Approach to imaging based diagnosis of an intracranial space-occupying lesion in a child Dr. Flip Otto Dept Diagnostic Radiology UFS

Introduction CNS tumours 2 nd 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 3 rd ventricle Colloid cyst (3 rd 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 4 th 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 6 th ed. Philadelphia: Lippincott Williams & Wilkins; Panigrahy, A., Blueml, S.(2009) Neuroimaging of Paediatric Brain Tumors: From Basic to Advanced Magnetic Resonance Imaging (MRI). Journal of Child Neurology. 24(11), Smithuis, R., Montanera, W. Brain Tumor - Systematic Approach. Weisleder, R, Wittenberg, J, Harisinghani, MG, Chen, JW. Primer of Diagnosic Imaging 5 th ed. St. Louis: Elsevier Mosby; 2011.