This chapter is a radiology-reading reference for neurologists — sequence-by-sequence interpretation, normal anatomy, and sign recognition. It pairs with the rest of the Diagnostics section: order tests via the Lab Diagnostics / Genetics / Neurophysiology chapters; read the images here. The focus is on what the image is telling you and what to do next, not on physics for its own sake.

🔹 How to Use This Chapter

Three-step framework: (1) Where is the lesion? (2) What does its signal characteristics tell you? (3) What clinical syndrome maps to that “where + what”?
Always start with anatomy — gray vs white matter, vascular territories, deep gray nuclei, brainstem levels. Misreading anatomy is the commonest cause of misinterpretation.
Match the modality to the question: acute stroke → CT then MRI DWI; SAH → non-contrast CT then CTA; mass → MRI + contrast ± perfusion + spectroscopy; demyelinating → MRI brain + cord with 3D-FLAIR; epilepsy presurgical → high-resolution 3T MRI epilepsy protocol; dementia → MRI volumetric + targeted PET.
Use a systematic search pattern on every study — don’t anchor on the first finding.
Signal-intensity rules: fluid (CSF, edema) is dark on T1 / bright on T2 / bright on FLAIR (except CSF which suppresses) / restricts on DWI only when cytotoxic. Fat is bright on T1. Blood signal changes over time (see SWI / GRE).
Always read the brain AND the bones AND the vessels AND the soft tissues on every CT and MRI. Subdurals, sinus disease, dissections, and skull base lesions live in those windows.

Chapter Layout

Subsection 1: Approach to Image Interpretation

Overview — this page; how to read this chapter.
Normal Anatomy on CT and MRI — landmarks, deep gray nuclei, internal capsule, ventricles, brainstem levels, vascular territories.
A Systematic Search Pattern — checklist-based reading that prevents satisfaction-of-search errors.
Physics Primer for Clinicians — T1 vs T2 vs FLAIR vs DWI/ADC vs SWI/GRE; contrast behavior; signal-intensity rules.

Subsection 2: Modality-Specific Interpretation

Non-Contrast CT — hyperdense vessel, loss of gray-white differentiation, ASPECTS, ICH patterns, SAH, mass effect, midline shift.
MRI Sequences — T1, T2, FLAIR, DWI/ADC, SWI/GRE, post-contrast T1: what each shows + classic patterns.
CTA / MRA / DSA / Venography — LVO, stenosis, dissection, aneurysm, AVM, vasculitis, dural fistula, CVT.
Perfusion & Advanced MR — CTP, DSC-MR, ASL; core vs penumbra; RAPID output; spectroscopy basics.
Nuclear & Molecular Imaging — FDG-PET, amyloid PET, tau PET, DAT-SPECT, brain perfusion SPECT.

Subsection 3: Pattern Recognition by Clinical Context

Stroke & Hemorrhage — acute ischemia, ASPECTS, ICH localization, SAH, CVT, dissection.
Demyelinating & Inflammatory — MS (Dawson, 2024 MAGNIMS criteria), NMO, MOG-AD, ADEM, PML.
Tumors — glioma vs metastasis vs lymphoma vs abscess; perfusion / spectroscopy; meningioma, schwannoma, pituitary.
Epilepsy — MTS, FCD, polymicrogyria, heterotopias, tubers, DNET, ganglioglioma; epilepsy MRI protocol.
Dementia & Neurodegeneration — atrophy patterns (AD, FTD, DLB), MSA / PSP signs, CJD, amyloid/tau PET.

The Three-Step Reading Framework

Almost every neuroimaging interpretation reduces to three questions, asked in order.

Step 1 — Where Is the Lesion?

Vascular territory: MCA (superficial vs deep), ACA, PCA, ophthalmic, AICA/PICA/SCA, lenticulostriate, thalamoperforator, anterior choroidal, basilar perforators, watershed.
Tissue compartment: cortical gray, subcortical white, juxtacortical, periventricular, deep gray, brainstem, cerebellum, spinal cord, leptomeningeal.
Symmetry: unilateral favors vascular / focal / tumor; symmetric bilateral favors metabolic / toxic / degenerative / hypoxic.
Pattern: solitary mass, multifocal nodular, confluent, gyriform, periventricular plaque-like.

Step 2 — What Are Its Signal Characteristics?

T1, T2, FLAIR signal: bright, intermediate, dark? Compare to gray, white, CSF.
Diffusion restriction (high DWI + low ADC): cytotoxic edema (acute infarct, abscess, hypercellular tumor like lymphoma, viscous fluid, certain prion lesions).
Susceptibility (SWI / GRE blooming): blood products (hemosiderin), calcium, iron, air, certain melanin-containing lesions.
Contrast enhancement: pattern (ring, nodular, gyriform, leptomeningeal, dural) + intensity. Implies blood-brain barrier breakdown.
Mass effect / edema: vasogenic (white-matter sparing of cortex, finger-like) vs cytotoxic (involves both gray and white).

Step 3 — What Clinical Syndrome Maps to “Where + What”?

Multiple discrete vascular-territory lesions of different ages → embolic source (cardiac, arch).
Confluent periventricular white matter without mass effect in older adult → small-vessel disease.
Multiple ovoid lesions perpendicular to ventricles (Dawson fingers) + spinal cord lesions in young adult → MS.
Ring-enhancing lesion with central restriction in immunocompromised → abscess / toxoplasmosis vs lymphoma.
Hyperdense vessel + cortical ribbon loss + lentiform obscuration in stroke window → hyperacute MCA stroke.
Symmetric thalamic / basal-ganglia T2 signal → metabolic / toxic / infectious / Wernicke / mitochondrial.
Mesial temporal sclerosis (hippocampal atrophy + T2 hyperintensity) → temporal lobe epilepsy.
Hummingbird sign (midbrain atrophy with preserved pons) → PSP.
Hot cross bun pons → MSA-cerebellar.
Cortical ribbon DWI signal + pulvinar bright on FLAIR → CJD.

What This Chapter Does Not Cover (Yet)

Spine imaging: degenerative, tumor, MS, NMO, infection — will get its own chapter.
Pediatric / neonatal imaging: myelination patterns, HIE, congenital malformations — dedicated chapter planned.
Functional imaging in depth: fMRI, DTI, tractography — covered briefly in epilepsy presurgical workup; full coverage later.
Interventional neuroradiology procedures: thrombectomy, coiling, embolization technique — covered procedurally elsewhere; angiographic appearance covered here.

Cross-References

Ordering imaging: see the relevant clinical chapter (Stroke, MS, Epilepsy, Headache, Tumor, Dementia).
Lab Diagnostics: paired CSF/serum studies for demyelinating, infectious, autoimmune.
Genetics: imaging-guided genetic workup (e.g., NBIA, leukodystrophy MRI patterns drive panel choice).
Neurophysiology: EEG/EMG complements imaging in epilepsy, encephalopathy, neuromuscular.

References

Osborn AG. Osborn’s Brain: Imaging, Pathology, and Anatomy. 2nd ed. Elsevier; 2018.
Smirniotopoulos JG, Murphy FM, Rushing EJ, et al. Patterns of contrast enhancement in the brain and meninges. RadioGraphics. 2007;27(2):525-551.
Filippi M, Preziosa P, Banwell BL, et al. Assessment of lesions on magnetic resonance imaging in multiple sclerosis: practical guidelines. Brain. 2019;142(7):1858-1875.
Wahlund LO, Westman E, van Westen D, et al. Imaging biomarkers of dementia: recommended visual rating scales with teaching cases. Insights Imaging. 2017;8(1):79-90.