approach to imaging based diagnosis of an intracranial space-occupying lesion in a child dr. flip...
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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.