Headache with red flag features

ACR AC Headache (2022 rev)

The counterpart to the uncomplicated headache card. Where a red flag is present the pre-test probability of structural disease rises enough to justify imaging, and MRI is the study because it answers far more of the differential than CT.

Headache with one or more of: new or changed pattern after age 50, progressive worsening, papilloedema or focal signs, known malignancy or immunocompromise, positional or Valsalva-provoked character, onset in pregnancy or the puerperium, or a preceding head injury.

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

Time since onset

Decides thrombolysis and thrombectomy windows, testicular salvage, and whether an ischaemic limb is still salvageable.

Immunosuppressed

Changes the differential rather than the modality.

Red flags

These accumulate rather than exclude. Back pain with one of these is a different question from back pain.

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 — routine unenhanced

MRI Brain

What we'd amend, and why

The differential behind a red flag headache is dominated by things CT resolves poorly or not at all: posterior fossa and pituitary lesions, early tumour, venous sinus thrombosis, intracranial hypotension, inflammatory and infective disease. MRI covers that whole list in one sitting without ionising radiation, which matters in a group who will often be scanned again. The ACR rates unenhanced MRI, contrast-enhanced MRI and unenhanced CT all as usually appropriate for this presentation, so this is a preference for breadth of coverage rather than a claim that CT is inappropriate.

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-paeds-sedation — Sedation or anaesthesia for a child; checked by Nurse before the scan

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)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.

Pathways

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

Headache measured in hours — CT answers within the hour

Role	Study & protocol	Why this answers the question
First line	CT Head CT Head — Unenhanced usually appropriate	A red flag headache of a few hours is a different question from a red flag headache of six weeks. The differential now leads with haemorrhage, and the ACR rates unenhanced CT as usually appropriate for this presentation — it reliably excludes what needs action tonight, it is deliverable in minutes, and MRI in the middle of the night usually is not. If the onset was thunderclap the subarachnoid haemorrhage pathway applies and the timing of the scan against the ictus is what decides whether a negative study stands alone.
Second line	MRI Brain MRI Brain — routine unenhanced	What the CT could not answer, once the emergency questions are closed: posterior fossa and pituitary lesions, early tumour, venous sinus thrombosis, intracranial hypotension, inflammatory and infective disease. A normal CT in an acutely presenting red flag headache narrows the differential; it does not close it, and the MRI that follows is where most of the diagnoses on this card are actually made.

Malignancy, immunocompromise or suspected infection — enhanced MRI is the study

Role	Study & protocol	Why this answers the question
First line	MRI Brain MRI Brain — with gadolinium usually appropriate	The named red flag decides the protocol, and in this group it decides it in one direction. Metastases, leptomeningeal disease, abscess, tuberculoma and the opportunistic infections of immunosuppression are defined by enhancement, and the unenhanced study that is a reasonable structural survey elsewhere is the study that reports a normal brain in a patient with thin meningeal deposits. Adding gadolinium at the outset costs one injection; discovering the need afterwards costs the appointment and the interval.
Reasonable alternative	CT Head CT Head — Unenhanced	Where MRI is contraindicated or the answer cannot wait for it. It excludes the findings that need action tonight and misses precisely what this arm was selected for — thin meningeal enhancement, small posterior fossa deposits, early cerebritis — so a normal CT in this group is a reason to arrange the MRI rather than to stop.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	MRI Brain MRI Brain — routine unenhanced usually appropriate	The differential behind a red flag headache is dominated by things CT resolves poorly or not at all: posterior fossa and pituitary lesions, early tumour, venous sinus thrombosis, intracranial hypotension, inflammatory and infective disease. MRI covers that whole list in one sitting without ionising radiation, which matters in a group who will often be scanned again. The ACR rates unenhanced MRI, contrast-enhanced MRI and unenhanced CT all as usually appropriate for this presentation, so this is a preference for breadth of coverage rather than a claim that CT is inappropriate.
Problem solving	MRI Brain MRI Brain — with gadolinium	Gadolinium is added for a specific suspicion rather than routinely: known malignancy or immunocompromise where metastatic or infective meningeal disease is the concern, suspected intracranial hypotension where diffuse pachymeningeal enhancement is the defining sign, or characterisation of an abnormality found on the unenhanced series.
Reasonable alternative	CT Head CT Head — Unenhanced	Appropriate where the presentation is acute enough to need an answer within the hour, where MRI is contraindicated, or where availability would otherwise push the study out by weeks. It reliably excludes the findings that need action tonight and misses a good deal of what MRI would show.

Pitfalls

Accepting the request without a stated red flag, which is the difference between this card and the uncomplicated headache card.
Truncating the study below the foramen magnum and missing a craniocervical junction or upper cord cause.
Missing pituitary and sellar lesions on a routine brain study, which needs dedicated thin sections when a visual field defect or endocrine abnormality is described.
Failing to recognise the signs of intracranial hypotension in a positional headache — brain sagging, dural enhancement, subdural collections — and reporting the collections in isolation.
Answering "new headache over 50" with a brain study and nothing else. Giant cell arteritis is the diagnosis in that age band that blinds people, it is not excluded by any brain scan, and the correct response is inflammatory markers and corticosteroid on suspicion with temporal artery ultrasound or biopsy to confirm — none of which should wait for the MRI.
Missing arterial dissection when the headache came with neck pain, a Horner syndrome or a transient deficit. The brain study can be normal; the answer is in the neck vessels.

Priors — what to pull first

A stable appearance on prior imaging converts many alarming-sounding headaches into a benign primary headache disorder.
In a patient with cancer, always compare with the most recent staging study before calling a new intracranial lesion.

What makes a good request

Name the red flag on the request. It is what converts an unjustified study into a justified one, and it also determines whether contrast is needed.
Contrast is added where the suspicion is neoplastic, infective or meningeal — known cancer, immunocompromise, suspected intracranial hypotension. It is not part of a general structural survey.
Thunderclap onset is a different card. That presentation is a subarachnoid haemorrhage pathway and starts with unenhanced CT.
The commonest dangerous cause of a new headache after 50 is not a structural intracranial lesion and is not answered by this pathway at all. Giant cell arteritis — new headache with scalp tenderness, jaw claudication, visual disturbance, polymyalgic symptoms or a raised ESR and CRP — is a clinical and laboratory diagnosis confirmed by temporal artery ultrasound or biopsy, treated with high-dose corticosteroid started on suspicion and not delayed for any test. A normal brain MRI is the characteristic false reassurance that precedes irreversible visual loss in the second eye. Where it is suspected, say so on the request: the imaging that helps is a temporal artery ultrasound or a large-vessel vasculitis study, not a brain scan.
Headache with neck pain, Horner syndrome, pulsatile tinnitus or a transient deficit raises carotid or vertebral dissection, which needs vascular imaging of the neck rather than a brain study alone.

How these studies are acquired

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

CT Head — Unenhanced MRI Brain — routine unenhanced MRI Brain — with gadolinium

Confirm locally

MRI Brain — routine unenhanced: 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.