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Drug-resistant epilepsy — pre-surgical assessment

ACR AC Seizures and Epilepsy (2020)

The study is the same anatomical region as a routine brain MRI and a completely different examination. What is being asked for here is a dedicated epilepsy protocol, and requesting or accepting a general brain MRI is the commonest way this pathway fails.

Focal seizures continuing despite adequate trials of two tolerated antiseizure medications, where resective surgery is under consideration and a resectable lesion must be found or excluded.

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 — epilepsy protocol
MRI Brain
What we'd amend, and why
  • Epileptogenic lesions are defined by their size and their location rather than by any signal abnormality a routine study would flag. Focal cortical dysplasia sits at the bottom of a sulcus and is a few millimetres across; hippocampal sclerosis is a volume and internal architecture judgement that requires thin coronal sections angled perpendicular to the hippocampal long axis. A standardised, repeatable protocol with volumetric acquisitions is therefore not a refinement of the routine study — it is the only version of it that can answer this question.

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

How was this decided?
  1. pathwayadult — Pre-surgical assessment
  2. rulerule-mr-device-screening — MR safety screening for implants and foreign bodies; checked by Radiographer at the scanner
  3. 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.

Pre-surgical assessment

Matches your inputsDefault
RoleStudy & protocolWhy this answers the question
First line
MRI Brain
MRI Brain — epilepsy protocol
usually appropriate
Epileptogenic lesions are defined by their size and their location rather than by any signal abnormality a routine study would flag. Focal cortical dysplasia sits at the bottom of a sulcus and is a few millimetres across; hippocampal sclerosis is a volume and internal architecture judgement that requires thin coronal sections angled perpendicular to the hippocampal long axis. A standardised, repeatable protocol with volumetric acquisitions is therefore not a refinement of the routine study — it is the only version of it that can answer this question.
Second line
FDG PET-CT
FDG PET-CT — skull base to mid-thigh
When the dedicated MRI is negative, interictal FDG PET localises the seizure onset zone by regional hypometabolism, which can be present where structural imaging is normal. Its role is lateralisation and localisation to guide intracranial electrode placement, not tissue diagnosis, and it is interpreted alongside the MRI rather than instead of it.

Pitfalls

  • Booking this as a routine brain MRI. The slice thickness, angulation and volumetric sequences are the entire point, and a general study reported as normal delays surgery by months.
  • Reporting hippocampal asymmetry without the coronal oblique acquisition, where partial volume effects make asymmetry unreliable.
  • Missing bottom-of-sulcus dysplasia by not reviewing the volumetric acquisition in all three planes with the appropriate window.
  • Treating an outside normal MRI as excluding a lesion when its protocol was never designed to find one.

Priors — what to pull first

  • Obtain the previous MRI and its actual sequence parameters, not just the report. The question is whether the earlier study was capable of showing the lesion.
  • Prior PET or ictal SPECT should be reviewed alongside the new MRI, because concordance across modalities is what drives the surgical decision.

What makes a good request

  • State the suspected seizure onset zone from the semiology and EEG. It determines where the high-resolution obliquely angled sequences are placed, and a protocol targeted at the wrong lobe is a wasted study.
  • A previously reported normal brain MRI performed with general parameters is not a negative result for this question. Re-imaging with a dedicated protocol reclassifies a meaningful proportion of these patients.
  • Contrast is not part of the standard epilepsy protocol; it is added when a neoplastic or inflammatory cause is specifically suspected.

How these studies are acquired

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

MRI Brain — epilepsy protocolFDG PET-CT — skull base to mid-thigh

Confirm locally

  • MRI Brain — epilepsy 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

  1. ACR Appropriateness Criteria — Seizures and Epilepsy (2020) · ACR Appropriateness Criteria
  2. American College of Radiology Manual on MR Safety: 2024 Update and Revisions. Radiology. · ACR MR Safety
  3. ACR Manual on MR Safety — zoning, MR Safe / MR Conditional / MR Unsafe labelling, and screening of patients and personnel · ACR MR Safety
  4. Safety of MRI in patients with cardiac implantable electronic devices — conditions of use, device interrogation and monitoring · Primary literature
  5. AAP/AAPD Guidelines for Monitoring and Management of Pediatric Patients Before, During, and After Sedation for Diagnostic and Therapeutic Procedures. Pediatrics 2019;143(6):e20191000. · Other
  6. Sedation and anaesthesia for imaging of the infant and neonate — a brief review (feed-and-wrap, fasting, monitoring) · Primary literature
  7. Image Gently — reducing the need for sedation through preparation and faster protocols in paediatric imaging · Image Gently

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