When to Order Imaging for Seizures and Epilepsy: ACR Appropriateness Decoded

When to Order Imaging for Seizures and Epilepsy: ACR Appropriateness Decoded

It’s 2 a.m. in the emergency department, and you’ve just stabilized a patient after their first-ever generalized tonic-clonic seizure. They have no history of trauma, and their neurologic exam is now non-focal. The immediate question is whether to order a CT or an MRI, and if contrast is necessary. This decision carries implications for diagnostic yield, radiation exposure, and cost. Choosing the right initial imaging study is critical for identifying underlying structural causes, from tumors and vascular malformations to cortical dysplasia, which can fundamentally alter management. This guide breaks down the American College of Radiology (ACR) Appropriateness Criteria for seizures and epilepsy, providing clear, evidence-based recommendations to help you select the most suitable imaging test for your patient’s specific clinical scenario.

What Does the ACR Guideline for Seizures and Epilepsy Cover?

The ACR Appropriateness Criteria for Seizures and Epilepsy provides guidance for the diagnostic workup of patients presenting with seizures. The scope is focused on structural neuroimaging and is designed to assist referring physicians and radiologists in choosing the most appropriate study based on the clinical context. These guidelines apply to both adult and pediatric patients and cover a range of common clinical situations.

This topic specifically addresses:

• Initial imaging for a new-onset seizure, both with and without a history of trauma.
• Imaging for patients with a known seizure disorder who experience a change in seizure type or develop new neurologic deficits.
• Evaluation of patients with a known seizure disorder and a history of a brain tumor.
• Pre-surgical planning for patients with medically refractory epilepsy.

These criteria do not cover the routine, repeat imaging of patients with a stable, established seizure disorder without any change in clinical status. They also primarily focus on the role of structural imaging (MRI and CT) and functional imaging (PET, SPECT, fMRI) in specific contexts, rather than the use of electroencephalography (EEG), which remains a cornerstone of epilepsy diagnosis and classification.

What Imaging Should I Order for Seizures and Epilepsy? Recommendations by Clinical Scenario

Selecting the optimal imaging study for a patient with seizures depends heavily on the clinical presentation. The ACR provides specific recommendations for six distinct variants, guiding the choice between modalities like MRI, CT, and functional imaging.

For a patient with a new-onset seizure unrelated to trauma, the initial imaging of choice is an MRI of the head without IV contrast, which is rated “Usually Appropriate.” MRI offers superior soft tissue resolution to detect subtle structural abnormalities like cortical dysplasia, mesial temporal sclerosis, or low-grade neoplasms that can cause seizures. A CT of the head without IV contrast is also “Usually Appropriate” and is often used in the acute setting to rule out emergent conditions like hemorrhage, especially if MRI is not immediately available. The addition of contrast (either for MRI or CT) is generally not necessary for the initial workup unless there is a specific concern for a tumor, infection, or inflammatory process.

In the setting of a new-onset seizure with a history of trauma, the priority shifts to rapidly identifying acute intracranial injury. For this scenario, a CT of the head without IV contrast is “Usually Appropriate” to quickly detect skull fractures or intracranial hemorrhage. An MRI may be considered but is less critical in the immediate post-traumatic setting.

For patients with a known seizure disorder, the imaging approach varies. If the patient has unchanged seizure semiology, routine imaging is often not indicated, with most modalities rated “May be appropriate” or “Usually not appropriate.” However, if there is a change in seizure semiology, a new neurologic deficit, or failure to return to baseline, further imaging is warranted. In this case, an MRI of the head without and with IV contrast, an MRI of the head without IV contrast, and a CT of the head without IV contrast are all considered “Usually Appropriate” to evaluate for a new or progressive underlying lesion.

In patients with a known seizure disorder and a history of a tumor, an MRI of the head without and with IV contrast is “Usually Appropriate” to assess for tumor recurrence or progression as the cause of worsening seizures. Finally, for patients being considered for epilepsy surgery, a more extensive workup is needed. For surgical candidates or surgical planning, an MRI of the head without and with IV contrast and an MRI of the head without IV contrast are “Usually Appropriate” for detailed structural mapping. Advanced functional studies like FDG-PET/CT brain are also “Usually Appropriate” to help localize the epileptogenic zone.

ACR Imaging Recommendations Table for Seizures and Epilepsy

Adult vs. Pediatric Seizures and Epilepsy Imaging: Radiation Dose Tradeoffs

When selecting imaging for seizures, particularly in pediatric patients, radiation dose is a critical consideration. The principle of ALARA (As Low As Reasonably Achievable) guides the preference for non-ionizing modalities like MRI whenever clinically appropriate. Children are more radiosensitive than adults, and their longer life expectancy provides more time for potential long-term effects of radiation exposure to manifest. The ACR guidelines reflect this by providing distinct pediatric relative radiation level (RRL) estimates.

For example, a non-contrast head CT, while often necessary in acute trauma, carries an RRL of ☢ ☢ ☢ (1-10 mSv) for adults but a lower range of ☢ ☢ ☢ (0.3-3 mSv) for children, reflecting dose-reduction techniques used in pediatric protocols. Despite these adjustments, the cumulative dose from repeated CT scans is a significant concern. This reinforces why MRI, which involves no ionizing radiation (O 0 mSv), is the preferred modality for the initial, non-traumatic seizure workup in both children and adults. The decision to use a CT in a child must always balance the immediate diagnostic need against the long-term risks of radiation.

Imaging Protocol Details for Seizures and Epilepsy

Once you’ve decided on the right study based on the clinical scenario, the specific imaging protocol is crucial for maximizing diagnostic yield. An epilepsy-protocol MRI, for instance, includes specialized sequences and slice thicknesses designed to detect subtle epileptogenic lesions. Our protocol guides cover the essential technical details, contrast parameters, and interpretation principles for the studies recommended in these guidelines.

• CT Brain Without Contrast

Tools to Help You Order the Right Study

Navigating imaging guidelines and protocols can be complex, but several tools can streamline the process. These resources are designed to support evidence-based decision-making at the point of care, ensuring patients receive the most appropriate and safest imaging exam.

The ACR Appropriateness Criteria Lookup provides a comprehensive, searchable interface for all ACR guidelines, extending far beyond seizures and epilepsy. It allows you to quickly find recommendations for thousands of clinical variants, ensuring your ordering patterns align with national standards.

For detailed procedural information, the Imaging Protocol Library offers in-depth guides on how specific studies are performed. This is invaluable for understanding the nuances of an epilepsy-protocol MRI versus a standard brain MRI, helping you communicate effectively with the radiology department.

To address patient concerns about radiation and to track cumulative exposure, the Radiation Dose Calculator is an essential tool. It helps you estimate the effective dose from various CT scans and other imaging studies, facilitating informed conversations with patients and their families about the benefits and risks of a recommended test.

Frequently Asked Questions About Imaging for Seizures and Epilepsy

Why is MRI preferred over CT for a first-time, non-traumatic seizure?

MRI is preferred due to its superior soft-tissue contrast, which allows for the detailed evaluation of brain parenchyma. It is significantly more sensitive than CT for detecting subtle structural causes of seizures, such as cortical dysplasia, mesial temporal sclerosis, low-grade tumors, or cavernous malformations. Furthermore, MRI does not use ionizing radiation, which is a key safety advantage, especially in younger patients.

In what situations is a CT scan the right first choice for a new seizure?

A non-contrast head CT is the most appropriate initial imaging study in the setting of a new-onset seizure with a history of significant head trauma. Its primary role is to rapidly and reliably detect acute intracranial hemorrhage, skull fractures, or other emergent traumatic injuries that require immediate intervention. CT is also a reasonable first choice in non-traumatic settings when MRI is unavailable, contraindicated (e.g., incompatible implanted device), or if the patient is too unstable for a lengthy MRI scan.

Is contrast always needed when imaging a patient with a history of a brain tumor and new seizures?

In patients with a known brain tumor who present with new or worsening seizures, an MRI with and without IV contrast is “Usually Appropriate.” The contrast-enhanced sequences are crucial for assessing tumor progression, recurrence, or treatment-related changes like radiation necrosis, which can be new seizure foci. The pre-contrast images are still vital for detecting hemorrhage and comparing with prior studies.

What is the role of advanced imaging like PET, SPECT, or fMRI in seizure evaluation?

These advanced imaging modalities are generally not used for the initial diagnosis of seizures. Their primary role is in the presurgical evaluation of patients with medically refractory epilepsy. FDG-PET can identify areas of interictal hypometabolism, helping to localize the seizure focus. SPECT can map cerebral blood flow during a seizure (ictal) and between seizures (interictal) to pinpoint the origin. Functional MRI (fMRI) is used to map eloquent cortex (e.g., language and motor areas) to help surgeons avoid these critical areas during resection.

Does a patient with a stable seizure disorder need routine surveillance imaging?

No, for a patient with a known seizure disorder whose seizure type and frequency are stable and who has a normal, non-focal neurologic exam, routine follow-up imaging is generally not indicated. The ACR rates most imaging modalities as “May be appropriate” or “Usually not appropriate” in this scenario. Repeat imaging is typically reserved for patients who experience a significant change in their clinical status, such as a new seizure type, a new neurologic deficit, or a failure to return to their neurologic baseline after a seizure.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 12, 2026