January 17, 2019
A 40-year-old man with headache and seizures during a trip to Cuzco, Peru.
HIGH ALTITUDE CEREBRAL EDEMA
- Background
- High altitude cerebral edema (HACE) is a unique and life-threatening condition which is seen in a chosen group of non-acclimated individuals who are exposed to higher altitudes (in general at altitudes over 2,500 meters).
- The minor form is called “acute mountain sickness” (AMS), the major form is called “high-altitude cerebral edema.” The incidence of HACE is from 0.5% to 4% and it varies depending on altitude.
- The syndrome is caused by hypoxia. Although several aspects of the pathophysiology remain unclear, cerebral edema is consistently found in neuroimaging studies. These findings indicate increased blood-brain barrier (BBB) permeability. Some hypotheses to explain this emphasize the role of increased intravascular pressure, increased cerebral blood flow, and the loss of autoregulation of intracranial pressure. Chemical factors (e.g. vascular endothelial growth factor, nitric oxide, cytokines) may also play a role by altering endothelial permeability with the consequent extravasation of liquid and hematies.
- Clinical Presentation
- The clinical course is usually acute, lasting hours to days.
- The mildest forms present with headache, dizziness, and vertigo. The most severe forms can present with ataxia, altered level of consciousness, hallucinations, seizures, papilloedema, retinal haemorrhage, paralysis of cranial nerves, stupor, and coma.
- Some cases may progress to cerebral herniation and intracranial hypertension resulting in death.
- Key Diagnostic Features
- Non-contrast CT scan of the brain shows diffuse cerebral edema involving white matter of bilateral cerebral hemispheres, mass effect in the form of the effacement of the overlying sulci and compression of the lateral ventricles and third ventricle.
- The most common MRI findings are predominant involvement of white matter, with increased T2 and FLAIR signal involving the corpus callosum, especially in the splenium, centrum semiovale, corona radiata, and posterior limb of bilateral internal capsules with or without restricted diffusion. On susceptibility weighted imaging (SWI) shows multiple small foci of signal dephasing corresponding to microbleeds, mostly in the corpus callosum and in the subcortical white mater.
- Differential Diagnoses
- Cerebral fat embolism: It typically occurs in patients with long bone fractures. DWI shows bright spots on a dark background with a “starfield pattern.” SWI may distinctly demonstrate multiple and diffuse minute hypointense foci in the brain.
- Cerebral air embolism: Brain MRI shows multiple, small foci of marked hypointensity on SWI and multiple small foci infarctions on DWI restricted to the sub cortical region. Brain CT reveals multiple, low-air density foci.
- Thrombotic microangiopathy: Often the triad of thrombocytopenia, elevated lactate dehydrogenase, and schistocytosis is sufficient to suggest the diagnosis. The most common neuroimaging findings are PRES, infarctions, and diffuse minute hemorrhages as well as focal hematoma and sulcal hemorrhage can be seen.
- Acute stroke: DWI demonstrates increased signal intensity and reduced ADC values following a vascular territory. Corpus callosum is infrequently affected.
- Treatment
- Patients with HACE should be brought to lower altitudes and provided supplemental oxygen, a rapid descent is sometimes needed to prevent mortality.
- Brain edema can be treated with the use of Acetazolamide, it provokes metabolic acidosis, thus increasing respiratory minute volume; Dexamethasone, and/or portable hyperbaric chamber, depending on intensity and severity of symptoms.
- Although AMS is not life-threatening, HACE is usually fatal within 24 hours if it is untreated. Without treatment, the patient enters into a coma and then dies. The recovery varies between days and weeks, but most patients recover in a few days. The follow-up brain MRI allows the evaluation of the brain edema improvement, as well as the possible complications.
