What is Posterior Reversible Encephalopathy Syndrome (PRES)?
PRES is an acute neurotoxic syndrome characterized by vasogenic brain edema—predominantly in the posterior parietal-occipital regions—that develops when cerebral autoregulation fails, causing blood-brain barrier breakdown and fluid extravasation into brain tissue. 1
Core Pathophysiology
The syndrome occurs when abrupt blood pressure changes or endothelial injury disrupts the blood-brain barrier, leading to vasogenic edema particularly in posterior brain regions where sympathetic innervation is less pronounced and therefore less effective at dampening blood pressure oscillations. 1, 2 This results in cerebral edema, microscopic hemorrhages, and potential infarctions. 2
Clinical Presentation
PRES manifests with a constellation of acute neurological symptoms: 1, 3
- Altered consciousness or encephalopathy
- Seizures (often generalized tonic-clonic)
- Visual disturbances (including cortical blindness)
- Severe headaches
- Focal neurological deficits
Symptoms typically present acutely or subacutely in specific clinical contexts. 4
Common Triggering Factors
The syndrome develops in patients with identifiable risk factors: 1, 3
- Hypertensive crises (most common etiology, though PRES can occur without hypertension) 5
- Eclampsia/preeclampsia
- Renal failure or impairment
- Immunosuppressive therapy (particularly cyclosporine)
- Chemotherapy or high-dose antineoplastic agents
- Autoimmune diseases (systemic lupus erythematosus)
- Solid organ or stem cell transplantation
- Specific medications (infliximab, anti-TNF therapy) 1
Diagnostic Imaging Characteristics
MRI is the gold standard for diagnosis, showing characteristic findings that distinguish PRES from other neurological emergencies: 1, 6
- T2-weighted and FLAIR sequences: Bilateral hyperintensities in parietal-occipital lobes, predominantly affecting subcortical white matter 1
- DWI with ADC maps: Confirms vasogenic (not cytotoxic) edema 6
- T2 GRE or SWI sequences*: Detects microhemorrhages if present 6
CT scanning has significant limitations—low tissue contrast may miss subtle edema and can appear completely normal in early PRES—but remains useful to exclude intracranial hemorrhage when MRI is unavailable. 6, 2
Atypical Imaging Features
While the classic pattern involves posterior regions, atypical presentations are common and should not exclude the diagnosis: 3, 7
- Anterior brain or brainstem involvement
- Cortical (not just subcortical) involvement
- Hemorrhagic transformation
- Contrast enhancement
- Restricted diffusion in severe cases
Prognosis and Reversibility
Complete spontaneous remission occurs in most cases without permanent sequelae when promptly recognized and managed. 1 However, severe forms can result in long-standing morbidity and mortality. 3
Poor prognostic factors include: 3
- Altered sensorium at presentation
- Hypertensive etiology
- Hyperglycemia
- Longer time to control the causative factor
- Elevated C-reactive protein
- Coagulopathy
- Extensive cerebral edema or hemorrhage on imaging
While seizures are common during the acute phase, development of chronic epilepsy is rare. 3 Radiologic improvement typically occurs within 1-2 weeks, though may take up to 1 month in some cases. 7
Critical Clinical Pitfalls
Failure to identify and discontinue the triggering agent (immunosuppressants, chemotherapy, or other offending medications) can lead to prolonged illness and increased complication risk. 1 Additionally, missing concomitant conditions such as sepsis, metabolic disturbances, or electrolyte imbalances can complicate management and worsen outcomes. 1
Anesthesiologists should maintain high clinical suspicion for PRES as a cause of delayed emergence from anesthesia, as delayed recognition can result in severe long-term neurological disability. 8