Approach to imaging based diagnosis of an intracranial space-occupying lesion in a child

Dr. Flip OttoDept Diagnostic Radiology

UFS

Introduction• CNS tumours 2nd most common after leukemia• Incidence 2.4:100,000 children <15 years• 15% of all paediatric neoplasms• 15-20% of all primary brain tumours• M>F• Usually presents with signs and symptoms of raised

intracranial pressure and/or increasing head size

Approach – Clues to diagnosis

• Age

• Location

• Local tumour spread

• Solitary or multifocal

• Specific imaging characteristics

• Tumour mimics

Age

• CNS tumours presenting at birth:• Teratoma (commonest)• Neuro-epithelial tumours:• Medulloblastoma• Astrocytomas• Ependymomas• Choroid plexus tumours

• After 2 months, neuro-epithelial tumours more common.• During this time, supratentorial tumours more common

than infratentorial

Age

• Brain tumours in infants <2 years• Two thirds are supratentorial• Most common tumours:• PNET (primitive neuroectodermal tumour)• Astrocytoma• Teratoma• Choroid plexus papilloma

Most common CNS tumours in paediatric patients older than 2 years

• Number of infratentorial tumours slightly exceeds supratentorial tumours• Medulloblastoma• Astrocytoma• Ependymoma• Craniopharyngioma• Gliomas

• Metastases are rare in paediatric population (vs. 50% in adults)

Location

• Intra- vs. extra-axial• Supra- vs. infra-tentorial• White matter vs. cortical based• Specific anatomic sites:• Sella/suprasellar• Pineal region• Intraventricular

Intra- vs. extra-axial

• Signs of extra-axial location:• CSF cleft• Displaced subarachnoid blood vessels• Cortical grey matter between mass and white matter• Displacement and expansion of subarachnoid space• Broad dural base• Bony reaction

• >80% extra-axial tumours are either meningioma or schwannoma

Intra-axial vs Extra-axial Brain Tumours

Intra-axial

• Glioma• Medulloblastoma• Hemangioblastoma• Metastases• Infarction/hematoma• AVM• Abscess/inflammation

Extra-axial

• Meningioma• Pituatary adenoma• Craniopharyngioma• Schwannoma• Chordoma• Dermoid/epidermoid cyst• Lipoma• Metastases, hematoma,

infection

Supra- vs. infra-tentorial• Common intra-axial CNS tumours in paediatric age group• Supratentorial:

• Astrocytoma• Pleomorphic xanthoastrocytoma• PNET• DNET• Ganglioglioma

• Infratentorial:• Juvenile pilocytic astrocytoma• PNET (Medulloblastoma)• Ependymoma• Brainstem astrocytoma/glioma

White matter vs. cortical based

•Most intra-axial tumours are white matter based• Differential diagnosis for cortical based

tumours:• DNET (Dysembryoplastic neuroepithelial

tumour)• Ganglioglioma

Cortical Based Tumour - DNET

Specific anatomic sites• Sella/suprasellar:• Optic pathway/hypothalamic glioma• Craniopharyngioma• Germ cell tumours

• Pineal region:• Germ cell tumours• Pinealblastoma (associated with retinoblastoma)• Astrocytoma• Ganglioglioma• Epidermoid

• Intraventricular:• Ependymoma• Choroid plexus papilloma/carcinoma• Subependymal giant cell astrocytoma (associated with tuberous sclerosis )• Lesions arising from suprasellar region may involve 3rd ventricle• Colloid cyst (3rd ventricle, usually young adults)

Intraventricular tumours: Choroid plexus papilloma and carcinoma

Pineal region: Pineal Germinoma

Suprasellar tumour: Craniopharyngioma

Local tumour spread

• Astrocytomas spread along white matter tracts and don’t respect lobar boundaries• Ependymomas in 4th ventricle may extend

through foramen of Magendie into cisterna magna, and through foramina of Luschka into cerebellopontine angles• Subarachnoid seeding: PNET; ependymomas;

choroid plexus carcinoma

Mass effect

• Primary brain tumours usually have less mass effect and oedema than expected for size, due to infiltrative growth pattern• Metastases and extra-axial tumours have more

significant mass effect due to expansile growth pattern

Solitary vs. multifocal lesions• Metastases and CNS lymphoma, often presenting with

multiple lesions, are rare in children• Seeding metastases may be seen with PNET-MB

(Medulloblastoma) and ependymoma• Multiple brain tumours may occur in phacomatoses:• NF I: optic gliomas; astrocytomas• NF II: meningiomas; ependymomas; choroid plexus papillomas• Tuberous sclerosis: subependymal tubers; ependymomas;

intraventricular giant cell astrocytomas• Von Hipple Lindau: hemangioblastomas

Specific imaging characteristics

• Fat• Calcification• Cystic mass vs. cyst• T1WI signal intensity• T2WI signal intensity• Contrast enhancement• Advanced MRI

Fat

• Fat is characterised by high signal on T1 and T2WI, with associated chemical shift artefact• Fat suppression sequences help distinguish

from other causes of high signal e.g. melanin, hematoma and slow flow•Masses containing fat include teratoma,

lipoma and dermoid cyst

Calcification

• Intra-axial:• Astrocytoma• Ependymoma• Choroid plexus papilloma• Ganglioglioma

• Extra-axial:• Meningioma• Craniopharyngioma

Cystic mass vs. cyst• Cystic lesions that may simulate tumours include epidermoid,

dermoid, arachnoid, neurenteric and neuroglial cysts• To differentiate cystic masses from cysts:• Morphology• Fluid/fluid level• Content intensity compared to CSF on T1, T2 and FLAIR

sequences• Restricted flow on DWI

T1WI signal intensity

• Most brain tumours have low to intermediate signal intensity on T1WI• High T1 signal may be due to:• Methaemoglobin in a haemorrhagic tumour• High protein content eg neurenteric cyst,

dermoid cyst

T2WI signal intensity

• Most brain tumours appear bright on T2WI due to high water content• Causes for low signal on T2:• Hypercellular tumours with high nuclear-cytoplasmic

ratio : PNET, meningioma, germinoma• Calcifications• Hemosiderin in old haematomas• High protein content e.g. colloid cyst• Flow voids e.g. haemangioblastoma

Contrast enhancement

• Extra-axial tumours, pituitary, pineal and choroid plexus tumours enhance (outside blood-brain barrier)• Contrast enhancement does not visualise full

extent of infiltrative tumours eg gliomas• In gliomas, enhancement indicates higher degree

of malignancy• Ganglioglioma and pilocytic astrocytomas are

exceptions, low grade tumours that enhance vividly

Contrast enhancement patterns• No enhancement:• Low grade astrocytoma• Cystic non-tumoral lesions

• Homogeneous enhancement• Germinoma and other pineal tumours• Pituitary adenoma• Pilocytic astrocytoma(solid component) and haemangioblastoma• Ganglioglioma• Meningioma, schwannoma

• Patchy enhancement • Radiation necrosis

• Ring enhancement• High grade glioma• Metastases• Abscess

Advanced MRI techniques

• Diffusion weighted imaging

• Diffusion tensor imaging

• Perfusion weighted imaging

•Magnetic resonance spectroscopy

Application of Advanced MRI in Paediatric Brain Tumours

• Improving the accuracy of the initial diagnosis

• Evaluating the risk at initial diagnosis

•Monitoring the effectiveness of therapy

DWI

• Most tumours do not show significant restriction

of diffusion

• High signal on DWI is seen with abscesses,

epidermoid cysts and acute infarction

DWI

PWI

• Signal intensity depends on vascularity, not on

breakdown of blood-brain barrier

• Better correlation with grade of malignancy than

degree of contrast enhancement

PWI

MRS

• H-1 MRS analyzes signal of protons attached to other molecules• Output is collection of peaks at different

radiofrequencies, representing proton nuclei in different chemical environments, proportional to number of contributing protons.• Peaks include: N-acetylaspartate; choline;

creatine; myo-inositol; taurine; lactate; methyl groups(lipids); methylene groups

MRS

Tumour mimics

• Abscesses can mimic metastases• Multiple sclerosis can present with mass like lesions with

enhancement (tumefactive MS)• Aneurysms should always be excluded in the parasellar region

Conclusion

• Primary CNS tumours relatively common in children

• Age of child helps narrow differential diagnosis

• Anatomical localization very important

• CT and MRI findings characterize tumour

composition

• Advanced MRI techniques can aid in diagnosis,

grading and monitoring treatment response

References• Daehnert, W. Radiology Review Manual 6th ed. Philadelphia:

Lippincott Williams & Wilkins; 2007.• Panigrahy, A., Blueml, S.(2009) Neuroimaging of Paediatric

Brain Tumors: From Basic to Advanced Magnetic Resonance Imaging (MRI). Journal of Child Neurology. 24(11),1342-1365.

• Smithuis, R., Montanera, W. Brain Tumor - Systematic Approach. www.radiologyassistant.nl

• Weisleder, R, Wittenberg, J, Harisinghani, MG, Chen, JW. Primer of Diagnosic Imaging 5th ed. St. Louis: Elsevier Mosby; 2011.