Most Common Locations of Posterior Reversible Encephalopathy Syndrome (PRES)
The most common locations of Posterior Reversible Encephalopathy Syndrome (PRES) are the parietal and occipital lobes (98%), followed by frontal lobes (68%), inferior temporal lobes (40%), and cerebellar hemispheres (30%). 1
Typical Distribution Pattern
PRES is characterized by vasogenic edema with a distinct predilection for posterior brain regions, but the distribution pattern is more extensive than originally thought. The classic and most frequent locations include:
- Parieto-occipital regions: Present in nearly all cases (98%) 1
- Frontal lobes: Affected in approximately 68% of cases 1
- Inferior temporal lobes: Involved in 40% of cases 1
- Cerebellar hemispheres: Affected in 30% of cases 1
Less Common but Important Locations
While posterior brain regions are predominantly affected, PRES can involve other areas:
- Basal ganglia: Involved in 14% of cases 1
- Brainstem: Affected in 13% of cases 1
- Deep white matter: Involved in 18% of cases, including the splenium of corpus callosum (10%) 1
- Thalamus: Affected in approximately 4% of cases 2
Major PRES Distribution Patterns
Three distinct patterns of hemispheric involvement have been identified:
- Holohemispheric watershed pattern (23%): Vasogenic edema distributed along the watershed zones between major cerebral arterial territories 1
- Superior frontal sulcal pattern (27%): Predominant involvement of frontal regions along the superior frontal sulcus 1
- Dominant parietal-occipital pattern (22%): Classic posterior predominant involvement 1
- Partial or asymmetric expression of these patterns (28%): Incomplete or uneven distribution of the above patterns 1
Imaging Characteristics
On MRI, PRES typically presents with:
- Hyperintense signals on T2-weighted and FLAIR sequences 3
- Predominant involvement of white matter more than gray matter 4
- Bilateral and symmetrical distribution in most cases, though asymmetric or unilateral involvement can occur 4
- Restricted diffusion (43%) and hemorrhage (9%) in some cases 3
Clinical Relevance
Understanding the distribution patterns of PRES is crucial for:
- Early and accurate diagnosis, as prompt recognition leads to better outcomes 5
- Distinguishing PRES from other neurological conditions with similar presentations
- Guiding appropriate management decisions, particularly in cases with atypical presentations
Pitfalls in Diagnosis
- PRES may not always be "posterior" or "reversible" as the name suggests 4
- Atypical locations and patterns may lead to misdiagnosis if not recognized
- The presence of hemorrhage or cytotoxic edema does not exclude the diagnosis of PRES 3
Early recognition of both typical and atypical imaging patterns is essential for prompt management to prevent irreversible neurological sequelae and improve patient outcomes.