Brain Tumors

Brain tumors are one of the more common causes of intracranial hypertension. They are subdivided into primary brain tumors, which arise from the brain tissue itself (either the neuroepithelial tissue or the neighboring mesenchymal tissues, e.g., the meninges), brain metastases, and tumors arising from the cells of the blood vessels. Brain tumors produce focal brain signs of different types depending on their location, as well as signs of intracranial hypertension that may progress more or less rapidly depending on the rate of tumor growth.




6.4.1 Overview


Epidemiology The incidence of tumors of the brain or spinal cord is approximately 5 per 100,000 persons per year in children and adolescents, and 28 per 100,000 persons per year in adults. Brain and spinal cord tumors are the most common kind of solid tumor in children; in adults, they are much rarer than the most common kinds of cancer (prostate, breast).


The frequency of different kinds of brain and meningeal tumors is shown in ▶ Fig. 6.13. The spectrum of brain tumors changes with age. In children and adolescents, the most common tumors are pilocytic astrocytoma, glioma, and medulloblastoma; in adults, the most common tumors are meningioma, glioblastoma, and pituitary tumors. Among the elderly, meningioma and glioblastoma are most common.




Note



Meningioma, schwannoma, and pituitary tumors are among the most common benign tumors; glioblastoma and astrocytoma are among the most common malignant tumors.


Classification and grading In the WHO classification, brain tumors are classified by their histologic type (for a simplified overview, see ▶ Table 6.10) and by their degree of malignity, ranked on a four-point scale ( ▶ Table 6.11): tumors of WHO grades I and II are benign, while those of grades III and IV are malignant.


























































Table 6.10 WHO histologic classification of tumors of the nervous system (2007, simplified)

WHO tumor type


Examples


Neuroepithelial tumors


Astrocytoma, glioblastoma


Oligodendroglioma


Mixed glioma


Ependymoma


Choroid plexus papilloma


Gangliocytoma


Pinealocytoma


Medulloblastoma


Peripheral nerve tumors


Schwannoma (= neurinoma)


Neurofibroma


Meningeal tumors


Meningioma



Hemangioblastoma


Neoplasias of the hematopoietic system


Primary CNS lymphoma



Malignant lymphoma


Germ-cell tumors


Germinoma



Teratoma


Tumors of the sellar region


Pituitary adenoma



Craniopharyngioma


Metastases


Carcinomas of the:




  • Lung



  • Breast



  • Kidney (renal cell carcinoma)



  • Colon


Abbreviation: CNS, central nervous system.





































Table 6.11 WHO grading of brain tumors

Grade


Features


MRI


Representative examples


I


Slowly growing, not malignant, cells appear nearly normal, long survival


T2-hyperintense, hardly any mass effect, no enhancement


Pilocytic astrocytoma


II


Relatively slowly growing, occasional atypical cells, can transform into higher-grade tumors or recur as higher-grade tumors after treatment


T2-hyperintense, mass effect, no enhancement


Astrocytoma, oligodendroglioma


III


Malignant, with anaplastic cells; recur as high-grade tumors


T2-hyperintense, mass effect, variable enhancement (from none to highly complex)


Anaplastic astrocytoma


IV


Malignant, with anaplastic cells; rapid, aggressive growth


T2-hyperintense, mass effect, ring-shaped enhancement


Glioblastoma


Source: From Mattle H, Mumenthaler M. Neurologie. Stuttgart: Thieme; 2013.



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Fig. 6.13 The frequency of tumors of the brain and meninges. (Data from www.cbtrus.org.)


Etiology Most brain tumors are of no known cause; in rare cases, they can be caused by a prior exposure to ionizing radiation or by a genetic syndrome. Examples include Li–Fraumeni syndrome (astrocytoma, primitive neuroectodermal tumors [PNET], sarcoma), Turcot syndrome (medulloblastoma, glioblastoma), and the phakomatoses (see section ▶ 6.1.8):




  • Neurofibromatosis, type 1 (neurofibroma, iris hamartoma) and type 2 (meningioma, bilateral acoustic neuroma, retinal hamartoma).



  • von Hippel–Lindau disease (hemangioblastoma of the cerebellum).



  • Tuberous sclerosis (cortical hamartoma, giant-cell astrocytoma).



  • Encephalofacial angiomatosis, that is, Sturge–Weber disease.


General clinical manifestations The general manifestations of brain tumors are presented in ▶ Table 6.12. These can progress more or less rapidly depending on the type and growth rate of the tumor. Malignant tumors typically manifest a “crescendo” course, in which overt signs and symptoms arise soon after the onset of the illness, and then worsen steadily and rapidly. The signs and symptoms of benign tumors, on the other hand, often progress slowly and insidiously, perhaps over many years. Hemorrhage into a brain tumor (either benign or malignant) may cause symptoms to arise very suddenly.














Table 6.12 General manifestations of brain tumors

Symptoms


Signs




  • Headache (diffuse, at night as well as in the daytime; an early symptom in half of all patients with brain tumors)



  • Possibly other signs of intracranial hypertension (vomiting, bradycardia)



  • Epileptic seizures (focal or generalized; the initial presentation of one quarter of all patients with brain tumors)



  • Mental changes (apathy, irritability, fatigability, impaired memory, and concentration)




  • Focal neurologic deficits depending on the localization of the tumor



  • Mental abnormalities and cognitive deficits (memory loss, other neuropsychological deficits)



  • Sometimes cranial nerve deficits



  • Often papilledema


Diagnostic evaluation Neuroimaging studies are essential: the best is generally contrast-enhanced MRI (cf. ▶ Table 4.2). CT may provide useful complementary information in some cases, for example, calcifications or accompanying osseous changes, but may fail to reveal some tumors (especially low-grade gliomas). Sometimes angiography is indicated for visualization of a tumor’s blood supply.


Brain tumors generally cannot be securely diagnosed by imaging studies alone; in most cases, at least some of the tumor must be surgically removed for histologic examination. If total resection is not possible because of the location of the tumor, or contraindicated for other medical reasons, then tissue can be obtained by a stereotactic brain biopsy. A secure histologic diagnosis is needed for the optimal planning of further treatment, such as chemotherapy or radiotherapy. Moreover, some “brain tumors” turn out, on biopsy, not to be tumors at all, but rather brain abscesses, foci of demyelination, etc. In such cases, diagnostic biopsies save the patient from needless and probably harmful treatment.




Practical Tip



CSF examination is generally neither necessary nor helpful in the evaluation of brain tumors. CSF cytology is clinically useful only in case of meningeal spread (e.g., in carcinomatous meningitis) and when the presence of oligoclonal bands in the CSF helps to establish the correct diagnosis of a large multiple sclerosis plaque that resembles a brain tumor on imaging studies.


Tumor markers may be useful for diagnosis and treatment.




Additional Information



Mass lesions of the CNS that may be misdiagnosed as tumors include:




  • Residual mass lesions after episodes of ischemia, inflammation, or thrombosis.



  • Infections (bacterial abscess, tuberculosis, fungal or parasitic infection).



  • Multiple sclerosis plaques (mainly of the “tumefactive” type).



  • Sarcoidosis.


Treatment Complete resection of the tumor is indicated whenever possible. The operability of brain tumors depends on their size, location, histologic grade, and relation to the surrounding brain tissue (infiltration vs. displacement). Not every tumor is neurosurgically accessible or fully resectable. Depending on the type of tumor, radiotherapy and/or chemotherapy may have to be used, either as the primary form of treatment or as adjuvant therapy after surgery.


The cerebral edema that usually accompanies malignant tumors is treated with corticosteroids (usually dexamethasone). Dexamethasone is also given preoperatively to reduce swelling in all cases of brain tumor with mass effect and elevated ICP. Epileptic seizures, if they arise, are treated with anticonvulsants, for example, levetiracetam. In some circumstances, prophylactic anticonvulsant administration may be helpful as well.




Practical Tip



Epileptic seizures are an important manifestation of brain tumors and can arise either before or after neurosurgical resection.


6.4.2 Astrocytoma and Glioblastoma




Note



Astrocytoma is the most common type of primary brain tumor and is classed as a neuroepithelial tumor. Grade III and IV astrocytomas are called anaplastic astrocytoma and glioblastoma, respectively; these forms are highly malignant and lead rapidly to death. Grade I and II astrocytomas are more benign, growing slowly and progressively over a period of years. Pilocytic astrocytoma (grade I), a tumor seen mostly in children and adolescents, is the only type of astrocytoma that generally does not recur after total resection.


Grade IV Astrocytoma (Glioblastoma)


A distinction is drawn between primary and secondary glioblastoma. Primary glioblastoma is already a grade IV tumor at the time it arises (or is first discovered); secondary glioblastoma develops by malignant progression from a preexisting lower-grade astrocytoma or other type of glioma. Glioblastoma was historically called “glioblastoma multiforme;” the second word adds no information and has been dropped from modern classifications.


Epidemiology Glioblastoma is the most common and most malignant type of primary brain tumor. It grows by infiltration into the brain tissue. Its highest incidence is in the fifth and sixth decades of life.


Localization and growth Glioblastoma arises in a cerebral hemisphere and can spread to the contralateral hemisphere by way of the corpus callosum (butterfly glioma). Glioblastomas grow rapidly, causing rapidly progressive clinical manifestations; they are, therefore, usually diagnosed within a few weeks or (at most) months of the onset of symptoms.


Clinical features Focal neurologic and/or neuropsychological deficits arise first, sometimes accompanied by epileptic seizures, soon followed by general signs of intracranial hypertension (see ▶ Table 6.9).


Diagnostic evaluation The diagnosis can be made fairly securely from the typical appearance in neuroimaging studies ( ▶ Fig. 6.14, ▶ Fig. 6.15), though this does not obviate the need for histologic examination of tumor tissue. Contrast-enhanced MRI or CT characteristically reveals ringlike enhancement with a central nonenhancing area, corresponding to necrosis in the interior of the tumor. Intratumoral hemorrhages may also be seen. Peritumoral brain edema is often extensive, causing mass effect and midline shift.



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Fig. 6.14 Glioblastoma. The T2-weighted (a) and T1-weighted (b) MR images reveal a butterfly-shaped tumor in the splenium of the corpus callosum and adjacent regions of the two cerebral hemispheres. A cyst (*) in the right occipital lobe is part of the tumor; like the rest of the tumor, the cyst wall displays contrast enhancement (b). Peritumoral edema is most marked in the right hemisphere (→) (a).

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Dec 28, 2017 | Posted by in NEUROLOGY | Comments Off on Brain Tumors
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