Hypertensive Encephalopathy: Isolated Pons Involvement Mimicking Central Pontine Myelinolysis

MRI of the brain was performed, and it demonstrated an isolated high signal on the T2 weighted and fluid attenuated inversion recovery sequences that involved only the central pons with sparing the periphery. There was no restricted diffusion on diffusion weighted imaging. The differential diagnosis included posterior reversible syndrome and central pontine myelinolysis; however, the blood sodium on admission was normal. The pathogenesis of HE is that the auto-regulatory mechanisms that control the cerebral blood flow are exceeded, resulting in hyper-perfusion. The consequent over-distension of the cerebral vessels, the breakdown of the blood brain barrier and ultimately, the extravasation of fluid into the interstitium all cause vasogenic edema. In most cases, the changes of hypertensive encephalopathy represent reversible vasogenic edema, which can be seen on T2-weighted images, and restricted diffusion is not seen on the diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) maps. Hypertensive encephalopathy that manifests as a reversible increased signal isolated to the pons on T2-weighted images is extremely uncommon. The differential diagnosis for such pontine T2 hyperintensity includes pontine glioma, ischemic and radiation changes (generally irreversible conditions), as well as central pontine myelinolysis (CPM) and demyelinating disorders such as multiple sclerosis, acute disseminated encephalomyelitis and rhomb-encephalitis. In CPM electrolyte imbalances provide a clue for the diagnosis, where as for glioma, there will be an expansion and mass effect. In conclusion, clinical recognition of brainstem HE may be difficult. The features of a lack of correlation between the severity of the radiological abnormality and the clinical status, combined with the rapid resolution following antihypertensive treatment, should suggest the diagnosis. It is important for the radiologist to be familiar with the imaging abnormalities of this life-threatening, but treatable condition