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Transient lesion of the splenium

Transient lesions of the splenium (also known as mild encephalitis / encephalopathy with a reversible isolated SCC lesion (MERS)) are occasionally encountered and may be due to a number of underlying aetiologies.

Transient lesions of splenium are only really appreciable on MRI where they have two distinct patterns 4

  1. well circumscribed, small, oval lesions in the midline within the substance of the corpus callosum
  2. more extensive ill defined irregular lesions extending throughout the splenium and into the adjacent hemispheres (boomerang sign

The smaller well circumscribed lesions is the typical lesion seen in the setting of seizures / cessation of anitepileptic medication, whereas the larger lesion is more typical of other aetiologies.  

Aeitiologies include 1-5

Clinical presentation

Unlike other causes of splenial lesions, the small transient lesions of the splenium seen in epiliepsy 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, visual apraxias etc...) 4

Radiographic features

MRI

These lesions tend to demonstrate the following signal characteristics 4

  • T1 - hypointense
  • T2 - hyperintense
  • DWI / ADC - restricted diffusion
  • T1 C+ - no enhancement

Treatment and prognosis

Prognosis generally depends on the underlying cause, but in the setting of eplilepsy or antiepilepic drug related lesions it is very good. 

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