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Brain MRI with Contrast

Contrast-enhanced brain MRI is the primary imaging modality for evaluating intracranial pathology owing to its superior soft-tissue contrast and multiparametric characterization. It combines anatomical, fluid-sensitive, diffusion, and post-gadolinium sequences to detect and characterize tumors, demyelination, ischemia, infection, and other processes. Gadolinium enhancement identifies blood-brain barrier breakdown and abnormal vascularity. It is central to diagnosis, treatment planning, and follow-up across neuro-oncology, neuroinflammatory, and neurodegenerative disease.

Indications

  • Suspected or known intracranial neoplasm (primary or metastatic) for detection, characterization, and treatment response
  • Evaluation and monitoring of multiple sclerosis and other demyelinating/inflammatory disease per revised McDonald criteria
  • Suspected CNS infection: abscess, meningitis, encephalitis, ventriculitis
  • New-onset seizures, focal neurological deficit, or suspected cortical malformation
  • Pituitary and sellar/parasellar lesions with dedicated thin-section dynamic pituitary protocol
  • Cognitive decline/dementia workup and characterization of neurodegenerative patterns
  • Cranial nerve palsy, sensorineural hearing loss (IAC protocol), and skull base pathology
  • Characterization of acute or subacute stroke and its complications when CT is indeterminate

Contraindications & Cautions

  • Non-MRI-conditional cardiac pacemakers/defibrillators, cochlear implants, certain neurostimulators, and ferromagnetic intracranial aneurysm clips
  • Intraocular or intracranial ferromagnetic foreign bodies (orbital radiograph if metalworker history)
  • Severe renal impairment (eGFR <30) is a relative contraindication to gadolinium due to nephrogenic systemic fibrosis risk; use macrocyclic agents and weigh risk-benefit
  • Known severe gadolinium hypersensitivity; prior anaphylactoid reaction
  • Pregnancy: avoid gadolinium unless the benefit clearly outweighs risk, as it crosses the placenta
  • Severe claustrophobia or inability to remain still may require sedation or anesthesia

Patient Preparation

  • Screen thoroughly for implants, devices, prior surgery, and metallic foreign bodies with a completed MRI safety questionnaire
  • Check renal function (eGFR) prior to gadolinium administration per local protocol
  • Obtain informed consent for contrast; document prior contrast reactions and allergies
  • No fasting required for a standard study; ensure hydration
  • Establish reliable IV access (typically 20-22G) for power or hand injection of gadolinium
  • Remove all metallic objects, dentures, hearing aids, and provide hearing protection
  • Position supine, head-first, immobilize head within the dedicated head coil; explain scan duration and provide alarm bulb

Technique & Parameters

  • Field strength 1.5T or 3T using a multichannel head/neurovascular coil
  • Sagittal T1 localizer, axial T2 FSE, axial and 3D FLAIR for edema and demyelination
  • Axial DWI with ADC map (b=0 and b=1000) for acute ischemia and cellularity
  • Axial or volumetric T1 pre-contrast, then T1 post-gadolinium in axial, coronal, and sagittal planes
  • Susceptibility-weighted imaging (SWI/GRE) for hemorrhage, microbleeds, and calcification
  • Slice thickness 3-5 mm (thinner 1 mm isotropic 3D for volumetric/tumor/pituitary work)
  • Gadolinium dose 0.1 mmol/kg IV; dynamic thin-section acquisition for pituitary microadenoma
  • Add MRA/MRV, perfusion, or spectroscopy as clinically indicated

Systematic Review

  • Assess gray-white differentiation, sulcal and ventricular size, and midline shift/herniation
  • Review each lobe, deep gray nuclei, and posterior fossa/brainstem systematically
  • Evaluate FLAIR for periventricular, juxtacortical, and infratentorial signal abnormality
  • Interrogate DWI/ADC for restricted diffusion (ischemia, abscess, hypercellular tumor)
  • Scrutinize post-contrast sequences for parenchymal, leptomeningeal, dural, or ependymal enhancement
  • Check the sella, cavernous sinuses, orbits, IACs, and craniocervical junction
  • Review SWI for microbleeds, hemorrhage, and mineralization
  • Inspect the extracranial soft tissues, paranasal sinuses, mastoids, and calvarium

Key Findings & Significance

  • Ring-enhancing lesion with central diffusion restriction suggests pyogenic abscess versus necrotic tumor
  • Periventricular ovoid FLAIR lesions perpendicular to ventricles (Dawson fingers) indicate demyelination
  • Restricted diffusion in a vascular territory signifies acute infarction
  • Homogeneous dural-based enhancing mass with a dural tail favors meningioma
  • Leptomeningeal enhancement suggests infectious, inflammatory, or carcinomatous meningitis
  • Mesial temporal/limbic T2-FLAIR hyperintensity raises herpes or autoimmune encephalitis
  • Sellar mass with delayed enhancement relative to gland suggests pituitary adenoma
  • Symmetric hippocampal atrophy supports Alzheimer-type neurodegeneration

Differential Considerations

  • Ring-enhancing lesions: metastasis, glioblastoma, abscess, demyelination (tumefactive), subacute infarct, resolving hematoma
  • Multiple T2 white matter lesions: MS, small vessel ischemia, migraine, vasculitis, ADEM, Lyme
  • Intra-axial mass: primary glioma, metastasis, lymphoma, tumefactive demyelination
  • Extra-axial mass: meningioma, schwannoma, metastasis, dural metastasis, hemangiopericytoma
  • Restricted diffusion: acute infarct, abscess, epidermoid, hypercellular tumor, acute demyelination
  • Sellar/suprasellar lesion: pituitary adenoma, craniopharyngioma, Rathke cleft cyst, meningioma, aneurysm

Pearls & Pitfalls

  • Always correlate enhancement with DWI/ADC to distinguish abscess from necrotic tumor
  • FLAIR is more sensitive than T2 for cortical and periventricular lesions but prone to CSF flow artifact
  • Post-contrast FLAIR increases sensitivity for subtle leptomeningeal disease
  • Do not mistake normal enhancing structures (pituitary, choroid plexus, vessels, dural sinuses) for pathology
  • Motion and susceptibility artifacts (dental, postoperative) can mimic or obscure lesions; review all planes
  • In suspected microadenoma, dynamic timing is critical as lesions are only transiently hypoenhancing
  • Delayed enhancement after high-dose or double-dose gadolinium increases metastasis conspicuity

Structured Report

  • State the clinical indication, comparison studies, and technique including contrast dose
  • Describe lesion location, size, signal characteristics, diffusion, enhancement pattern, and mass effect
  • Report presence/absence of hemorrhage, herniation, midline shift, and hydrocephalus
  • Comment on white matter burden, atrophy pattern, and incidental extracranial findings
  • For MS, quantify new/enlarging and enhancing lesions relative to prior studies
  • Impression: succinct diagnosis or ranked differential with recommended follow-up or correlation
  • Flag urgent findings (acute infarct, hemorrhage, herniation, abscess) and communicate directly

References

  • ACR-ASNR Practice Parameter for the Performance of MRI of the Brain
  • ACR Appropriateness Criteria (headache, seizure, dementia, focal neurologic deficit)
  • Thompson et al., 2018 Revised McDonald Criteria for MS diagnosis (Lancet Neurology)
  • Osborn's Brain: Imaging, Pathology, and Anatomy, 3rd edition
  • RadioGraphics review articles on intracranial ring-enhancing lesions and CNS infection

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.