Posterior Reversible Encephalopathy Syndrome (PRES): A Comprehensive Clinical and Radiological Overview

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Posterior Reversible Encephalopathy Syndrome (PRES): A Comprehensive Clinical and Radiological Overview

Introduction

Posterior Reversible Encephalopathy Syndrome (PRES) is a complex clinical and radiological condition that has garnered increasing recognition due to advancements in neuroimaging. Despite its misleading name, PRES is not confined to the posterior regions of the brain and is not always reversible. Early diagnosis and appropriate management are essential to prevent permanent neurological sequelae.

This article aims to present a globally competitive, expert-level review of PRES, incorporating real-world case material, CT imaging, pathophysiological mechanisms, diagnostic strategies, and management guidelines. Designed with Google SEO principles and AdSense compliance in mind, this content serves both educational and clinical value.

Case Snapshot: Left-Hand Paralysis in a Middle-Aged Male with Prior Infarction

In the accompanying CT image, a male in his 40s with residual left-hand paralysis presents for neuroimaging evaluation. Axial brain CT reveals an irregular low-density area (LDA) in the right frontal lobe, consistent with a prior cortical-subcortical infarct. Such subtle changes, particularly on initial CT, may be challenging to detect, underscoring the necessity of follow-up imaging and MRI when warranted.

Understanding such chronic infarcts is crucial for differentiating them from PRES and other acute conditions.

Etiology of PRES

PRES arises from a multitude of causes, often involving abrupt changes in blood pressure and vascular autoregulatory failure. The syndrome is frequently observed in the following clinical scenarios:

  • Hypertensive crisis (e.g., ≥180/120 mmHg)

  • Preeclampsia/eclampsia

  • Renal failure and dialysis

  • Sepsis

  • Autoimmune diseases (e.g., SLE, vasculitis)

  • Immunosuppressive drugs (e.g., cyclosporine, tacrolimus)

These conditions share a common pathogenic thread: disruption of endothelial integrity and blood–brain barrier (BBB) permeability.

Pathophysiology

Although the exact mechanism remains elusive, three leading theories attempt to explain PRES:

  1. Hypertensive Hyperperfusion Theory
    Severe hypertension exceeds cerebral autoregulation, leading to arteriolar dilatation, BBB breakdown, and vasogenic edema, primarily in the posterior circulation.

  2. Cerebral Vasoconstriction Theory
    A reflexive vasoconstriction to protect the brain results in ischemia, with subsequent edema from reperfusion injury.

  3. Endothelial Dysfunction Theory
    Circulating toxins (endogenous or exogenous) damage the endothelium, as seen in conditions like sepsis, autoimmune diseases, or chemotherapy.

These mechanisms are not mutually exclusive and may act synergistically in susceptible patients.

Epidemiology

  • Age: Most commonly affects adults aged 20–50

  • Sex: Female predominance, particularly in eclamptic patients

  • Prevalence: Estimated at 0.1–0.4% among hospitalized individuals

  • Risk Groups: Oncology patients, renal disease, and autoimmune disorders

Clinical Presentation

PRES is characterized by a constellation of acute neurological symptoms:

  • Severe headache

  • Seizures (generalized or focal)

  • Altered mental status (encephalopathy, confusion, lethargy)

  • Visual disturbances, including cortical blindness

  • Focal neurological deficits (hemiparesis, aphasia)

  • Ataxia, vertigo, or tinnitus

Symptoms are highly variable and may be mistaken for stroke, epilepsy, or infectious encephalitis.

Radiological Features

CT Findings

  • May appear normal in early stages

  • Low-attenuation areas in parieto-occipital white matter in more advanced cases

MRI Findings

  • T2/FLAIR hyperintensity in bilateral parieto-occipital lobes (seen in 70–90% of cases)

  • Affects both cortical and subcortical white matter

  • High ADC values on DWI, indicating vasogenic rather than cytotoxic edema

  • Hemorrhage and infarction may occur in 10–25% of cases

  • Enhancement patterns are variable and do not correlate with outcome

Though the term “posterior” is used, PRES may involve:

  • Frontal lobes

  • Inferior temporal lobes

  • Cerebellum

  • Brainstem

Differential Diagnosis

PRES can mimic or be mistaken for:

  • Ischemic stroke

  • CNS infections (e.g., encephalitis)

  • Autoimmune encephalopathy

  • Acute demyelinating diseases

  • Toxic leukoencephalopathy

Accurate diagnosis hinges on clinical context combined with neuroimaging patterns.

Treatment and Management

PRES is generally reversible with prompt recognition and targeted treatment.

Mainstay Treatments:

  • Blood pressure control (e.g., labetalol, nicardipine)

  • Withdrawal of offending agents (e.g., immunosuppressants)

  • Seizure management (antiepileptic drugs)

  • Supportive care: hydration, oxygen, management of underlying systemic illness

No corticosteroids unless PRES is part of a broader inflammatory condition.

Prognosis

  • Recovery: Most patients recover within 2–8 days

  • Imaging: Normalization on MRI usually occurs within 2 weeks

  • Sequelae: 10–20% may develop permanent deficits if infarction or hemorrhage occurs

  • Mortality: 3–6% depending on severity and comorbidities

Delayed recognition increases the risk of permanent disability or death.

Quiz

1. What is the most characteristic MRI finding in PRES?

A. Frontal lobe hemorrhage
B. Bilateral occipital and parietal T2/FLAIR hyperintensities
C. Hypointensity in basal ganglia
D. Diffuse meningeal enhancement

Explanation: PRES classically presents as bilateral hyperintense lesions in the parieto-occipital regions on T2/FLAIR, representing vasogenic edema.

2. Which of the following is the most common precipitating factor of PRES?

A. Hypoglycemia
B. Viral meningitis
C. Acute hypertension
D. Hypothermia

Explanation: Acute elevation in blood pressure is the most frequently associated trigger for PRES, often overwhelming cerebral autoregulation.

Conclusion

Posterior Reversible Encephalopathy Syndrome is a critical yet treatable neurologic condition characterized by acute symptoms and distinct neuroimaging findings. Given its reversible nature, early detection and intervention are key. Clinicians must remain vigilant, particularly in high-risk populations such as hypertensive, renal, and immunocompromised patients. MRI remains the cornerstone of diagnosis, and therapeutic success hinges on managing underlying causes and supportive care.

References

  1. Fugate JE, Rabinstein AA. Posterior reversible encephalopathy syndrome: clinical and radiological manifestations, pathophysiology, and outstanding questions. Lancet Neurol. 2015;14(9):914-925. doi: 10.1016/S1474-4422(15)00111-8

  2. Bartynski WS. Posterior reversible encephalopathy syndrome, part 1: fundamental imaging and clinical features. AJNR Am J Neuroradiol. 2008;29(6):1036-42. doi: 10.3174/ajnr.A0928

  3. Hinchey J, Chaves C, Appignani B, et al. A reversible posterior leukoencephalopathy syndrome. N Engl J Med. 1996;334(8):494-500. doi: 10.1056/NEJM199602223340803

  4. Lee VH, Wijdicks EF, Manno EM, Rabinstein AA. Clinical spectrum of reversible posterior leukoencephalopathy syndrome. Arch Neurol. 2008;65(9):1157-62. doi: 10.1001/archneur 65.9.1157

  5. Roth C, Ferbert A. The posterior reversible encephalopathy syndrome: what’s certain, what’s new? Pract Neurol. 2011;11(3):136–144. doi: 10.1136/practneurol-2011-000030

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