Two Cases of Hypertensive Encephalopathy Involving the Brainstem

The clinical presentations of our patients were not consistent with HE, although they initially presented with severe hypertension, and subsequently improved after normalization of blood pressure. The MRI features of our patients were unusual in that they spared the parieto-occipital lobes and predominantly involved the brainstem. Although previous studies of HE have found brainstem abnormalities on MRI, such changes are usually associated with hemispheric abnormalities in the occipital regions.9, 10 The posterior predilection is thought to be related to dense sympathetic innervation of the anterior circulation that protects neural structures if the blood pressure exceeds the limits of autoregulation.8

There are a few reports that the presence of brainstem or cerebellar edema on neuroimaging is the principal feature of HE. Our two patients had high-intensity signals in the brainstem on T2-weighted and FLAIR images. However, the signal intensity in DWI was similar to that in surrounding regions, whereas that of ADC mapping was higher, respectively. HE presenting with predominant involvement of the brainstem must be differentiated from brainstem infarction, brainstem tumor, encephalitis, and central pontine myelinolysis. Brainstem infarction was ruled out by the lack of major brainstem signs, normal DWI, and the rapid clinical recovery. Also, the absence of abnormal serum sodium levels, the clinical recovery, and the resolution of the MRI lesions reduced the possibility of central pontine myelinolysis being present.

It has been suggested that DWI and ADC values help to differentiate abnormal signals on T2-weighted and FLAIR images from brainstem infarction.6, 11 The lack of an increased signal on DWI and the presence of increased ADC values suggest the absence of cytotoxic edema in regions of hyperintense T2-weighted lesions. Such cases would favor a diagnosis of HBE. According to the results of DWI and ADC mapping performed on our patients, most of the regions showing high-intensity signals on T2-weighted images demonstrated vasogenic edema rather than cytotoxic edema. These MRI changes may support the hypothesis that presence of severe hypertension exceeding the autoregulation limit results in segmental vasodilatation and increased vascular permeability, leading to vasogenic edema.5, 12 Therefore, with proper application, DWI and ADC mapping can be conveniently utilized to differentiate HBE from other brain diseases, which show decreased ADC values consistent with cytotoxic edema.

The clinical manifestations of the brainstem variant are similar to those of the more common form of HE. One-third of patients reportedly have only hypertension as the precipitating factor, with most having comorbidities such as renal failure.8 Interestingly, despite the presence of extensive neuroimaging lesions, that study found few symptoms or signs of brainstem or cerebellar dysfunction, indicating clinical radiologic dissociation. Our patients did not have any clinical signs of brainstem dysfunction, as in the case described by Morello et al.13 We suggest that a typical characteristic of HBE is the paucity of clinical signs, which certainly bear no relationship to the severity indicated in MRI.

We have presented two patients with clinical and radiological features characteristic of HBE. Brainstem and cerebellar variants of HE are rare, and generally affect younger people with secondary hypertension such as renal failure. This diagnosis must be considered in the presence of severe hypertension with clinical radiologic dissociation.