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- MATERIALS AND METHODS
Objective To analyze the clinicopathological features of odontogenic keratocysts in Chinese patients.
Study Design Retrospective analysis.
Methods The clinical records and pathological features of odontogenic keratocysts from 69 ethnic Hong Kong Chinese patients (40 male and 29 female patients) were reviewed.
Results The male-to-female ratio was 1.4:1; patient age ranged from 6 to 69 years with a modal peak in the third decade (mean age, 28 y; median age, 23 y). The preoperative diagnosis was correct in 78% of the cases and the most common misdiagnosis was dentigerous cyst. Sixty-two percent of the cysts were found in the mandible, and 38% in the maxilla. Multiple cysts occurred in 9% (including three cases of basal cell nevus syndrome). Histologically, 82.6%, 5.8%, and 11.6% of the cysts were parakeratinized, orthokeratinized, and mixed types, respectively. Patients with multiple cysts all showed parakeratinization. The majority (80%) of the cysts were lined by epithelia with a thickness of five to eight cells. Surface corrugation, subepithelial split, suprabasal split, satellite microcysts, epithelial islands, significant inflammation, hyaline bodies, and dystrophic calcification were present in 100%, 81%, 25%, 38%, 42%, 46%, 7%, and 10% of cysts, respectively. The overall recurrence rate was 24%, with a median time for first recurrence of 19 months (range, 1 mo–22 y). Cysts showing orthokeratinization or mixed types of keratinization recurred less often than parakeratinized cysts. Recurrence had the same type of keratinization as the initial cyst.
Conclusions Pathological examination of keratocysts is important, because keratocysts have different clinicopathological features and carry a risk for clinical misdiagnosis.
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- MATERIALS AND METHODS
Sixty-nine patients with odontogenic keratocysts were identified (Table I). Forty (58%) were male and 29 (42%) were female patients, giving a male-to-female ratio of 1.4:1. The age of the patients at the initial operation ranged from 6 to 84 years (median age, 23 y) with the modal peak in the third decade. For men and boys, the age ranged from 7 to 69 years (median age, 25 y) with the model peak in the second decade. For women and girls, the age ranged from 6 to 84 years (median age, 22 y) and the modal peak was in the third decade. However, the difference in the age distribution between the two sexes was not significant (NS) statistically (P = NS).
Table Table 1.. Age and Sex Distribution of Patients With Keratocysts in Hong Kong Chinese.
A tentative diagnosis of keratocyst was made in 54 patients (78% of all cases) before surgery; the other cases (15 cases) were diagnosed as dentigerous cysts (8 cases), radicular cysts (2 cases), residual cysts (2 cases), ameloblastomas (2 cases) and a lateral periodontal cyst (1 case).
A total of 81 cysts were studied, with six patients (9%) having multiple cysts. Fifty cysts (62%) were found in the mandible and 31 (38%) in the maxilla. The cysts were situated posterior to the canine in 84% of the cases in the maxilla and in 92% of cases in the mandible. Forty cysts (49%) were found on the right side and 35 (43%) on the left; 6 cysts (7%) involved the midline.
The follow-up period in 55 patients was longer than 2 years (median follow-up, 6 mo; maximum follow-up, 13 y). Of these patients, 13 patients (9 male and 4 female patients) with recurrence were noted, giving a recurrence rate of 24% for this study period. One of these patients had two episodes of recurrence that were noted 5 and 8 years after the initial definitive operation. Within the group of six patients with multiple cysts, three patients had recurrence. In two cases, patients had multiple episodes of recurrence at intervals of more than 10 years after the initial operation. In the first case, a woman who was 26 years old at initial presentation in 1978 had four episodes of recurrence 10 to 15 years after the initial operation. In the second case, an 18-year-old male patient had two episodes of recurrence 20 and 22 years after the initial presentation in 1970. Among the 13 recurrent cases, recurrences occurred 19 months (median) after the initial operation (range, 1 mo–22 y). The male-to-female ratio of 2.3:1 was slightly higher than that in the group without recurrence (male-to-female ratio, 1.2:1). However, the age and sex of the two groups of patients were similar (P = NS).
Histologically, all the keratocysts examined showed a prominent basal cell layer and surface corrugation. Satellite microcysts, epithelial islands, subepithelial split, suprabasal cleft, and significant inflammation were found in 26 (38%), 29 (42%), 56 (81%), 17 (25%), and 32 (46%) of the cases. The inflammatory cells comprised a mixture of polymorphs, lymphocytes, plasma cells, and histiocytes and in these areas; rete pegs were often observed (Fig. 3). Hyaline bodies and calcification were identified in five (7%) and seven (10%) cases, respectively. Epithelial dysplasia, ameloblastoma, and carcinoma were not found.
Figure Fig. 3.. Inflamed keratocyst with formation of rete pegs. Although the epithelium gives no clue to the nature of the cyst, characteristic keratocyst lining present in other areas helps to pinpoint the diagnosis (H&E stain, original magnification × 200).
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Of the keratocysts from the 69 patients studied, 57 (82.6%) showed pure parakeratinization (P), 4 (5.8%) pure orthokeratinization (O), and 8 (11.6%) mixed parakeratinization and orthokeratinization (M). The type of keratinization in the recurrence followed that of the primary cyst in all cases. Group M (median age, 38 y) was slightly older than the groups O and P (median ages, 25 and 27, respectively). The age of the patients in group M was significantly different from that in group P (P = .034). Multiple cysts all showed parakeratinization. Mandibular involvement was observed in 62%, 75%, and 50% of groups P, O, and M, respectively. Recurrence was found in 10 parakeratinized cysts (20%) and in 1 cyst (13%) in the mixed group. Table II lists other clinical and histological features of the three groups.
Table Table 2.. Clinical and Histological Findings of Parakeratinized, Orthokeratinized, and Mixed Keratocysts.
The number of cell layers of the epithelial lining ranged from 5 to 13 (median, 7 layers), and 80% of all the cases had a thin lining (5 to 8 cell layers in thickness). Significant inflammation was found in 45% of the cases with thin epithelial lining and in 57% of the cases with a higher number of cell layers. However, the difference was not statistically significant (P = NS). Also, there was no significant difference in the number of cell layers among the three histological subtypes (P = NS).
Three cases of Gorlin's syndrome were identified in this study. They were all in young male patients (ages, 11, 15, and 19 y, respectively) presenting with multiple cysts. Microscopic examination showed satellite microcysts and epithelial islands in the wall of these cysts. All three cases were lined by parakeratinized epithelium, and dystrophic calcification was noted in the wall in two of the cases. No recurrence was detected on follow-up of these cases (follow-up of 11 years for two patients and 1 year for one patient).
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Keratocysts are generally slightly more frequent in male than in female patients with the male-to-female ratio ranging from 1.3:1 to 2:1 in most large series. 3,6,7 The male-to-female ratio of 1.4:1 in the present study falls within the range reported in these series. Also, in keeping with keratocysts elsewhere, the peak frequency of occurrence in our patients was in the third decade of life.
Dentigerous cyst is the most common clinical misdiagnosis for keratocysts. 6,8,9 This is partly because many keratocysts are found around unerupted teeth. In our study, too, the most common misdiagnosis was dentigerous cyst, but the correct diagnosis of keratocyst was made clinically in 78% of the cases. This findings was similar to that of a Malaysian study (with 57% of the study population being Chinese patients) in which the correct diagnosis of keratocyst was made clinically in 50% of the cases. 4
Keratocysts are more common (60%–80% of cases) in the mandible, 1,3,6,8,10 and most of them are in the posterior mandible. In our series, the mandible was more commonly involved than the maxilla (62% vs. 38%), and the posterior mandible was the most common site. There was no predilection for either side of the jaws. Multiplicity occurred in 9% of the patients, similar to the range of 6% to 12% reported in other series. 3,6,12
None of the cysts from the 69 patients in the present series showed evidence of malignancy or dysplasia. The same negative finding was observed by Crowley et al., 11 who examined 449 odontogenic keratocysts. Thus the clinical importance of diagnosing keratocyst probably lies in its marked tendency to recur, rather than in the risk of malignancy. The recurrence rate of odontogenic keratocysts varies from 3% to 62%. 3 The major difference in the recurrence rate is probably related to the duration of the follow-up period, histological types, and surgical procedures. Nevertheless, it is generally agreed that keratocysts have a higher potential than other odontogenic cysts to recur, and they should be managed by more definitive surgical procedures with careful follow-up. In the present series, a recurrence rate of 20% was observed. In agreement with the findings by other authors, 10,11 recurrence occurred nearly exclusively in parakeratinized keratocysts, and more often in those showing subepithelial split and satellite cysts. In concurrence with the observation of Ahlfors et al., 6 there was a slight male predominance. In general, recurrence seldom occurs more than 10 years after the initial treatment, but a case of recurrence 41 years after the initial treatment was reported by Crowley et al. 11 In the present study, late recurrence was seen in two patients 10 and 20 years, respectively, after the initial treatment. The episodes of recurrence may represent the development of new cysts within the original operative field rather than genuine recurrences. Nevertheless, life-long follow-up of patients with keratocysts is recommended.
Keratocysts occur in a high proportion of patients with basal cell nevus syndrome; many of them are young female patients. There was an increased incidence of multiplicity and recurrence, and the cyst wall frequently showed calcification, satellite cysts, and solid islands of epithelial proliferation. 1 In the present study, all three patients with Gorlin's syndrome were young and had multiple cysts, and satellite microcysts and epithelial islands were found in the cyst wall. Dystrophic calcification was present in the cyst wall in two of the three cases. However, all three cases were in male patients, and they were free of recurrence 1 year to 11 years after the initial treatment. Similar to other series, all these cases were parakeratinized keratocysts 7; the reason for this is unknown.
In the present study, cysts in 82.6%, 5.8%, and 11.6% of the cases were parakeratinized, orthokeratinized, and of mixed type, respectively. It is difficult to compare the incidence of orthokeratinized keratocysts, because studies used various criteria to diagnose orthokeratinized cysts and the mixed types. Nevertheless, parakeratinized keratocysts accounted for the majority of keratocysts in all the reported series throughout the world, including the present one (range, 68.8%– 98.3%). 1–15 For the 2086 keratocysts reviewed from 16 series in the literature, the overall incidence of parakeratinized keratocysts was 83%. Also, in general, studies involving Chinese patients usually showed a higher proportion of cysts with orthokeratinized epithelium either in pure or mixed form when compared with Western series (Table III). The difference (20.6% vs. 16.2%) was statistically significant (P = .04). This finding supports the suggestion that this type of keratocyst may be more prevalent in Chinese. 9 The age and sex of our patients with orthokeratinized keratocysts and the site distribution of the cysts are similar to those of the parakeratinized keratocysts, which is in agreement with the findings of Crowley et al. 11 The most important difference between the various types is the low recurrence rate with the orthokeratinized and mixed types as compared with the parakeratinized type. This may be partly attributable to the absence of satellite cysts and the low frequency of epithelial islands in the wall of the orthokeratinized and the mixed types.
Table Table 3.. Summary of the Findings of Parakeratinized and Orthokeratinized Keratocysts in Various Series.
*These studies include Asian populations in addition to Chinese.
P = parakeratinized keratocysts; O + M = orthokeratinized and mixed keratocysts.
All the keratocysts in the present study showed the classic features of corrugated keratinized stratified epithelium and a prominent basal layer. There were cysts lined by squamous epithelium that was more than 10 cell layers thick, but 80% of our cysts were lined by epithelium with a thickness of 5 to 8 cell layers. The subepithelial split, which might partly have accounted for the high incidence of recurrence in keratocysts, has been reported in more than 90% of cases. 7,8 This feature was noted in 81% of our cases. Suprabasal split was found in 35.6% and 53%, respectively, in two large series 6,7 but was less commonly observed (25%) in the present study.
Satellite microcysts were found in 38% of our cases, which falls within the range of 7% to 44% as described in the literature. 1–3,6,7,13 Epithelial islands, which were closely associated with satellite microcysts, were found in 42% of our cases (range in the literature, 3%–69%). 1,2,6–8
Inflammation is generally absent in keratocysts as compared with other odontogenic cysts such as the radicular cyst. However, Haring and Van Dis 8 found inflammation in 98% of the cysts in their study, and Geng et al. 3 noted significant inflammation in 22.5%. We found significant inflammation in 46% of cases. Inflammation was more often associated with cysts lined by epithelium that was more than 8 cell layers thick, although this finding was not statistically significant. The presence of marked inflammation, which was often associated with the formation of rete pegs and loss of prominence of the basal layer, might lead to an erroneous diagnosis of radicular or residual cyst. In these situations, typical areas of keratocyst, even if present in small foci only, provide the correct diagnosis if adequate material is available for histological examination. The importance of adequate sampling in these cases cannot be overemphasized.
Histological features such as hyaline bodies and calcification were infrequently described in the literature, and their reported incidence ranged from 4.2% to 11.2% and from 3.3% to 17%, respectively. 1,3,7 The frequency of 7% for hyaline bodies and 10% for calcification in the present study lies within this range.