Osmotic Demyelination Syndrome

Images are from a 40-year-old man transferred to our institution with history of "pancreatitis and hyponatremia." As is typical, no symptoms or other clinical history was provided in the 120-character-limit space for history (medicine by twitter).

Sagittal T1-weighted image shows a hypointense lesion in the pons, seen in the axial T1-weighted image as a trident-shaped lesion that spares the ventrolateral pons and the pontine portion of the corticospinal tracts. The axial T2-weighted image shows hyperintensity in this region, while the FLAIR image at the same level shows a trident-shaped area of hyperintensity surrounding an area of encephalomalacia in the central pons. The GRE image shows no evidence of hemorrhage. The diffusion-weighted image shows a trident-shaped rim of hyperintensity surrounding the central pons, while the apparent diffusion coefficient map at the same level shows no signal dropout in the region of hyperintensity, indicating T2 shine-through.

On the clinical side, symptoms typically occur 2-4 days after correction of hyponatremia. The earliest imaging finding of osmotic demyelination syndrome is restricted diffusion, which may be apparent as early as 24 hours after onset of clinical symptoms. The appearance of myelinolytic lesions on MRI lags clinical symptoms by 2 weeks:

• T1: Hypointense, but can also be isointense. Images obtained 1-4 months later may be normal or demonstrate hyperintensity, representing coagulative necrosis.
• T2: Hyperintensity that may also include the basal ganglia. Images obtained 1-4 months later may show complete resolution.
• FLAIR: Hyperintense
• GRE: Hyperintense. Hemorrhage is rare
• DWI: Hyperintense
• ADC: Normal to mildly hyperintense
• Post-contrast: Typically no enhancement, but may also see mild enhancement.

Differential considerations for T2-hyperintensity in the pons includes:

• Ischemia: Look for restricted diffusion.
• Infection: Look for enhancement.
• Brainstem glioma:
• Demyelination: Progressive multifocal leukoencephalopathy, osmotic demyelination syndrome.

References

• Hall J. Osmotic Demyelination Syndrome. StatDx. 2008-06-05.
• Howard SA, Barletta JA, Klufas RA, Saad A, De Girolami U. Best cases from the AFIP: osmotic demyelination syndrome. Radiographics. 2009 May-Jun;29(3):933-8.
• Ruzek KA, Campeau NG, Miller GM. Early diagnosis of central pontine myelinolysis with diffusion-weighted imaging. AJNR Am J Neuroradiol. 2004 Feb;25(2):210-3.