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Case Report

Posterior Reversible Encephalopathy Syndrome After Epilepsy Surgery Alerted by Low-Processed Electroencephalography Levels: A Case Report

Karan, Nupur DM; Ramesh, V. J. MD; Sriram, Vidya MD

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doi: 10.1213/XAA.0000000000001590
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Posterior reversible encephalopathy syndrome (PRES) was first described in 1996.1 Since then, it has been noted in several conditions, including pregnancy, renal failure, chemotherapy, autoimmune disease, and with the use of immunosuppressant drugs.2 Magnetic resonance imaging (MRI) findings reveal bilateral symmetrical or asymmetrical vasogenic brain edema that mostly affects the cerebellum, brainstem, thalamus, basal ganglia, and other parieto-occipital areas.3 The exact mechanism underlying PRES is not well understood. Most patients with PRES have previous hypertension, which suggests that hypertension may be a common trigger for PRES.4 However, patients can develop PRES even without hypertension. Thus, other factors might also induce PRES. In these cases, it is assumed that a systemic inflammatory response mediated by T cell activation and specific inflammatory cytokine secretion leads to systemic vasoconstriction, causing hypoperfusion.5 The development of PRES after resection of a supratentorial tumor has not been described previously. We report a case of PRES after resection of epileptogenic foci in a 19-year-old male. The patient and his relatives provided written informed consent for the publication of this case report.

This article adheres to the applicable Enhancing the Quality and Transparency of Health Research (EQUATOR) guidelines.


A 19-year-old male patient with refractory left complex partial seizures was diagnosed with right medial temporal sclerosis on MRI. He was scheduled for a right anterior temporal lobectomy and selective amygdalo-hippocampectomy with electrocorticography monitoring. His neuropsychological workup revealed moderate mental retardation. The patient had poor seizure control and had experienced his most recent seizure 1 month before surgery. He was on antiepileptics, including clobazam (10 mg twice daily), sodium valproate (200 mg twice daily), and carbamazepine (300 mg 3 times daily). He had no other known comorbidities.

On the day of surgery, we used standard American Society of Anesthesiologists monitors. A processed electroencephalogram (pEEG) was recorded using a GE Entropy module (GE Healthcare) placed on the right forehead. The state entropy (SE) and response entropy (RE) obtained from the pEEG were monitored throughout surgery. We administered fentanyl (2 µg·kg1), thiopentone (4 mg·kg1), and atracurium (0.5 mg·kg1), and the airway was secured with an 8.5-mm cuffed endotracheal tube. Anesthesia was maintained with oxygen, air, and sevoflurane at a minimal alveolar concentration of 0.4 and intermittent atracurium boluses. Dexmedetomidine (0.2–0.5 µg/kg/min) was administered to maintain the RE and SE levels at 40 to 50. No adverse events were reported during the surgical resection. Dexmedetomidine was discontinued after electrocorticography monitoring was completed. After this, anesthesia was maintained with sevoflurane titrated to the pEEG level.

The pEEG level suddenly dropped from 56 to 12 during closure without any change in the patient’s hemodynamic parameters (Table). The pEEG electrode placement and wire connections were unchanged. The pEEG parameters did not improve despite reducing the depth of anesthesia and increasing the blood pressure. The patient’s paralysis was reversed, and the depth of anesthesia was reduced after surgical closure. Even at an end-tidal sevoflurane of 0.2, the SE and RE remained low, without any improvement. The patient’s ventilatory effort was minimal, and he did not respond to painful stimuli. Arterial blood gas was normal, and there were no electrolyte abnormalities or hypoglycemia. The train-of-four count was 4. Hypothermia and other reversible causes of delayed emergence were ruled out. The patient was transferred to the intensive care unit (ICU), and the frontal EEG monitoring showed a low spectral edge frequency of 5 to 6 Hz (Figure 1). Differential diagnoses of delayed recovery from anesthesia, postictal state, and global hypoxic or ischemic brain insult were considered. A postictal state was unlikely, as his brain electrical activity and hemodynamics were monitored throughout surgery, and no abnormal activity suggestive of intraoperative seizure was noticed. The patient had minimal ventilatory attempts in the ICU. Computed tomography showed postoperative changes with minimal pneumocephalus and an operative site hematoma with no midline shift or effacement of the basal cisterns. The patient was ventilated and managed with mannitol (20 g 3 times a day) and antiepileptic drugs, along with supportive measures for 24 hours.

Table. - Monitored Parameters of the Patient Across Various Time Points
Time points BP HR SE RE Etco 2 MAC Spo 2 Temp
09:05 (baseline) 110/71 74 31 31 41 0 99 --
09:35 (postinduction) 96/46 63 38 39 41 0.5 100 36
10:18 (preincision) 99/52 53 33 34 38 0.5 100 35.7
10:28 (postincision) 99/50 53 35 35 37 0.5 99 35.6
13:28 99/50 63 57 58 37 0.4 99 36.5
13:30 101/52 63 51 52 37 0.4 99 36.5
13:32 102/51 63 59 56 38 0.4 99 36.5
13:34 (drop in pEEG levels noted) 100/55 57 11 12 38 0.4 99 36.5
13:36 110/64 59 12 14 38 0.4 99 36.5
13:38 113/60 60 10 10 38 0.4 99 36.5
13:40 126/63 64 12 13 39 0.4 99 36.5
13:42 123/60 60 10 10 41 0.4 100 36.5
13:50 (prereversal) 128/62 62 10 12 41 0.4 100 36.5
14:10 (postreversal) 145/80 72 12 12 46 0.0 99 36.5
Abbreviations: BP, blood pressure; Etco2, end-tidal carbon dioxide; HR, heart rate; MAC, minimum alveolar concentration; pEEG, processed encephalogram; RE, response entropy; SE, state entropy; Spo2, oxygen saturation; Temp, temperature.

Figure 1.:
Electroencephalogram recording at various time points. A, Immediate postoperative frontal electroencephalogram. B, Electroencephalogram recording on postoperative day 3. C, Electroencephalogram recording after clinical recovery.

The patient’s Glasgow Coma Scale (GCS) score improved to E2V1TM2 status. An MRI done on postoperative day (POD) 1 showed hyperintensity in the bilateral basal ganglia, thalamus, and parieto-occipital cortex in T2-weighted and fluid-attenuated inverse ratio sequences, indicating vasogenic edema, which suggested a provisional diagnosis of PRES (Figure 2A). On POD 3, the EEG showed pan cortical diffuse slowing (Figure 1C), which further supported our diagnosis of PRES. He had normal blood pressure in the postoperative period. Supportive care along with mannitol 20 g 3 times a day and antiepileptics were continued. His GCS remained low, and his postoperative MRI showed vasogenic edema. A provisional diagnosis of PRES was made, and the patient was managed with supportive care, mannitol, and antiepileptic drugs. His GCS score gradually improved to E4V5M6 by POD 4. He was weaned from the ventilator and extubated on POD 6. An MRI after extubation showed resolution of the cerebral edema (Figure 2B). An EEG after extubation showed a dominance of high-frequency activity (Figure 1A). On POD 20, the patient was discharged on antiepileptic drugs with a GCS score of 15.

Figure 2.:
MRI of the patient. A, POD 1. B, Postclinical recovery. MRI indicates magnetic resonance imaging; POD, postoperative day.


Patients with PRES usually present with headaches, seizures, and visual disturbances. A diagnosis of PRES mostly relies on classical MRI findings, such as vasogenic edema.3 Different hypotheses have been proposed regarding the pathophysiology of PRES. One hypothesis proposes that brain edema may be due to global cerebral ischemia, secondary to cerebral vasoconstrictive autoregulatory responses to systemic hypertension.4 Another theory suggests that vasogenic edema is potentially caused by hypertension exceeding the cerebral autoregulatory limits, leading to global cerebral vasodilatation and increased hydrostatic pressure.5 However, patients may develop PRES despite normal blood pressures. In such cases, PRES is thought to be initiated by a combination of hypoperfusion and brain endothelial injury, potentially caused by a systemic inflammatory response. Brain surgery has been shown to initiate a neuroinflammatory response.6 Niwa et al7 proposed that a sudden drop in intracranial pressure may lead to mechanical stress on the blood vessels, causing mechanical vasoconstriction and edema. We found another case that described PRES as having developed after a transnasal endoscopic resection of a pituitary tumor.8 The potential cause for PRES was thought to be lumbar cerebrospinal fluid drainage that led to intracranial hypotension. PRES is also frequently reported with posterior fossa surgery, during which the proximity of the tumor to the rostral ventrolateral medulla and brainstem dysregulation may be a potential triggering factor.9 Although our patient was diagnosed with PRES 24 hours after surgery, we believe that it developed at the time the pEEG levels dropped. The patient did not experience seizures intraoperatively or postoperatively. However, there was a delay in his recovery. The neuroinflammatory response initiated by the resection of the brain lesion may have triggered PRES, which may have delayed recovery. Entropy is a technology that combines data obtained from EEG signals and the electromyography of facial muscles. It is a mathematical concept used for the interpretation of nonlinear dynamic data that gives 2 values: SE and RE. This is commonly used to monitor the depth of anesthesia. Previously published data on EEG findings in PRES indicate that most of the patients exhibit diffuse slowing of cortical waves.10,11 In a recent retrospective trial, Murray et al12 showed that EEG findings in PRES can range from normal to generalized periodic discharges. PRES is a rare condition, and the majority of the findings are based on small sample sizes. In our case, the RE and SE dropped to low levels, which suggested slowing of cortical waves, a finding that was persistent in the ICU as well. This helped support the diagnosis of PRES. Entropy levels are derived parameters and should be interpreted with caution. Intraoperatively, it is not feasible to apply a recording device for multiple EEG channels. Any unexplained drop in pEEG readings should be investigated. The neuroinflammatory response to surgery and rapid debulking may have been triggering in our patient, leading to development of PRES without hypertension.

Treatment of PRES consists of controlling underlying conditions and triggering factors, along with supportive measures and aggressive management with antihypertensives and antiepileptic drugs.13 Because our patient’s blood pressure was normal, we managed him with supportive care, mannitol, and antiepileptic drugs. Important criteria for the diagnosis of PRES are the presence of vasogenic edema on neuroimaging and the reversibility of clinical and radiological findings.14 Prolonged poor GCS, the presence of vasogenic edema on postoperative MRI, the gradual clinical recovery, and resolution of cerebral edema on subsequent imaging confirmed the diagnosis of PRES. The insight provided by the pEEG monitoring was useful in supporting the diagnosis. This case report highlights the correlation between these EEG findings and PRES. Nevertheless, uncertainty exists about whether these EEG findings and PRES have causal relation.


Name: Nupur Karan, DM.

Contribution: This author helped with concept, design, literature search, data acquisition, manuscript preparation and editing, and manuscript review.

Name: V. J. Ramesh, MD.

Contribution: This author helped with concept, design, and manuscript editing and review.

Name: Vidya Sriram, MD.

Contribution: This author helped with data acquisition and manuscript editing.

This manuscript was handled by: BobbieJean Sweitzer, MD, FACP.


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