1、Posterior reversible encephalopathysyndrome (PRES),Posterior reversible encephalopathy syndrome (PRES) was first reported by Hinchey in 1996.1. It may occur due to a number of causes predominantly malignant hypertension, eclampsia, drugs such as tacrolimus, cyclosporine, autoimmune disease and patie
2、nts undergoing organ transplant. After the timely and effective treatment of the clinical manifestation and neuroimaging changes can fully recover, neurological sequelae generally does not exist,The most common clinical symptoms and signs are headache, altered alertness and behavior changes ranging
3、from drowsiness to stupor, seizures, vomiting, mental abnormalities including confusion and abnormalities of visual perception. Seizures may begin focally but usually become generalized.,Classically PRES ：characterized by hyperintensity on T2-weighted and FLAIR images bilaterally and symmetrically i
4、n the parieto occipital regions which is caused by subcortical white matter vasogenic edema.,Atypical PRES：other regions of the brain are involved except the parieto-occipital lobes .Includes brain stem, cerebellum, basal ganglia, and frontal lobes. Atypical imaging appearances include contrast enha
5、ncement , hemorrhage, unilaterality and restricteddiffusion on MRI and involvement of gray matter.,1、The more popular theory suggests that hypertension leads to failure of autoregulation , subsequent hyperperfusion, and vasogenic edema.2、The other theory suggests that vasoconstriction and hypoperfus
6、ion leads to brain ischemia and subsequent vasogenic edema. The relative paucity of sympathetic innervations in the posterior brain results in increased susceptibility to hyperperfusion and vasogenic edema during acute blood pressure elevations. Most authorities believe that hypertensive encephalopa
7、thy and eclampsia share similar pathophysiologic mechanisms,Pathophysiology,A 25-year old lady, primigravida；On the 3rd day of postpartum with sudden onset of giddiness, headache, vomiting, bilateral blurring of vision followed by generalized tonic-clonic seizure. Her BP was within normal limits. Bl
8、ood and urine routine assays were normal, and no proteinuria was detected during both the pregnancy and puerperium. She underwent Persistent Occipito-posterior position and delivered a healthy male baby and her BP both during her surgery and postpartum period was normal.,Case 1,Fig. 1 Case 1: MRI br
9、ain FLAIR(A), T2(B), Diffusion(C) and apparent diffusion coefficient (D) showing changes in bilateral caudate, anteriorlimb of internal capsule, right thalamus and bilateral parieto-occipital subcortical white matter,Case 1,Fig. 2: Case 1: Follow up MRI brain T2 (A) and FLAIR(B) same areas in Fig. 1
10、 being normal,A 21-year old lady,primigravida with 30 weeks gestation；On the 6th day of postpartum with h/o sudden onset of headache, vomiting, bilateral blurring of vision followed by recurrent generalized tonic- clonic seizure. She had regular ANC checkup and her BP was withinnormal limits. Blood
11、and urine routine tests were normal, and no proteinuria was detected during both the pregnancy and puerperium. She underwent emergency LSCS for PROM delivered a still-birth and her BP both during her surgery and postpartum period was,Fig. 3: Case 2: MRI brain T2 (A), diffusion (B) and apparent diffu
12、sion coefficient (C) showingchanges in bilateral caudate, globus pallidus, putamen and bilateral parietooccipitalsubcortical white matter,Case 2,Fig. 4: Case 2: Follow up MRI brain T2 (A), diffusion (B) and apparent diffusion coefficient(C) same areas in Fig. 3 being normal,FIGURE 2. Atypical presen
13、tation of posterior reversible encephalopathy syndrome: Non-contrast (A) and post-contrast (B) brain computerized tomography indicating a hypodense lesion in the left basal ganglia with no contrast enhancement; Brain magnetic resonance imaging illustrating diffusion restriction on diffusion-weighted
14、 imaging (C) and high values on apparent diffusion coefficient (D).,Atypica PRES,FIGURE 3. Atypical presentation of posterior reversible encephalopathy syndrome. The brain computerized tomography revealed global brain edema with a large left parietal hematoma (A), and hemorrhage in the pons (B); the
15、 axial magnetic resonance tomogram also demonstrates atypical presentation of the areas with increased signal intensities in the pons brain stem (C).,Changes in diffusion-weighted magnetic resonance imaging (DWI) and apparent diffusion coefficient (ADC) in posterior reversible encephalopathy is well
16、 documented, and can successfully differentiate PRES from early cerebral ischemia. DWI is the study of choice in PRES to discriminate between vasogenic and cytotoxic edema ,thereby, being helpful as a screening imaging methodology in the setting of ischemic complications of PRES in identifying irrev
17、ersible tissue damage . ADC mapping can be useful to rule out other conditions that can mimic PRES, such as central pontine myelinolysis.,CONCLUSION,It is of particular importance not to exclude PRES as a possible diagnosis when we have the appropriate clinical presentation which is not accompanied by the typical radiological findings since this clinical-radiological syndrome can often be manifested with atypical MRI findings. The success of the therapy lies primarily in recognizing these findings.,
