|Year : 2014 | Volume
| Issue : 1 | Page : 24-29
Salivary gland tumors, a twenty-year retrospective study
Uchendu Obiora Jude1, Adesuwa Noma Olu-Eddo2
1 Department of Pathology, Central Hospital, Benin City, Nigeria
2 Department of Histopathology, University of Benin Teaching Hospital, Benin City, Nigeria
|Date of Web Publication||25-Aug-2014|
Dr. Uchendu Obiora Jude
Department of Pathology and Forensic Medicine, Central Hospital, Benin City, Edo State
Source of Support: None, Conflict of Interest: None
This is a retrospective study of salivary gland tumor (SGT) specimens seen at the University of Benin Teaching Hospital (UBTH) over a 20-year period. It is aimed at determining the epidemiological pattern of these tumors. The materials for this study that consisted of available slides and paraffin-embedded blocks of all SGT specimens received during the study period were evaluated. Data on age, sex, anatomical sites and histologic diagnosis were obtained from the departmental surgical records. Data analysis was done using SPSS version 16.0. SGTs are very rare, accounting for 0.32% of specimens received in the UBTH. The female to male ratio was 1:1.3, and the ratio of benign to malignant tumors was 1.8:1. The mean ages for benign and malignant tumors were 37.0 and 43.5 years, respectively. The peak age for benign SGTs was in the 3 rd decade, while malignant tumors showed a peak in the 6 th decade. The parotid gland was most commonly affected (57%). Overall, pleomorphic adenoma was the most common SGT seen, accounting for 53.2% of all the cases. Adenoid cystic carcinoma was the most frequently encountered malignant SGT (10.1%). The epidemiological pattern of SGT in the study populace is similar to those of other African-based studies but differ slightly from those of the Caucasians.
Keywords: Retrospective, salivary, tumor
|How to cite this article:|
Jude UO, Olu-Eddo AN. Salivary gland tumors, a twenty-year retrospective study. Afr J Med Health Sci 2014;13:24-9
| Introduction|| |
The salivary glands are responsible for the production, modification and secretion of saliva, which aid mastication, deglutition, digestion and protection of teeth and soft tissues.  These are exocrine glands, organized into major bilaterally paired glands (parotid, submandibular and sublingual glands) and minor glands, located throughout the oral and the oropharyngeal mucosa. Ectopic salivary glands have also been reported commonly in the periparotid and intraparotid lymph nodes, soft tissue and other organs in the head, neck and chest region, rectum, vulva, stomach, pterygopalatine fossa and cellebellopontine angle. These glands recapitulate normal salivary glands. ,
Salivary glands often give rise to different pathologic conditions, ranging from cystic, inflammatory, tumor-like and neoplastic lesions.  Salivary gland tumors (SGT) are particularly important to the pathologist and the head and neck surgeons because of their associated morbidity and mortality, and more specially because important head and neck structures like the facial nerve transverse these glands. 
Despite the relatively simple morphology of the salivary gland, over 35 different neoplasms have been associated with them.  Considering the diverse anatomical sites and histological subtypes, it is easy to understand why otolaryngologists, head and neck surgeons, oncologists and pathologists accumulate only restricted exposure to specific types of SGTs. , Heterogeneity within the individual histological subtype also posses further diagnostic challenge to the pathologist. 
Studies have shown significant geographical variation in incidence of these tumors. It is however estimated that SGT accounts for 0.5-2% of all tumors globally  and between 3-6% and 2.8-10% of head and neck tumors in western countries and Africa, respectively. 
The earliest study of SGTs as a distinct entity in Nigeria was performed by Edington and Shelhan in Ibadan.  Since then, a few other studies have been performed across the country, mostly in Ibadan, Lagos, Enugu, Maiduguri, Ife and Jos. 
This study presents the first comprehensive study of the histological pattern of SGTs in the University of Benin Teaching Hospital (UBTH), aimed at understanding the epidemiological pattern of these tumors and to compare our findings with reports done elsewhere.
| Materials and Methods|| |
This is a 20-year retrospective study of biopsied salivary gland specimens received at the Department of Histopathology, UBTH, Benin City, Edo State, Nigeria, between January 1990 and December 2009. Cases histologically diagnosed as SGTs formed the focus of this study. These biopsies were received from the UBTH and other hospitals within Edo state and its neighboring states.
Information relevant for this study was retrieved from the surgical pathology register. Additional information where necessary was retrieved from duplicate copies of histological reports and the case notes of the patients. Corresponding slides were also retrieved and, where necessary, new sections were made from the corresponding paraffin-embedded tissue blocks. These sections were later stained with hematoxylin and eosin stains. Special stains were applied where necessary.
These SGTs were classified in accordance with the 2005 World Health Organization (WHO) Histological Classification of Salivary Gland Tumours,  and their frequency distribution was analyzed using SPSS version 16.0 (Microsoft Corporation, Chicago, 2007) and presented in tables and figures.
Cases with recurrence, unknown origin and uncertain histological diagnosis were excluded from this study. Specimens in which the corresponding slides or tissue blocks could not be retrieved were also excluded from the study.
This study was approved by the ethical clearance committee of the UBTH, Benin City (ADM/E 22A/VOL VII/296), before the work was commenced.
| Results|| |
A total of 38,000 surgical specimens were received in the Department of Pathology, UBTH, during the study period. Of these, 8500 specimens were neoplastic. SGTs accounted for 123 cases, constituting 0.32% of all surgical specimens and 1.43% of all neoplasms received. Of the 123 cases of SGTs received, 109 cases met the inclusion criteria and were used for this study.
The study shows a stable incidence of SGTs within the study period, with double peaks in 2005 and 2009. The average incidence of SGTs is 5.5 cases annually. Details of the yearly distribution of SGTs are shown in [Figure 1] and [Figure 2].
The age range of patients was 2-75 years, with a mean age of 39.34 ± 17.19 years. The mean ages for benign and malignant SGTs were 37.03 ± 15.44 and 43.50 ± 19.46 years, respectively. The peak incidence for the benign and the malignant tumors were in the 3 rd and 6 th decades, respectively. The age distribution of SGTs is shown in [Table 1] and [Figure 3].The age range and mean age of various SGTs is also shown in [Table 2].
|Figure 3: Comparison of cases of salivary gland tumors across various age groups|
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Forty-four percent of the cases occurred in males, giving an M:F ratio of 1:1.3 for all SGTs. An M:F ratio of 1:1.26 was observed for both the benign and the malignant SGTs.
The anatomical distributions of the tumors include parotid gland (57%), submandibular gland (16%) and minor salivary glands (27%). The palate, buccal mucosa, tongue, lip, retromolar mucosa and neck were the anatomical sites of the minor SGTs in this study, with the palate accounting for 79% of the cases. The benign-malignancy ratio for the parotid, minor salivary gland and the submandibular tumors were 1.3:1, 1.9:1 and 4.6:1, respectively.
Sixty-four percent of these tumors were benign, with pleomorphic adeoma accounting for 83% of them. Other benign tumors seen in this study were basal cell adenoma, adenolymphoma (Warthin's tumor), capillary hemangioma, myoepithelioma and fibrolipoma.
The most common malignant tumors in this study were adenoid cystic carcinoma, mucoepidermoid carcinoma and acinic cell carcinoma, accounting for 28.2%, 23.1% and 18% of all malignant tumors seen. Few cases of squamous cell, basal cell, salivary duct and small cell carcinomas, sialoblastoma, hemangiopericytoma, myxoid liposarcoma and polymorphous low-grade adenocarcinoma were also seen.
| Discussion|| |
In this study, SGTs accounted for 1.43% of all neoplasm seen at the histopathology unit of the UBTH. This is similar to the findings by Ochicha et al. in Kano, northern Nigeria, but lower than the 2% reported in the western population. , This difference may be explained by the poor health-seeking behaviors of our populace. Also, there may be slight variations in the geographical distributions of various neoplasms. Our findings are also remarkably lower than the report from the Canadian Eskimos where SGTs accounted for a quarter of all malignant tumors seen in their population. 
A stable incidence of SGTs was noted with peaks in 2005 and 2009. We have no explanation for these peaks. This may call for further investigations.
The age of patients seen in this study ranged from 2 to 75 years. This parallels the reports from Ochicha et al. in Kano, Nigeria (13-65 years),  Bahra et al. in Kenya (8-80 year)  and Thomas et al. in Malawi (1-75 years).  Our findings are however at variance with reports in the western literature, where SGTs occurred over a wider age group with a peak age reported in the 7 th and 8 th decades. , It can therefore be implied that there are relatively more elderly patients with SGTs in the western population. The fewer number of elderly patients seen in African studies may be ascribed to its lower life expectancy.
The peak for benign and malignant SGTs was observed in the 3 rd and 6 th decades, respectively. Similarly, Otoh et al. in Maiduguri (Nigeria),  Silas et al. in Jos (Nigeria)  and Chatterge et al. in Asia  reported a peak incidence in the 3 rd decade for benign SGTs. In Ibadan (Nigeria)  and in South Africa,  a peak incidence for benign tumors was reported in the 4 th decade. On the contrary, the peak incidence in the 5 th decade was reported among Caucasians for benign SGTs.  Abiose et al. in Ibadan (Nigeria),  Van heerden in South Africa,  Vulhulu in Uganda  and Chatterge in Asia  reported a peak for malignant tumors, a decade lower than our observation. On the contrary, studies has shown that the peak incidence for malignant tumors among Caucasians occurred in the 7 th and 8 th decades.  The mean age of presentation for benign and malignant tumors in our study were 37.03 and 49.10, respectively, which is comparable to other African reports with a mean age range of 25-45 and 45-55 years, respectively, for the benign and malignant tumors. ,, Comparatively, reports from Europe and the US show that the mean age for benign and malignant SGTs are either a decade or two later than the observations from African studies.  This difference may be attributed to our low life expectancy and probable genetic or environmental factors that are unique to the African population.
There were more females than males with SGTs in this study population, which is similar to the previous studies performed in Ibadan (Nigeria),  Enugu (Nigeria),  Uganda,  Zimbabwe,  Kenya  and the UK.  Equal gender distribution was reported in India,  Parkistan,  Brazil  and in another study in Ibadan (Nigeria),  while in Tanzania a male dominance was reported.  There was no significant association between the gender of our patients and the histological type of SGT.
Apart from the sublingual gland that was not involved, all other major salivary glands were affected. The percentage distributions were 57%, 16% and 27% and for the parotid, submandibular and minor salivary glands, respectively, giving an approximate ratio of 3.5:1:1.5. Our finding is slightly similar to the 1:1:1 ratio reported in Uganda  and the 2:1:1 ratio reported in Kano (Nigeria).  On the contrary, salivary neoplasm follows a distribution ratio of 100:10:10 in Europe and the US.  The low prevalence of sublingual tumors, as seen in this study, is similar to its general global low incidence. ,,
The incidence of parotid tumor in our report (57%) is comparable to the 60% reported by Ezeanolue et al. in Enugu (Nigeria) and Moatemri et al. in Tunisia. , Our review is however intermediate between the 32% and 49% reported in other African series and the 71% and 80% reported in Asia, South America, Europe and the US. ,,,,,,,
The palate was the most common site affected among the minor salivary glands, accounting for 21% of all SGTs and 79% of minor SGTs. This is comparable to the reports by Ochich et al. in Kano (Nigeria), Thomas et al. in Malawi and Massanja et al. in Tanzania, where palatine tumors accounted for 15%, 18.9% and 24%, respectively, of all SGTs. ,, This is however at variance with the findings in Europe where palatine tumors accounted for 3.8-7.5% of SGTs. 
Our present data show a high prevalence of benign tumors, giving an approximate benign-malignancy ratio of 2:1, which is similar to the findings in China and the UK. , This is however intermediate between the 1:1 ratio reported in Ibadan (Nigeria), Kano (Nigeria), Kenya, Tanzania and Uganda and 3-4:1 ratio reported in Zimbabwe and Pakistan. ,,,,, This may be attributed to the differences in methodologies and inclusion criteria used in the different studies.
Pleomorphic adenoma was the most common SGT in our study, accounting for 87% of all benign cases and 53.5% of all cases. This finding is consistent with its general global high incidence.  A mean age of 37.1 years was reported in our study for pleomorphic adenoma, which is similar to the mean age of 31 years reported by Odukoye et al. in Lagos (Nigeria), but about a decade lower than the mean age reported among the European population. , This difference may also be explained by the low life expectancy of the study population, which was 51.9 years as in 2011. 
It has been generally observed that Warthin's tumor is very rare in African series. ,,,,,, This is evident in our study, as only a single case was found in our 20-year audit of SGTs. However, in India, China, Europe and America, Warthin's was reported as the second most common benign SGT. ,, It has earlier been adduced that there is a strong association between cigarette smoking and the incidence of Warthin's tumor; the relatively lower rate of smoking as compared with the Asian and Western populations may partly explain this difference in incidence. 
Considering only the malignant tumors, adenoid cystic carcinoma was the most common condition in this sample (28.8%), followed by mucoepidermoid carcinoma (23%). As in our study, some reports have suggested that adenoid cystic carcinoma is the most common malignant SGT. ,,,, Other researchers have however reported that mucoepidermoid carcinoma is the most common malignant SGT. ,, However, there is no doubt in the literature that either mucoepidermoid or adenoid cystic carcinoma has remained the most common malignant SGT globally.
A changing pattern in the incidence of these two tumors was observed in our study. Mucoepidermoid carcinoma was the predominant malignant tumor in the first decade of our study, with the second malignant SGT accounted for by adenoid cystic carcinoma. A relatively sharp rise in the incidence of adenoid cystic carcinoma was observed in the second decade of this study, with adenoid cystic carcinoma becoming the most common malignant SGT. This finding of a changing pattern in the occurrence of these malignant SGTs in our environment calls for further research.
Acinic cell carcinoma was the 3 rd most common malignant SGT in this study, accounting for 6.4% of all SGTs and 18% of malignant SGTs, and having a female to male ratio of 6:1. Our finding was comparable to the report from Eveson et al., where acinic cell carcinoma showed a female predominance and accounted for 17% of malignant SGTs. 
The rarity of polymorphous low-grade adenocarcinoma, carcinosarcoma, small cell carcinoma, salivary duct carcinoma, sialoblastoma, myxoid liposarcoma, capillary hemangioma and fibrolipoma in our study is comparable to their general global low incidence. 
| Conclusion|| |
We found a mean annual incidence of SGTs of 5.5 cases. The peak incidences of benign and malignant tumors were in the 3 rd and 6 th decades, respectively. Pleomorphic adenoma and adenoid cystic carcinoma were the most common benign and malignant SGTs in our study populace.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]
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