The role of computed tomography (CT) and magnetic resonance imaging (MRI) in the diagnosis of patients with seizures

Discover how CT and MRI are used in the diagnosis of underlying brain disorders for patients with seizures.
Last update18th Dec 2020

Let’s review several examples of brain abnormalities that are difficult—if not impossible—to detect on computed tomography (CT).

Whenever a patient has had multiple seizures, or if there is a strong clinical suspicion that a seizure is secondary to an underlying brain lesion (and the CT scan is normal), magnetic resonance imaging (MRI) is usually warranted.

Case 1: A small metastatic lesion is best viewed on contrast-enhanced MRI

Small metastatic lesions can lead to seizures, but are difficult (or even impossible) to see on non-contrast MRI. Our first case features two MRI scans with contrast that demonstrates small metastatic lesions. One of these lesions is within the cortex and could represent the source of the seizures.

Figure 1. Magnetic resonance imaging (MRI) with contrast demonstrating two small metastatic lesions in a patient with seizures. The lesion within the cortex could represent the source of the seizures.

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Case 2: A cerebellar metastasis is more evident on enhanced MRI

In the next case, a patient’s cerebellar metastasis is much more evident on an enhanced MRI scan than on the non-contrast fluid-attenuated inversion recovery (FLAIR) scan.

Figure 2. A cerebellar metastasis is much more evident on the enhanced magnetic resonance imaging (MRI) scan than on the non-contrast fluid-attenuated inversion recovery (FLAIR) scan.

Case 3: A herpes encephalitis abnormality is better viewed using FLAIR MRI

Our third case involves a patient with seizures secondary to herpes encephalitis. The abnormality in the patient’s right temporal lobe is much more apparent on the FLAIR MRI compared to CT (Fig. 3).

Figure 3. Computed tomography (CT) scan showing an abnormality due to herpes encephalitis in the patient’s right temporal lobe, and a fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) image which more clearly shows the abnormality.

Case 4: A small cavernoma is best viewed with gradient echo MRI

In our fourth case, the patient had a cavernoma involving the left insular cortex. In this circumstance, the CT scan might show some high attenuation within the cavernoma, but the CT appeared normal since the lesion was small and barely visible on T2-weighted MRI. Small cavernomas are best seen on gradient echo or susceptibility-weighted MRI images.

Figure 4. A T2-weighted magnetic resonance image (MRI) scan from a patient with a cavernoma involving the left insular cortex where the lesion is barely visible, and a gradient echo MRI scan where the small cavernoma is more conspicuous.

Case 5: A cavernoma is much more evident on MRI

Keep in mind the concept of conspicuity when considering the role of CT and MRI in patients with seizures. In our fifth case, even though the CT demonstrates a small area of high attenuation in the white matter, the cavernoma is much more conspicuous on MRI.

Figure 5. Computed tomography (CT) demonstrates a small area of high attenuation in the white matter in a patient with a cavernoma, but the magnetic resonance imaging (MRI) makes it much more conspicuous.

Case 6: Left-sided mesial temporal sclerosis on MRI in a patient with epilepsy

In our sixth case, the MRI from a patient with epilepsy demonstrated left-sided mesial temporal sclerosis. The right hippocampus is normal and appears larger and lower in signal intensity than the left hippocampus. This is a typical finding with this disease and would be almost impossible to detect on CT. In appropriate circumstances, the patient may be a candidate for surgery and would have a high likelihood of improved seizure control afterward.

Figure 6. MRI from a patient with epilepsy demonstrating left-sided mesial temporal sclerosis. The normal right hippocampus is larger and lower in signal intensity than the left hippocampus, which are typical findings with this disease and would not be evident on CT.

So, we’ve covered imaging approaches for patients with seizures. In patients with one or more new seizures, even when the CT scan is normal, consider MRI with contrast when you have a reasonably high degree of suspicion that the patient has an underlying brain lesion. But, in patients with epilepsy, there is almost no reason to start with CT because an MRI is much more likely to demonstrate subtle changes in the brain that may be the source of the seizures.

That’s it for now. If you want to improve your understanding of key concepts in medicine, and improve your clinical skills, make sure to register for a free trial account, which will give you access to free videos and downloads. We’ll help you make the right decisions for yourself and your patients.

Recommended reading

  • Bronen, RA, Fulbright, RK, Spencer, DD, et al. 1996. Refractory epilepsy: comparison of MR imaging, CT, and histopathologic findings in 117 patients. Radiology201: 97–105. PMID: 8816528
  • Salmenpera, TM and Duncan, JS. 2005. Imaging in epilepsy. J Neurol Neurosurg Psychiatry76: iii2–iii10. PMID: 16107387
  • Friedman, E. 2014. Epilepsy imaging in adults: getting it right. AJR Am J Roentgenol203: 1093–1103. PMID: 25341150

About the author

Alexander Mamourian, MD
Professor Emeritus of Radiology at the University of Pennsylvania and Professor of Radiology, Neurosurgery, and Neurology at Penn State, Hershey Medical Center, USA.
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