Let’s begin by clarifying the difference between the words seizures and epilepsy since they are not equivalent. When the history for a patient sent from the emergency room reads seizure, it may indicate that the patient had their first or second seizure. On the other hand, the term epilepsy indicates that the patient has experienced multiple seizures for years or even decades.
Keep in mind that some patients who are sent from the emergency room for head computed tomography (CT) with a history of seizures might have had seizure-like activity that may or may not have been a true seizure. And, it may never occur again.
Let’s review how to approach CT imaging for patients who present with new seizures. A CT is usually the first step for patients with new seizures, which ensures that there is no underlying hemorrhage or tumor. Most of these CT scans will be normal because there is no lesion, or if there is a lesion it may not be visible on CT.
But, some of the CT scans ordered for patients with new seizures will be abnormal. So, you need to look carefully at each one, particularly near the cortex of the brain since most seizures arise from an abnormality in or around the brain cortex—rather than in the white matter or the cerebellum. Diseases such as neoplasms, vascular malformations, and infection can all cause seizures.
Keep in mind these three strategies when using CT imaging to assess patients with new seizures:
- Carefully examine the cortex
- Look for fluid in the extra-axial space
- Obtain magnetic resonance imaging (MRI) when a focal brain abnormality is likely
Carefully examine the cortex for mass effect or abnormal attenuation on CT
Case 1: New seizures related to a metastatic tumor
In our first case, an adult, with a history of cancer, presented with new seizures, and his CT scan demonstrated a rounded mass near the cortex with surrounding low attenuation edema (Fig. 2). The MRI obtained shortly afterward revealed a rim enhancing mass that proved to be a metastatic tumor.
Case 2: New seizures related to an enhancing meningioma
Some tumors, like the one visible in our next case, resemble brain tissue on non-contrast CT and can only be detected by their mass effect on the brain or the ventricles.
The 50-year-old patient presented with new seizures, so the abnormal asymmetry of the cortical sulci noted on non-contrast CT led to a follow-up enhanced CT because the patient could not have an MRI (Fig. 3). That CT demonstrated an enhancing meningioma that was likely the cause of her new seizures.
Case 3: New seizures related to an arteriovenous malformation
In our next case, a 25-year-old patient with new seizures had a small area of high attenuation with calcification on their CT scan (Fig. 4). When you see these findings on CT, you should consider that the patient may have a vascular malformation, since these can also cause seizures!
Follow-up imaging with MRI or CT angiography (CTA) was warranted in this case. The MRI demonstrated prominent flow voids that proved to be due to an arteriovenous malformation (AVM) that was found on CTA.
Cases 4 and 5: New seizures related to herpes encephalitis
When you see an abnormality in the medial temporal lobe in an adult patient with new seizures, be sure to think of infections such as herpes encephalitis or a neoplasm.
In our next two patient cases, herpes encephalitis was the cause of low attenuation in the right temporal lobes on both CT scans (Fig. 5).
Look for fluid in the extra-axial space on CT since abscesses can form in the epidural and subdural spaces
Case 6: New seizures related to an epidural abscess
Our next case involves a patient who presented with seizures, headache, and a fever. The enhanced CT demonstrated an abnormality on the surface of the brain (Fig. 6). This proved to be a pus collection in the epidural space (called an epidural abscess) that can cause seizures.
Case 7: New seizures related to an abscess in the subdural space
The diffusion MRI from our next patient showed abnormally restricted diffusion outside of the brain (Fig. 7). This is another case of an abscess, but this time in the subdural space. Magnetic resonance offers greater sensitivity and specificity in such cases, although blood products can resemble pus on diffusion imaging which can be misleading in postoperative cases.
Case 8: New seizures and a cortical mass from a brain abscess
Keep in mind that not all patients with a cortical mass and seizures have a tumor! In our next example, a right-sided mass with considerable edema proved to be a brain abscess (Fig. 8).
Use MRI when there is a high likelihood of a focal brain abnormality
The patient’s history is not usually definitive for establishing the diagnosis of a brain abscess since the patient may not have the usual features of infection, such as an elevated white blood cell count or a fever. Magnetic resonance imaging can be very helpful in establishing the diagnosis since abscesses have a well-defined enhancing rim alongside centrally restricted diffusion on MRI.
Case 9: New seizures and a hemorrhage related to herpes encephalitis
From these cases we’ve discussed, you’ll notice that the abnormalities on CT in patients with new seizures range from the obvious to nearly undetectable. And even when the findings are visible, they can be easily misinterpreted!
For example, the CT findings in our final case are from a patient with new seizures. At first, a temporal lobe abnormality was thought to represent an underlying hemorrhagic tumor (Fig. 10). On additional testing, this proved to be another case of herpes encephalitis. The hemorrhage, while distracting, is not uncommon with this particular type of infection.
In all patients with new seizures, you should carefully evaluate the cortex and extra-axial spaces on CT, and order an MRI if a focal brain abnormality is likely. Keep in mind that a variety of diseases can present with new-onset seizures in adults, including hemorrhages, neoplasms, vascular malformations, and infections.
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.
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