Findings - MR Venogram showing abnormal T2/FLAIR  hyperintense signal in frontal and parieto occipital lobes b/l.

Reversible Posterior Leukoencephalopathy Syndrome (RPLS) or Posterior Reversible Encephalopathy Syndrome (PRES)

Introduction

Reversible Posterior Leukoencephalopathy Syndrome (RPLS) or Posterior Reversible Encephalopathy Syndrome (PRES) is a newly recognized clinicoradiological entity. It is characterized predominantly by subcortical edema without infarction mainly involving the parietal and occipital lobes bilaterally in a relative symmetric pattern1. Most patients show complete clinical and radiological recovery on follow up imaging in 2-4 weeks

PRES presents with nonspecific signs and symptoms including headaches, confusion, visual disturbances, elevated blood pressure and seizures. Clinical findings are not sufficiently specific to establish the diagnosis, however, magnetic resonance imaging (MRI) pattern is often characteristic and represents an essential component of the diagnosis of PRES. PRES is an acute episode of vasogenic edema in the cerebral white matter, with a predilection for the posterior temporal, parietal and occipital regions. The vasogenic edema is likely due to autoregulatory dysfunction and endothelial dysfunction. The explanation for predilection for the posterior circulation is uncertain

 
Etiopathogenesis

PRES has been described with a number of medical conditions including hypertensive encephalopathy, eclampsia, and cytotoxic and immunosuppressive drugs (i.e. cisplatin, cyclosporin, tacrolimus, antiretroviral therapy, and erythropoietin). The reversibility of the clinical and radiologic abnormalities is dependent on prompt control of blood pressure and/or discontinuing the offending drug. If unrecognized, conversion to irreversible cytotoxic edema may occur. Rapidly developing, fluctuating or intermittent hypertension is a particular risk

The pathogenesis of the syndrome is poorly understood and two main mechanisms have been suggested. One hypothesis is that cerebral vasospasm results in cerebral ischemia and subsequent development of T2 hyperintensity. Alternatively it has been suggested that there is a temporary failure of autoregulatory capabilities of the cerebral vessels, leading to hyperperfusion, breakdown of blood-brain barrier, and consequent vasogenic edema. The preferential involvement of the parietal and occipital lobes is thought to be related to the relatively poor sympathetic innervation of the posterior circulation. Drugs have been postulated to contribute to this physiological effect by cytotoxic effects on the vascular endothelium or by inducing or exacerbating hypertension.

Hypertensive encephalopathy, immunosuppressive treatment, renal failure and eclampsia are most common causes of posterior reversible encephalopathy syndrome with a greater predilection for females than males. Multiple factors may be contributory in some patients who develop PRES.

Posterior reversible encephalopathy syndrome (PRES) is typically characterized by headache, altered mental functioning, seizures, and visual loss associated with imaging findings of bilateral subcortical and cortical edema with a predominantly posterior distribution

FLAIR is the most sensitive sequence to the characteristic cortical and subcortical edema of PRES. The FLAIR sequence shows involvement of gray matter to be a much greater part of this syndrome than previously thought; the vasogenic edema may even originate in the cortex. The syndrome does not appear to represent a true leukoencephalopathy and they thus prefer a new name: posterior reversible encephalopathy syndrome (PRES).

CT Findings
Non enhanced CT shows patchy bilateral white matter nonconfluent hypodensity, and contrast enhanced CT images show variable mild patchy punctuate enhancement. The findings in the subcortical white-matter are hyperintense on T2-weighted images, hypointense or isointense on diffusion-weighted images, and hyperintense on apparent diffusion coefficient (ADC) images.