Specific Imaging Findings

In central pontine myelinolysis (CPM) CT shows hypodensity in the central mid to lower pons, typically of a somewhat triangular shape with its base located posteriorly and resembling a trident, due to sparing of the corticospinal tracts. The brainstem is not expanded and the abnormality tends to regress and even disappear with time. The lesions are T2 hyperintense with usually less prominent T1 hypointensity. Hemorrhage is not present and contrast enhancement is absent or minimal. DWI shows the lesion to be bright and ADC maps reveal reduced diffusion. Diffusion changes may precede T2 findings by up to 24 hours. MRS may in the acute period show elevated choline, probably due to breakdown of myelin. NAA is decreased and lactate may occasionally be present. DTI may show swelling and displacement of white matter tracts but no frank destruction.

Extrapontine myelinolysis presents as areas of high T2 signal and reduced diffusion involving the supratentorial deep gray matter and/or the corpus callosum. Involvement of the deep gray matter occurs in 10% of patients with CPM. Involvement of the corpus callosum, primarily the body, is generally known as the Marchiafava–Bignami syndrome (MBS). The entire thickness of the callosum is affected, the anterior and posterior commissures as well as the subcortical U-fibers may be involved. The lesions are T1 hypointense and bright on T2 sequences. Peripheral contrast enhancement may occur during the acute to subacute periods. Reduced diffusion correlates with a worse prognosis.