Teaching Case

A 44-year old man with sudden onset of persistent headache, visual disorders accompanied by spasms and altered consciousness. Acute elevation of the systemic blood pressure (BP) (systolic BP: 220mmHg and diastolic BP: 130mmHg) preceded the clinical symptoms. The patient didn’t have any clinical history of high blood pressure or other systemic diseases. The patient underwent a brain MRI.

Brain MRI revealed on axial T2 - weighted images high signal of the pons, the cerebellar, the midbrain, the basal ganglia and the thalami. The periventricular white matter (WM) was also involved. The WM lesions come quite close to but spare subcortical WM and cerebral cortexes (Fig.1). Apparent Diffusion Coefficient (ADC) maps from Diffusion Weighted Images revealed the involved areas with increased diffusivity (Fig.2). After appropriate treatment and regulation of patient’s blood pressure, a follow-up ΜRI after 20 days showed complete resolution of the lesions (Fig.3).

Posterior Reversible Encephalopathy Syndrome (PRES) is a neurotoxic state with unique imaging features. PRES has been reported in people from age 4 up to age 90 years old. It has been associated with conditions such as chronic hypertension, chronic renal failure, bone marrow or solid organ transplantation, sepsis, cytotoxic or chemotherapy medications, autoimmune disease and preeclampsia - eclampsia. Clinical manifestations of PRES include seizures, visual disturbances, headache, nausea, vomiting, acute hypertension and altered mental status [1-2]. The underlying pathophysiology of PRES is contradictory. The first hypothesis suggests that hyperperfusion is the responsible mechanism. When the mean arterial blood pressure exceeds 170mmHg, the brain’s auto-regulation mechanism is implied, vasodilators, cytokines and other substances are released which cause damage to the vascular endothelium, blood-brain disruption and vasogenic oedema. The second theory supports that cytotoxicity is the underlying mechanism. Immune system activation leads to the release of mediators which eventually cause vascular instability with vasoconstriction and hypoperfusion so blood-brain barrier dysfunction and vasogenic oedema [3]. PRES has the unique pattern of vasogenic oedema predominating in the parietal and occipital lobes thus the name posterior. Rarely radiologic lesions are not limited to the posterior regions. There are a number of varying patterns and atypical radiologic presentations of PRES [1-3]. One such variant is the central with involvement of brainstem and basal ganglia. The central variant of PRES has been previously described by others using terms such as hypertensive brainstem oedema encephalopathy, hypertensive brainstem encephalopathy, reversible pontine oedema, or reversible brainstem hypertensive encephalopathy [4,5].

MRI is the modality of choice to highlight PRES. T2-weighted images show lesions of high signal intensity. T1-weighted images might show low intensity foci in the affected areas and half of the cases show contrast enhancement. Diffusion-weighted images with apparent diffusion coefficient (ADC) maps are important to differentiate vasogenic oedema (reversible form) from cytotoxic oedema (irreversible form).  Vasogenic rather than cytotoxic oedema is the principal basis for PRES lesions.  Regions demonstrate with high signal intensity on T2-weighted images, revealed increased signal intensity on ADC maps [6-8].

In most cases, as the name implies, PRES is a reversible condition. If it is recognized and treated quickly, the clinical and radiologic features usually fully resolve within days to weeks. The central variant of PRES is also reversible, hence an awareness of this variant of PRES is necessary to prevent inappropriate treatment or, in the worst case, biopsy [5].