Transient corpus callosum lesion & boomerang sign on MRI in COVID-19 paediatric patient

A 13-year-old boy was admitted to the emergency department with a five-day history of headaches, dizziness, and pyrexia. Physical examination demonstrated no other neurology. Blood tests showed raised inflammatory markers with negative cultures. Further blood tests only revealed a positive COVID-19 antibody test.

An MRI scan booked to investigate the headaches and dizziness showed an oval-shaped lesion in the splenium of the corpus callosum. This was hyperintense on T2 and FLAIR sequences and isointense to hypointense on T1 sequences. DWI and ADC sequences demonstrated restricted diffusion. Imaging findings were consistent with a cytotoxic lesion referred to as the boomerang sign.

Subsequent contrast-enhanced MRI brain imaging after the initial presentation showed complete resolution of the splenial lesion. There was no enhancement noted on post-contrast sequences and no evidence of restricted diffusion. The radiological findings were consistent with a transient cytotoxic splenial lesion.

Various biochemical mechanisms can explain the transient signal changes found. A cytokine-mediated immunologic reaction leading to microvascular endothelial injury and perivascular oedema is a proposed mechanism leading to these abnormal lesions. The corpus callosum is particularly susceptible to a cytokine-mediated response due to a higher concentration of cytokine and glutamate receptors relative to other segments of the brain [1].

Signal alterations in the splenium of the corpus callosum have an established link with infections, seizures, anti-epileptic medications, malignancy, and trauma [1]. In literature, patients with reversible lesions often present with mild encephalopathy following recent viral infections. They demonstrate full clinical and radiological recovery on follow-up assessment and imaging with no active intervention required [2-5].

There is a recognised association in patients with neurological presentations and COVID-19, particularly in the paediatric population. Patients typically presented with headaches and clinically mild encephalopathy. In the instance of lesions in the corpus callosum, patient symptoms resolved without intervention and the only hypothesised cause for these patients was a proposed COVID-19 infection [6-9].

Clinicians need to consider a variety of differentials in this cohort of patients. Our patient had no history of trauma or seizures and was not on any regular medication associated with the imaging findings. With an unremarkable neurological examination demonstrating only headaches and dizziness, there was no apparent cause for this patient’s presentation apart from a previous COVID-19 infection. A systems review demonstrated no other potential source of infection in our patient.

In summary, this is a rare case of a 13-year-old boy with a boomerang sign in the splenium of the corpus callosum on imaging, presumed to be secondary to a COVID-19 infection. COVID-19 should remain on the list of differentials in the presence of central nervous system signs on imaging. Clinicians should consider COVID-19 as a potential precipitant in patients with unexplained neurological presentations. Our patient had complete neurological recovery on follow-up.

Learning Points

1. COVID-19 is a potential trigger for central nervous system lesions
2. Cytotoxic splenial lesions can resolve without intervention
3. Clinical presentations in patients with splenial lesions are often non-specific

Written informed patient consent for publication has been obtained.