Abbreviations

• T1 – T1-weighted MRI
• T2 – T2-weighted MRI
• FLAIR – Fluid-Attenuated Inversion Recovery
• DWI – Diffusion-Weighted Imaging
• GRE/SWI – Gradient Echo/Susceptibility-Weighted Imaging
• MRA/MRV – Magnetic Resonance Angiography/Venography
• CSF – Cerebrospinal fluid
• WBRT – Whole Brain Radiotherapy

1) Arachnoid Cyst

Overview

• Benign, CSF-filled lesion between arachnoid layers.
• Can cause mass effect (cerebellar compression, hydrocephalus).
• No solid components or enhancement.

Key Imaging Features

• T1: Isointense to CSF, no enhancement.
• T2: Hyperintense, follows CSF.
• FLAIR: Complete suppression.
• DWI: No restricted diffusion (differentiates from epidermoid).
• Post-contrast: No enhancement.
• Cine MRI: Assesses CSF flow, surgical relevance.

2) Cavernoma

Overview

• Vascular malformation with slow blood flow.
• Can be asymptomatic or present with haemorrhage, seizures.

Key Imaging Features

• CT - "Popcorn-like" appearance due to haemorrhage and thrombosis on CT due to calcification.
• T1: Heterogeneous "salt-and-pepper" signal.
• T2: Mixed-signal core with hypointense hemosiderin rim.
• GRE/SWI: Blooming artefact (sensitive for small lesions).
• FLAIR: Perilesional oedema if recent bleed.
• DWI: No restricted diffusion.
• Post-contrast: Minimal or no enhancement.

3) Dysplastic Cerebellar Gangliocytoma (Lhermitte-Duclos Disease)

Overview

• Rare, benign cerebellar hamartoma.
• Associated with Cowden syndrome (PTEN mutations).
• Causes mass effect (ataxia, hydrocephalus).

Key Imaging Features

• T1: Hypo- to isointense.
• T2: "Tiger-striped" hyper- and hypointense bands.
• FLAIR: Mild hyperintensity, retains striated pattern.
• DWI: No restricted diffusion. May get T2 shine through.
• Post-contrast: Little to no enhancement.

4) Ependymoma

Overview

• Glial tumour of the fourth ventricle.
• May extend through foramina of Luschka & Magendie causing hydrocephalus and often presents with features of raised ICP.

Key Imaging Features

• T1: Iso- to hypointense.
• T2: Heterogeneous; cystic/necrotic areas, calcifications.
• FLAIR: Perilesional oedema, hydrocephalus.
• DWI: Variable; anaplastic variants show restriction.
• Post-contrast: Heterogeneous enhancement
• GRE/SWI: Susceptibility from calcifications/haemorrhage.

5) Epidermoid

Overview

• Congenital, slow-growing ectodermal inclusion.
• Common in the CPA and fourth ventricle.
• Fat density on CT, encases neurovascular structures but does not displace.

Key Imaging Features

• T1: Hypointense to CSF, may be hyperintense if cholesterol rich.
• T2: Hyperintense, heterogeneity due to keratin.
• FLAIR: Incomplete suppression (unlike arachnoid cysts).
• DWI: Bright (restricted diffusion).
• Post-contrast: No enhancement.
• GRE/SWI: Hemosiderin deposition if prior haemorrhage.

6) Haemangioblastoma

Overview

• Highly vascular tumour, common in Von Hippel-Lindau disease.
• Arises in cerebellum, brainstem, spinal cord.
• Causes ataxia, hydrocephalus, cyst formation.

Key Imaging Features

• T1: Hypointense, strongly enhancing solid portion.
• T2: Cystic with an hyperintense mural nodule. Can have flow voids.
• FLAIR: Hyperintense mural nodule, cystic suppression.
• DWI: No restricted diffusion.
• Post-contrast: Strong homogeneous enhancement of the mural nodule. Cyst wall does not typically enhance.
• MRA/MRV: Prominent feeding arteries.

7) Metastases

Overview

• Most common intracranial tumours in adults.
• Common primaries: lung, breast, melanoma, renal.

Key Imaging Features

• T1: Hypointense; hyperintense if haemorrhagic.
• T2: Hyperintense; extensive perilesional oedema.
• FLAIR: Hyperintense tumour & oedema.
• DWI: Restricted diffusion in solid portions.
• Post-contrast: Ring/nodular enhancement.
• GRE/SWI: Blooming due to haemorrhage/calcifications.

8) Pilocytic Astrocytoma

Overview

• Most common primary brain tumour in children bur also seen in adults.
• Slow-growing, well-circumscribed, often cystic with an enhancing mural nodule.
• Associated with BRAF mutations, particularly in NF1 cases.

Key Imaging Features

• T1: Iso- to hypointense mural nodule; cystic portion follows CSF signal.
• T2: Hyperintense cystic component; iso- to hyperintense mural nodule.
• FLAIR: Hyperintense solid nodule; cystic component follows CSF signal.
• DWI: No significant restricted diffusion (differentiates from high-grade gliomas).
• Post-contrast: ; cyst wall typically non-enhancing.• GRE/SWI: May show microbleeds or hemosiderin deposits.

9) Rosette-Forming Glioneuronal Tumour

Overview

• Rare, slow-growing tumour.
• Arises in the posterior fossa, mainly affecting the fourth ventricle and cerebellum.
• Mixed glioneuronal tumour with characteristic rosette-like architecture.
• Typically affects young adults.

Key Imaging Features

• T1: Hypointense to grey matter; may contain cystic or mucinous components.
• T2: Hyperintense with cystic changes; often well-defined; may show multiple small non-enhancing cysts.
• FLAIR: Hyperintense solid areas; cystic components may follow CSF signal.
• DWI: No restricted diffusion (differentiates from high-grade gliomas or medulloblastomas).
• Post-contrast: Mild to moderate enhancement, often patchy or rim-like rather than strong nodular enhancement.
• GRE/SWI: No significant susceptibility artefacts (no haemorrhage or calcification).

10) Solitary Fibrous Tumour

Overview

• Rare mesenchymal tumour arising from the dura, commonly near the posterior fossa, tentorium, or CPA.
• Previously grouped with haemangiopericytomas; exhibits a spectrum from benign to aggressive.
• Originates from fibroblastic/pericytic cells, often hypervascular.
• More common in middle-aged adults.

Key Imaging Features

• T1: Iso- to hypointense relative to grey matter; well-circumscribed, dural-based lesion.
• T2: Variable, often heterogeneous signal; prominent flow voids indicating hypervascularity.
• FLAIR: Hyperintense solid components; may show perilesional oedema.
• DWI: Mild restricted diffusion in hypercellular areas (notable in higher-grade variants).
• Post-contrast: Intense, homogeneous enhancement; may show a "dural tail sign," similar to meningiomas.
• GRE/SWI: Susceptibility artefacts due to vascularity, aiding differentiation from meningiomas.

11) Subependymoma 

Overview

• Benign, slow-growing tumour arising from subependymal glial cells.
• Most commonly found in the fourth ventricle and lateral ventricles.
• Non-invasive with low mitotic activity and an excellent prognosis.

Key Imaging Features

• T1: Iso- to hypointense relative to grey matter; well-demarcated, often attached to the ventricular wall.
• T2: Hyperintense with a heterogeneous speckled appearance due to microcysts or calcifications; typically non-invasive without surrounding oedema.
• FLAIR: Hyperintense, particularly in solid components.
• DWI: No restricted diffusion (helps differentiate from higher-grade ependymomas or medulloblastomas).
• Post-contrast: Minimal to no enhancement; larger lesions may show patchy enhancement.
• GRE/SWI: Punctate blooming artefacts due to calcifications (useful in differentiation from ependymomas).

12) Diffuse Midline Glioma

Overview

• High-grade, infiltrative tumour affecting brainstem, thalamus, and spinal cord.
• Primarily in children but also seen in adults.
• Easy to overlook on CT due to beam hardening artefact.
• Sagittal reconstructions are helpful to identify the tumour.• Associated with poor prognosis.

Key Imaging Features

• T1: Hypointense or isointense; often poorly defined; expansile growth in midline structures.
• T2: Hyperintense; diffusely infiltrates midline structures; may extend along white matter tracts.
• FLAIR: Hyperintense with poorly defined borders, reflecting oedema and infiltration.
• DWI: Variable restricted diffusion; more aggressive variants show increased restriction.
• Post-contrast: Minimal to no enhancement in early stages; patchy or ring-like enhancement in advanced stages, particularly in necrotic areas.
• GRE/SWI: Common microhaemorrhages and vascular abnormalities.