographic, and histopathological characteristics of both lesions, along with the effectiveness of decompression followed by enucleation and long-term follow-up results.
Ⅱ. CASE REPORTS
Case 1: Odontogenic Keratocyst
An 18-year-old male patient presented to our hospital with the chief complaint of painless swelling in the left mandibular area. The patient was referred after a cyst was incidentally discovered on panoramic radiography during a visit to another dental clinic for caries treatment. There were no significant medical history findings, and he was a high school senior at the time. Clinical examination revealed no pain in the left mandible, and no sensory disturbance of the lower lip and chin was observed. Electric pulp testing (EPT) showed 2+ response for #36 and 3+ response for #37.
Panoramic radiography revealed a unilocular radiolucent lesion approximately 3.5×2.4cm in size, extending from the left mandibular first molar (#36) through the impacted third molar (#38) to the anterior border of the ramus (Fig. 1A). The lesion had a well-defined corticated border, with the apices of #36 and #37 partially involved in the lesion. CBCT examination confirmed buccal cortical bone resorption and lingual cortical bone expansion with partial perforation (Fig. 1B). The inferior alveolar canal was displaced inferiorly and buccally by the lesion. Tooth #38 was horizontally impacted within the lesion.
Considering the patient's age, lesion size, proximity to the inferior alveolar nerve, and need for adjacent tooth preservation, a staged treatment plan was established consisting of initial decompression followed by secondary enucleation after sufficient size reduction. Under local anesthesia, decompression and extraction of impacted tooth #38 were performed. An elliptical incision was made in the mucosa corresponding to the buccal bone resorption area, and after exposing the cyst wall, approximately 1.2×1.2cm of the cyst wall was excised to open the cyst cavity. Cheesy material was drained from the cyst cavity, and the impacted tooth #38 was simultaneously extracted. A Penrose drain was inserted to maintain an open state for decompression. Histopathological examination confirmed the diagnosis of OKC, showing a cystic lesion lined by a uniform layer of stratified squamous epithelium and including a corrugated parakeratotic surface and a basal layer composed of palisaded, hyperchromatic columnar cells (Fig. 2A, B).
Wound care and Penrose drain changes were performed weekly for the first 2 months, then every 2 weeks. At 2 months postoperatively, panoramic radiography showed reduction in cyst size and new bone formation at the anterior, inferior, and posterior borders of the cyst (Fig. 1C). The inferior alveolar canal showed gradual recovery to its original position. The Penrose drain was removed 3.4 months after marsupialization. At 4.5 months after decompression, enucleation of the residual cyst was performed under general anesthesia. A sulcular and horizontal incision was made from #36 to the ascending ramus, and a full-thickness flap was elevated. After bone removal on the lingual side of #37, the cyst was completely enucleated. Histopathological examination of the enucleated tissue reconfirmed OKC (Fig. 2C, D).
The postoperative course was favorable; however, 9 months after the first enucleation, follow-up radiography and CBCT revealed a recurrent cystic lesion measuring 16×12mm on the lingual and inferior aspect of #36 and #37. After approximately 2 months of observation, CBCT showed size increase to 1.8×1.4×1.6cm, confirming recurrent OKC.
A second cyst enucleation was performed under general anesthesia. A vertical incision was made on the lingual side from the mesial of #35 to the ascending ramus, and after bone removal on the lingual side of #37, the cyst was enucleated using a piezosurgery device. Histopathological examination confirmed an odontogenic cyst lined with keratinized epithelium. At final follow-up (27 months after the second enucleation), clinically favorable healing was observed without symptoms. Teeth #36 and #37 showed negative percussion response, no mobility, and maintained normal pulp vitality (EPT #36 3+, #37 4+). Panoramic radiography confirmed complete bone regeneration at the surgical site with no signs of recurrence (Fig. 1D).
Case 2: Unicystic Ameloblastoma
A 22-year-old male patient presented to our hospital with the chief complaint of swelling in the left mandibular area. The patient had noticed swelling of the left cheek for approximately 8 months but neglected it, and was referred to the dental department after being diagnosed with a dentigerous cyst based on ultrasound and neck CT examination at the Department of Otolaryngology approximately 1 month prior. There was no significant medical history.
Clinical examination revealed prominent swelling of the left buccal area with tenderness. Maximum mouth opening was 45mm, and there was no sensory disturbance of the lower lip. Teeth #36 and #37 showed no response on EPT, and tooth #38 was impacted. Panoramic radiography revealed a unilocular radiolucent lesion approximately 5.5×2.1cm in size involving #36 to #38 (Fig. 3A), with root resorption of teeth #36 and #37. Neck CT performed at the Department of Otolaryngology showed a large benign cystic bone lesion containing an impacted tooth in the left mandibular angle area. Extensive buccal cortical bone resorption and buccal expansion of the lesion were confirmed. The radiological diagnosis was dentigerous cyst (Fig. 3B).
Based on clinical and radiographic findings, dentigerous cyst was suspected and incisional biopsy was planned. Although the large cyst size and severe bone resorption suggested possible extraction of teeth #36 and #37 due to lack of pulp vitality, the patient strongly desired tooth preservation, and it was decided to perform initial decompression and observe the course. Under local anesthesia, decompression and incisional biopsy were performed on the buccal side of #36 and #37. A Penrose drain was inserted to maintain an open state. Initial histopathological examination reported fibrous tissue with chronic inflammation. The specimen obtained from decompression showed only scanty bony tissue with osteoid and surrounding fibrotic tissue (Fig. 4A). Dressing and drain changes were performed weekly. Clinically, buccal swelling gradually decreased, and drainage also decreased. At 2.6 months after decompression, panoramic radiography confirmed new bone formation at the anterior, posterior, and inferior borders of the cyst (Fig. 3C). The cyst size decreased, and the decompression effect was favorable.
Root canal treatment was initiated to preserve teeth #36 and #37. Root canal shaping and obturation were completed for tooth #36; however, tooth #37 was only partially obturated due to difficult canal access. The Penrose drain was removed approximately 4 months after decompression.
At 5 months after decompression, cyst enucleation, extraction of #38, and apicoectomy of #37 were performed under general anesthesia. A sulcular and vertical incision was made from #36 to the ascending ramus, and a full-thickness flap was elevated. After bone removal with a low-speed handpiece, the cyst was completely enucleated and tooth #38 was extracted. Since the mesiolingual canal of #37 was incompletely obturated, apicoectomy was performed followed by retrograde filling with MTA. After hemostasis with Surgicel, suturing was performed. Final histopathological examination revealed ameloblastoma with cystic space lined by odontogenic epithelium with fibrous connective tissue wall and intraluminal extending tumor showing plexiform pattern (Fig. 4B-D). Immunohistochemical staining showed positive CK19 and BRAF V600E.
At 6 months after cyst enucleation, zirconia crown restoration was performed on #36 and #37. The patient was informed that the crowns were fabricated with short roots and short crown length, and was instructed to be careful during mastication. At final follow-up (37 months after enucleation), clinically favorable healing was observed without symptoms. The zirconia crowns on #36 and #37 showed negative percussion response, no mobility, and maintained good function. Panoramic radiography showed favorable bone healing at the surgical site (Fig. 3D). CBCT axial view demonstrated favorable bone healing at the left mandibular surgical site with no signs of recurrence (Fig. 3E).
Ⅲ. DISCUSSION
OKC and ameloblastoma are representative odontogenic lesions of the jaw, showing similar clinical and radiographic features that make differential diagnosis difficult. In the present cases, both were initially presumed to be cystic lesions, but final pathological diagnoses were confirmed differently as OKC and ameloblastoma.
Radiographically, both lesions appear as well-defined radiolucent lesions and may present as unilocular or multilocular patterns. According to Kitisubkanchana et al.6, OKC appears unilocular in 82% of cases, while ameloblastoma shows a multilocular pattern in 68.3%. Both present cases appeared unilocular, making initial differential diagnosis difficult. Al-Moraissi et al.7 network meta-analysis compared various treatment modalities for OKC and reported that decompression followed by enucleation significantly reduced recurrence rates compared to simple enucleation. However, histological examination is essential for definitive diagnosis.
Histologically, OKC is lined with parakeratinized stratified squamous epithelium (5-8 cell layers) and is characterized by palisading arrangement and hyperchromasia of basal layer cells1,2. The underlying connective tissue is generally thin with minimal inflammatory cell infiltration. High epithelial proliferative activity leads to formation of satellite cysts or epithelial islands, which are the main causes of high recurrence rates3,8.
In Case 2, the initial incisional biopsy result reporting fibrous tissue with chronic inflammation was presumably due to sampling only the superficial layer of the cyst wall or severe inflammatory changes. This suggests the importance of adequate tissue sampling and appropriate site selection. Ameloblastoma was confirmed in the final enucleated tissue, and positive BRAF V600E confirmed the molecular biological characteristics of ameloblastoma.
Unicystic ameloblastoma was divided into three subtypes according to the pattern of proliferation of the ameloblastomatous epithelium: luminal, intraluminal and mural1. Case 2 was intraluminal type with cystic space lined by odontogenic epithelium with fibrous connective tissue wall and intraluminal extending tumor showing plexiform pattern. Immunohistochemically, CK19 is positive in approximately 80-90% of ameloblastomas, and BRAF V600E mutation is detected in approximately 50-60% of unicystic ameloblastomas1. These molecular biological markers are helpful in confirming diagnosis and predicting prognosis.
The therapeutic effect of decompression is based on reduction of intracystic pressure and consequent reduction in epithelial activity. According to Nakamura et al.8, the epithelium of OKC changes from parakeratinization to orthokeratinization after marsupialization, with increased epithelial thickness (average 5.7-fold) and loss of palisading arrangement of the basal layer. These changes reflect decreased epithelial proliferative activity and act as a mechanism to lower recurrence rates.
Oh et al.11 reported that epithelial thickness of OKC increased by 921% after decompression, changing histomorphologically to a pattern similar to normal oral mucosa. Park et al.9 reported that the decompression period for 50% volume reduction of OKC was 270 days (approximately 9 months). In Case 1, enucleation was performed 4.5 months after decompression, achieving clinically satisfactory size reduction.
For ameloblastoma, Nakamura et al.5 reported that the epithelium of the cyst wall becomes thinner and connective tissue fibrosis increases after marsupialization. The effect is particularly excellent in adolescent patients, and expansive type ameloblastoma responds better to marsupialization than invasive type. Yang et al.10 7-year study of 63 cases reported an average size reduction rate of 65.6% after decompression of unicystic ameloblastoma, consistent with the results of Case 2.
Compared to traditional enucleation or resection, decompression followed by enucleation has the following advantages. First, preservation of important anatomical structures (inferior alveolar nerve, adjacent teeth) is possible. In both present cases, treatment was completed without inferior alveolar nerve damage, and in Case 2, teeth #36 and #37, which initially lacked pulp vitality, could be preserved. Second, it reduces the risk of pathologic fracture. Immediate enucleation of large cysts greatly weakens mandibular continuity, increasing fracture risk; however, decompression can gradually induce new bone formation while recovering bone strength12,13. Third, there is a cost-saving effect through tooth preservation. In Case 1, if only immediate cyst enucleation had been performed, preoperative root canal treatment of teeth #36 and #37 and postoperative prosthodontic treatment would have been necessary, incurring additional treatment costs. However, through decompression followed by enucleation, cyst size was reduced and surrounding bone tissue was regenerated, maintaining pulp vitality of teeth #36 and #37, ultimately eliminating the need for preoperative root canal treatment and prosthodontic treatment, greatly reducing treatment costs. In Case 2, immediate enucleation would have made extraction of tooth #37 inevitable, requiring prosthodontic restoration such as implant or bridge. However, by performing decompression followed by enucleation, tooth #37 could be preserved, and treatment was completed with only root canal treatment and crown restoration, achieving considerable cost savings compared to implant costs. This economic benefit is particularly important in young patients and is also significant in that it can prevent additional bone resorption following tooth loss and movement of adjacent teeth in the long term.
Pogrel12 proposed the following indications for decompression: (1) large cysts in proximity to the inferior alveolar nerve, (2) when preservation of adjacent teeth is necessary, (3) growing adolescent patients, (4) when there is high risk of pathologic fracture, (5) when extensive surgery is difficult due to poor general condition. Both present cases met these criteria.
Kolokythas et al.13 comparative study showed no significant difference in recurrence rates between decompression followed by enucleation and immediate resection (12.5% vs 8.3%, respectively), while complication rates were significantly lower in the decompression group. Maurette et al.14 study also demonstrated the safety and effectiveness of conservative treatment protocols.
The recurrence rate of OKC varies depending on treatment method. While simple enucleation has recurrence rates of 25-60%, decompression followed by enucleation significantly reduces recurrence rates15,16. Brøndum et al.15 long-term follow-up study (7-17 years) reported 0% recurrence rate after decompression, and Zhao et al.16 studyof 255 cases reported 0% recurrence rate with marsupialization alone and 17.4% with enucleation alone.
The recurrence at 9 months after the first enucleation in Case 1 is presumed to be due to residual epithelial cells or satellite cysts. This reflects the high recurrence tendency of OKC, and although there has been no recurrence for 27 months after the second enucleation, continuous long-term follow-up is necessary. While most OKC recurrences occur within 5 years postoperatively, cases of recurrence after 10 years have been reported, recommending lifelong follow- up3.
For ameloblastoma, the recurrence rate of unicystic type is lower than solid type (10-15% vs 50-90%). Zheng et al.17 long-term follow-up study of 116 cases reported 12% recurrence rate after marsupialization of unicystic ameloblastoma, with most occurring within 3 years postoperatively. Case 2 showed no recurrence even at 37 months after enucleation, but follow-up of at least 5 years is necessary.
Han et al.18 recent study evaluated mandibular symmetry recovery after decompression through 3D quantitative analysis, reporting that bone growth and morphological recovery were favorable in most cases. In the present cases, mandibular symmetry was also favorably recovered at final follow- up.
The two cases showed similarities in several aspects but also important differences. Age (18 vs 22 years), location (left mandible), and size (approximately 3.5cm vs 5.5cm) showed some differences, and both were treated with decompression followed by enucleation. However, final pathological diagnoses differed, and there were differences in clinical course. Case 1 (OKC) had a relatively short decompression period of 4.5 months, and pulp vitality of adjacent teeth was maintained. However, recurrence occurred after the first enucleation, requiring a second surgery. Case 2 (unicystic ameloblastoma) had a decompression period of 5 months, and although adjacent teeth lacked pulp vitality requiring root canal treatment, tooth preservation was successful. There has been no recurrence to date after the first enucleation.
These differences reflect the biological characteristics of the two lesions. OKC requires more aggressive follow-up and reoperation when necessary due to high recurrence tendency, while unicystic ameloblastoma shows relatively low recurrence rates but requires long-term follow-up considering the possibility of malignant transformation.
Limitations of this case report include: first, statistical analysis is impossible as only two cases are included. Second, the relatively short follow-up period (approximately 3 years) makes it difficult to evaluate long-term recurrence. Third, in Case 2, final diagnosis was delayed due to limitations of the initial incisional biopsy.
In conclusion, the present cases demonstrated the effectiveness of decompression followed by enucleation in large odontogenic lesions of the mandible. Although OKC and unicystic ameloblastoma are similar clinically and radiographically, making differential diagnosis difficult, histopathological confirmation is essential. Decompression followed by enucleation is a conservative treatment method that provides effective treatment results while preserving the inferior alveolar nerve and adjacent teeth. OKC requires more thorough follow-up due to high recurrence tendency and can be managed through reoperation when recurrence occurs. Unicystic ameloblastoma shows relatively low recurrence rates, but monitoring for recurrence and malignant transformation through long-term follow-up is essential. Appropriate patient selection, accurate pathological diagnosis through adequate tissue sampling, and systematic long-term follow-up are key elements for successful treatment.
