Piglet and trident signs in osmotic demyelination syndrome

Case contribution: Dr Radhiana Hassan


  • A 48 years old male with underlying DM and HPT
  • Admitted and treated for meningitis
  • Noted to have abnormal sodium level during admission, correction done
  • After 2 weeks patient requested AOR discharge from ward
  • Presented again with fluctuant level of conciousness and spastic quadriparesis

MRI findings:

  • A lesion seen within the pons, which is centrally located.
  • It is hypointense on T1, hyperintense on T2/FLAIR, no restricted diffusion and not enhanced post contrast
  • Sparing of peripheral and descending corticospinal tract region
  • No swelling focal expansion of pons
  • Trident sign and piglet signs are seen
  • A few deep white matter hyperintense foci on FLAIR sequence is seen.
  • No periventricular or juxtacortical lesion
  • No hydrocephalus, no abnormal leptomeningeal enhancement.

Diagnosis: Osmotic demyelination syndrome


  • Osmotic demyelination syndrome refers to acute demyelination from rapid shift of osmolality, typically with the rapid correction of hyponatremia.
  • It has replaced the term central pontine myelinolysis due to extra-pontine structures that can be affected in this condition.
  • It is commonly seen in chronic alcoholics, chronically debilitated patients, transplant recipients and pregnancy-related hyperemesis.
  • Imaging shows central pons T2-hyperintensity with sparing of periphery. Involvement is in pons (50%) and extrapontine in 50% (basal ganglia, cerebral white matter, hippocampi and central fibers). Regardless of site, demyelination often bilateral and symmetric
  • Initial study may be normal, findings may be transitory, resolve completely, however persistent hyperintensity in 1-4 months can be seen (coagulative necrosis).
  • On MRI classically it is mild/moderate hypointense on T1, hyperintense on T2/FLAIR in central pons with sparing of periphery, no hemorrhage, restricted diffusion in acute phase, usually does not enhanced.
  • The piglet sign seen in osmotic demyelination syndrome. It refers to the appearance of upper pons in axial T2 or FLAIR. The abnormal T2-hyperintense signal within the pons reminiscent of a pig’s snout. The rest of the piglet features are formed by temporal lobes (ears), the carotid arteries (eyes) and the fourth ventricle (mouth)
  • The trident sign describe the abnormal T2/FLAIR hyperintensity within the pons which is shaped like a trident (a three-pronged spear). The predominance involvement of the transverse pontine fibers and relative sparing of the descending corticospinal tracts is responsible for this characteristic appearance.
Author: radhianahassan