Orthokeratinized Odontogenic Cyst Research Articles

Orthokeratinized Odontogenic Keratocyst: Report of Nine Cases with Review of Literature

Abstract Formerly believed to be a subtype of odontogenic keratocyst (OKC), orthokeratinized odontogenic cyst (OOC), a rare developing odontogenic cyst, is now believed to be distinct. The clinical, radiographic, histological data are included in this report, along with a review of the literature to aid in comprehending the cyst. A retrospective search in the oral pathology department between 2018 and 2022 was conducted to recover all cases reported as OOC in SRM Dental College, Ramapuram. Radiographs and Haematoxylin and Eosin stained histological slides were re-examined. Overall, there were nine cases in which men were engaged in 80% of the instances and the group’s ages varied from 20 to 35. The primary symptoms of all of the patients were pain and edema. The vast majority of cases had an impacted tooth in the jaw. All of the lesions showed clearly visible radiolucency on orthopantomographs [OPG], with the exception of one specific case. Additionally, histological examination of each patient revealed the characteristic microscopic traits and enucleation was done to treat all the cases. OOC has a more favourable outcome than OKC due to variations in prognosis, management and must be considered distinct from OKC. Most of our cases—a large majority—involved adolescent males’ mandibles and involved pain and edema. Most were unilocular and all were radiolucent. The literature-recommended histopathological findings were present and all cases were enucleated.

Interdisciplinary Management of Orthokeratinized Odontogenic Cyst

Wright in 1981 identified orthokeratinized variant of the odontogenic keratocyst and named it as orthokeratinized odontogenic cyst (OOC). Due to its different histopathology and reduced likelihood to recur, he held it to be distinct from the parakeratotic type. It usually occurs in the mandible and after surgical removal, it showed rare recurrence. Numerous studies have shown that OOC has typical characteristic clinicopathologic features when compared to other developmental odontogenic lesions such as keratocystic odontogenic tumors and dentigerous cysts. This case report is a typical example of an odontogenic lesion diagnosed histopathologically as OOC in the maxilla having clinic-radiographic features similar to dentigerous cyst. Interdisciplinary management of OCC helps in proper diagnosis, plan treatment, and provide the best quality of care to the patient.

Orthokeratinized odontogenic cyst: a case report

Orthokeratinized odontogenic cysts (OOC) are rare developmental odontogenic cysts characterized by an ortho-keratinized stratified squamous epithelial lining. They were originally believed to be part of the spectrum of Odontogenic Keratocyst but are now considered a distinct entity.They comprise approximately 1% of all odontogenic cysts and about 10% of cases previously coded as odontogenic keratocysts. They usually occur as a single radiolucent lesion.In this paper, we present a case of OOC and compare them to previous case reports and a literature review.

An unusually extensive orthokeratinized odontogenic cyst: A case report

While odontogenic keratocysts (OKC) are fairly common and well-known, orthokeratinized odontogenic cysts (OOCs) are quite rare accounting for less than 1% of odontogenic cysts. The entity is characterized by the presence of a predominant orthokeratinized lining. OOC is much less aggressive as compared to OKC and simple enucleation is discerned as adequate treatment with minimal chances of recurrence. The present case report describes an extensive OOC that involved most of the angle and ramus of the mandible in a 25-year-old female.

BILATERAL ORTHOKERATINED ODONTOGENIC CYST: A REPORT OF TWO NEW CASES

Orthokeratinized odontogenic cyst (OOC) is an uncommon developmental cyst of the jaws that usually occur singly, as a unilocular radiolucency affecting the posterior mandible of males. Bilateral OCCs are exceedingly rare, with less than 10 cases reported in the literature. Our study presents two new cases of bilateral OOCs. The first patient was an 18-year-old man who presented two bilateral well-circumscribed unilocular radiolucent lesions in the posterior mandible. The second patient was a 29-year-old woman with bilateral well-circumscribed unilocular (left) and multilocular (right) radiolucent lesions, located in the posterior mandible. The unilocular lesions were associated with unerupted lower molars. Microscopically, the cysts were entirely lined by orthokeratinized stratified squamous epithelium, confirming the diagnosis of OOC. Both patients were treated conservatively, and to date, no recurrence was evident. Clinicians should consider OOC during the evaluation of bilateral pericoronal radiolucent lesions in the posterior mandible of young adults. Orthokeratinized odontogenic cyst (OOC) is an uncommon developmental cyst of the jaws that usually occur singly, as a unilocular radiolucency affecting the posterior mandible of males. Bilateral OCCs are exceedingly rare, with less than 10 cases reported in the literature. Our study presents two new cases of bilateral OOCs. The first patient was an 18-year-old man who presented two bilateral well-circumscribed unilocular radiolucent lesions in the posterior mandible. The second patient was a 29-year-old woman with bilateral well-circumscribed unilocular (left) and multilocular (right) radiolucent lesions, located in the posterior mandible. The unilocular lesions were associated with unerupted lower molars. Microscopically, the cysts were entirely lined by orthokeratinized stratified squamous epithelium, confirming the diagnosis of OOC. Both patients were treated conservatively, and to date, no recurrence was evident. Clinicians should consider OOC during the evaluation of bilateral pericoronal radiolucent lesions in the posterior mandible of young adults.

Types, Complications, and Prognosis of Inflammatory and Developmental Odontogenic Cyst

In general, odontogenic cysts might have an inflammatory or developmental origin. The review study aims to increase understanding of the various categories of odontogenic cysts by describing their primary characteristics, consequences, treatments, and prognoses of lesions. Different types of developmental odontogenic cysts are the dentigerous cyst, eruption cyst, odontogenic keratocyst (OKC), orthokeratinized odontogenic cyst (OOC), gingival cyst (adult and new-born), lateral periodontal cyst (LPC), glandular odontogenic cyst, and calcifying odontogenic cyst (COC). Periapical or lateral radicular cysts, residual cysts, and paradental cysts are forms of inflammatory odontogenic cysts. The mandible and maxilla are affected by these inflammatory lesions. The most prevalent developmental odontogenic cysts were dentigerous cysts and OKC. Most developmental cysts reported rare recurrence and excellent prognosis except for glandular odontogenic cysts (30 to 55% recurrence) and OKC (30%). Glandular odontogenic cysts, OKC, and COC have the propensity to behave aggressively and recur frequently compared to others. Although most inflammatory cysts are asymptomatic and benign, because of their continuous growth, these lesions have the potential to become destructive because they damage and infect the nearby bone. Malignant transformation has been reported in periapical and residual inflammatory cysts. As a result, they should be properly diagnosed and treated. All inflammatory cysts have a favorable prognosis.

Multiple orthokeratinized odontogenic cysts: clinical, pathological, and genetic characteristics

Background:Orthokeratinized odontogenic cyst (OOC) is a rare developmental odontogenic cyst of the jaw. It was originally believed to be a variant of odontogenic keratocyst (OKC) but is now considered to be a distinct entity. OOC usually presents as a single lesion and recurs infrequently. On the other hand, OKC often presents with multiple lesions and displays locally aggressive behavior and a high recurrence rate associated with the protein patched homolog 1 (PTCH1) gene mutation. Multiple OOC cases are extremely rare and seem to be aggressive, but their pathogenesis is not fully understood. This study aimed to determine the clinical, pathological, and genetic characteristics of multiple OCC.Methods:Three cases of multiple OOC were evaluated for clinical and histological findings, and immunohistochemical expression of Ki-67 and Bcl-2. Furthermore, PTCH1 mutations were analyzed by next-generation sequencing using a custom panel to cover the entire exon of PTCH1.Results:The three cases of multiple OOC included two men and one woman with a mean age of 25.3 years old (range, 18–38 years old). Each case had two or three OOCs (total of seven OOCs), all of which were simultaneously detected. Of the seven OOCs that manifested as multiple jaw cysts, seven (100%) occurred in the posterior regions, four (57.1%) occurred in the mandible, and four (57.1%) were associated with an impacted tooth. Histological examination revealed cysts lined by orthokeratinized stratified squamous epithelium. Immunohistochemistry showed a low Ki-67 labeling index and no Bcl-2 expression in the seven OOCs. No pathogenic PTCH1 mutations were detected in any of the seven OOCs. None of the patients had any other symptoms or signs of recurrence at the last follow-up (6–60 months).Conclusion:Multiple OOCs appeared to occur more often in younger patients than solitary OOC. Both multiple and solitary OOCs may be related diseases within the entity of odontogenic cysts. Multiple OOCs are clinicopathologically and genetically distinct from OKC.

A series of six uncanny orthokeratinized odontogenic cysts: Revisiting the literature

Orthokeratinized odontogenic cyst is a rare odontogenic cyst which was considered to be a variant of odontogenic keratocyst, but has been recognized as a separate entity due to its varied behavior and histology. Commonly associated with an unerupted tooth in the posterior mandible, it mimics various lesions like dentigerous cyst, odontogenic keratocyst, unicystic ameloblastoma etc. Orthokeratinized odontogenic cyst was thought to be less destructive compared to odontogenic keratocyst. This case series highlights the clinically aggressive nature of Orthokeratinized odontogenic cyst.In this case series six cases of diagnosed Orthokeratinized Odontogenic cyst have been described along with one case of multiple Orthokeratinized odontogenic cysts in a female patient. The clinical, radiographic and histopathologic features have been described in great detail in order to correlate with the previous literature and highlight their clinically aggressive behavior.Orthokeratinized odontogenic cyst can be deceptive and should be diagnosed appropriately to avoid aggressive treatment protocol. Most of these cysts are associated with inflammation which makes it harder to be diagnosed as the epithelium and connective tissue would have undergone structural changes. Differentiating the cystic lesions of the oral cavity is utmost important to devise appropriate treatment suitable for the patient and for assessing the prognosis, recurrence and rehabilitation to improve the quality of life.

MULTILOCULAR APPEARANCE OF ORTHOKERATINIZED ODONTOGENIC CYST: A CASE REPORT

Orthokeratinized odontogenic cyst (OOC) was initially defined as the uncommon orthokeratinized type of odontogenic keratocyst (OKC) by the World Health Organization (WHO). Several studies have shown that OOC has different clinicopathologic aspects when compared with other developmental odontogenic cysts, especially OKC. So OOC now emerges to be a distinct entity, according to the 4th edition of the WHO Classification of Head and Neck Tumors which was published in January 2017. Clinically, it usually occurs as a single cyst with a unilocular radiographic appearance in posterior mandible with a predilection in males and mostly is seen between the third and fourth decades. In this case we present an OOC arise as a multilocular lesion causes thinning and expansion of the buccal cortical plate treated by enucleation and curettage.

SECONDARY INFECTION ASSOCIATED WITH AN ORTHOKERATINIZED ODONTOGENIC CYST IN THE MANDIBLE

Orthokeratinized odontogenic cyst (OOC) is a pathologic entity that was once described as an uncommon variation of odontogenic keratocyst, although the 2005 World Health Organization classification considers this as distinct pathologic entity due to its diverse biological behaviors. Literature on OOC describes a greater prevalence in White men aged 30 years and older and reports its low growth rate and aggressiveness as responsible for the lower recurrence rate. Because of its asymptomatic clinical course, the diagnosis may be delayed, increasing morbidity associated with the disease. The objective is to present a case of a distinguished OOC in the mandibular posterior region of a 30-year-old woman who presented with a significant odontogenic infection associated to the pathologic cavity, which was not noted before. The lesion was treated with enucleation and the mandible was reinforced using internal rigid fixation. After 1 year of follow-up there are no signs of recurrence. Orthokeratinized odontogenic cyst (OOC) is a pathologic entity that was once described as an uncommon variation of odontogenic keratocyst, although the 2005 World Health Organization classification considers this as distinct pathologic entity due to its diverse biological behaviors. Literature on OOC describes a greater prevalence in White men aged 30 years and older and reports its low growth rate and aggressiveness as responsible for the lower recurrence rate. Because of its asymptomatic clinical course, the diagnosis may be delayed, increasing morbidity associated with the disease. The objective is to present a case of a distinguished OOC in the mandibular posterior region of a 30-year-old woman who presented with a significant odontogenic infection associated to the pathologic cavity, which was not noted before. The lesion was treated with enucleation and the mandible was reinforced using internal rigid fixation. After 1 year of follow-up there are no signs of recurrence.

Orthokeratinized odontogenic cysts: A clinicopathologic study of 159 cases and molecular evidence for the absence of PTCH1 mutations.

Orthokeratinized odontogenic cyst (OOC), a newly designated entity of odontogenic cysts, is an intraosseous jaw cyst that is entirely or predominantly lined by orthokeratinized squamous epithelium. The aim of this study was to report a large series of OOC to substantiate its clinicopathologic profiles and to investigate PTCH1 mutations in OOCs. The clinicopathologic features of 167 OOCs from 159 patients were analyzed and the immunohistochemical expression of markers related to cell differentiation and proliferation was evaluated. Furthermore, PTCH1 mutations were analyzed in 14 fresh samples of OOC. OOCs occurred mostly in the third and fourth decades (60.4%) with a male predilection (66.7%). The lesions developed more often in the mandible than maxilla, primarily in the posterior mandible and ramus. Eight patients (5.0%) showed multiple locations of either bilateral posterior mandible (n=6) or both the maxilla and mandible. Radiographically, the majority of OOCs (91.2%) showed a well-demarcated, unilocular radiolucency with 14 multilocular cases (8.8%). A follow-up of 131 patients (123 treated by enucleation with or without marsupialization and eight by peripheral ostectomy) revealed no recurrence during an average period of 4.56 years after surgery. Immunohistochemistry indicated lower proliferative activity and a varying epithelial differentiation pattern in OOC compared with odontogenic keratocysts (OKC). No PTCH1 mutation was detected, except for three known single nucleotide polymorphisms. The clinicopathological and molecular differences between OOC and OKC justified their separation, and unlike OKCs, OOCs did not harbor PTCH1 mutations, suggesting different pathogenesis underlying these two jaw cysts.

Orthokeratinized odontogenic cyst (OOC): Clinicopathological and radiological features of a series of 48 cases

ObjectivesTo demonstrate the clinicopathological and radiological features of orthokeratinized odontogenic cysts (OOCs), and analyze the epithelial cell proliferative activity between OOCs and odontogenic keratocysts (OKCs). Materials and methodsClinicopathological and radiological analyses were performed in all OOC cases. The expression of cell proliferation markers, Ki-67 and cyclin D1, was detected by immunohistochemistry. ResultsA total of 48 OOC patients, 28 males and 20 females, were included. The mean age was 33.50 years, with a range of 13–61 years. The mandible was affected five times as frequently as the maxilla (mandible 40, maxilla 8). All OOCs were unilocular radiolucencies with well-defined margins, and 30 of 36 showed loss of continuity of the buccal or lingual cortices based on computed tomography (CT) images. Three cases exhibited root resorption; tooth displacement occurred in 4 cases. The average volume of the cysts on CT was 7794.25 ± 6952.98 mm3. All cysts were treated by enucleation or enucleation after decompression. The average follow-up time was 32.50 ± 27.58 months (ranging from 6 to 65 months), and the overall recurrence rate was 4.44% (2 of 45). Compared with OKCs, Ki-67 and cyclin D1 expression were significantly lower in OOCs (P < 0.001). ConclusionsOOCs occur more frequently in mandible with a slight male predilection and have a lower proliferative activity than OKCs. Radiologically, OOCs are more likely associated with buccolingual expansion and destruction of cortical bone. Due to the lower aggressiveness and recurrence rate, enucleation or decompression combined with enucleation is the first treatment choice for OOC.

Expression of BMP4 and FOXN1 in orthokeratinized odontogenic cyst compared to odontogenic keratocyst suggests an epidermal phenotype

ABSTRACT Odontogenic keratocysts (OKC) and orthokeratinized odontogenic cysts (OOC) are odontogenic cysts that share histological and immunohistochemical similarity with epidermal appendages and cutaneous cystic lesions despite exhibiting contrasting biological behavior. In epidermal appendages, BMP4 induces expression of FOXN1, which participates in terminal differentiation of keratinocytes and control of proliferation. We compared BMP4 and FOXN1 expression in OOC and OKC to investigate their role in the epithelial differentiation of these cysts. BMP4 and FOXN1 expression was assessed using immunohistochemistry in 20 primary sporadic OKC and compared to 16 OOC. BMP4 epithelial expression was detected in 81.25% OOC compared to 35% in OKC, while its expression in connective tissue was observed in 65% OKC and 75% OOC. FOXN1 was detected in 75% OOC vs. 30% OKC. The “triple positive” phenotype, i.e., BMP4 epithelial and connective tissue positivity and FOXN1 epithelial positivity, was seen in 56.25% OOC compared to 10% OKC. The greater expression of BMP4 and FOXN1 in OOC suggests greater activation of this pathway in OOC, which suggests a role in its more mature epithelium; it also resembles an epidermal phenotype.

Orthokeratinized versus parakeratinized odontogenic keratocyst: Our institutional experience.

Introduction:The odontogenic keratocyst (OKC) is quite unique among odontogenic cysts in its specific histological features and in clinical characteristics. The OKC has two variants orthokeratinized odontogenic cyst (OOC) and parakeratinized odontogenic cyst (POC), and POC is considered to be more aggressive and has a high recurrence rate. Therefore, OKC has generated considerable controversy with regard to its true nature.Aim:The purpose of this study was to determine the differences between POC and OOC variants of odontogenic cysts on the basis of clinical as well as radiological features.Materials and Methods:A total of 85 cases were included in the present study. There was a marked difference in the age of occurrence, sex, location and radiological presentation of both these entities.Results:Our institutional experience suggests that POC is more common than OOC and both the variants were commonly found in males. Most of the cases of POC were found in the third decade of life and most of the cases of OOC were frequently seen in the second, fourth and fifth decades. Mandibular posterior area was frequently occurring in both variants. Left side involvement was seen in maxilla and right side in mandible in both variants. Most of the cases were clinically diagnosed as OKC.Conclusion:The treatment and prognosis varies in both the variants of OKC, hence such epidemiological studies are helpful to ensure proper treatment for these distinct entities.

A Comparative Immunohistochemical Study of Expression of Syndecan-1 (CD138) and Podoplanin in Keratocystic Odontogenic Tumor, Orthokeratinized Odontogenic Cyst and Dentigerous Cyst

Background: Odontogenic lesions can bring about diagnostic challenges due to overlapping histology among pathologists. Thus, there are few tumor markers that provide accurate diagnosis. Syndecan-1 (CD-138) and podoplanin (PDPN) are proteoglycans that have been described as substantial diagnostic and prognostic markers in various odontogenic lesions. Aim: This study aims to evaluate and compare the immunohistochemical expression of syndecan-1 (CD-138) and podoplanin in keratocystic odontogenic tumor, orthokeratinized odontogenic cyst (OOC), and dentigerous cyst (DC). Materials and Methods: The formalin-fixed paraffin-embedded tissue blocks of KCOT, OOC, and DCs were retrieved form the archives of department. Three sections each of 3 μm thickness were made using a rotary microtome and they were stained with syndecan-1 (CD-138) and podoplanin (PDPN) using immunohistochemical methods and standard hematoxylin and eosin stain. Results: Immunohistochemical expression of syndecan-1in KCOT was found to be weakly to moderately positive in 6 cases with 2 cases exhibiting positive expression. In OOC, 3 cases displayed negative expression-1 whereas 7 cases were weakly to moderately positive. Immunohistochemical expression of podoplanin in KCOT was observed to be weakly to moderately positive in 4 cases with 5 cases exhibiting strongly positive expression. In OOC, 3 cases displayed negative immunohistochemical expression for podoplanin and 4 cases were strongly positive. Immunoreactivity for podoplanin in DC was negative in 3 cases whereas 5 cases were weakly to moderately positive. Conclusion: The absence of significant correlation between expression of syndecan-1 and podoplanin reinforces the exact role of these proteins in the differentiation of odontogenic lesions which need to be elucidated further.

A comparative immunohistochemical analysis of cortactin in orthokeratinized odontogenic cyst (OOC), sporadic odontogenic keratocyst (OKC), and syndromic OKC

ObjectivesTo evaluate and compare the immunohistochemical expression of cortactin in the epithelial lining of orthokeratinized odontogenic cyst (OOC), sporadic odontogenic keratocyst (OKC), and syndromic OKC. MethodsFormalin-fixed paraffin-embedded tissue blocks of histopathologically diagnosed cases of OOC, OKC, syndromic OKC, normal buccal mucosa (NBM), and oral squamous cell carcinoma (OSCC) were examined for immunohistochemical expression of cortactin. Clear brown cytoplasmic and membranous staining was considered positive. ResultsA statistically significant difference was observed between OOC and syndromic OKC (p < 0.001), as well as between sporadic OKC and syndromic OKC (p < 0.001). Although not statistically significant, the expression of cortactin was slightly higher in the basal layer of NBM (mean = 0.47), OOC (mean = 0.27), sporadic OKC (mean = 0.47) syndromic OKC (mean = 1.53), and OSCC (mean = 0.67) than in the parabasal layers of NBM (mean = 0.27), OOC (mean = 0.20), sporadic OKC (mean = 0.47), syndromic OKC (mean = 1.27), and OSCC (mean = 0.60). ConclusionThe expression of cortactin in the basal layer may suggest the formation of invadopodia in the basal layer where the invasion mechanism occurs. This finding is further supported by the higher localization of cortactin in areas of epithelial budding and daughter cysts in syndromic OKC, thereby reaffirming its possible association with recurrence.

A comparative study of the expression of cyclin D1, COX-2, and KI-67 in odontogenic keratocyst vs. ameloblastoma vs. orthokeratinized odontogenic cyst

BackgroundOdontogenic keratocysts (OKCs) and orthokeratinized odontogenic Cysts (OOCs) are distinct clinicopathological entities. OKC appears to behave in a way more similar to that of a neoplasm, such as ameloblastoma (AB). The aim of this study is to compare the influence of Ki-67, Cyclin D1 and COX-2 in the diagnosis and pathogenesis of OKC, OOC and AB. Materials and methodsA cross-sectional observational study of 41 samples was organized into 3 groups: (1) OKC n=22; (2) AB n=13 and (3) OOC n=6. Paraffin blocks were sectioned and stained with hematoxylin and eosin (H&E). Immunohistochemical study using Bond Polymer Refine Red Detection Kit, Leica, Wetzlar, Germany, was performed for the following antibodies: Ki-67, Cyclin D1 and COX-2. Double blind immunostaining was quantified subjectively. Staining: nuclear or cytoplasmic; nuclear (Ki-67 and Cyclin D1>5% positive) and cytoplasmic (COX-2; 1; 1–30 cytoplasm: 2; 31–60 cytoplasm; 3; 61–100 cytoplasm). Considering positive stained 61-100 cytoplasms. ResultsThe expression of Ki-67 was higher in the OKC group than in the AB group (p<0.05). Cyclin D1 showed a higher expression in OKC vs. OOC and OKC vs. AB (p<0.05). Finally, expression of COX-2 was higher in OKC vs AB (p<0.05). ConclusionsCOX-2, Ki-67 and Cyclin D1 show statistically significant differences between the groups, suggesting that they could be useful tools in the differential diagnosis between OKCs and OOC and a predictive indicator for their biologic behaviour. The higher expressions of these 3 markers of OKC vs AB highlight once more the aggressive behaviour of this now re-considered cystic lesion. These markers could prove useful in the choice of more aggressive surgical treatment in OKCs as their behaviour appears to be similar to that of a neoplasm.

Expect the unexpected – A rare case of Orthokeratinized Odontogenic Cyst and its surgical management

Orthokeratinized Odontogenic Cyst (OOC) is a rare, developmental odontogenic cyst of the dental lamina. It was initially defined as the uncommon orthokeratinized variant of the Odontogenic Keratocyst (OKC), until the World Health Organization’s (WHO’s) classification in 2005 and 2017, where it was separated from the Keratocystic Odontogenic Tumor (KCOT) and has been included as a separate entity from the category of developmental odontogenic cysts respectively. It presents as a unilocular radiolucent lesion involving the posterior mandible and is frequently related to impacted teeth, often similar to other odontogenic cysts. Due to low local aggressiveness and less proliferative activity, it has to be differentiated from the other cysts in terms of surgical management. Here we report a rare case of OOC involving the maxilla along with an impacted canine and discuss the surgical management and why a secondary surgical intervention is unnecessary.

Orthokeratinized odontogenic cyst: A large series and comprehensive literature review with emphasis on synchronous multiple occurrence and neoplastic transformation

The objective of this study was to demonstrate the clinical, radiologic, and histologic features of orthokeratinized odontogenic cyst (OOC); determine the characteristics of multiple OOCs; and present rare but significant manifestations of OOC. A clinical, radiologic, and histopathologic study of 65 primary and 2 recurrent OOC cases was performed retrospectively along with a comprehensive literature review. OOCs shared similar radiologic findings with odontogenic keratocyst, yet some showed features that have not been previously described: root resorption and radiopaque foci. Histologic review revealed a unique histiocytic lining and some findings suggestive of the multipotentiality of the odontogenic epithelium. The analysis of patients with multiple OOCs demonstrated that multiple OOCs occurred synchronously with a marked predilection for young male adults. Two unusual cases were also identified: an OOC combined with a BRAFV600E ameloblastoma and a recurrent OOC with malignant transformation. This largest series presents previously unreported radiographic and histopathologic features that can be seen in OOC. Multiple OOCs have clinical characteristics distinct from those of solitary cases. The first reported OOC associated with ameloblastoma suggests the involvement of oncogenic mutations in odontogenic tumorigenesis. Although OOC shows a low recurrence rate, the possibility of malignant transformation of recurrent OOCs should be emphasized.

A CLINICOPATHOLOGIC STUDY OF 144 ORTHOKERATINIZED ODONTOGENIC CYSTS

<h3>Background</h3> Orthokeratinized odontogenic cysts (OOCs) are uncommon intraosseous cystic lesions and are distinguished as an individual entity of odontogenic cysts in the new World Health Organization classification. <h3>Objective</h3> To analyze the clinicopathologic features of OOC in a Chinese population. <h3>Methods</h3> All cases reported as OOCs and odontogenic keratocysts (OKCs) were reviewed from the files of the Department of Oral Pathology, Peking University School and Hospital of Stomatology, from 2000 to 2018. We identified 144 OOC cases and analyzed clinical and pathological information. <h3>Results</h3> In the present study, we report the largest series of OOC cases, to our knowledge. There were 98 male and 46 female patients with a peak incidence in the third to fourth decades of life. One hundred thirty-six cases (94.4%) were solitary, and 8 cases (5.6%) were multiple. The most common sites were in the mandibular molar and ramus region. Radiographically, 12 lesions showed multilocular radiolucency with bone destruction, whereas others were unilocular. All the cases were primary. In follow-up of 116 patients, 114 were treated by simple enucleation, which revealed no recurrence over a period of 0.5-17 years after surgery. Compared with OKCs, OOCs revealed different histologic and immunohistochemical features. <h3>Conclusions</h3> OOC is clinicopathologically distinct from OKC and should constitute its own clinical entity according to histologic features and biologic behavior. Further study is needed to investigate the pathogenesis and mechanism of OOCs.