Case of the Month: August, 2011, Page 2

Answer: All of the above.

Findings:

Subcortical edema in the medial parietal lobes extending into the occipital lobes bilaterally. Additionally, areas of edema are seen in the bilateral cerebellar hemispheres.

Given the clinical and radiographic presentation, findings are most consistent with posterior reversible encephalopathy syndrome.

Discussion:

Posterior reversible encephalopathy syndrome is a variant of hypertensive encephalopathy characterized by headache, visual disturbances, and altered mental status. This entity is most commonly caused by hypertension, although other etiologies include preeclampsia/eclampsia, drug toxicity (chemotherapy), and uremic encephalopathies. Microscopically, acute hypertension damages the vascular endothelium, disrupting the blood-brain barrier, resulting in vasogenic edema.  

There is a predilection for involvement of the posterior circulation including the occipital lobes and cortical watershed zones. CT will show bilateral nonconfluent hypodense foci, with or without lesions in the basal ganglia. MRI will show T2/FLAIR hyperintensities in the parietooccipital lobes 95% of the time. Variable patchy enhancement can be seen. Occasionally (as in this case), the cerebellum can be affected.

Treatment consists of controlling hypertension and removal of other precipitating factors. Once this occurs, the majority of patients will recover without residual abnormalities.

Imaging characteristics of the listed lesions in the differential diagnosis include: 1) acute ischemia-infarction: MCA distribution will be much more common than PCA distribution. Infarct will also demonstrate restricted diffusion on MRI, PRES usually does not.  2) Hypoglycemia: Severe parietooccipital edema, so history is very important. The patient’s glucose in this case was normal. 3) Gliomatosis cerebri: The entire lobe is affected rather than patchy cortical/subcortical involvement. Additionally, occipital lobe involvement is generally less common.

References:

  1. Sweany JM et al: “Recurrent” posterior reversible encephalopathy syndrome: report of 3 cases—PRES can strike twice! Comput Assit Tomogr.31(1):148-56,2007
  2. Pande AR et al: Clinicoradiological factors influencing the reversibility of posterior reversible encephalopathy syndrome: a multicenter study. RadiatMed.24(10):659-68,2006
  3. Thambisetty M et al: Hypertensive brainstem encephalopathy:clinical and radiographic features.JNeurolSci.208(1-2):93-9,2003

 

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