19-year audit of benign jaw tumours and tumour-like lesions in a teaching hospital in Nairobi , Kenya

Background: The diversity of benign jaw tumours may cause difficulty in a correct diagnosis and institution of an appropriate treatment. Data on the prevalence of these tumours is scarce from the African continent. We present a 19-year audit of benign jaw tumours and tumour-like lesions at a University teaching hospital in Nairobi, Kenya. Methods: Histopathological records were retrieved and re-examined from the Department of Oral and Maxillofacial pathology, University of Nairobi from 1992 to 2011. The jaw tumours were classified according to the latest WHO classification. Results: During the 19-year audit, 4257 biopsies were processed of which 597 (14.02%) were jaw tumours within an age range of between 4 to 86 years. There was greater number of odontogenic tumours 417 (69.85%) than the bone related lesions 180 (30.15%). Of the odontogenic tumours, the epithetlial and in the bone related types, the fibro-osseous lesions were frequent. Conclusion: Ameloblastoma and ossifying fibroma were the most frequent tumours reported in this audit. The information regarding the prevalence of these tumours is scarce from the continent and can be useful in early detection and management before they cause facial deformity.


INTRODUCTION
The importance of oral and maxillofacial tumours lies in the fact that they are rare, cause disfiguring of the face necessitating subsequent reconstructive surgery [1].The skull, jaws and facial bones are not only the site of a number of unusual lesions but, also pose unique histological problems often associated with intra-oral variation in oral structure ranging from potentially malignant to pseudo-malignant features [2,3].Odontogenic tumours (OT) are exclusive to the jaws, as they are derived from epithelial and mesenchymal elements that are part of the tooth forming apparatus.There is a variance in the frequency of the various types of OT geographically [4][5][6].They account for between 1% to 30% of oral lesions [7][8][9].While there have been various studies done in some countries across the continents including Africa, there remain unanswered questions as to the frequency and incidence of some OT.[10,11].Bone related lesions (BRL) include the fibro-osseous lesions (FOLs) in addition to cherubism and aneurysmal bone cysts (ABC) in accordance with the latest classification [12].The WHO classifies the following as FOL among the non-odontogenic tumours (NOT): fibrous dysplasia (FD), Ossifying fibroma (OF) and cementosseous dysplasia (COD) [13].FOLs are a group of poorly defined lesions with more than 70% affecting the head and neck region [14].Wakiaga et al. in 1997 have documented a Kenyan series while, Kamulega and Boniface in 2008 presented a combined series in from Tanzania and Uganda [15,16].
The purpose of the present study was to conduct a 19-year audit of benign tumours of the jaws diagnosed at a teaching University teaching hospital in Kenya.cluding age at initial presentation, gender, site of lesion where specified and the histopathological diagnosis.The case definition in this study was any benign tumour/tumour-like lesion diagnosed for the first time in this centre.Recurrent tumours and tumour-like lesions with a previously diagnosed primary site were excluded.Benign tumours were coded according to the WHO classification [12].Since, throughout the years, many of the cases presented late with extensive lesions it was difficult to delineate the exact site of affliction by some these lesions.Parameters of interest were analysed with SPSS version 12.0.1.

RESULTS
During the 19-year-period there were 4257 biopsies processed among which 597 (14.02%) were diagnosed as tumours of the jaw bones with an equal gender predilection.There was a greater number of OT 417 (69.85%) than BRLs 180 (30.15%).The M: F ratio of OT was 1:1 while, that of the BRL 1:1.6.The age range of cases was from 4 -86 years (mean = 25.4 yrs), with the majority (76.5%) having been between 10 to 39 years of age.There were remarkably very few patients presenting with these lesions below the age of 9 and above the age of 70 years (Figure 1).

Odontogenic Tumours
The age range of the OT was between 5 -85 years (mean = 24.1)with equal gender distribution.The most commonly affected age was between 11 -50 years, and surprising with hardly any patients in the less than 10 and above the 50 year age group (Figure 2).Among the OTs those arising from the epithelial (58%) component were the most common whilst those from the mesoderm and mixed type consisted of only 6%.The ameloblastoma was the most frequent epithelial OT (45.9%), followed by the keratocystic odontogenic tumour (KCOT) at 11.2%.Other tumours included 0.8% calcifying epithelial odontogenic tumour (CEOT) and 0.2% adenomatoid odontogenic tumour (AOT).There were two types mesodermal OTs recorded: the myxoma (4.9%) presenting at an average age of 25.6 yrs and the cementoma (1.2%) at 47.1 yrs.The mixed OTs had the lowest of frequency of between 0.2% -2.7% (Table 1).

OPEN ACCESS
lence was equal in FD, with female predominance noted in both COD and OF.The mean age (51.9 yrs) of those with COD was much higher than the rest of the BRL while that of the ABC was the lowest 21.6yrs.Both FD and OSF presented over a wide age range (4 -72 yrs) compared to other BRLs (Table 2).

Odontogenic Tumours
OT have a specific histological structure reflecting various stages of odontogenesis and are located mainly in the jaws, they are however infrequent in gnathic bones and must be considered in the differential diagnosis of bony lesions in the jaws [16,17].The reported relative frequency of OT is generally low: India (4.13%), Asia (2.14%), S. America (1.82%), N America (1.55%) Euro-pean (0.74%), the highest values being in Africa (Nigeria) (9.6% -19%).Not surprisingly, a value of 14.2% for this study is well within the high range.Clearly there is variation seen in the geographically distribution of OT [4,9,15,[18][19][20][21][22].OT were most frequent in the 1 st to the 4 th decade in this study which is almost similar to previous reports [8,15,23].Female preponderance has been seen in Michigan and in Hongkong while males were more in China, Brazil and Nigeria [15,20,24,25].However, there was equal gender distribution in this group as also documented by others [8,9,[26][27][28].
Ameloblastoma was the most common OT which is in agreement with other reports from Africa, Hong Kong, China, Jamaica, Brazil, Turkey and India [10,11,14,15,18,27,[29][30][31][32][33].This is in contrast to studies from US, Canada, Mexico, Chile, Jordan and Estonia where odontoma is the most prevalent [19,20,22,26,[34][35][36][37].Simon et al. had equal gender distribution, similar to our finding while, some had a male prevalence and others a female [7,8,10,15,26,28,32,33,38,39].Ameloblastoma presents more in the 3 rd -5 th decades of life with a peak incidence in the 3 rd decade: Mullapudi documented a younger age group which was similar to Reichart who stated that ameloblastoma occur in a younger age group in the developing countries [12,33].The mean and age range was the same as in some reports, although higher than documented by Stypulkowska and Parkin et al. [10,15,16,29,33,40].The greater percentage of ameloblastoma could be due to to referral patterns and late presentation in Africa [8,41].It is not surprising that Sweden reports an incidence as low as 0.3 per million per year [42].
The second most common tumour in this study was KCOT followed by myxoma, which is different from the findings of Simon et al. who reported the myxoma as the most prevalent after ameloblastoma [10].The gender distribution was equal although Stoelinga reported a male predominance [43].The WHO has recently classified calcifying odontogenic cyst (COC) a benign cystic neoplasm of odontogenic origin, similarly, the odontogenic keratocyst has been redesignated as KCOT due to the aggressive behaviour, histology and genetics [44,45].KCOT has been known to occur in patients over a wide age range of between 7 to 93 years with a peak in the third decade [46].Our age range comparatively was narrower and the mean a decade younger.
Myxoma was the third most common in this population representing a 4.90% of the OT.When the 1992 classification was used, this lesion accounted for 8% of all OTs in a study done by Avelar et al., to determine the world incidence of OT and this was in agreement with several studies showing a wide variation in the prevalence of this tumour (4.7% to 17.7%) [8,20,25,31,35].It shows a lower distribution in Asia with a higher trend in America, Africa and Europe [15,18,34].There were almost twice as many females as males similar to other reports from Nigeria, Brazil, Turkey and Chile [19,21,25,31].It typically occurs between the 2 nd and 4 th decades, however, there was a wider age range in this series although the mean age was 25.6 yrs [47,48].
Odontoma, a hamartomatous malformation was the next common with an equal gender distribution this was in contrast to observation by others who had a slight male predominance [4,22,34,31].They are usually diagnosed in the second decade of life, the average age in this series was 16.5 years.They have been reported as the commonest lesions by Scholl et al.Buchner et al. and Mosqueda-Taylor et al. which is in contrast to our results [34,36,48].Odontoma is a rare lesion in the Africa region, probably because it is asymptomatic and patients rarely seek medical treatment.It is most likely for the ones that are excised would not be sent for histopathology (due to cost) which may explain the reason for the under reporting.
The AOT is more common in females than males (1.9:1).It represents approximately 3% of OT and appears between the ages of 5 and 30 years.Pogrel and Schmidt 2006 and Ladeinde et al. found AOT as second most frequent OT after ameloblastoma in contrast to other studies in Africa.[8,9,25,49].There was only one female in this series with AOT.Simon et al., who reported very low frequency (0.9% -2.6%) of odontoma, CEOT, cementoblastoma, ameloblastic fibroma, COC and AOT [10].Ladeinde too reported low frequency of CEOT, exclusive to females, confirming the rarity of these tumours [15,19,36].In our population the number of patients with AOT, CEOC, myxofibroma, CCOT and amelofibrodontoma were few.

Bone Related Lesions
The epidemiology of OF and COD is unclear due to the confusion between the two lesions.OF is known to occur over a wide age range, it presents mostly in 3 rd and 4 th decades of life, with a female predilection.There were more females in our series and our age followed the same pattern.OF are believed to be confined to the jaws and craniofacial complex [50,51].
In our study the most common FOL was OF, FD followed by COD.FD of the monostotic type is most common accounting for up to 80% -85% of all cases with the jaws being the most commonly affected sites.It is mostly diagnosed during the 2 nd decade of life with an equal M:F predilection [51].There was equal gender distribution, although the age range was wide the mean was in the second decade as in the previous report.[49].COD occurs in tooth bearing areas of the jaws and is probably the most common FOL encountered in clinical practise.The fewer cases of COD in this data could be due to their asymptomatic nature, they are an incidental finding and rarely subject to a biopsy.It is predominant in the 4 th to 5 th decade, there was only one male diagnosed with COD the rest were females presenting at an average age in the 5 th decade [52].
GCG of the jaws are most often found in children and young adults, with up to 75% of cases occurring before 30 years of age.Females are affected twice as frequently as males.ABCs of the jaws are uncommon and the mean age of presentation is 20 yrs with a female predilection, this was identical to our data [49].The majority (60%) of GCG of the jaws occur before the age of 30 yrs, its presentation in this study had a mean age of 21.6yrs and a limited age range unlike that reported [51].The number of cases of both GCG and ABC are too few to make any comparisons, although the M:F ≈ 1, the patients pre-sented below the age of 40 years and mean age was similar that reported.

Figure 3 .
Figure 3. Shows the gender distribution and frequency BRLs.

Table 1 .
Illustrates the frequency, age range/mean and gender distribution of the OT.

Table 2 .
Show the age range, mean and standard deviation of BRLs.