Segmentation of medial temporal subregions reveals early right-sided involvement in semantic variant PPA.
BACKGROUND
Semantic variant of primary progressive aphasia (svPPA) is a subtype of frontotemporal dementia characterized by asymmetric temporal atrophy.


METHODS
We investigated the pattern of medial temporal lobe atrophy in 24 svPPA patients compared to 72 controls using novel approaches to segment the hippocampal and amygdalar subregions on MRIs. Based on semantic knowledge scores, we split the svPPA group into 3 subgroups of early, middle and late disease stage.


RESULTS
Early stage: all left amygdalar and hippocampal subregions (except the tail) were affected in svPPA (21-35% smaller than controls), together with the following amygdalar nuclei in the right hemisphere: lateral, accessory basal and superficial (15-23%). On the right, only the temporal pole was affected among the cortical regions. Middle stage: the left hippocampal tail became affected (28%), together with the other amygdalar nuclei (22-26%), and CA4 (15%) on the right, with orbitofrontal cortex and subcortical structures involvement on the left, and more posterior temporal lobe on the right. Late stage: the remaining right hippocampal regions (except the tail) (19-24%) became affected, with more posterior left cortical and right extra-temporal anterior cortical involvement.


CONCLUSIONS
With advanced subregions segmentation, it is possible to detect early involvement of the right medial temporal lobe in svPPA that is not detectable by measuring the amygdala or hippocampus as a whole.
['Bocchetta|Martina|M|0000-0003-1814-5024', 'Iglesias|Juan Eugenio|JE|', 'Russell|Lucy L|LL|', 'Greaves|Caroline V|CV|', 'Marshall|Charles R|CR|', 'Scelsi|Marzia A|MA|', 'Cash|David M|DM|', 'Ourselin|Sebastien|S|', 'Warren|Jason D|JD|', 'Rohrer|Jonathan D|JD|']
D000368:Aged D018888:Aphasia, Primary Progressive D018450:Disease Progression D005260:Female D007839:Functional Laterality D006801:Humans D007091:Image Processing, Computer-Assisted D008279:Magnetic Resonance Imaging D008297:Male D008875:Middle Aged D013702:Temporal Lobe
Medial temporal subregions Semantic variant PPA Magnetic resonance imaging