Cerebral MRI
Cerebral MRI changes in MOGAD are highly dependent on age. In children,
typical MRI findings of ADEM are found in 40-50% of MOGAD cases (7).
These include widespread supra- and infratentorial, asymmetrical diffuse
white matter T2-hyperintensive lesions (32,73). Additional bilateral
thalamic lesions were more common in MOG-IgG positive compared to
MOG-IgG negative ADEM paediatric patients (74). In adults, brain MRI
lesions are typically few and often either found infratentorially or
presenting as cortical lesions (75,76), however there have been
observations of large, confluent T2-hyperintense lesions in the white
matter similar to ADEM (11).
Brainstem lesions can be found in up to 30% of adult MOGAD patients
(6,77). These lesions are typically poorly demarcated, often located in
the pons, around the 4th ventricle, or the cerebellar
peduncles and show resolution over time (75). Importantly, isolated
brain or brainstem lesions are rare in adults and more often occur in
combination with optico-spinal lesions (6). One patient presented with
an initial MRI pattern typical of chronic lymphocytic inflammation with
pontine perivascular enhancement responsive to steroids (CLIPPERS) and
then subsequently developed LETM leading to a diagnosis of MOGAD (78).
Isolated T2-hyperintense cortical lesions visible on fluid-attenuated
inversion recovery (FLAIR) sequences in both adult and paediatric
patients with seizures were identified and referred to as FLAMES:
FLAIR-hyperintense Lesions in Anti-MOG-associated Encephalitis with
Seizures (76,79). In these patients, cerebral MRI demonstrates
unilateral or bilateral cortical T2-hyperintense lesions, but can also
include deep grey matter, white matter, and brainstem lesions
(55,57,80). In paediatric MOG-associated autoimmune encephalitis,
cerebral MRI findings include extensive cortical and/or subcortical grey
matter involvement without the typical white matter lesions seen in ADEM
(4,60). Importantly, cerebral MRI in these children was normal in only
9% of the cohort, which is much less compared to other types of
autoimmune encephalitis, such as anti-NMDA-receptor encephalitis where
MRI can be normal in around 50% of the patients (81). In young children
presenting with the rare leukodystrophy-like MOGAD phenotype, cerebral
MRI shows extensive confluent symmetrical white matter lesions with
progression over time (61).
Since MOGAD represents an important differential diagnosis from MS and
AQP4-NMOSD using radiological features, several studies assessed
potential differences on MRI. A distinct pattern of MRI lesions defined
by the so-called Matthews-Jurynczyk criteria can help differentiating
MOG-NMOSD vs. MS strongly favouring MS over MOGAD, when: i) ≥ 1 lesion
adjacent to a lateral ventricle and in the inferior temporal lobe, ii)
subcortical U-fibre lesions, and iii) Dawson’s finger-type lesions
(75,82,83). However, these studies did not report criteria to help
discriminate between MOGAD and AQP4-NMOSD patients (84). The brainstem
is a location where both MOGAD and AQP4-NMOSD patients can present with
lesions (75,83), while cortical and juxtacortical lesions are more
frequently found in MOGAD versus AQP4-NMOSD patients. Moreover, the area
postrema syndrome that often affects AQP4-NMOSD patients with its
corresponding MRI lesions, is not a characteristic feature in MOGAD
(54).