Glioma

With approximately 12,500 deaths and 20,500 new cases every year in the United States, gliomas are the most common primary tumors of the brain [1] [2]. Although numerous risk factors of various origins have been proposed (such as viral infections by varicella zoster virus - VZV and cytomegalovirus - CMV, genetic predisposition, nonionizing radiation from cellular phones, etc.), occupational exposure to pesticides or organic solvents and ionizing radiation have the strongest association with the development of gliomas [1] [2] [3] [4]. These tumors are encountered in two age groups - In the first decade of life (0-8 years) and in late adulthood/the elderly (50-70 years of age) [1]. The clinical presentation can vary widely depending on the tumor location, but the two main symptoms are convulsions and a decrease in cognitive function [5]. In addition, memory and speech deficits, gait disturbances, headaches, nausea, vomiting, visual and/or auditory impairment, as well as personality changes are all mentioned in the literature as possible symptoms of gliomas [1] [6]. Furthermore, tumors originating from the brainstem produce an array of clinical signs, including cranial nerve palsies (predominantly of the V, VI, and VIII) and pyramidal weakness [4]. Progression of symptoms can be either slow or rapid, depending on the subtype. An early diagnosis is mandatory in either case, however, survival rates for gliomas diagnosed in the most advanced stages rarely exceed 1 year [6].

Having in mind the very poor prognosis of late-stage gliomas, all patients with the undisclosed central nervous system (CNS)-related symptoms must be evaluated in a thorough manner. Firstly, the course of symptoms should be noted during history taking, whereas a meticulous physical examination, with an emphasis on the neurological exam and cognitive assessment, can provide vital clues about the location of the lesion. Imaging studies are the cornerstone of diagnosing gliomas. Magnetic resonance imaging (MRI), sometimes supported by magnetic resonance spectroscopy (MRS), is the modality of choice in identifying the exact site of the tumor and in determining the extent of tissue and nodal invasion [1] [4]. To confirm the diagnosis, however, a biopsy and a histopathological examination are necessary, which aids in classifying tumor into one of its three main categories [1] [2] [3] [5] [6]:

• Astrocytomas - Encompassing about 80% of all gliomas, astrocytomas are diagnosed either as low-grade tumors of limited proliferative capacities (stage I), or as highly malignant lesions (well-differentiated, anaplastic, and glioblastoma multiforme are terms used to describe stages II, III and IV, respectively) [1] [3] [6]. The two main forms are diffuse (malignant) and pilocytic (more often benign), and the distinguishing feature of astrocytomas on pathohistological examinations is the positive staining for glial fibrillary acidic protein (GFAP) on immunohistochemistry [1] [6].
• Oligodendrogliomas - Contrary to astrocytomas, oligodendrogliomas are principally benign tumors arising in the frontal lobes of the cerebral cortex. This tumor, based on its histological characteristics, is classified into stage II, but more severe anaplastic forms (stage III) carry a somewhat poorer prognosis, although the outcome is much better compared to astrocytomas [1] [6].
• Ependymomas - These tumors are very rarely encountered and comprise about 5-10% of all gliomas, developing in close proximity of the fourth ventricle in the majority of case.

1. Gladson CL, Prayson RA, Liu W (Michael). The Pathobiology of Glioma Tumors. Annual review of pathology. 2010;5:33-50.
2. Schwartzbaum JA, Fisher JL, Aldape KD, Wrensch M. Epidemiology and molecular pathology of glioma. Nat Clin Pract Neurol. 2006;2(9):494-503.
3. Ostrom QT, Bauchet L, Davis FG, et al. The epidemiology of glioma in adults: a “state of the science” review. Neuro-Oncology. 2014;16(7):896-913.
4. Reyes-Botero G, Mokhtari K, Martin-Duverneuil N, Delattre J-Y, Laigle-Donadey F. Adult Brainstem Gliomas. Oncologist. 2012;17(3):388-397.
5. Posti JP, Bori M, Kauko T, et al. Presenting symptoms of glioma in adults. Acta Neurol Scand. 2015 Feb;131(2):88-93.
6. Aster, JC, Abbas, AK, Robbins, SL, Kumar, V. Robbins basic pathology. Ninth edition. Philadelphia, PA: Elsevier Saunders; 2013.