Brain MRI contributes to make diagnosis of all diseases by showing typical images.
Case 154
【Progress】
He is given anti-convulsant and has not experienced a seizure since then. He is forbidden to take a driver license now but if a seizure onset does not occur for three years, he would be allowed to take it.
【Discussion】
Mechanism of seizure or epilepsy is believed to result from electric imbalance of excitement and inhibition. When the imbalance occurs in a focal site, the seizure occurs based on the local electric abnormality (1, 2). When the imbalance occurs in the whole cerebrum, the generalized seizure occurs in a big scale. When the imbalance improves with age, the seizure may go away. But the medically untreatable seizures exist. The seizure is categorized into two types: focal and generalized. Focal seizures are subdivided into focal seizure without loss of consciousness and focal seizures with impaired awareness. Generalized seizures are subdivided into 6 types: tonic, clonic, myoclonic, tonic-clonic, atonic, absence. In our case, it is considered that based on abnormal peak at several points in brain wave examination and his symptoms, generalized absence seizure occurred (1, 2).
Meanwhile, from a point of view of MRI imaging, various diseases are listed in patients with medically untreatable seizures. Cortical and subcortical lesions cause the seizure. As cortical lesions, focal cortical dysplasia, heterotopic grey matter, polymicrogyria and mega are listed. As subcortical lesions, meso-temporal sclerosis, neurocutaneous syndromes (Sturge-Weber, tuberous sclerosis), gliosis, cavernous hemangioma and epilepsy associated tumors (DNET, ganglioglioma, pleomorphic xanthoastrocytoma) are listed. Of these, meso-temporal sclerosis and focal cortical dysplasia are the most common causes (3).
Brain MRI with diffusion weighted imaging (DWI) and with FLAIR play a role of detectability of the responsible lesions. Especially, MRI with DWI is eligible to check neuron loss with enlarged extracellular space resulting in higher values of ADC and conversely to check swollen cortex with restricted diffusion resulting in lower values of ADC (3). MRI with DWI does not contribute to detect brain tumor because brain tumors usually maintain the diffusion ability except malignant lymphoma and meningioma.
Brain MRI with FLAIR plays a role for detecting not only temporal sclerosis or gliosis having water component but also brain tumors. Brain MRI with T1WI plays a role to check the difference of between abnormal cortex irrespective of thick or thin and healthy cortex.
In our patient, brain MRI with DWI, ADC, T1WI showed no abnormality but brain MRI with FLAIR showed hypertense area in periventricular and deep white matter which is often found in aging brain. It is reported that hyperintense in the periventricular/deep white matter results from interstitial water due to increase of blood-brain-barrier permeability and plasma leakage (4). Probably, this hyperintense on FLAIR MRI is not related to the cause of the seizure but maybe to be the result. The real cause of the seizure in our case is uncertain.
【Summary】
We present a fourteen year-old boy suffering from transient loss of consciousness. Seizure or epilepsy is believed to arise from electric imbalance of excitement and inhibition. This imbalance can occur at the cortex or subcortex and locally or generally. As cortical lesions, cortical dysplasia, heterotopic cortex, polymicrogyria, and mega. As subcortical lesions, meso-temporal sclerosis, gliosis, neurocutaneous syndromes (Sturge-Weber, tuberous sclerosis), cavernous hemangioma and epilepsy associated tumors (DNET, ganglioglioma, pleomorphic xanthoastrocytoma). Brain MRI withT1WI, FLAIR, DWI and ADC map play a role to detect and differentiate these lesions. In our patient, brain MRI with FLAIR showed hypertense area in periventricular and deep white matter. It is reported that hyperintense in the periventricular/deep white matter results from interstitial water due to increase of blood-brain-barrier permeability and plasma leakage.
【References】
1.Stafstrom CE, et al. Seizures and epilepsy: an overview for neuroscientists. Cold Spring Harb Perspect Med. 2015 Jun 1;5(6).
2.Fitzpatrick AP, et al. Diagnosis and management of patients with blackouts. Heart. 2006 Apr; 92(4): 559–568.
3.Kanner AM, et al. Diffusion-Weighted Imaging: Can It Play A Role in the Evaluation of Patients with Epilepsy? Epilepsy Curr. 2006; 6: 121–123.
4.Haller S, et al. Do brain T2/FLAIR white matter hyperintensities correspond to myelin loss in normal aging? A radiologic-neuropathologic correlation study. Acta Neuropathol Commun. 2013; 1: 14.
2019.7.24