Histopathologic patterns of intracranial neoplasms at Lagos University Teaching Hospital, Nigeria. A ten-year hospital-based retrospective study

Background The most common intracranial neoplasm worldwide is meningioma, followed by gliomas, and then pituitary adenomas. There are geographical differences in the pattern of occurrence of intracranial neoplasms. The purpose of this study is to establish the pattern of occurrence of different histological types of intracranial neoplasms with their age and sex distributions in our environment – Lagos, Nigeria. The histological patterns, age, and gender distributions of all the intracranial neoplasms diagnosed within the study period at the Department of Anatomic and Molecular Pathology, LUTH, Lagos, Nigeria were noted and analysed with SPSS version 23. Result There were 296 patients (165 females, 131 males; mean age of 37.0 years) diagnosed with an intracranial neoplasm within the study period. The most frequently diagnosed intracranial neoplasm was meningioma (105 cases; 35%, median age of 42 years, male to female ratio of 1:2.2), followed by pituitary adenoma (78 cases; 26%, median age of 47 years, male to female ratio of 1.3:1), and then gliomas (71 cases; 24%, median age of 28, male to female ratio of 1:1.39). Conclusion The result of the study shows pituitary adenoma to be more common than gliomas, unlike what is seen in Caucasians where the reverse is the case.


Introduction
Tumors of the central nervous system account for 1-2% of tumors in adults worldwide. 1 An intracranial tumor/ neoplasm (ICT/ICN), also colloquially known as a brain tumor, may arise from the brain or its covering structures (primary intracranial tumor) or may be a metastasis from another organ (metastatic intracranial tumor). Awodele et al., in a study based on the Lagos and Ibadan Cancer reg-istries in Nigeria, between 2005 and 2009, reported that brain tumors constitute 3.9% of all cancer types. 2 Over 150 different brain tumors have been documented and they have distinct diagnostic histological features, some with distinct molecular/cytogenetic characteristics while some are common in certain gender or age groups. 3 There are many prognostic factors that influence the clinical outcomes of patients with intracranial tumors. Some of the prognostic factors include tumor's histological grade and biologic behaviour, the patient's age at diagnosis (young patients have better prognosis), and tumor location (tumors with pressure effect on vital structures pose poorer prognosis). 4 The most common intracranial neoplasm worldwide is meningioma, followed by gliomas, most especially astrocytic tumors, and then pituitary adenoma. 1,3 There are geographical differences in the pattern of occurrence of intracranial neoplasm and increasing incidence of primary brain tumors worldwide in recent decades. 5 The global pattern of intracranial tumors is as shown in Table 1, and it depicts meningioma and glioma as the two commonest ICT and pituitary adenoma as the 3rd most common ICT globally. [6][7][8][9][10][11][12][13][14][15][16]  Few studies have been conducted in Nigeria to demonstrate the pattern of occurrence, age, and sex distributions of these intracranial neoplasms. The result of most of these studies carried out in Nigeria still showed meningioma as the commonest ICT. However, most of these studies showed that pituitary adenoma is rather the second most common ICT in Nigeria, (see Table 2). [17][18][19][20][21][22][23]  Patients' data were retrieved from the archives of the Department of Anatomic and Molecular Pathology, LUTH, Idi-Araba, Lagos. Histological patterns of these intracra-nial tumors, with their grade, age and gender distribution were retrieved and recorded for analysis. Cytological smears (squash cytology) and immunohistochemistry were not carried out on these samples. Due to the old manual recording system of the medical record of the hospital, the exact locations of some of these intracranial tumors could not be obtained. The data obtained was analysed with SPSS version 23. Due to unavailability of facilities for appropriate molecular studies in our centre, diffuse astrocytoma, anaplastic astrocytoma, glioblastoma and oligodendroglioma were regarded as "not otherwise specified" (NOS), according to the 2016 WHO classification of intracranial tumors guidelines.

Result
Two hundred and ninety-six patients (165 females, 131 males) were diagnosed with intracranial neoplasm/tumor (ICT) within the study period at the department (Table 3). Intracranial neoplasms constituted 1.06% of the total biopsies received at LUTH from 1st of January, 2008 to 31st of December, 2017, with a male to female ratio of 2:3 (Table 3). Overall, the department saw the highest number ICT diagnosis in 2017 (51 cases, 17% of the total 296 cases), while 2014 had the lowest number of diagnosed cases (10 cases, 3% of the total 296 cases) ( Figure 1).
Majority of the patients with intracranial neoplasm were between 41-50 years of age (23.6% of the total intracranial neoplasm) ( Table 1). The median age of ICTs was 40.50 years (IQR=30.3), while the mean age of ICTs was 37.0 years (Table 3). Primary ICTs accounted for 98.3% (291cases) of the total ICTs, whereas metastatic ICTs accounted for 1.7% (5 cases, 4 metastatic carcinoma and one metastatic osteo-sarcoma) of the total ICTs ( Figure 2). The median age of patients with histology confirmed metastatic ICTs was 39 years (Table 4).   Lymphomas and tumors of the pineal gland were the least diagnosed intracranial neoplasms. There was one case of pineal gland tumor and one case of lymphoma diagnosed in patients aged 3 years and 74 years respectively ( Figure 2). Amongst the gliomas, pilocytic astrocytoma (22 cases, median age of 7.5 years, male to female ratio of 1:1) and glioblastoma NOS (22 cases, median age of 56.5years, male to female ratio of 4:7) were the most frequently diagnosed. Oligodendroglioma (1 case, 26 years, female) was the least diagnosed glioma (Tables 6).  Majority (88.3%) of all the intracranial tumors diagnosed within the study period were supratentorial. However, among children less than 20 years of age diagnosed with ICT within the study period, majority (61.3%) had the tumor infratentorially located, whereas only 5.3% of the intracranial tumors diagnosed in adults were infratentorially located. The sellar/suprasellar region was the commonest location among the supratentorial tumors diagnosed in children less than 20 years of age, with pilocytic astrocytoma (2 cases), craniopharyngioma (2 cases), pleomorphic xanthoastrocytoma (1 case) and meningioma (1 case) being the diagnosis. (Table 8). Most of the meningioma cases diagnosed within the study period occurred at the frontal lobe (eleven cases). This is followed by the olfactory groove and sphenoidal wing (eight meningioma cases occurred in each of these locations), then the parafalcine region (six meningioma cases occurred in this location). The cerebellum is the least common area where meningioma occurred, with only one case of meningioma reported in this location (Table 8) Most of the diffuse astrocytoma occurred at the frontal lobe, while anaplastic astrocytoma cases were mostly located at the tempoparietal region. Glioblastoma (NOS) cases occurred mostly in the temporal lobe followed by the frontal lobe. (Table 8). The cases of Pilocytic astrocytoma, medulloblastoma, and ependymoma diagnosed within the study period were mostly located within theosterior cranial fossa. (Table 8) The commonest suprasellar mass was pituitary adenoma (76 cases). This was followed by craniopharyngioma (13 cases). (Table 8). The most diagnosed tumor of the cranial nerve was schwannoma (3 cases) and all of them were located at the cerebellopontine angle. (Table 8)

Discussion
From this study, except for a drop in the number of ICTs diagnosed in the year-2014, there was an increment in the frequency of diagnosis of intracranial tumors at LUTH during the decade studied. The reduction in the number of diagnosed intracranial tumors at LUTH in 2014 can be explained by the protracted strike action by the local resident doctors and the Ebola disease epidemic in Lagos, Nigeria that occurred in Lagos, between June and August, 2014. The increasing frequency of diagnosis of ICTs in our environment (Lagos, Nigeria) over the years can be attributed to the increase in diagnostic expertise and the availability and increased use of neuroimaging studies including CT and MRI scans. More so, the increasing public awareness of brain tumors and an increasing life expectancy in Nigeria may have contributed to the rising number of diagnosed ICTs in Nigeria.
The result of this index study, like many other studies done in Nigeria and across the globe, shows that the commonest intracranial neoplasm is meningioma.. 1,3,8,9,10,15,19,21,23 However, unlike studies done outside Africa, where gliomas ranked second in incidence tomeningiomas, pituitary adenomas was the second most frequent ICT in the index study. 8,9,10,15 (Table 2) This is in contrast with the global reports, especially from the Western world and Asia, in that both meningioma and gliomas remain relatively more common than pituitary adenomas (Table1). [6][7][8][9][10][11][12][13][14][15][16] Potential etiological factors to explain this geographical difference, including genetic predisposition, infectious agents, radiation, etc., requires investigation. 5 The discrepancy in the pattern of occurrence of ICTs in Nigeria when compared with Caucasians may also be attributed to the poor availability of quality health services and poor health seeking behaviour of its citizens, as most people in Nigeria seek for treatment only when there are complications. However, based on evidence from epidemiological research work, some authors have advised cautious interpretation of geographical variations in occurrence of intracranial tumors, since unlike other neoplasms, the criteria and registration of brain tumors is not always consistent. 5 Our study showed that pilocytic astrocytoma (WHO  23 This study also shows that lymphomas and tumors of the cranial nerves including schwannoma are uncommon in our environment unlike other parts of the world. 8,9,12,13,15 Similar observation was made by Ndubuisi et al. 21 Result of most studies, including those done in Nigeria and globally, showed equal rate of occurrence of intracranial tumors in both genders or a slight male preponderance; many reported a male to female ratio of 1:1. 6,7,14,18,19,20,21,22 However, our study showed a slight female preponderance in the rate of occurrence of intracranial tumors with male to female ratio of 1:1.3. More so, most studies, including the index one, showed a rather increased frequency of occurrence of meningioma in females. 6 17 Additionally, Ohaegbulam et al. reported one case of parasellar juvenile astrocytoma, whereas three cases of juvenile astrocytoma (two pilocytic astrocytoma and one pleomorphic xanthoastrocytoma) were reported here. 17 Despite the limitations that exist in the accurate collation of epidemiological data on intracranial tumors in Nigeria, the similarity of the pattern of occurrence of intracranial tumors in various part of Nigeria points to the possibility of a genetic or environmental undertone to its etiology.
The result of the study is similar to other studies done in Nigeria that showed a higher frequency of occurrence of meningioma and pituitary adenoma when compared to gliomas. This is however different from studies done in Caucasians which showed a higher frequency of occurrence of gliomas when compared to pituitary adenoma. This shows that though the rate of occurrence of intracranial neoplasm in our environment, Lagos, Nigeria, is similar to the rate of occurrence worldwide, the pattern of occurrence of different histological types of intracranial neoplasms is different.