Year : 2009 | Volume
: 52 | Issue : 4 | Page : 473--476
A histopathologic study of salivary gland tumors in Kano, northern Nigeria
Ochicha Ochicha, Sani Malami, Aminu Mohammed, Akinfenwa Atanda
Department of Pathology, Bayero University / Aminu Kano Teaching Hospital, Kano, Nigeria
Pathology Department, Aminu Kano Teaching Hospital, PMB 3452 Kano
Significant differences in the global distribution of salivary gland tumors have been reported, but no formal study has been carried out here in Kano, the largest city in northern Nigeria. We therefore undertook this eight-year retrospective study of all histologically diagnosed salivary neoplasms at the histopathology laboratory of our referral teaching hospital in Kano. Seventy-eight salivary gland tumors were diagnosed during the eight-year study period accounting for 0.4% of all neoplasms. Benign tumors were more prevalent, comprising 56.4%, while malignancies were 43.6%. Pleomorphic adenoma and mucoepidermoid carcinoma were the commonest histological types constituting 48.7% and 23.1% respectively, while the most frequent sites were parotid, submandibular and minor salivary glands accounting for 49%, 26% and 24% respectively. As in most studies of black populations there were no adenolymphomas. Age distribution was bimodal with a benign peak in the third decade and a malignant peak in the sixth. Our findings were broadly similar to most other African reports but somewhat at variance with Western literature. Improved hospital attendance with more comprehensive reporting would yield more representative data.
|How to cite this article:|
Ochicha O, Malami S, Mohammed A, Atanda A. A histopathologic study of salivary gland tumors in Kano, northern Nigeria.Indian J Pathol Microbiol 2009;52:473-476
|How to cite this URL:|
Ochicha O, Malami S, Mohammed A, Atanda A. A histopathologic study of salivary gland tumors in Kano, northern Nigeria. Indian J Pathol Microbiol [serial online] 2009 [cited 2022 Dec 9 ];52:473-476
Available from: https://www.ijpmonline.org/text.asp?2009/52/4/473/56121
Accounting for less than 2% of all human neoplasms, salivary gland tumors are relatively uncommon. , Their clinical importance, however, far outweighs their relatively low frequency, due to their confounding histological and behavioral diversity as well as their proximity to important head / neck structures that pose considerable clinical management challenges. 
Although a variety of etiological factors (radiation, race, smoking, chronic sialadenitis, diet etc) have been implicated in some salivary tumors, most salivary gland neoplasms are idiopathic making it difficult to explain the striking epidemiological differences in their global distribution. ,,,, Parotid tumors, for instance, account for a much lower fraction of salivary gland neoplasms in African series than in Western studies. ,,,,,,,, Warthin's tumor, said to be the second commonest salivary gland tumor in the Western world, is conspicuously absent in most African reports. ,,,
Even here in Africa, there appear to be considerable epidemiological differences in different parts of the continent.  The proportion of malignant tumors in the salivary gland varies from as low as 16.7% in Senegal to as much as 46% in Uganda. ,,
This apparent variable distribution of salivary gland tumors in Africa makes it imperative for us to evaluate the pattern in our locality, as data from other parts of the continent obviously does not reflect the actual picture. Furthermore, the paucity of data on this group of neoplasms in northern Nigeria makes this retrospective review even more relevant. This paper therefore endeavors to document the pattern of salivary neoplasms in Kano, the most populous state in northern Nigeria.
Materials and Methods
This is an eight-year (2000-07) retrospective study of all salivary gland tumor biopsies received at our referral teaching hospital in Kano, northern Nigeria. The teaching hospital is the major tertiary health institution offering histopathology services to the entire Kano state as well as the neighboring states of Jigawa, Katsina, with occasional specimens from Gombe and Bauchi. All of which have a combined population of over 23 million (2006 census).
Biodata (age, sex, site) were obtained from laboratory records derived from information provided on histology request forms.
All biopsy specimens were fixed in 10% formol saline, then processed into paraffin-embedded sections and stained with hematoxylin and eosin. Specials stains (e.g. for mucin) were occasionally employed. Immunohistochemistry was not employed, as this diagnostic technique is not available in our laboratory. All histology slides were reviewed by the authors, and classified according to the World Health Organization (WHO) histological typing of tumors (2005). 
Seventy-eight salivary gland neoplasms were diagnosed between January 2000 and December 2007 comprising 0.4% of all histologically diagnosed neoplasms. Their ages ranged from 13 to 63 years, with an overall slight female preponderance (F>M 1.1:1). Female preponderance was somewhat more marked among malignancies (F>M = 1.3:1), while benign tumors were equally prevalent in both sexes. All cases were unilateral with no dominance of either side.
[Table 1] shows the histological types, relative frequencies and site distribution of salivary gland neoplasms in Kano. Benign tumors were more common (56.4%) with pleomorphic adenoma as the most frequent (48.7%) salivary neoplasm, followed by mucoepidermoid carcinoma (23.1%), which was the commonest malignancy. Pleomorphic adenoma was slightly more common among males, while mucoepidermoid carcinoma exhibited marked female preponderance (F>M = 2:1). Polymorphous low-grade carcinoma only occurred in minor salivary glands. Significantly, there was no Warthin's tumor.
Parotid gland was the commonest site for most salivary neoplasms accounting for nearly half (49%) of all cases. The submandibular and minor salivary glands respectively comprised 26% and 24%, with the palate as the commonest site (12 cases) of minor salivary tumors.
[Table 2] shows the age distribution of the salivary gland neoplasms and [Table 2] illustrates its bimodal age distribution. The first peak mostly composed of benign tumors was in the second decade, while the second mostly malignant peak was in the sixth. Half of all salivary neoplasms occurred between the second and fourth decades. Pleomorphic adenoma most frequently occurred in the second to fourth decade while mucoepidermoid peaked in the sixth decade.
[Figure 1]a, b and c are photomicrographs of acinic cell carcinoma, adenoid cystic carcinoma and polymorphic low-grade adenocarcinoma respectively.
In this study, salivary gland tumors constituted a meager 0.4% of all neoplasms, which is much smaller than 2% of tumors in the Western world. , Under-reporting of the much more prevalent benign salivary tumors is the most likely reason for this relatively low frequency in our review. Here, in poverty stricken northern Nigeria, where there is no comprehensive healthcare coverage, many patients with non-life-threatening, low-morbidity conditions such as benign salivary tumors don't bother with orthodox medical care they can ill afford. Consequently, in this review, as in several other African studies, benign tumors were under-represented, and malignancies accounted for a relatively larger proportion (44%) of salivary gland neoplasms in contrast to ≤20% in the developed Western world. ,,,,,, Accordingly, in Uganda and Tanzania malignancies accounted for 46% of salivary neoplasms. , However Ouoba et al. (1998)  in Senegal, documented lower frequency of salivary malignancies (16.7%), albeit with a paltry sample size (48 cases) of uncertain statistical significance. In the Middle East, Eastern Europe and Far East the proportion of malignancies was intermediate between African and Western studies, ranging from 26-32%. ,,,
Parotid, submandibular and palatal minor salivary glands were the most commonly involved sites in this series accounting for 49%, 26% and 24% respectively. This predominance of parotid tumors relative to other salivary glands is also evident in other published reports although the magnitude of parotid dominance varies markedly. In the Western world, parotid tumors were overwhelmingly preponderant comprising 70-86%, thus outnumbering all other salivary gland tumors together. On the other hand African series only show modest prominence of parotid tumors relative to other salivary glands. ,,,,,,,,, Thus in Congo parotid tumors accounted for 36.6%, Uganda 34%, Lagos - Nigeria 32.1%. ,,
Again, the tendency of African studies to under-report low-morbidity, benign salivary neoplasms, which most commonly occur in the parotid, partly explains our lesser parotid prominence. Non-parotid salivary tumors often in the oral cavity are more likely to be malignant, but even when benign have higher morbidity as they interfere with ingestion and cause oral discomfort; hence are more likely to present in the hospital and be reported in African series.
El-Ghazayerli and Abdel-Aziz  postulated that malnutrition and infection-induced parotid disease prevalent in several developing countries diminishes the risk of parotid neoplasms, and thus may explain the reported disparity in the relative prevalence of parotid tumors between the Third world and the West.
Pleomorphic adenoma was overwhelmingly the commonest tumor in this study constituting 48.7% of all salivary neoplasms, which is comparable to 44.3% in Maiduguri, a neighboring northern Nigerian city and 44.4% in Tanzania. , This is slightly lower than in Europe and America where pleomorphic adenoma comprised over half of all salivary neoplasms. ,, As the most prevalent benign neoplasm in this study, mixed tumor comprised 87% of benign salivary tumors. The prominence of pleomorphic adenoma among benign salivary tumors in this series was accentuated by the conspicuous absence of Warthin's tumor - the second most frequent benign tumor in Western and Asian reports ,,,, presumably because of racial genetics, as adenolymphoma is also rare among blacks in the USA. 
In accordance with most other studies, ,,,, mucoepidermoid carcinoma (MEC) was the most prevalent salivary malignancy constituting 22% of all salivary tumors, which is much higher than the 10-15% documented in the Western literature. , The relatively higher proportion of MEC in this and several African series has already been ascribed to the higher proportion of malignancies in African studies.
Age distribution of salivary neoplasms in this study was bimodal with a higher peak mostly composed of benign tumors in the third decade and a mostly malignant peak in the sixth decade. This is comparable to the Masanja et al.  report from Tanzania, in which salivary neoplasms peaked between the third to fifth decades.  In Uganda and South Africa, salivary malignancies also peaked in the fifth decades, although their benign peak was slightly later (fourth decade) than in this review (third decade). , In general the age profile of these African studies was much younger than the Western literature where benign lesions appeared in the fifth to seventh decade and malignancies a decade or two later among the elderly. ,
While the earlier malignant peak and the relative absence of salivary tumors among the elderly in the African series may be partly explained by our shorter lifespan, the prominent peak among youths in the third decade is more difficult to explain. Yet to be identified environmental factors rather than race may be responsible, as Brazil a tropical country with a majority Caucasian/non-Negroid population also reports a third decade peak of benign salivary tumors. 
Although poor hospital attendance by the impoverished, poorly educated populace somewhat skews the observed pattern of salivary neoplasms in this hospital-based study, our findings were broadly in conformity with most African reports but differed significantly from the Western world.
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