Central nervous system tumours

Published on 09/04/2015 by admin

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Last modified 09/04/2015

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16 Central nervous system tumours

Introduction

Primary central nervous system (CNS) tumours can arise from any structures in the cranial vault. Around 4000 new patients with malignant brain tumours are diagnosed per year in the UK and 22,000 new patients in USA. There is a bimodal distribution with small peak in children (p. 323) and a steady increase starting at the age of 20 years. Males are more commonly affected, particularly with malignant tumours, whereas women have a higher rate of non-malignant tumours, particularly meningiomas.

Aetiology

The majority of brain tumours are sporadic with an unknown cause. A small proportion of tumours are associated with genetic syndromes and other factors.

Pathology

Box 16.1 shows WHO classification of brain tumours. WHO grading system (Box 16.2) is important in deciding management and prognosis. Molecular features can be incorporated in this grading system to yield important prognostic information. Clinico-pathological features of individual tumours are discussed later.

Investigations

Imaging

CT scan

Contrast enhanced CT scan is usually the initial investigation in patients suspected to have a brain lesion. CT scan is not an ideal investigation for low-grade tumours or tumours in the posterior fossa. CT scan may also show features of oedema, hydrocephalus, haemorrhage and calcification depending on the histological variant of brain tumour. Table 16.1 shows radiological appearance of common tumours.

Table 16.1 Radiological appearance of common brain tumours

Type of tumour Imaging characteristic
Pilocystic astrocytoma Well-circumscribed, contrast enhancing tumour with a cystic or enhancing mural nodule.
Grade II astrocytoma Isodense or hypodense on CT. Hypointense on T1W image and hyperintense on T2W and FLAIR images. No contrast enhancement and if present suggest malignant transformation. No associated cerebral oedema.
Oligodendroglioma Same CT/MRI as grade II astrocytoma; but can be associated with areas of contrast enhancement, calcification and haemorrhage.
Anaplastic astrocytoma and GBM

Anaplastic oligodendroglioma Contrast enhancing heterogeneous mass with frequent cystic components, calcifications and necrosis. Medulloblastoma

Ependymoma Heterogeneously enhancing lesion with cystic component. There may be associated calcification and haemorrhage. Primary CNS lymphoma Solitary or multiple periventricular homogenously enhancing diffuse lesions (‘cotton wool’ appearance). Ring enhancement common in immunocompromised patients. Meningioma Homogenously contrast enhancing lesion arising from the dura. There is little associated brain oedema. There will be enhancement of dura (’dural tail’ sign). Craniopharyngioma Solid and cystic lesion on CT scan. MRI appearance depends on the composition of tumour. T1W can be hypo, iso or hyperintense with variable contrast enhancement. T2W can also be hypo, iso or hyperintense. Pituitary Contrast enhancing seller/suprasellar lesion on CT. T1W iso-hypointense and T2W hyperintense. Metastasis Solitary or multiple irregularly contrast enhancing lesion which may be solid or cystic at the junction of grey and white matter. Location and characteristic depends on type of tumour.

MRI scan

MRI scan with gadolinium and FLAIR (fluid-attenuated inversion recovery) sequence is the standard investigation for brain tumours. T1W imaging demonstrates anatomy and areas of contrast enhancement and T2W and FLAIR images are useful in demonstrating oedema. Appearance of tumour on T1W image is similar to that on CT, but better delineated on MRI. Tumour and oedema demonstrate increased signal on T2 and the area of increased T2 signal on MRI usually includes the hypodense area on CT (Figure 16.1).

Various MR imaging techniques are being evolved to improve the diagnostic ability in the imaging of brain tumours.

Evaluation of the craniospinal axis

MRI of the craniospinal axis and CSF evaluation is needed for tumours with a high risk of CSF dissemination such as medulloblastoma, germ cell tumours, CNS lymphoma, PNET and ependymoma (Figure 16.2). CSF evaluation includes CSF biochemistry (typically elevated protein >40 mg/dL and reduced glucose <50 mg/mL), cytology and in cases of suspected germ cell tumours, the estimation of tumour markers (AFP and beta hCG) in CSF and serum. Evaluation of the craniospinal axis is best done prior to surgery or >3 weeks after surgery to avoid false positive results.

Principles of management

Surgical management

Surgery in brain tumours helps in pathological diagnosis, symptom control and definite treatment.

Biopsy can be either stereotactic guided or an open biopsy. Surgery is useful in relieving pressure symptoms as well as decreasing the frequency and intensity of seizures. Surgical resection is constantly evolving in brain tumours. It is common practice to confirm the diagnosis with an intraoperative frozen section or smear prior to attempting a full resection. Complete or maximal resection with minimal injury to neighbouring critical structures is the aim of surgery. The importance of surgical resection in specific tumours is discussed later. The various resection techniques are:

Radiotherapy in brain tumours

Radiotherapy has a major role in the management of CNS tumours. Radiotherapy is proven to improve local control and/or survival in grade 3–4 tumours whereas its role in grade 2 tumours is doubtful and has limited role for grade 1 tumours. Radiotherapy is delivered by the following methods:

A summary of radiotherapy details for common tumours are given in Table 16.2.

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