Brain Tumors: Meningiomas and Gliomas

Brain Tumors


Meningiomas and Gliomas



Primary brain tumors are tumors that arise from brain tissue itself as compared with metastatic tumors, whereby tumor cells travel to the brain from a distant site. This chapter deals specifically with primary brain tumors of adults, using the subcategories of benign tumors—meningiomas, realizing that a small subset can be malignant—and malignant gliomas (oligodendrogliomas and astrocytomas).



DEFINITION






PATHOPHYSIOLOGY


Only about 5% of primary brain tumors have known hereditary factors. Specifically, the Li-Fraumeni syndrome, p53 defects, neurofibromatosis 1 (NF1) and 2 (NF2), tuberous sclerosis, von Hippel-Lindau disease, Turcot’s syndrome, and familial polyposis increase the risk of brain tumors. The polymerase chain reaction (PCR) assay and direct sequencing analysis can be used to diagnose von Hippel-Lindau disease.


For meningiomas, the strongest genetic link has been associated with NF2, with an almost 50% incidence. Sporadic meningiomas have been linked to chromosome 22 in the region of the NF2 gene.4 Meningiomas are known to express estrogen and progesterone receptors, with the former being more common. A high incidence of somatostatin receptors has also been found. The significance of these findings is uncertain but has led to diagnostic tests (e.g., octreotide single-photon emission computed tomography [SPECT], using the somatostatin receptors) and treatment strategies (antiprogesterone; mifepristone [RU-486]). Radiation is the only definite cause. Studies have shown that children receiving as little as 10 Gy for tinea capitis have increased risk for meningiomas, with tumor development taking at least 20 years from exposure.5,6 Head injury is often cited as a causative factor, but a prospective study of 3000 patients with head injuries found no increased incidence.7


Viral infections, specifically the JC virus, has been implicated in oligodendrogliomas, but the data are inconclusive. The incidence of PMBTs (specifically astrocytomas) is increased in children with acute lymphocytic leukemia who have had prior brain radiotherapy. There have been reports8 of low-grade astrocytoma development in patients with inherited multiple enchondromatosis type I. Even though many of the molecular alterations involved in the progression of low-grade astrocytomas to higher grade tumors (glioblastoma multiforme) are known, the underlying causative factors are not well understood (Fig. 1).




SIGNS AND SYMPTOMS


For meningiomas, the clinical symptoms are usually dependent on the anatomic site involved, but many are found incidentally. Most meningiomas are slow growing and cause signs and symptoms by compression of nearby structures. The three most common symptoms are headaches, mental status changes, and paresis, and the most common signs are paresis, normal examinations, and memory impairment.9 For PMBTs, the most common signs and symptoms are seizures and headache. The lower-grade glial tumors have a more indolent course that may persist over years, whereas the most aggressive tumors (e.g., anaplastic oligodendrogliomas, anaplastic astrocytomas, glioblastoma multiforme) may have a rapid onset of neurologic decline. Patients may, however, present with signs and symptoms of increased intracranial pressure, including nausea, vomiting, headache, and confusion.



DIAGNOSIS


As with most disease processes, the medical history is the most important initial step in the process of brain tumor diagnosis. Because many meningiomas are found incidentally, imaging studies are important. A physical examination usually follows the medical history. Computed tomography (CT) is probably used most often as the initial imaging study, but magnetic resonance imaging (MRI) is considered to be the gold standard when done with and without gadolinium contrast. On MRI, meningiomas are typically isodense, dura-based masses that often show homogeneous enhancement (Fig. 2).





Primary Malignant Brain Tumors


As with meningiomas, MRI with and without contrast is the test of choice for PMBTs. Oligodendrogliomas are more likely to demonstrate calcifications on CT than astrocytomas. With MRI scans, PMBTs are typically hypointense on T1-weighted images and hyperintense on T2-weighted and fluid-attenuated inversion recovery (FLAIR) images. The higher-grade lesions (WHO III and IV) are more likely to demonstrate enhancement (anaplastic oligodendrogliomas, anaplastic astrocytomas, glioblastoma multiforme), although ring enhancement is less common in anaplastic oligodendrogliomas and usually is associated with a worse prognosis.10 Glioblastoma multiforme often has ring enhancement around a central area of necrosis (Fig. 4). Tumor-associated cysts are more common with the astrocytomas. The higher-grade lesions also tend to exhibit more peritumoral edema. Newer technologies such as magnetic resonance spectroscopy can help in the differential diagnosis of intracranial lesions. Gliomas tend to demonstrate decreased N-acetyl aspartate, increased choline, and decreased creatine levels. A lactate peak is common in higher grade tumors.11 The diagnosis is ultimately made histologically after surgical biopsy or resection. Figure 5 shows a hematoxylin-eosin slide from an oligodendroglioma, and Figure 6 represents a glioblastoma multiforme at low power. As we increase our understanding of the molecular genetics of tumors, this technology will play an increasing role in tumor diagnosis (see later, “Advances”).


Jul 18, 2017 | Posted by in GENERAL SURGERY | Comments Off on Brain Tumors: Meningiomas and Gliomas
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