Intracranial tumours in adults
IMAGING TECHNIQUES AND GENERAL FEATURES
COMPUTED TOMOGRAPHY
high attenuation areas within a tumour indicate tumour calcification or recent intratumoural haemorrhage
it provides a limited area of coverage (compared with MRI) 
unlike MRI it can provide a direct relationship between the CT attenuation value and tissue contrast material concentrationMAGNETIC RESONANCE IMAGING
T2WI/FLAIR: high SI
signal loss is seen within any cystic tumour components
it may also be seen with certain low-grade tumours (e.g. pilocytic astrocytomas)
this is more conspicuous on T2*WI (stronger magnetic susceptibility effects)Dynamic susceptibility-weighted contrast-enhanced (DSC) MR perfusion imaging
• This can assess tumour blood vessel density (an indirect measure of tumour neovascularity malignancy)
rCBV measurements correlate closely with markers of tumour vascularity and angiogenesis
Higher rCBV values with high-grade tumours
rCBV maps can aid stereotactic tumour biopsies
In radiation necrosis the residual enhancing lesion has a low rCBV (higher with tumour recurrence due to new vessel formation)
• DSC imaging differs from contrast enhancement, which is an indicator of vascular endothelial (blood–brain barrier) integrity
MR diffusion imaging
• Useful in identifying acute infarcts or abscesses (which can mimic brain tumours)
• ADC measurements correlate inversely with the histological glioma cell count
ADC measurements of any enhancing components in radiation necrosis are significantly higher than with recurrent tumour (mirroring the higher cellular density with a recurrent neoplasm)
• Diffusion tensor imaging (DTI) provides additional information about the direction of water diffusion 
the normally high anisotropy within white matter tracts can be lost if infiltrated by tumour
fMRI
• BOLD imaging detects changes in regional cerebral blood flow during various forms of brain activity
• This is used for preoperative localization of important cortical regions that may have been displaced by tumour
CLASSIFICATION OF INTRACRANIAL TUMOURS
Extra-axial tumours
Tumours arising from the tissues covering the brain (e.g. the dura or arachnoid) 
these occur much more frequently in adults than children (accounting for the majority of the primary infratentorial adult tumours)
Patient age and tumour site are useful indicators to the likely tumour type
• Children: primary tumours usually occur infratentorially and within the posterior fossa between the ages of 2 and 10 years (e.g. pilocytic astrocytoma, pontine glioma, ependymoma and medulloblastoma) 
below 2 and above 10 years of age supratentorial tumours are more common (paediatric supratentorial tumours will preferentially affect the midline structures) 
intracranial metastases are rare
Features distinguishing an extra- from an intra-axial tumour
| Extra-axial tumour | Intra-axial tumour | |
| ‘Buckling’ and medial displacement of the grey–white matter interface | Yes | No |
| CSF cleft separating the base of the mass from adjacent brain | Yes | No |
| Broad base along a dural or calvarial surface | Yes | No |
| Associated bone changes | • Meningioma: hyperostotic bone reaction• Dermoid cyst/schwannoma: bone thinning (with enlargement of the middle cranial fossa or internal auditory meatus) | Rare |
| Grey–white matter junction | Preserved | Destroyed |
Astrocytoma: this is the most common primary childhood brain tumour (the majority are pilocytic astrocytomas and characteristically occur within the cerebellum, hypothalamus and optic nerves)
• Adults: 70% of intracranial tumours are primary (30% are metastases) 
the vast majority of tumours are supratentorial – the posterior fossa is rarely affected by a primary tumour (a metastasis is more likely at this location)
| Tumour | Typical site |
| Colloid cyst | Foramen of Monro/third ventricle |
| Meningioma | Trigone of lateral ventricle |
| Choroid | Fourth ventricle |
| Ependymoma | Lateral ventricle (more common in children) and fourth ventricle |
| Neurocytoma | Lateral ventricles (involving septum pellucidum) |
| Metastases | Lateral ventricles, ependyma and choroid plexus |
Common calcified and haemorrhagic lesions*
| Common calcified lesions | Common haemorrhagic lesions |
| Oligodendrogliomas (90%)Choroid plexus tumoursEpendymomaCentral neurocytomaMeningiomaCraniopharyngiomaTeratomaChordoma | GBM (grade IV glioma)OligodendrogliomaMetastases– Melanoma– Lung– Breast |
Primary cerebral tumours and age groups†
| Tumour | Age group |
| Brainstem glioma, optic nerve glioma | 0–5 |
| Medulloblastoma, cerebellar astrocytoma, papilloma choroid plexus, pinealoma, craniopharyngioma | 5–15 |
| Ependymoma | 15–30 |
| Glioma, meningioma, acoustic neuroma, pituitary tumour, hemangioblastoma | 30–65 |
| Meningioma, acoustic tumour, glioblastoma | 65+ |
The 2007 WHO classification of tumours of the central nervous system (abridged)
| TUMOURS OF NEUROEPITHELIAL TISSUEAstrocytic tumoursAnaplastic astrocytoma Diffuse astrocytoma Glioblastoma Gliomatosis cerebri Pilocytic astrocytoma Pleomorphic xanthoastrocytoma Subependymal giant cell astrocytoma Oligodendroglial tumoursOligodendroglioma Anaplastic oligodendroglioma Oligoastrocytic tumoursOligoastrocytomaAnaplastic oligoastrocytomaEpendymal tumoursEpendymoma Subependymoma Anaplastic ependymoma Myxopapillary ependymomaChoroid plexus tumoursChoroid plexus papilloma Choroid plexus carcinoma Other neuroepithelial tumoursAstroblastoma Chordoid glioma of the third ventricleAngiocentric glioma Neuronal and mixed neuronal-glial tumoursGanglioglioma and gangliocytomaDesmoplastic infantile gangliogliomaDysembryoplastic neuroepithelial tumourCentral neurocytoma and extraventricular neurocytic tumoursTumours of the pineal regionPineoblastomaPineocytoma | Embryonal tumoursMedulloblastomaCNS primitive neuroectodermal tumourAtypical teratoid/rhabdoid tumourTUMOURS OF CRANIAL AND PARASPINAL NERVESSchwannoma (neurilemoma, neurinoma) Neurofibroma PerineuriomaMalignant peripheral nerve sheath tumour (MPNST)TUMOURS OF THE MENINGESTumours of meningothelial cellsMeningioma Mesenchymal tumoursPrimary melanocytic lesionsOther neoplasms related to the meningesHaemangioblastoma LYMPHOMAS AND HAEMATOPOIETIC NEOPLASMSMalignant lymphomasPlasmacytomaGranulocytic sarcomaGERM CELL TUMOURSGerminoma Embryonal carcinoma Yolk sac tumour Choriocarcinoma Teratoma Mixed germ cell tumour TUMOURS OF THE SELLAR REGIONCraniopharyngioma Granular cell tumour Pituicytoma Spindle cell oncocytoma of the adenohypophysis METASTATIC TUMOURS |
Differentiating between an infarct and tumour ©12
| Tumour | Infarct | |
| Grey matter changes | This is usually centred on the cerebral white matter and spares the overlying grey matter | This often simultaneously involves the cerebral cortex and juxtacortical white matter |
| Shape | Spherical or ovoid | Wedge or box shaped (with its base towards the brain surface) |
| Distribution | Not confined to a vascular territory | Confined to a vascular territory |
| Contrast enhancement | Gyriform enhancement is rare | Gyriform enhancement can be present |
GLIOMAS
ASTROCYTOMA
DEFINITION
• A benign or malignant tumour arising from an astrocyte
• Astrocyte: a structural or supporting cell type within the brain
• This is the largest group of primary brain neoplasms (75% of all glial tumours)
• Location: supratentorial (50%) 
cerebellum (35%) 
brainstem (15%)
WHO classification
(the majority will eventually progress to a more malignant type over time):
• Grade I (benign pilocytic astrocytoma): this is potentially resectable with a low proliferative potential (up to 40% of all paediatric intracranial tumours)
It characteristically occurs within the cerebellum in children 
it can also occur within the hypothalamus and optic nerves (optic nerve involvement is a feature of NF-1)
• Grade II (diffuse astrocyoma): an infiltrating (rather than destroying) low-grade tumour 
it results in a relatively mild neurological deficit and a generally good prognosis
• Grade III (anaplastic astrocytoma): although there is increased mitotic activity and anaplasia there is no necrosis
• Grade IV (glioblastoma multiforme): this is the commonest primary adult intracranial neoplasm 
it is very malignant (with the worst prognosis) 
tumour necrosis is a hallmark
predominantly cystic (70%) or solid (30%) 
an associated strongly enhancing mural nodule when cystic 
calcification is rare 
no adjacent oedema
T2WI: high SI 
T1WI + Gad: avid homogeneous enhancement of any solid component
hypothalamic or chiasmatic tumours may be more aggressive
often large and lobulated when at the chiasm and can extend into the hypothalamus 
haemorrhage and necrosis is uncommon
T1WI: low SI 
T2WI: high SI
poor enhancement (there is an intact blood–brain barrier)
T2WI/FLAIR: high SI 
T1WI + Gad: enhancement suggests progression to a higher histological grade
although tumours may appear well-defined they are always infiltrative (commonly extending along the white matter tracts)
T1WI + Gad: an irregularly thick enhancing peripheral ‘ring’ (active mitosis) 
a multicentric tumour with seeding via the CSF space (5%) 
a lower ADC than with a low-grade gliomaPEARLS
it typically involves the hemispheric white matter 
it presents between the 2nd and 4th decades (M = F)MRI
A diffuse ill-defined ‘mass-like’ lesion with ventricular effacement 
T1WI: a homogeneous intermediate-to-low SI infiltrating mass 
T2WI/FLAIR: a homogeneous high SI infiltrating mass 
T1WI + Gad: no or minimal enhancement
• Differential: lymphomatosis cerebri 
viral encephalitis 
acute disseminated encephalomyelitis (ADEM) 
vasculitis
| Pilocytic astrocytoma | Diffuse astrocytoma | Anaplastic astrocytoma | Glioblastoma multiforme | |
| Malignant potential | Benign | Low grade | High grade | Very malignant |
| Age (approximate) | Children | 3rd or 4th decade | 5th decade | 6th decade |
| Location | Optic chiasm or hypothalamus > cerebellum > brainstem* | Hemispheres (cortex + white matter) | Hemispheres (cortex + white matter) | Hemispheres (cortex + white matter) |
| Enhancement | Mild | Mild | Moderate (ring) | Intense |
| Vasogenic oedema | Minimal | Minimal | Moderate | Significant |
| Calcification | Common | Up to 20% | Occasional | Rare |
*It is typically cystic with a mural nodule and located within the posterior fossa – it tends to be solid or lobulated when seen elsewhere.
GLIOMAS
OLIGODENDROGLIOMA
DEFINITION
• A relatively benign slow-growing neoplasm arising from the oligodendrocyte
Oligodendrocyte: a cell that insulates the central nervous system axons and which is equivalent to a Schwann cell within the peripheral nervous system
• It is classified as a WHO grade II (well-differentiated, low-grade) or WHO grade III (anaplastic high-grade) tumour 
it is chemosensitive
• It occurs predominantly in adults (during the 4th decade) and accounts for 5–10% of all intracranial neoplasms
RADIOLOGICAL FEATURES
it may erode the calvarium
cysts or haemorrhage can be seen in 20% but necrosis and oedema is rare
T2WI/FLAIR: heterogeneous high SIEPENDYMOMA
DEFINITION
• A low-grade tumour arising from the ependyma
Ependyma: this forms the epithelial lining of the ventricular system, cerebral hemispheres, brainstem and cerebellum, central canal of the spinal cord, and tip of the filum terminale
• It accounts for 5% of all intracranial tumours (a higher incidence is seen in the paediatric population)
25% are supratentorial (arising from white matter ependymal cells) 
10% arise within the spinal cord
they predominantly affect young adults
there are two age peaks at 5 and 35 years of ageRADIOLOGICAL FEATURES
CT
An isodense-to-hyperdense, well-demarcated, lobulated mass lesion which takes on the shape of the 4th ventricle and frequently extends through the foramina of Magendie and Luschka to seed via the subarachnoid space (a ‘plastic’ ependymoma) 
calcification is seen in > 50% of cases and cystic elements can also be demonstrated 
there can be an associated obstructive hydrocephalus
it is more frequently calcified or cystic than an infratentorial tumour
T1WI: normal-to-low SI 
T2WI: predominantly high SI 
T1WI + Gad: mild-to-moderate enhancement (which is often heterogeneous)PEARLS
it occurs mainly in elderly males and presents as an intraventricular mass in the lateral or 4th ventricle 
it is relatively benign and does not disseminateDifferentiating features of a medulloblastoma
• An important differential of a posterior fossa ependymoma
• It calcifies less frequently 
it arises from the roof of the 4th ventricle 
it demonstrates a rounded shape compared with an ependymoma (that moulds to the ventricular margins)
INFRATENTORIAL TUMOURS
CEREBELLAR HAEMANGIOBLASTOMA
DEFINITION
• A benign tumour of endothelial origin that is composed of thin-walled blood vessels 
it is predominantly found within the posterior fossa (supratentorial lesions are rare) and is the commonest primary intra-axial and infratentorial adult tumour
CLINICAL PRESENTATION
• It usually presents in young adults (M>F)
• Common symptoms include headache, ataxia, nausea, vomiting and vertigo
• 20% are associated with von Hippel–Lindau (VHL) disease – these generally present at an earlier age
• Multiple haemangioblastomas are only seen with von Hippel–Lindau disease 
it is an unusual paediatric tumour unless in the context of von Hippel–Lindau disease
RADIOLOGICAL FEATURES
there is little surrounding oedema 
cyst wall enhancement indicates tumour extension (as for a pilocytic astrocytoma)Angiography
A vascular nodule within an avascular mass 
there may be draining veins present
Differentiating between a haemangioblastoma and a juvenile pilocystic astriocytoma
| Haemangioblastoma | Juvenile pilocystic astrocytoma | |
| Age | 30–40 years | 5–15 years |
| Pial attachment | Yes | No |
| A tiny nodule with a huge cystic component | More likely | Less likely |
| Arteriogram | Hypervascular nodule | Hypovascular nodule |
| Multiplicity and association with VHL disease | More likely | Less likely |
BRAINSTEM GLIOMA
DEFINITION
• This accounts for up to 30% of all paediatric infratentorial tumours (they may occur in adults) 
80% of tumours are high grade, but symptoms occur late as the tumour infiltrates rather than destroys adjacent tissues (hydrocephalus is a late feature)
there is poor enhancement 
it can encase the basilar arteryFocal type
CT/MRI
This has similar imaging features to a pilocytic astrocytoma seen elsewhere
MEDULLOBLASTOMA
DEFINITION
• This is an aggressive tumour, accounting for 30-40% of all posterior fossa tumours 
it is also known as the PNET of the posterior fossa
• It classically arises from the roof of the 4th ventricle and is therefore usually a midline cerebellar mass (a lateral cerebellar location is more common in older children and adults) 
subsequent hydrocephalus is common
a 2nd peak is seen in young adults who present with a ‘desmoplastic’ and less aggressive form
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