British Journal of Radiology (2005) 78, 967-968
© 2005 British Institute of Radiology
doi: 10.1259/bjr/25021344
A pressing case of transient blindness
S Puppala, FRCSEd, FRCR
and
M D Hourihan, FRCR
Department of Radiology, University Hospital of Wales, Cardiff CF14 4XW, UK
Correspondence: Dr Margaret D Hourihan
A 21-year-old male with chronic renal failure on dialysis was referred for emergency medical admission with sudden loss of vision. The symptoms, which started with bi-temporal field loss, progressed within hours to complete loss of vision in both eyes. The admission blood pressure was 180/120. An emergency CT of the brain (Figure 1
) was performed. The patient was treated for his raised blood pressure with intravenous labetelol and progressive return of the patients' vision occurred over the ensuing 24 h.
What findings are observed on the CT? What is the diagnosis? What other imaging techniques would help in the diagnosis?
The unenhanced CT of the brain shows low attenuation in the sub cortical white matter and cortical areas of both occipital lobes. This is the appearance of vasogenic oedema which indicates the diagnosis is posterior reversible encephalopathy syndrome, also called PRES. The patient's hypertension was treated successfully. The repeat CT scan (Figure 2) demonstrates some resolution of the vasogenic oedema, which correlated with the return of normal vision to the patient.
PRES, or posterior reversible encephalopathy syndrome, has also been described as hypertensive encephalopathy, reversible posterior cerebral oedema syndrome and posterior leukoencephalopathy syndrome, which was originally described by Hinchey et al in 1996. It is suggested that this condition represents a localized manifestation of hypertensive encephalopathy occurring secondary to a hypertensive crisis [1]. These terms are all used to describe a group of clinical disorders presenting with some combination of headache, visual loss, seizure, alteration in mental status, occasional focal neurological signs and rarely coma [2–4]. The clinical condition is usually reversible on the prompt treatment of the inciting cause, but it has been shown to progress to irreversibility and possibly death if not treated. While PRES was described in patients with an acute hypertensive episode, it may also occur in conditions with vascular endothelial damage or in the presence of endotoxins as in pre-eclampsia and eclampsia, in haemolytic uremic syndrome, systemic lupus erythematosus, thrombotic thrombocytopenic purpura and cryoglobulinaemia [2]. Its occurrence has been reported following the use of immunosuppressants such as cyclosporine A and tacrolimus, chemotherapeutic agents, cisplatin, interferon alpha, intrathecal methotrexate and indinavir, an antiretroviral agent [5]. Hypercalcaemia is also implicated as a cause with one report suggesting the pathophysiology to be due to micro vascular spasm or direct neurotoxic effect [6]. In PRES there is pathological breakdown of the cerebral vascular auto regulatory mechanism, triggered by either a hypertensive episode or by the presence of histiotoxin substances in the circulation, where vascular endothelial damage causes leakage of fluid (vasogenic oedema) into the brain substance. This occurs predominantly and symmetrically in the parieto-occipital white matter, but can affect the cortical grey matter. It occurs because the normal auto regulatory mechanisms need both myogenic and neurogenic responses to maintain cerebral perfusion [2]. The vertebro-basilar system has poor sympathetic innervation in comparison with the anterior cerebral vessels, and therefore the territories supplied by the vertebro-basilar system are most often affected [2, 7]. The role of neuroimaging is to make the initial diagnosis while excluding other causes for the neurological symptoms and signs. An initial unenhanced CT shows vasogenic oedema predominantly of the parieto-occipital sub cortical white matter, but involvement of the brain stem, cerebellum, frontal lobes and basal ganglia are possible in all or part. The vasogenic oedema is usually symmetrical but this is not a rule as is non involvement of grey matter. MRI has been explored as a diagnostic and as a prognostic tool. With PRES the vasogenic oedema is seen as hyperintensity on T2 weighted imaging and suppressed on fluid attenuated inversion recovery (FLAIR) sequences. It can and needs to be differentiated from ischaemia/cytotoxic oedema using diffusion weighted imaging (DWI) and by calculating apparent diffusion co-efficient (ADC) [8, 9]. These lesions are hypointense or isointense on DWI with an increase in the ADC suggesting vasogenic oedema [9]. In a study by Covarrubias et al [8], DWI revealed foci of increased signal intensity in areas at high risk of or undergoing infarction. These areas have normal or mildly elevated ADC values which result from intravoxel averaging of values from cytotoxic and vasogenic oedema. The authors describe this finding as pseudo normalization and suggest it could represent an early sign of irreversibility [2, 8, 10].
Received for publication April 13, 2005.
Accepted for publication April 22, 2005.
 |
References
|
|---|
- Hinchey J, Chaves C, Appignani B, et al. A reversible posterior leukoencephalopathy syndrome. N Engl J Med 1996;334:494–500.[Abstract/Free Full Text]
- Schwartz RB, et al. Preeclampsia-eclampsia: clinical and neuroradiographic correlates and insights into the pathogenesis of hypertensive encephalopathy. Radiology 2000;217:371–6.[Abstract/Free Full Text]
- Servillo G, et al. Posterior reversible encephalopathy syndrome (PRES) in critically ill obstetric patients. Intensive Care Med 2003;29:2323–6.[CrossRef][Medline]
- Keswani SC, Wityk R. Don't throw in the towel! A case of reversible coma. J Neurol Neurosurg Psychiatry 2002;73:83–4.[Abstract/Free Full Text]
- Giner V, et al. Reversible posterior leucoencephalopathy secondary to indinavir – induced hypertensive crisis: a case report. Am J Hypertens 2002;15:465–7.[CrossRef][Medline]
- Kastrup O, Maschke M, Wanke I, Diener HC. Posterior reversible encephalopathy syndrome due to severe hypercalcemia. J Neurol 2002;249:1563–6.[CrossRef][Medline]
- Johansson B. The blood brain barrier and cerebral blood flow in acute hypertension. Acta Neurol Scand 1974;50:366–72.[Medline]
- Covarrubias DJ, Luetmer PH, Campeau NG. Posterior reversible encephalopathy syndrome: prognostic utility of quantitative diffusion – weighted MR images. AJNR Am J Neuroradiol 2002;23:1038–48.[Abstract/Free Full Text]
- Lamy C, Oppenheim C, Meder JF, Mas JL. Neuroimaging in Posterior reversible encephalopathy syndrome. J Neuroimaging 2004;14:89–96.[CrossRef][Medline]
- Casey SO, et al. CT perfusion imaging in the management of posterior reversible encephalopathy. Neuroradiology 2004;46:272–6.[CrossRef][Medline]
Top
References
