DWI ABNORMALITIES IN STATUS EPILEPTICUS

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Figures 1, 2, 3, 4 and 5 ( T2, T1, DWI, ADC, FLAIR) show cortical swelling with increased signal intensity in left parieto-occipital region( mainly cortical) on T2/ FLAIR, hypointense signal on T1, increased signal on DWI( suggestive of restricted diffusion) with corresponding low signal on ADC.

A 14 year old girl with history of seizures presented with ongoing generalized seizure activity for the last 3 days. MRI showed altered signal in left frontal( not shown here), parietal and occipital regions involving cortex and minimal subcortical white matter with cortical swelling and increased gyral volume of the affected areas. There was restricted diffusion in these areas suggestive of cytotoxic oedema. The area of abnormal signal did not conform to any vascular territory and was hence thought to be due to sustained seizure activity rather than cerebral ischaemia.

DIFFUSION WEIGHTED IMAGING IN STATUS EPILEPTICUS:

Diffusion weighted imaging( DWI) is an MR technique that allows characterization of tissues according to the degree of water mobility.

Its widest application is still in evaluation of cerebral ischemia where restricted water diffusion is seen early after onset of ischemia. Increased signal on DWI reflects the presence of cytotoxic edema.

DWI abnormalities are also reported in prolonged seizure activity.

DWI signal abnormalities are accompanied by abnormal signal on T2/ FLAIR if MRI is done 24 hours after onset of sustained seizure activity.
If however, MRI is done earlier, DWI may show restricted diffusion in the absence of signal changes on T2/ FLAIR ( as in early cerebral ischemia).

The areas of involvement do not correspond to any vascular territory. Morever, the changes are transient and return to normal after the seizure activity ceases.

Changes are seen as increased signal intensity and swelling of the cortical gray matter, subcortical white matter, or hippocampus on periictal T2/ FLAIR and diffusion-weighted images. These findings reflect transient cytotoxic and vasogenic edema induced by seizure, although this has not been proven pathologically. 

To conclude, it is  important to remember that abnormal processes other than cerebral ischemia can also cause acute diffusion-weighted imaging changes.

 REFERENCES:
1. Kassem-Moussa H, Provenzale JM, Petrella JR et al:Early Diffusion Weighted MR Imaging Abnormalities in Suatained Seizure Activity. AJR 174(5):1304-6, 2000
2.Kim JA, Chung JI, Yoon PH: Transient MR signal changes with Generalized Tonicoclonic Seizures or Status Epilepticus: Periictal Diffusion-weighted Imaging. AJNR 22:1149-60, 2001