Immediate priorities in the ICU

1. Continuous video-EEG now
   • Sedation can mask motor seizures. Establish whether seizures are ongoing and whether there is nonconvulsive status epilepticus.
   • Titrate antiseizure and anesthetic therapy to electroclinical seizure cessation, preferably under pediatric epileptologist guidance.
   • Refractory status epilepticus requires PICU-level respiratory support and continuous IV anesthetic therapy with EEG monitoring. Goldman-Cecil Medicine describes ICU respiratory support and IV sedation sufficient to suppress epileptic EEG discharges in refractory status epilepticus.
2. Clarify the vascular diagnosis urgently
   • Review MRI diffusion/ADC, FLAIR, SWI/GRE, and contrast sequences with neuroradiology.
   • Obtain MRA or CTA of head and neck, including the aortic arch to intracranial circulation. Add vessel-wall MRI if available.
   • Obtain MR venography or CT venography. A large cortical lesion extending fronto-temporo-parieto-occipitally can be arterial, but cerebral venous sinus thrombosis with venous infarction must be actively excluded.
   • Repeat imaging if the lesion appears to expand, there is unexplained deterioration, or the first angiogram is normal but suspicion for arteriopathy remains. MRI with diffusion sequences plus vascular imaging is the preferred diagnostic approach in pediatric stroke, as summarized in this pediatric stroke imaging review.
3. Prevent secondary brain injury
   • Avoid hypoxia, fever, hypotension, hypo/hyperglycemia, and major sodium disturbance.
   • Maintain euvolemia and adequate cerebral perfusion. Avoid unnecessary hyperventilation, which can worsen ischemia, unless used transiently for impending herniation.
   • Monitor for malignant hemispheric edema: serial pupils, neuro-examination whenever sedation permits, imaging, sodium/osmolality, and early neurosurgical review for possible decompressive hemicraniectomy if there is mass effect or herniation risk.
   • Screen for aspiration, infection, drug toxicity, hepatic/renal dysfunction, and metabolic triggers.
4. Antithrombotic treatment only after defining mechanism and excluding hemorrhage
   • The choice between antiplatelet treatment, anticoagulation, or neither depends on arterial dissection, cardioembolism, cerebral venous thrombosis, hemorrhagic transformation, thrombocytopenia, infection, and planned procedures.
   • Do not assume this is a simple non-cardioembolic arterial infarct. The pediatric stroke protocol cited by Texas Children’s uses aspirin, UFH, or LMWH initially depending on whether dissection and embolic causes have been excluded. Local pediatric stroke and hematology protocols should govern treatment.

Key differential diagnoses

A. Arterial ischemic stroke causes

1. Cerebral arteriopathy
   • Focal cerebral arteriopathy, often post-infectious
   • Intracranial arterial dissection, including after minor neck trauma
   • Primary CNS vasculitis or systemic vasculitis
   • Moyamoya disease/syndrome
   • Reversible cerebral vasoconstriction syndrome, less likely but possible
   • Genetic arteriopathies: ACTA2, RNF213, COL4A1/COL4A2, connective-tissue disorders

1. Cardioembolic stroke
   • Congenital heart disease or previously unrecognized structural lesion
   • Arrhythmia
   • Endocarditis or septic emboli
   • Cardiomyopathy
   • Patent foramen ovale with paradoxical embolus, if venous thrombosis is present
   • Intracardiac thrombus
2. Prothrombotic state
   • Antiphospholipid syndrome
   • Protein C, protein S, or antithrombin deficiency
   • Factor V Leiden/prothrombin variant depending on ancestry and local testing policy
   • Elevated factor VIII, lipoprotein(a), hyperhomocysteinemia
   • Dehydration, severe infection, nephrotic syndrome, inflammatory disease, malignancy
   • Iron deficiency anemia can be a contributing risk factor in children
   • Consider COVID-19 or other recent viral illness only in proper clinical context
3. Sickle cell disease or other hematologic disease
   • Hb electrophoresis if status is unknown, plus CBC/reticulocyte count and peripheral smear.
   • Sickle vasculopathy may present with infarction and seizures. Bradley and Daroff’s Neurology in Clinical Practice reports seizures and focal neurologic deficits among common neurological manifestations in sickle cell disease.
4. Infectious vasculopathy
   • Recent or active varicella, meningitis/encephalitis, tuberculosis, HIV, syphilis where epidemiologically relevant
   • Endocarditis with embolic stroke
   • Sepsis/DIC

B. Venous stroke

1. Cerebral venous sinus thrombosis or cortical vein thrombosis
   • Can cause seizures, hemorrhagic infarction, extensive cortical involvement, fluctuating consciousness, and raised intracranial pressure.
   • MRV/CTV is essential if not already performed.

C. Stroke mimics or mechanisms that can coexist with true infarction

1. Peri-ictal MRI abnormality from focal status epilepticus
   • Prolonged focal seizures may produce cortical diffusion restriction, swelling, and perfusion changes. This can mimic infarction.
   • However, a true infarct can also trigger status epilepticus. MRI lesion distribution, ADC evolution, perfusion, vascular imaging, and serial scans distinguish them.
2. MELAS or another mitochondrial cytopathy
   • Consider especially if lesions cross arterial territories or migrate, and there is lactic acidosis, hearing loss, migraine/vomiting, diabetes, short stature, myopathy, maternal family history, or recurrent “stroke-like” episodes.
   • MELAS commonly involves seizures and stroke-like episodes, but lesions characteristically do not respect a vascular distribution. Miller’s Anesthesia, 10e notes that MELAS lesions are inconsistent with vascular territories and that seizures are common.
   • Send lactate, pyruvate, blood gas, CK, glucose, liver profile, plasma amino acids/acylcarnitines as indicated, urine organic acids, and arrange mitochondrial/genetic testing. Interpret lactate cautiously, because seizures, shock, and beta-agonists can elevate it.
   • If POLG-related disease is plausible, discuss antiseizure drug selection urgently with neurology. Valproate can cause catastrophic hepatic failure in POLG disease.
3. Metabolic and inflammatory mimics
   • Hypoglycemia/hyperglycemia, hyperammonemia, severe electrolyte disorders
   • Urea-cycle disorder or organic acidemia, if clinical/lab pattern supports it
   • PRES, particularly with hypertension, renal failure, immunosuppressants, or posterior-predominant vasogenic edema
   • Autoimmune encephalitis or infectious encephalitis, if there is encephalopathy, fever, CSF inflammation, or new psychiatric/movement symptoms

Syndromes specifically worth considering

Focused investigations once stabilized

Neurovascular

• MRI brain with DWI/ADC, FLAIR, SWI/GRE, contrast as appropriate
• MRA/CTA head and neck
• MRV/CTV
• Vessel-wall MRI if vasculitis, dissection, or focal cerebral arteriopathy suspected
• Catheter angiography if noninvasive imaging is inconclusive or moyamoya/revascularization is being considered
• Repeat vascular imaging, because pediatric arteriopathy may evolve

Cardiac and embolic source

• ECG and telemetry
• Transthoracic echocardiography with bubble study when appropriate
• Transesophageal echo if there is high suspicion for endocarditis, thrombus, or unclear embolic source
• Blood cultures before antibiotics if fever/endocarditis suspected

Hematology and thrombosis

• CBC with smear, platelets, reticulocyte count
• PT/INR, aPTT, fibrinogen, D-dimer
• Sickle screen/Hb electrophoresis where relevant
• Thrombophilia testing in coordination with hematology. Some results are distorted by acute thrombosis, sepsis, liver dysfunction, transfusion, anticoagulants, and critical illness, so a normal or abnormal acute-phase result may need confirmation later.
• Antiphospholipid antibody testing
• Lipoprotein(a), fasting lipids, homocysteine

Infection, inflammation, metabolic, genetic

• ESR, CRP, renal/liver profile, urinalysis, CK, glucose, thyroid function if indicated
• Lactate, pyruvate, ammonia, blood gas, serum/urine metabolic studies if a mitochondrial/metabolic disorder is plausible
• CSF only if safe and if infection/vasculitis/autoimmune encephalitis is suspected. It should not delay vascular evaluation or be performed with unsafe raised intracranial pressure.
• Genetics consultation and targeted panel/exome/genome testing after phenotype review.

Seizure management considerations

• Determine the current antiseizure medication list, adherence, serum levels where measurable, recent changes, and drug interactions.
• Check glucose, sodium, calcium, magnesium, phosphate, renal and liver function, ammonia, infection markers, and antiseizure drug concentrations.
• Treat electrographic seizures promptly, but distinguish refractory status epilepticus from sedation-related EEG suppression or periodic patterns.
• Because this infarct has major cortical involvement, the risk of continued acute seizures and future epilepsy is high. A 2025 systematic review found pooled pediatric post-stroke epilepsy risk of 27.6%; cortical involvement, MCA involvement, acute symptomatic seizures, and prolonged acute seizures increased risk (Alqahtani and Makke, 2025, PMID 41674782).
• Post-stabilization, reassess drug burden and choose a maintenance regimen based on seizure type, renal/hepatic function, stroke mechanism, behavioral adverse effects, and possible mitochondrial/genetic diagnosis.

A practical working formulation

Acute pediatric arterial ischemic stroke or venous infarction with refractory focal/multifocal status epilepticus, with urgent exclusion of large-vessel arteriopathy/dissection/moyamoya, cerebral venous thrombosis, cardioembolism, thrombophilia, infection-associated vasculopathy, and mitochondrial stroke-like disease.

Acute left hemispheric arterial ischemic stroke with refractory focal/multifocal status epilepticus, most likely due to an underlying cerebral arteriopathy until angiography proves otherwise.

• seizures since day 2 of life,
• neurodevelopmental disorder,
• refractory multifocal seizures,
• fronto-temporo-parieto-occipital involvement, and
• possible non-single-arterial-territory lesion,

Bottom line

• If MRI/MRA shows arterial-territory infarction plus MCA/ICA stenosis or irregularity: most likely focal cerebral arteriopathy causing pediatric AIS.
• If the lesion crosses vascular territories, migrates/enlarges atypically, angiography is normal, and lactate is elevated: most likely MELAS stroke-like episode rather than thromboembolic infarction.
• Also urgently exclude cerebral venous sinus thrombosis with MRV/CTV, because extensive cortical seizure-associated infarction may be venous.

Working diagnostic probability chart

Most likely working conclusion

Acute left anterior-circulation arterial ischemic stroke, probably related to focal cerebral arteriopathy, complicated by refractory focal/multifocal status epilepticus.

The two diagnoses that must be separated urgently

1. Focal cerebral arteriopathy with true arterial ischemic infarction
2. MELAS stroke-like episode

MELAS: diagnosis and management

Suspected mitochondrial stroke-like episode with refractory focal/multifocal status epilepticus, pending neurovascular and genetic confirmation.

1. When to diagnose MELAS

1. One or more stroke-like episodes
   • Acute/subacute focal deficit, altered sensorium, visual symptoms, headache/vomiting, or seizures.
2. Epileptic and/or encephalopathic features
   • Focal seizures, status epilepticus, dementia/decline, confusion, or behavioral change.
3. Evidence of primary mitochondrial dysfunction
   • A pathogenic mitochondrial DNA variant, especially MT-TL1 m.3243A>G, or supporting biochemical/muscle-histology evidence.

Clinical features supporting MELAS

2. Critical distinction: MELAS stroke-like episode versus arterial infarct

Diagnostic approach for this patient

A. Immediate investigations

Neuroimaging

1. MRI brain with DWI/ADC, FLAIR, SWI/GRE, and contrast if appropriate
   • Map whether lesions follow an MCA/ICA distribution.
   • Look for cortical predominance, bilateral/migrating lesions, hemorrhage, edema, and old infarcts.
2. MRA or CTA of head and neck
   • Mandatory to exclude ICA/MCA occlusion, focal cerebral arteriopathy, moyamoya, and dissection.
3. MRV or CTV
   • Mandatory if extensive cortical involvement, hemorrhage, unexplained seizures, or non-arterial pattern. Excludes cerebral venous sinus thrombosis.
4. Repeat MRI with perfusion imaging if possible
   • Particularly useful if the first scan is equivocal between peri-ictal diffusion changes, MELAS, and infarction.

Seizure evaluation

• Continuous video-EEG while ventilated and sedated.
• Multifocal electrographic seizures strongly support active cortical dysfunction but do not by themselves distinguish MELAS from arterial stroke.
• Correlate EEG seizure onset zones with MRI lesions.

Basic emergency metabolic tests

• Arterial or venous blood gas
• Serum lactate and pyruvate, ideally processed correctly and drawn without prolonged tourniquet/struggle
• Blood glucose, electrolytes, calcium, magnesium, phosphate
• Ammonia
• CBC, liver function, renal function, CK
• Serum ketones and urine ketones
• Plasma amino acids
• Acylcarnitine profile
• Urine organic acids
• Consider CSF lactate/pyruvate only if lumbar puncture is safe and clinically indicated

B. Genetic confirmation

First-line test

• Mitochondrial DNA sequencing with heteroplasmy quantification, including MT-TL1 m.3243A>G.
• Ideally test blood and urine epithelial cells. Urine often has a higher detectable heteroplasmy level than blood in older children and adults.
• If blood is negative but clinical suspicion remains high, test urine, buccal cells, and/or skeletal muscle.

If mtDNA testing is negative

• Order a comprehensive mitochondrial disease nuclear gene panel or rapid exome/genome sequencing, including genes such as:
  • POLG
  • TWNK
  • MPV17
  • OPA1
  • mitochondrial respiratory-chain genes
  • other epilepsy/mitochondrial disease genes

Role of muscle biopsy

• It is not usually first-line if genetic testing is rapidly available.
• Consider biopsy when genetic testing is non-diagnostic and suspicion remains strong.
• Findings may include ragged-red fibers, COX-negative fibers, and respiratory-chain enzyme defects.

Acute management of a suspected MELAS stroke-like episode

1. Treat seizures/status epilepticus aggressively

• Continue continuous EEG.
• Treat electrographic seizures even if no motor convulsions are seen under sedation.
• Use an antiseizure regimen appropriate to renal/hepatic status and current drugs.
• Maintain adequate levels of established antiseizure medication and use enteral administration via NG tube whenever feasible.
• In refractory status epilepticus, anesthetic infusion with EEG-directed titration may be necessary.

Medication cautions

• Avoid sodium valproate if possible until POLG disease has been excluded, particularly in a child with early-onset epilepsy, liver dysfunction, developmental impairment, or suspected mitochondrial disease. Valproate can precipitate severe or fatal hepatic failure in POLG-related disease.
• Use topiramate cautiously, particularly when metabolic acidosis is present, because it may worsen acidosis.
• Monitor ammonia and liver enzymes closely, especially if valproate has already been given.
• Avoid prolonged fasting and ensure carbohydrate-containing nutrition unless contraindicated.

2. Stabilize energy metabolism and physiology

• Maintain oxygenation, ventilation, normothermia, normoglycemia, and adequate cerebral perfusion.
• Avoid hypotension, hypoxia, prolonged fever, dehydration, severe anemia, and metabolic acidosis.
• Avoid prolonged fasting. Provide early nutrition, usually with glucose-containing maintenance fluid and enteral nutrition if tolerated.
• Treat infection promptly after cultures where appropriate.
• Monitor serial blood gas, lactate, glucose, electrolytes, renal and liver function.
• Treat raised intracranial pressure/cerebral edema using standard neurocritical-care principles with neurosurgical involvement.

3. L-arginine

• The Mitochondrial Medicine Society recommends urgent IV arginine hydrochloride in acute stroke-like episodes associated with MT-TL1 m.3243A>G, and consideration in other primary mitochondrial cytopathies while alternative causes are being excluded (Mitochondrial Medicine Society standards).
• A recent international consensus notes that the benefit of arginine, citrulline, taurine, CoQ10, and vitamins remains unproven in definitive trials (recent MELAS consensus).

Practical instruction

• Discuss immediate IV L-arginine hydrochloride with metabolic genetics/pharmacy and use the institution’s pediatric mitochondrial emergency protocol.
• Do not use an adult stroke-thrombolysis protocol as a substitute.
• Monitor blood pressure, potassium, acid-base status, renal function, and fluid balance during infusion.
• Reassess clinical course, EEG, and imaging after approximately 3 days of continuous treatment, as recommended in the Mitochondrial Medicine Society standards.

4. Corticosteroids

• IV corticosteroids are not established standard treatment.
• Recent consensus allows consideration on a case-by-case basis in severe acute stroke-like episodes, after excluding infection and considering competing diagnoses.
• They should not replace seizure control, vascular imaging, or metabolic stabilization.

5. Antiplatelets, anticoagulation, thrombolysis

• If the episode is confirmed to be a mitochondrial stroke-like episode without arterial thrombosis or venous thrombosis, routine antiplatelet treatment, anticoagulation, and thrombolysis are generally not indicated for MELAS itself.
• In this patient, however, these treatments must be decided only after MRA/CTA and MRV/CTV exclude:
  • true arterial occlusion/arteriopathy
  • dissection
  • cardioembolism
  • cerebral venous thrombosis

Long-term management after stabilization

Suggested immediate orders/checklist

1. Continue continuous video-EEG and treat electrographic status.
2. Obtain urgent MRA head/neck plus MRV/CTV.
3. Review MRI with neuroradiology: vascular-territory versus stroke-like pattern.
4. Send lactate, pyruvate, ABG, glucose, ammonia, CK, CMP, plasma amino acids, acylcarnitines, urine organic acids.
5. Send mtDNA sequencing with heteroplasmy, starting with blood and urine.
6. Arrange rapid mitochondrial/nuclear epilepsy gene testing, including POLG, if initial mtDNA testing is unrevealing.
7. Consult pediatric metabolic genetics urgently for possible IV L-arginine protocol.
8. Avoid further valproate if an alternative exists, until POLG-related disease is addressed.
9. Maintain glucose-containing fluids/nutrition, hydration, normothermia, oxygenation, and acid-base/electrolyte control.
10. Continue parallel work-up for true pediatric ischemic or venous stroke until definitively excluded.

Sepsis and septic shock: current pediatric guidance, 2026

1. Current definitions

Pediatric sepsis

Suspected or confirmed infection plus life-threatening organ dysfunction, identified by a Phoenix Sepsis Score of 2 or more.

• Respiratory dysfunction
• Cardiovascular dysfunction
• Coagulation dysfunction
• Neurologic dysfunction

Pediatric septic shock

Sepsis plus cardiovascular dysfunction, defined by at least 1 cardiovascular point in the Phoenix Sepsis Score.

• Severe age-adjusted hypotension
• Lactate >5 mmol/L
• Requirement for vasoactive medication

• MAP 38-51 mmHg: cardiovascular dysfunction
• MAP <38 mmHg: severe cardiovascular dysfunction

2. First-hour bundle for suspected septic shock

3. Antimicrobial timing

Empiric antibiotics

• Community versus hospital-acquired infection
• Current antibiotic exposure
• Central venous catheter
• Ventilator-associated pneumonia risk
• Immunosuppression/neutropenia
• Meningitis/encephalitis possibility
• Local antibiogram and resistance patterns
• Renal/hepatic function

4. Fluids: revised, reassessment-based treatment

For a child in septic shock with PICU capability

• Use balanced crystalloid first if available, such as lactated Ringer's or Plasma-Lyte.
• Give 10-20 mL/kg per bolus.
• May give up to 40-60 mL/kg in the first hour, but only with repeated reassessment.
• Stop fluid boluses if shock resolves or signs of fluid overload appear.

Reassess after every bolus

• Heart rate, blood pressure/MAP, pulse quality
• Capillary refill, skin temperature gradient, mental status
• Urine output
• Lactate trend
• Hepatomegaly, gallop rhythm, crepitations, rising oxygen/PEEP requirement
• Bedside cardiac and lung ultrasound, if trained personnel are available
• IVC assessment only as part of an integrated assessment, not alone

5. Vasoactive medication

When to start

• Persistent hypotension or poor perfusion after initial limited fluid bolus
• Fluid overload or high risk of overload
• Severe shock where fluid administration would delay restoration of perfusion
• Suspected myocardial dysfunction

First-line agent in children

6. Hemodynamic targets

• Age-appropriate MAP and systolic BP
• Normalizing/reducing lactate, while interpreting it in context
• Capillary refill improvement
• Improved peripheral pulses and warm extremities
• Improving mental state where assessment is possible
• Urine output generally at least 1 mL/kg/hour in children
• Improved bedside echocardiographic cardiac output/function
• Avoiding fluid accumulation

7. Respiratory and ventilator care

• Use lung-protective ventilation if ARDS is present.
• Avoid hypoxemia and hypercapnia that may worsen intracranial pressure or cerebral perfusion.
• SSC 2026 suggests avoiding etomidate for intubation in pediatric sepsis.
• The guideline suggests conservative oxygen targeting after resuscitation in many septic children, but this child has cerebral infarction and ongoing seizures, so oxygen targets should be individualized by the neurocritical-care team. Do not accept hypoxemia in acute neurologic injury.
• Assess for ventilator-associated pneumonia and obtain suitable respiratory cultures if indicated.

8. Corticosteroids

• Fluid-refractory, catecholamine-resistant shock
• Suspected or proven adrenal insufficiency
• Chronic corticosteroid exposure
• Possible adrenal crisis

9. Blood products and coagulopathy

• Use a restrictive red-cell transfusion approach once stable, commonly hemoglobin threshold around 7 g/dL, unless active bleeding, severe hypoxemia, cyanotic heart disease, myocardial ischemia, or other individualized indication exists.
• Platelet/FFP/cryoprecipitate should not be given solely for abnormal laboratory values without bleeding or a planned invasive procedure.
• In suspected DIC, trend platelets, PT/INR, aPTT, fibrinogen, D-dimer, and assess bleeding/thrombosis clinically.

10. Glucose, nutrition, renal support

• Check glucose repeatedly. Treat hypoglycemia immediately.
• Initiate insulin for persistent hyperglycemia, commonly at glucose ≥180 mg/dL (10 mmol/L), with intensive monitoring.
• Begin enteral nutrition early after hemodynamic stabilization if gut perfusion is adequate.
• Avoid prolonged fasting, especially if MELAS/mitochondrial disease remains possible.
• Consider renal replacement therapy for refractory hyperkalemia, severe metabolic acidosis, fluid overload, or uremic complications.

11. Source control: must occur early

• Central-line infection
• Pneumonia, aspiration, ventilator-associated infection
• Urinary obstruction or pyelonephritis
• Meningitis/encephalitis
• Intra-abdominal infection
• Skin/soft-tissue or necrotizing infection
• Osteomyelitis/septic arthritis
• Endocarditis
• Sinus/ear/mastoid infection
• Infected thrombus or cerebral venous thrombosis

12. Special points in this patient

1. Sepsis can trigger MELAS stroke-like episodes and status epilepticus. Culture and treat infection early.
2. Do not interpret lactate alone as proof of septic shock. Lactate can rise from seizures, hypoxia, epinephrine, hepatic dysfunction, mitochondrial disease, or shock. Evaluate perfusion and infection evidence together.
3. Use cautious fluid boluses with frequent reassessment, because fluid overload can worsen pulmonary function and cerebral edema.
4. Ensure antibiotics have adequate CNS penetration if CNS infection or infectious vasculitis is possible.
5. Continue continuous EEG, because sepsis and fever can worsen nonconvulsive status epilepticus.
6. Send blood cultures before antibiotics only if this does not delay therapy.
7. Consider line-related bloodstream infection and ventilator-associated pneumonia early in the source evaluation.

Simple bedside algorithm

Suspected infection + organ dysfunction
        |
        v
Screen for septic shock:
Hypotension, poor perfusion, lactate >5 mmol/L, or vasoactive need
        |
        v
Within 1 hour:
- ABCs, monitoring, IV/IO access
- Cultures and lactate, without delaying treatment
- Broad IV antibiotics
- 10-20 mL/kg balanced crystalloid and reassess
- Start epinephrine or norepinephrine early if persistent hypoperfusion
- Search for and control source
        |
        v
PICU:
- Serial perfusion/lactate/urine output/POCUS assessment
- Titrate vasoactives to shock phenotype
- Limit further fluids if overloaded
- Treat seizures, respiratory failure, DIC, AKI, hypoglycemia
- Daily antibiotic review and de-escalation

Is PRES favored in this patient?

Acute arterial ischemic stroke or stroke-like lesion with refractory multifocal seizures/status epilepticus.

Why PRES is plausible

Why PRES is not yet favored

MRI features that decide the diagnosis

Practical diagnostic statement for this child

Possible atypical PRES, potentially sepsis- or hypertension-associated, with refractory status epilepticus; however, acute left arterial ischemic infarction, focal cerebral arteriopathy, cerebral venous thrombosis, peri-ictal MRI change, and MELAS remain unexcluded.

Immediate steps if PRES is suspected

1. Review all blood-pressure recordings
   • Look for absolute hypertension and rapid rise from the child’s baseline.
   • At age 13, interpret BP against age, sex, and height percentiles.
   • Avoid abrupt excessive BP reduction, especially because true infarction remains possible.
2. MRI review with neuroradiology
   • DWI, ADC, FLAIR, SWI/GRE.
   • Determine vasogenic versus cytotoxic edema.
   • Look for hemorrhage, which can coexist with PRES.
3. MRA/CTA head and neck plus MRV/CTV
   • Exclude arterial occlusion, focal cerebral arteriopathy/dissection, and cerebral venous thrombosis.
4. Identify and reverse triggers
   • Treat sepsis promptly and obtain source control.
   • Correct renal failure, fluid overload, electrolyte disturbance, and hypomagnesemia.
   • Stop or reduce potential offending drugs, such as calcineurin inhibitors, cytotoxic agents, or high-dose steroids when clinically appropriate.
   • Review immunosuppressants and blood-pressure-raising drugs.
5. Control seizures
   • Continuous EEG is appropriate in this sedated, ventilated child.
   • Treat electrographic seizures/status aggressively.
6. Repeat MRI
   • Improvement of lesions after trigger control supports PRES.
   • Progression to a fixed infarct favors arterial ischemia or complicated PRES with infarction.

Bottom line

• Extensive left cerebral hemispheric subcortical and deep white-matter edema, involving left frontoparietal regions and corpus callosum
• Patchy contrast enhancement
• Additional multifocal diffusion-restricting foci in right centrum semiovale/corona radiata, bilateral periventricular parietal areas, left temporal and left occipital lobes
• Small GRE blooming foci in the left hemisphere, suggesting microhemorrhage
• Major mass effect: 6 mm midline shift, ventricular compression, basal cistern effacement, and midbrain/pons compression

MRI-pattern differential diagnosis comparison

Key MRI report features being compared

• Extensive left cerebral hemispheric subcortical and deep white-matter T2/FLAIR hyperintensity with T1 hypointensity
• Involvement of left frontoparietal region and body and splenium of corpus callosum
• Patchy contrast enhancement
• Additional scattered diffusion-restricting foci in right centrum semiovale/corona radiata, bilateral periventricular parietal regions, left temporal and left occipital areas
• A few left hemispheric GRE blooming foci, suggesting microhemorrhage
• Severe edema/mass effect: 6-mm rightward midline shift, ventricular and basal-cistern effacement, compression of midbrain/pons
• No collection or discrete mass described

This is a multifocal, largely white-matter-predominant inflammatory/edematous pattern with callosal involvement and small hemorrhagic components. It is not typical of a single uncomplicated arterial infarct.

Most favored working diagnosis

Fulminant inflammatory demyelinating disease, most concerning for acute hemorrhagic leukoencephalitis, or severe MOG-associated ADEM with hemorrhagic transformation.

Findings that make this a neurocritical-care emergency

• 6-mm midline shift
• Basal cistern effacement
• Midbrain and pontine compression
• Ventricular compression
• Extensive cerebral edema
• Ongoing multifocal seizures/status epilepticus
• Possible microhemorrhage

Immediate diagnostic priorities

1. MR venography or CT venography to exclude cerebral venous thrombosis.
2. MRA/CTA head and neck, ideally with vessel-wall MRI, to evaluate vasculitis, focal cerebral arteriopathy, dissection, or moyamoya.
3. Continuous video-EEG and aggressive treatment of electrographic status.
4. Repeat MRI with DWI/ADC, SWI, contrast, and perfusion if feasible.
5. Blood tests: CBC/platelets, coagulation profile, fibrinogen, D-dimer, renal/liver profile, CRP/ESR, cultures, lactate, ammonia.
6. Serum MOG-IgG and AQP4-IgG, obtained before immunotherapy if possible.
7. CSF infectious/autoimmune/demyelination studies only after imaging and neurosurgical assessment confirms lumbar puncture is safe. With effaced basal cisterns and midline shift, LP may be dangerous.