Suspected brain metastases

ACR AC Brain Tumors (2025 rev)

Contrast-enhanced MRI is the study, and the reason is countability: the number and location of lesions determines whether the patient receives stereotactic radiosurgery, whole-brain radiotherapy or neither.

Known or strongly suspected extracranial malignancy with new neurological symptoms, or asymptomatic staging in a tumour type with a high rate of occult intracranial spread.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

MRI Brain — tumour protocol

MRI Brain

What we'd amend, and why

Metastases are enhancing lesions at the grey-white junction, often only a few millimetres across, in a distribution CT cannot resolve — particularly in the posterior fossa, where beam-hardening artefact is worst. Gadolinium is not optional, because a small metastasis may be invisible before contrast and obvious after it. The count matters as much as the diagnosis: the threshold between focal stereotactic treatment and whole-brain radiotherapy is a number of lesions, so an under-sensitive study produces the wrong treatment rather than merely a less detailed report.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-mr-device-screening — MR safety screening for implants and foreign bodies; checked by Radiographer at the scanner
rulerule-contrast-reaction-premed — Prior contrast reaction and elective premedication; checked by Nurse before the scan
rulerule-gadolinium-renal — Kidney function and gadolinium-based contrast; checked by Radiographer at the scanner
rulerule-paeds-sedation — Sedation or anaesthesia for a child; checked by Nurse before the scan
rulerule-pregnancy-gadolinium — Gadolinium in known or possible pregnancy; checked by Radiographer at the scanner
rulerule-iv-access — Intravenous access adequate for the planned injection; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(2)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

MR safety screening for implants and foreign bodies
Complete the MR safety questionnaire, verify implant labelling and its stated conditions of use against this scanner and this protocol, and ensure no ferromagnetic object enters Zone IV.
Radiographer at the scannerBefore the scan
Flags back if: An implant or retained foreign body that is MR Unsafe, unlabelled, or cannot be identified; or an MR Conditional device whose stated conditions this scanner or the requested protocol cannot satisfy; or a credible unexcluded intraocular metallic foreign body history.
Intravenous access adequate for the planned injection
Site and test a cannula that supports the protocol flow rate, preferring an antecubital or large forearm vein, and observe the injection for extravasation. A 20-gauge or larger cannula is preferred for flow rates of 3 mL/s or more.
Radiographer at the scannerAt the scanner
Flags back if: No cannula can be sited that supports the protocol flow rate — for example only a 22-gauge hand or foot cannula for a CT angiogram needing 4–5 mL/s; or the only available access is a central line or port that is not labelled power-injectable; or an extravasation occurs.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	MRI Brain MRI Brain — tumour protocol usually appropriate	Metastases are enhancing lesions at the grey-white junction, often only a few millimetres across, in a distribution CT cannot resolve — particularly in the posterior fossa, where beam-hardening artefact is worst. Gadolinium is not optional, because a small metastasis may be invisible before contrast and obvious after it. The count matters as much as the diagnosis: the threshold between focal stereotactic treatment and whole-brain radiotherapy is a number of lesions, so an under-sensitive study produces the wrong treatment rather than merely a less detailed report.
Second line	CT Head CT Head — Unenhanced and Post-Contrast	Reserved for the patient who genuinely cannot have MRI — a non-conditional device, an unmanageable claustrophobia, or an acute deterioration where MRI cannot be obtained in time. It will show large or oedematous lesions and will miss small ones, so a negative contrast-enhanced CT does not exclude metastatic disease and should be reported as such.

Pitfalls

Accepting an unenhanced MRI request for this question, which systematically under-detects and produces the wrong radiotherapy decision.
Thick post-contrast sections that miss millimetric lesions; if radiosurgery is being planned, the acquisition must be volumetric and thin.
Calling a solitary ring-enhancing lesion a metastasis without looking at diffusion — abscess restricts centrally and is managed entirely differently.
Failing to distinguish radiation necrosis from progression on morphology alone in a previously treated patient.

Priors — what to pull first

Retrieve the previous brain MRI and compare lesion-by-lesion. New lesion count on treatment is a response criterion, not an incidental observation.
Check for prior stereotactic radiosurgery to the same site, because treatment effect and progression look alike and the treatment history is what separates them.

What makes a good request

Say which primary and which treatment decision is pending. Screening a stage III melanoma and characterising a solitary lesion before resection are different requests that happen to share a study name.
Thin-section volumetric post-contrast T1 is what makes small lesions countable, and it is also what a radiosurgery plan is built on. Thick two-dimensional post-contrast sections systematically under-count.
Susceptibility and diffusion sequences matter here, because haemorrhagic metastases and abscesses are the two things most often mistaken for one another.

Scoring this once it is done

The classification and risk tools this question ends in.

RECIST 1.1 Tumor Response RANO Criteria (High-Grade Glioma)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

MRI Brain — tumour protocol CT Head — Unenhanced and Post-Contrast

Confirm locally

MRI Brain — tumour protocol: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.