Transient lesions of the splenium of the corpus callosum, also known as mild encephalitis/encephalopathy with a reversible isolated SCC lesion (MERS), are occasionally encountered on MRI studies and may be due to a number of underlying aetiologies.
Unlike other causes of splenium of corpus callosum (SCC) lesions, the small transient lesions of the splenium seen in epilepsy and antiepileptic drug cessation use do not demonstrate convincing signs or symptoms of hemispheric disconnection, such as pseudo-neglect, alien hand syndrome, apraxia of the left hand, agraphia, alexia, and visual apraxias 4.
Aetiologies include 1-5:
- classic presentation is seen in patients with sudden cessation of antiepileptic drugs
- seizures: focal lesions have been described after focal status epilepticus and unusually after single seizures and were explained as focal brain oedema.
- electrolyte imbalance
- multiple sclerosis (MS)
- acute disseminated encephalomyelitis (ADEM)
- posterior reversible encephalopathy syndrome (PRES)
- Marchiafava-Bignami disease
- diffuse axonal injury (DAI)
- AIDS dementia complex
- haemolytic-uremic syndrome with encephalopathy
Transient lesions of the splenium are only really appreciable on MRI where they have two distinct patterns 4:
- well circumscribed, small, oval lesions in the midline within the substance of the corpus callosum
- more extensive ill-defined irregular lesions extending throughout the splenium and into the adjacent hemispheres (boomerang sign)
The smaller well-circumscribed lesions are the typical lesion seen in the setting of seizures/cessation of antiepileptic medication, whereas the larger lesion is more typical of other aetiologies.
These lesions tend to demonstrate the following signal characteristics 4:
- T1: hypointense
- T2: hyperintense
- DWI/ADC: restricted diffusion
- T1 C+: no enhancement
Studies have shown that patients recover completely on MRI studies within 1 month, mostly within 1 week following the neurologic recovery 7.
Treatment and prognosis
The prognosis generally depends on the underlying cause, but in the setting of epilepsy or antiepileptic drug-related lesions, it is very good.
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