A.Meningiomas

Meningiomas are the most common brain tumors in adults accounts about 36% of all brain tumors in the central brain tumor registry of the united states (CBTRUS). In 2015 CBTRUS estimates that there will be approximately 24,000 new meningiomas diagnosed in the united states [37]. The incidence of meningioma steadily increases with age being twice as common in women as in men and 20% more common in blacks than in whites. A majority of meningiomas are benign (grade I), with 5–20% atypical (grade II) and 1–3% malignant in type (grade III) [38, 39].

Although benign meningiomas are a minor cause of death, skull-based tumors can cause considerable morbidity. Atypical and malignant meningiomas, on the other hand, are linked to high rates of recurrence and substantial morbidity and death [40, 41]. Meningioma is shown in **Figure 2**. Because telomerase activity is detected in all anaplastic/malignant (WHO grade III)

#### **Figure 1.**

*CNS tumor epidemiology -the incidence of brain tssumor in different regions of brain.*

and the majority of atypical (WHO grade II) meningiomas, there is a link between telomerase activity and tumor grading in meningiomas [42, 43].

B. Glioma

Glioma is the second most common brain tumor in adults. In 2015 the CBTRUS estimates approximately 20,000 newly diagnosed gliomas in the united states. Approximately one-half of gliomas is glioblastoma, the commonest malignant primary brain tumor in adults. Glioma occurs almost in all four lobes in the brain: frontal (23.6%), temporal (17.4%), parietal (10.6%), occipital (2.8%), a small percentage in the brain stem, cerebellum and spinal cord [20].

Glioma is shown in **Figure 3.** Secondary glioblastomas are considered to develop as a result of progression from pre-existing astrocytomas, thus this finding is fascinating [44].

C. Pituitary tumor

The third most common brain tumor in adults is the pituitary tumor and it accounts for 15%. A majority of brain tumors are benign adenomas [45]. Even people who do not produce hormones might have symptoms as a result of the intracranial mass effect. Hormones that control normal pituitary function, as well as growth factors implicated in normal fetal pituitary development, appear to stimulate tumor growth [46, 47]. Pituitary tumor is shown in **Figure 4**.

D.Pediatric brain tumor

CNS tumors in children are the second most frequent malignancy in children and the most common solid tumor in children. According to CBTRUS, about 2000 children in the United States are diagnosed with a brain tumor before the age of 14. The most frequent solid tumor in babies and toddlers is a brain tumor. More than 8% of children and adolescent cancers are caused by genetic predisposition syndromes, and this percentage is anticipated to climb as research continues [3].

**Figure 3.** *Glioma.*

**Figure 4.** *Pituitary tumor.*

Non–posterior fossa embryonal tumors, also known as CNS-primitive neuroectodermal tumors (PNETs), are a kind of uncommon juvenile brain tumor that accounts for less than 3% of all cases and has a dismal prognosis [46]. All CNS embryonal tumors are very malignant and are classified as WHO grade IV tumors by the World Health Organization. Many tumors classified as supratentorial embryonal tumors histologically cluster with other tumor types, such as high-grade gliomas and ependymomas, according to molecular studies; this has major therapeutic implications in terms of the amount of radiotherapy required for tumor control and the choice of adjuvant chemotherapy or biologic therapy [47, 48].
