Radio-Pathologic Correlation of the “Pig’s Snout” Sign in Osmotic Demyelination Syndrome

Electroencephalography 12 days after admission for decreased level of consciousness revealed nonconvulsive status epilepticus, while brain magnetic resonance imaging (MRI) 13 days after admission showed central pontine diffusion restricting signal abnormality resembling a trident (Figure 1A). On chart review, we noted that over the first 6 days of his admission his serum sodium increased from 132 to 161 mmol/L (normal: 135−145 mmol/L), with a maximum 24-h increase of 8 mmol/L. ODS is typically a complication of treatment of patients with severe hyponatremia.1 However, additional risk factors (e.g., alcoholism, malnutrition, liver disease) may predispose to ODS even with milder degrees of hyponatremia, as in our patient.1 While initially described as a disease of the pons (central pontine myelinolysis), later recognition of lesions outside the pons (extra-pontine myelinolysis) render the broader term ODS more appropriate.1 The precise underlying disease mechanisms are unclear, but demyelination is thought to be due to osmotic stresses causing oligodendrocyte death.2 The "trident" sign is a classical neuroimaging finding in ODS that reflects demyelination of crossing pontocerebellar fibers.2 In contrast, the “pig’s snout” sign or “piglet” sign has only been rarely reported and refers to larger pontine lesions that extend ventrolaterally while sparing the peripheral pons and corticospinal tracts.3,4 Progression from the trident sign to the pig’s snout sign in our case supports that they exist on a spectrum of disease severity.