🌍 Introduction
Posterior Reversible Encephalopathy Syndrome (PRES) is a neurological condition characterized by acute or subacute onset of headache, seizures, visual disturbances, and altered mental status. The syndrome represents a clinico-radiologic entity where neuroimaging, particularly MRI, reveals reversible vasogenic edema predominantly affecting the parieto-occipital regions.
Although the term “reversible” suggests full recovery, PRES can lead to permanent deficits or even mortality if not promptly recognized and treated. Since its first description by Hinchey et al. in 1996, awareness and diagnosis of Posterior Reversible Encephalopathy Syndrome (PRES) have significantly increased, especially due to advancements in MRI technology.
1. Pathophysiology of Posterior Reversible Encephalopathy Syndrome (PRES)
The exact mechanism of PRES remains multifactorial, but two principal hypotheses dominate current understanding.
1. Hypertensive Hyperperfusion Theory
A sudden and severe rise in blood pressure surpasses cerebral autoregulatory capacity, leading to breakdown of the blood-brain barrier, increased vascular permeability, and extravasation of plasma into the interstitial brain tissue.
This cascade culminates in vasogenic edema, which predominantly affects the posterior circulation territories — the parieto-occipital lobes — due to their relatively sparse sympathetic innervation.
2. Endothelial Dysfunction Theory
Even in the absence of hypertension, PRES can develop from endothelial injury caused by sepsis, autoimmune diseases, cytotoxic drugs, or immunosuppressive therapy (e.g., cyclosporine, tacrolimus). Damaged endothelium allows fluid leakage and triggers inflammatory cascades, compounding the vasogenic process.
Recent insights suggest a combined mechanism: abrupt hypertension, endothelial injury, and inflammatory activation jointly precipitate Posterior Reversible Encephalopathy Syndrome (PRES).
2. Epidemiology
Posterior Reversible Encephalopathy Syndrome (PRES) is rare but increasingly recognized.
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Incidence: Uncertain in the general population but estimated in 0.4–0.8% of ICU patients.
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Gender Predilection: More common in females, especially in cases associated with eclampsia or preeclampsia.
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High-Risk Groups:
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Hypertensive crises
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Chronic kidney disease or dialysis patients
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Autoimmune diseases (e.g., lupus, vasculitis)
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Cytotoxic or immunosuppressive drugs
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Sepsis and systemic inflammatory states
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Understanding these risk profiles is crucial for early detection and prevention of PRES in vulnerable patients.
3. Clinical Presentation
The clinical spectrum of Posterior Reversible Encephalopathy Syndrome (PRES) is broad but typically includes acute neurological manifestations developing over hours to days.
| Symptom | Frequency / Notes |
|---|---|
| Seizures | Most common (60–75% of cases) |
| Headache | Sudden, diffuse, often severe |
| Visual disturbances | Blurred vision, hemianopia, cortical blindness |
| Altered consciousness | Confusion, somnolence, stupor |
| Focal neurological deficits | Weakness, sensory loss, aphasia |
Case Example:
A 26-year-old postpartum woman presented with hypertension and acute confusion. MRI revealed symmetrical parieto-occipital subcortical hyperintensities consistent with Posterior Reversible Encephalopathy Syndrome (PRES).
4. Imaging Features of Posterior Reversible Encephalopathy Syndrome (PRES)
Neuroimaging is pivotal in diagnosing PRES. MRI remains the most sensitive and specific modality.
Figure 1. MRI FLAIR Sequence
Findings: Bilateral subcortical hyperintensities in occipital and parietal lobes representing vasogenic edema.
Caption: Figure 1. FLAIR MRI demonstrating symmetric high-signal lesions in the parieto-occipital subcortical white matter — characteristic of Posterior Reversible Encephalopathy Syndrome (PRES).
Figure 2. Diffusion-Weighted Imaging (DWI) and ADC Map
Findings: No restricted diffusion; ADC values are elevated, consistent with vasogenic rather than cytotoxic edema.
Caption: Figure 2. DWI and ADC images show increased ADC values without diffusion restriction, confirming vasogenic edema typical of 후방 가역성 뇌병증 증후군 (PRES).
Figure 3. GRE/SWI Sequence
Findings: Small foci of microhemorrhage in parieto-occipital regions.
Caption: Figure 3. GRE MRI revealing punctate microbleeds — an ancillary finding sometimes associated with poor prognosis in Posterior Reversible Encephalopathy Syndrome (PRES).
Radiologic Summary
| Sequence | Typical Findings in PRES |
|---|---|
| T2/FLAIR | Hyperintensity in parieto-occipital subcortical white matter |
| DWI/ADC | Absence of restricted diffusion, increased ADC |
| GRE/SWI | Possible microhemorrhage |
| Contrast MRI | Usually minimal or no enhancement |
| CT | May appear normal or show low-density lesions |
5. Differential Diagnosis
The imaging findings of Posterior Reversible Encephalopathy Syndrome (PRES) can mimic several neurological disorders. Differentiation is essential for proper management.
| Disorder | Distinguishing Features |
|---|---|
| Ischemic Stroke | Restricted diffusion (cytotoxic edema), irreversible infarction |
| Hypertensive Encephalopathy | More diffuse cortical involvement |
| Encephalitis | Contrast enhancement, CSF abnormalities |
| PML (Progressive Multifocal Leukoencephalopathy) | Immunocompromised hosts, progressive course |
| RCVS (Reversible Cerebral Vasoconstriction Syndrome) | Vessel narrowing on angiography, may coexist with PRES |
6. Diagnosis
The diagnosis of PRES relies on the triad of clinical context, radiologic pattern, and reversibility.
Diagnostic criteria include:
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Acute neurologic symptoms (seizure, headache, vision loss, confusion)
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MRI evidence of posterior-predominant vasogenic edema
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Reversibility on follow-up imaging and symptom resolution
7. Treatment
1. Blood Pressure Management
The cornerstone of therapy for Posterior Reversible Encephalopathy Syndrome (PRES) is controlled blood pressure reduction.
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Target: Gradual 10–25% mean arterial pressure reduction
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Agents: Labetalol, nicardipine, or nitroprusside
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Avoid rapid drops to prevent ischemic injury
2. Seizure Control
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First-line: Levetiracetam or valproate
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Continuous seizures: Follow status epilepticus protocol
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Tapering possible after resolution
3. Supportive and Etiologic Management
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Correct causative factors (withdraw immunosuppressants or cytotoxics)
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Manage intracranial pressure with mannitol or hypertonic saline
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For eclampsia-related cases, expedited delivery is often life-saving
8. Prognosis
Most patients with PRES recover completely within 2–3 weeks if managed promptly. MRI abnormalities typically resolve.
Poor prognostic indicators include:
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Extensive diffusion restriction (cytotoxic edema)
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Intracerebral hemorrhage
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Brainstem or cerebellar involvement
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Delayed diagnosis or inadequate treatment
Mortality: ~5–6%
Permanent neurological sequelae: 10–15%
9. Quiz Section – Medical Licensing Preparation
Question 1. Pathophysiology
Which mechanism best explains the development of Posterior Reversible Encephalopathy Syndrome (PRES)?
A. Chronic hypertension causing ischemic leukoencephalopathy
B. Sudden rise in BP exceeding autoregulatory limits leading to vasogenic edema
C. Hypoxic vasoconstriction resulting in cytotoxic edema
D. Immune-mediated cortical inflammation
E. Reversible demyelination
✅ Answer: B
Explanation: Acute hypertension overwhelms autoregulation, causing hyperperfusion and breakdown of the blood-brain barrier — the hallmark of PRES.
Question 2. MRI Findings
Which diffusion pattern is characteristic of Posterior Reversible Encephalopathy Syndrome (PRES)?
A. Marked restricted diffusion on DWI
B. Decreased ADC values
C. DWI hyperintensity with elevated ADC (vasogenic edema)
D. Strong contrast enhancement
E. Gray matter–restricted lesions
✅ Answer: C
Explanation: Vasogenic edema in PRES results in DWI hyperintensity with high ADC, distinguishing it from ischemic infarction.
Question 3. Eclampsia-Associated PRES
Which is not appropriate in treating eclampsia-associated Posterior Reversible Encephalopathy Syndrome (PRES)?
A. Gradual BP control
B. Anticonvulsant administration
C. Consideration of prompt delivery
D. Osmotic therapy for edema
E. High-dose corticosteroids as first-line therapy
✅ Answer: E
Explanation: Corticosteroids are not first-line therapy in PRES management.
Question 4. Differential Diagnosis
Which disorder mimics PRES but is irreversible?
A. Hypertensive encephalopathy
B. Ischemic stroke
C. Encephalitis
D. RCVS
E. Subarachnoid hemorrhage
✅ Answer: B
Explanation: Ischemic stroke demonstrates cytotoxic edema and permanent injury, unlike the reversible nature of PRES.
Question 5. Prognostic Factors
Which factor is most associated with poor outcome in Posterior Reversible Encephalopathy Syndrome (PRES)?
A. Mild headache only
B. No restricted diffusion
C. Lesions limited to occipital lobes
D. Diffusion restriction or hemorrhage
E. Rapid BP correction
✅ Answer: D
Explanation: The presence of cytotoxic edema or hemorrhage indicates a severe course and worse prognosis.
References
[1] J. E. Fugate and R. A. Rabinstein, “Posterior reversible encephalopathy syndrome: Clinical and radiological manifestations, pathophysiology, and outstanding questions,” The Lancet Neurology, vol. 14, no. 9, pp. 914–925, 2015.
[2] A. Hinduja, “Posterior reversible encephalopathy syndrome: Clinical features and outcome,” Frontiers in Neurology, vol. 11, p. 71, 2020.
[3] N. Sheikh-Bahaei et al., “Advanced imaging techniques in diagnosis of PRES,” Frontiers in Neurology, vol. 11, p. 165, 2020.
[4] B. W. Bartynski, “Posterior reversible encephalopathy syndrome, part 2: Pathophysiology of vasogenic edema,” AJNR Am. J. Neuroradiol., vol. 29, no. 6, pp. 1043–1049, 2008.
[5] S. M. Smith et al., “Experimental models and endothelial mechanisms in PRES,” Stroke, vol. 55, no. 2, pp. 414–425, 2023.
[6] C. Q. Thavamani et al., “Epidemiology and outcomes of PRES in children,” Pediatric Neurology, vol. 103, pp. 21–26, 2020.
[7] Q. Z. Zhang et al., “Risk factors for poor outcome in PRES: A meta-analysis,” Quantitative Imaging in Medicine and Surgery, vol. 8, no. 8, pp. 835–842, 2018.
[8] C. M. Staykov et al., “PRES associated with eclampsia and hypertensive crises,” European Journal of Neurology, vol. 27, no. 5, pp. 875–885, 2020.
[9] R. A. Rabinstein, “PRES and RCVS: Distinct or overlapping disorders?” Current Opinion in Neurology, vol. 34, no. 1, pp. 28–35, 2021.
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