Exercise: Seizure and Epilepsy

EXERCISE 12-8. SEIZURE AND EPILEPSY

12-18. In Case 12-18, what is the most likely diagnosis (Figure 12-38 A–C)?

A.         Alzheimer’s dementia

B.         Gray matter heterotopia

C.         Hemimegalencephaly

D.         Mesial temporal sclerosis

E.         Multiple sclerosis

Radiologic Findings

12-18. Coronal FMPIR MRI (Figure 12-38 A) demonstrates marked atrophy of the left hippocampus with loss of normal laminar architecture (white arrowhead). Ictal SPECT (Figure 12-38 B) shows increased radiotracer uptake in the left medial temporal lobe (double ar-rows), whereas the interictal PET (Figure 12-38 C) demonstrates diminished metabolic activity in the left temporal lobe (black arrow). The constellation of findings is highly suggestive of mesial temporal scle-rosis (D is the correct answer to Question 12-18). Pronounced cerebellar atrophy (Figure 12-38 A) in this case is the result of long-standing antiepileptic medication (white arrows).

Discussion

Although a comprehensive review of seizure and epilepsy classification is beyond the scope of this section, it is impor-tant to note the central role that imaging serves in the evalu-ation and management of these patients. The etiology of seizure varies significantly with patient age. In young chil-dren (3 months to 5 years), fever is the most common precip-itant of seizure. The exact pathophysiology is not fully understood; however, there is likely a relationship to an in-flammatory cascade as well as a low seizure threshold in young children. Imaging is generally not performed in the setting of a simple febrile seizure (seizures that last less than 15 minutes, are generalized, and do not recur in a 24-hour period). Febrile seizures that do not meet these criteria are classified as complex and imply a more serious underlying abnormality including meningitis, abscess, or encephalitis, for which imaging may be indicated. Other potential causes of seizure in young children include cerebral anoxia, metabolic abnormalities, cortical malformations (refer to Case 12-2), infection, or inherited neurocutaneous diseases such as tuberous sclerosis.

In older children and adults, common causes of seizure in-clude vascular malformations, cerebral injury due to prior trauma or ischemia, or underlying tumor, among others. Note-worthy tumors associated with intractable seizure include gan-glioglioma, dysembryoplastic neuroepithelial tumor (DNET), and pleomorphic xanthoastrocytoma; these generally occur in childhood or in young adulthood.

The most common cause of medically refractory epilepsy is mesial temporal (hippocampal) sclerosis. Although this entity is most commonly seen in adult patients, there is likely a link to febrile seizures earlier in childhood or other remote cerebral insult such as trauma or infection. On MR imaging, there is characteristic atrophy and gliosis of the hippocam-pus, often with dilation of the ipsilateral temporal horn due to volume loss. There may be atrophy and gliosis of ipsilateral fornix and mammillary body as well. These patients are po-tential candidates for temporal lobectomy, and additional imaging with ictal SPECT and interictal PET is generally per-formed as described earlier.