Mild encephalopathy with reversible splenial lesion

Case contributed by Dr Chris O'Donnell


Two day history of drowziness, lethargy and now unrouseable.

Patient Data

Age: 20 years
Gender: Male

Focal swelling and restricted diffusion (confirmed as low signal on the ADC map) in the splenium of the corpus callosum and white matter of the parietal lobes.

Note underlying right frontal and maxillary sinusitis (fluid levels) with swelling in the adjacent right frontal lobe indicative of cerebritis.  Diffuse pachymeningeal thickening and enhancement over the right hemisphere with a small subdural empyaema overlying the right frontal lobe extending parafalcine on the right.  There is also patchy leptomeningeal enhancement.

Findings are consistent acute sinustitis and extension of infection into the cranial cavity involving the dura and leptomeninges producing a thin subdural empyaema. Cerebritis but not abscess involving the right frontal lobe.  Features of MERS in the splenium and white matter of the parietal lobes.

Follow-up MRI following 2 days of antibiotics, gram -ve bacillus in blood cultures


Resolution of restricted diffusion in the splenium (arrow).  Worsening of right frontal subdural empyaema.  Persistent "cerebritis" in right frontal lobe.

Case Discussion

Tada et al in 2004 identified clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) as a new type of acute encephalopathy, characterized by transient splenial lesions with high-signal intensity on diffusion-weighted magnetic resonance imaging (MRI), a mild clinical course, and a good outcome. MERS has been associated with various infectious diseases including influenza A and B (the most common pathogens), following by mumps virus, adenovirus, rotavirus, streptococci, and E.coli.

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