Type:
Educational Exhibit
Keywords:
Performed at one institution, Observational, Retrospective, Epidemiology, Drugs / Reactions, Acute, Education, MR, CT, Neuroradiology brain, Neuro
Authors:
P. ELVIRA RUIZ, M. J. García Redondo, M. M. Manrique Zegarra, M. F. Arenas García, P. Patilla Vázquez, I. Garrido Morro, J. A. Guzmán de Villoria Lebiedziejewski, P. Fernández García; Madrid/ES
DOI:
10.26044/ecr2020/C-14603
Background
Posterior reversible encephalopathy syndrome (PRES) is an acute onset and usually reversible neurological disorder characterized by headache, disorders of consciousness, visual disturbance and acute arterial hypertension associated with intracranial vasogenic oedema.
Etiology:
There are two main theories:
- Hyperperfusion hypothesis: elevation of blood pressure above the upper limit of cerebrovascular autoregulation leads to vascular leakage and vasogenic oedema in brain. The lesser density of sympathetic innervation in the posterior circulation in contrast to the anterior circulation would explain the high incidence of involvement of parietal and occipital lobes.
- Endothelial dysfunction:PRES is not only present in hypertensive emergencies but also in a heterogeneous group of conditions such as pre-eclampsia, bone marrow and solid organ transplantation, chemotherapy, autoimmune disorders, kidney failure and sepsis. The common feature of these diverse entities is endogenous or exogenous toxins and they are supposed to cause endothelium injury in different ways such as impairment of inter-cellular adhesion proteins and release of vasoactive and immunogenic molecules. This leads to altered permeability with oedema formation as well as vasoconstriction and ischaemic injury. In this toxic hypothesis, endothelial dysfunction is the cause of elevated blood pressure and might justify the prevalence of normal or mild elevated arterial pressure observed in PRES.
Predisposing factors:
- Hypertension. Moderate to severe elevation of blood pressure is detected in a 75% of patients. However, the upper limit of cerebrovascular auto regulation (150 mmHg) is not reached in most cases.
- Preeclampsia/eclampsia. PRES is found up to 90% of eclamptic and 20% of preeclamptic women. Altered placentation is thought to be the cause of toxaemia.
- Inmunosuppressants. Reported incidence of PRES in bone marrow transplantation and solid organ transplantation recipients treated with tacrolimus and cyclosporine is up to 9% and to 6%, respectively. Discontinuation, dosage reduction or switch of these agents usually leads to a clinical and neuroradiological improvement.
- Infection/sepsis/shock. 40% of these patients show normal or mild elevation of blood pressure. Normotensive patients tend to show larger areas of vasogenic oedema than hypertensive patients.
- Autoimmune diseases such as systemic lupus erythematous, granulomatosis with polyangiitis, systemic sclerosis and polyarteritis nodosa. Apart from immunosuppressant toxicity, high levels of cytokines are supposed to increase vascular permeability inducing brain vasogenic oedema.
- Chemotherapy. PRES relation to multidrug chemotherapy treatment is well established.
Neurological manifestations:
Oedematous tissue mass effect induces headache and encephalopathy. Visual disturbances are justified by frequent occipital lobe involvement. Additionally, perirrolandic extension of oedema can manifest as motor deficit. Another common clinical feature of PRES is seizures, reported in up to 74% of patients.
Image findings:
Typical features of PRES:
On CT, focal or patchy areas of hypodensity are depicted in subcortical white matter of parietal and occipital lobes with variable involvement of adjacent cortex, consisting in vasogenic oedema. On MRI, vasogenic oedema is observed as areas T2 and DWI hyperintensity and T1 hypointensity. ADC map values are increased in these lesions. Those abnormalities frequently are bilateral and symmetric with variable extension to frontal and temporal lobes.
There are three primary PRES patterns reported:
- Dominant parieto-occipital pattern in 22% of reported cases. It represents the classical posterior hemispheric involvement of PRES.
- Holohemispheric watershed pattern in 23 % of patients. Vasogenic oedema is noted in a linear fashion crossing frontal, parietal, occipital and temporal lobes, corresponding with vascular watershed areas between anterior and middle cerebral arteries as well as posterior and middle cerebral arteries.
- Superior frontal sulcus pattern in 27% of cases. Lineal vasogenic oedema distributes in the middle and posterior aspect of to the superior frontal sulcus with variable involvement to parieto-occipital regions. Sparing of frontal poles and lesion circumscription to frontal sulcus is the main difference between this pattern and the holohemispheric watershed distribution.
Oedema distribution and extension has not showed relationship with type or clinical severity of PRES.
Atypical image features of PRES:
- Asymmetric distribution of oedema is not uncommon (27,9%) even a rare unilateral expression (2,6%) has been reported.
- Cerebellum, thalamus, brainstem and basal ganglia involvement is not unusual (up to 34%).
- Haemorrhagic lesions (17%) including microbleeds, subarachnoid haemorrhage, subdural and intraaxial haematomas.
- As opposite as we expected, high signal on DWI with low/normal ADC values can be depicted, reflecting cytotoxic oedema. Conflicting outcome concerning this finding has been described.
- Contrast enhancement (37,7%), keeping relation with blood-brain barrier disruption.
Prognosis:
In the majority of cases, PRES completely resolves clinically and at imaging after removal of PRES triggers. Nevertheless, up to 36% poor clinical outcome has been reported and image sequelae are well demonstrated.