Acute necrotizing encephalopathy

Last revised by Mostafa El-Feky on 29 Jul 2022

Acute necrotizing encephalopathy, also referred as acute necrotizing encephalopathy of childhood, is a rare type of encephalopathy characterized by multiple bilateral brain lesions, mainly involving the thalami, but also the putamina, internal and external capsules, cerebellar white matter, and the brainstem tegmentum.

Acute necrotizing encephalitis is a rare condition. From the first case described in 1995, many cases have been reported in Asia as well as many Western countries. Most cases are sporadic; however, a few cases of recurrent and/or familial episodes have been reported, secondary to mutations in the RANBP2 gene 10.

Although the initial publications were in the pediatric population, multiple further reports showed the condition to also occur in adulthood 8.

Clinically, it is characterized by acute encephalopathy, with dramatic neurological deficits/symptoms. A viral etiology has been proposed in some cases; viral prodrome hence may precede the neurological deficits.

The etiology and the pathogenesis of acute necrotizing encephalitis are only partially clear. Usually, it develops secondary to viral infections, including influenza A and influenza B, parainfluenza, varicella, and enterovirus. A recent case report, in the setting of the COVID-19 pandemic, has also implicated the virus SARS-CoV-2 as a possible trigger 9.

Pathologically, the lesions show edema, hemorrhage and necrosis. Acute necrotizing encephalopathy is characterized by the lack of inflammatory cells in affected brain parenchyma in comparison to the more common entities of acute disseminated encephalomyelitis and acute hemorrhagic encephalitis 1.

On CT, the corresponding thalamic, putamina, cerebral, cerebellar and brainstem abnormalities are hypodense.

Intracranial hemorrhage and cavitation may also be seen, both of which are associated with a worse prognosis.

In most cases of acute necrotizing encephalitis of childhood, there is bilateral symmetrical thalamic involvement. Abnormal signals on MRI are hypointense on T1 and hyperintense on T2. Restricted diffusion of the involved regions can be seen. 7 These findings can be quite extensive. Hemorrhage, cavitation, and post-contrast enhancement are also seen.

Acute necrotizing encephalitis of childhood carries a very poor prognosis; the mortality rate is near 70%. Treatment is mainly supportive, as the precise etiology remains unknown.

If characteristic symmetric imaging findings are present, the differential diagnosis is limited. Lactic acidosis is not a classic finding of ANEC. Otherwise, the differential diagnoses include:

Clinically, acute necrotizing encephalitis of childhood may be differentiated from ADEM by an early onset of encephalitic features just after the prodromal illness while in ADEM, they may take 1 to 2 weeks to develop. 

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Cases and figures

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