A thirteen-year-old female presented with four recent episodes of tonic clonic seizures associated with vomiting. She had one episode of epistaxis. She was a known case of thalassemia major on regular blood transfusions. She received her last blood transfusion four days ago. Her birth and development history was normal. She was afebrile at the time of admission and laboratory investigations revealed mild thrombocytopenia (platelet count of 1.19 lakh per microlitre). Her blood pressure was 150/90 mm of Hg. There was no leukocytosis and serum electrolytes were normal.
A non-contrast Magnetic Resonance Imaging (MRI) of the brain was performed. T2 and FLAIR hyperintense areas were seen in the bilateral frontal, parietal and occipital lobes, predominantly involving cortex & subcortical white matter. There was sulcal effacement with no significant diffusion restriction in the above areas. Few of the altered signal intensity areas in the parieto-occipital lobes showed fluid levels. Multiple intraparenchymal areas of blooming were seen with hemorrhagic fluid levels. There were minimal dependent hemorrhagic levels in the occipital horns of the lateral ventricles. T2 flow voids of intracranial vessels were maintained. There was no midline shift or cerebral herniation. TOF venography and angiography appeared normal. Diffuse thickening of the calvarium with marrow expansion was present. She was treated symptomatically with antihypertensive and antiepileptic drugs with advice in further follow-up.
Posterior reversible encephalopathy syndrome (PRES) commonly affects young to middle-aged females but may occur in any age group. Eclampsia, accelerated hypertension, post-transplantation status, autoimmune disease, infection and sepsis are risk factors. The presenting symptoms include headache, visual disturbances, confusion, focal neurological deficits and seizures. It is usually reversible but recurrence is known to occur.  The typical pattern of involvement on MRI includes bilaterally symmetrical cortical and subcortical T2 & FLAIR hyperintensity in parieto-occipital lobes, suggestive of vasogenic oedema. However, other locations such as frontal lobes, brainstem and deep grey nuclei may be involved. Haemorrhage may be present, atypical findings include restricted diffusion, contrast enhancement and mass effect in the form of herniation.  Few patients may show cerebral vasoconstriction such as seen in reversible cerebral vasoconstriction syndrome.
PRES should be included in the list of differential diagnosis of patients presenting with encephalopathy in the background of diseases like vasculitis, nephritis, leukaemia, lymphoma, known hypertension and drugs including steroids or anti-cancer medications. It needs to be differentiated from cortical venous thrombosis, infections, herpes encephalitis and myelinolysis.  This can be achieved with clinical history, CSF & laboratory investigations, venography, and radiological pattern of involvement.  In certain cases, post-treatment follow up imaging may be useful. PRES after blood transfusion is rare and may occur due to failure of autoregulation following acute volume overload, thus resulting in vasogenic oedema. Another postulation is that sudden increase in haemoglobin can give rise to increased blood viscosity and loss of hypoxic vasodilatation. Following this, endothelial damage and capillary leakage can result in PRES.  MRI findings considered atypical in adults have been found to be common in the pediatric population. Thus involvement of frontal lobes and grey matter can occur in paediatric population and this knowledge can prevent misdiagnosing PRES.  Treatment is mainly symptomatic and includes antihypertensive and antiepileptic medications. Management of underlying disease is most important and withdrawal of precipitating drug may be required in certain cases. 
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