🩺 Introduction
Intracranial neoplasms range from benign extra-axial tumors (like meningiomas) to highly aggressive intra-axial gliomas. MRI is the gold standard for characterization, local staging, surgical planning, and treatment follow-up.
🖼️ MRI Sequences in Brain Tumor Imaging
| Sequence | Use in Neoplasms |
|---|---|
| T1-weighted | Anatomy, hemorrhage, fat, post-contrast enhancement |
| T2-weighted / FLAIR | Tumor extent, peritumoral edema, cystic/necrotic changes |
| Post-contrast T1 | Enhancement pattern (solid, ring, nodular, dural tail) |
| Diffusion (DWI/ADC) | Tumor cellularity (restricted diffusion = high grade), abscess vs tumor |
| Perfusion MRI | Tumor vascularity, grading (rCBV ↑ in high-grade gliomas) |
| MR Spectroscopy (MRS) | Metabolic profile: ↑ choline, ↓ NAA, presence of lactate/lipid in high-grade tumors |
| SWI (Susceptibility) | Calcification, hemorrhage, microvascularity |
| Cine phase-contrast / CSF flow | Helpful in tumors compressing ventricles/CSF pathways |
🧩 General MRI Features of Neoplasms
- Location
- Intra-axial: Gliomas, metastases, lymphoma.
- Extra-axial: Meningioma, vestibular schwannoma, pituitary adenoma.
- Margins
- Benign → well-circumscribed.
- Malignant → irregular, infiltrative.
- Signal Characteristics
- T1: Hypo- to isointense.
- T2/FLAIR: Hyperintense, heterogeneous.
- Enhancement: Varies by vascularity and BBB breakdown.
- Edema & Mass Effect
- Peritumoral edema = vasogenic, best seen on FLAIR/T2.
- Midline shift, ventricular compression assessed on T2/FLAIR.
- Enhancement Patterns
- Homogeneous → meningioma, low-grade astrocytoma (sometimes non-enhancing).
- Ring-enhancing → glioblastoma, metastasis, abscess (DWI helps).
- Dural tail → meningioma.
🎯 Role of Advanced MRI
- Perfusion: Distinguishes high vs low grade (rCBV ↑ in glioblastoma, metastasis).
- Spectroscopy:
- ↑ Choline = increased cell turnover.
- ↓ NAA = neuronal loss.
- Lipid-lactate peak = necrosis (seen in high-grade tumors).
- Diffusion: Low ADC = high cellularity (lymphoma, medulloblastoma).
🧠 Teaching Pearls
- Always localize (intra-axial vs extra-axial) → it narrows differential.
- Enhancement + advanced sequences help grade tumors.
- Use DWI to separate abscess from tumor (abscess cavity = restricted diffusion).
- Perfusion & spectroscopy = indispensable in grading & recurrence vs radiation necrosis.
📊 MRI Features of Common Intracranial Tumors
| Feature | Glioblastoma (GBM) | Metastasis | Primary CNS Lymphoma (PCNSL) | Meningioma |
|---|---|---|---|---|
| Location | Intra-axial (cerebral hemispheres, often crossing corpus callosum – “butterfly”) | Intra-axial, usually at grey–white junction, multiple common | Deep periventricular, basal ganglia, corpus callosum | Extra-axial, along dura, falx, sphenoid wing, parasagittal |
| Margins | Irregular, infiltrative | Well-circumscribed, round | Ill-defined but can be solid, homogenous | Well-defined, broad dural base |
| T1 signal | Hypo- to isointense | Hypo- to isointense | Iso- to hypointense | Iso- to hypointense |
| T2/FLAIR | Heterogeneous hyperintensity with necrosis | Hyperintense, surrounding vasogenic edema | Relatively isointense to hypointense (due to cellularity) | Iso- to slightly hyperintense |
| Enhancement | Heterogeneous, ring-enhancing (central necrosis) | Usually ring-enhancing (solid/rim), multiple lesions common | Homogeneous, intense, solid enhancement | Homogeneous, strong enhancement; “dural tail” sign |
| Edema | Marked vasogenic edema | Disproportionately large perilesional edema | Mild to moderate | Mild |
| Diffusion (DWI/ADC) | Variable; necrotic areas non-restricting | Usually no marked restriction | Marked restricted diffusion (hypercellularity hallmark) | No restriction |
| Perfusion (rCBV) | High rCBV (neovascularity) | High rCBV | Low rCBV (unlike GBM) | Moderate rCBV |
| Spectroscopy | ↑ Choline, ↓ NAA, lactate-lipid peaks (necrosis) | Similar to GBM, less specific | ↑ Choline, ↓ NAA, no necrosis | Alanine peak (characteristic) |
| Other signs | “Butterfly glioma” when crossing corpus callosum | Multiple lesions, hemorrhagic in melanoma/choriocarcinoma | In immunocompromised, can mimic toxoplasmosis | Calcification, hyperostosis, CSF cleft sign |
🧠 Key Differentiators
- GBM → Irregular, necrotic, heterogeneous, crosses corpus callosum, high perfusion.
- Metastasis → Often multiple, grey–white junction, ring-enhancing with large edema.
- Lymphoma → Solid, homogeneous enhancement, restricted diffusion, low perfusion.
- Meningioma → Extra-axial, strong homogeneous enhancement, dural tail, possible calcification/hyperostosis.
✅ Conclusion
MRI provides unparalleled detail in localization, characterization, and grading of intracranial neoplasms. Conventional + advanced MRI sequences together help distinguish tumor types, plan surgery, and monitor treatment response.
