Claude Nguyen, MD

Although many patients with cryptogenic strokes have a patent foramen ovale (PFO), the high prevalence of PFO in the general population suggests that some of these may be incidental. Therefore, neuroimaging in patients with PFO may assist with understanding the etiology in this stroke subtype. Thaler et al. sought to look at radiographic characteristics of such patients with cryptogenic stroke and PFO, also comparing those with “high risk” PFO characteristics (large shunt, shunt at rest, or associated hypermobile septum).

Using a database from the Risk of Paradoxical Embolism (RoPE) Study, which was constructed from 12 component databases, Thaler et al. reviewed neuroimaging, with preference for MRI over CT when available, based on established definitions for the index stroke size, location, and whether multiple or prior strokes were seen. Generalized linear mixed models were used to attempt to control for heterogeneity between component databases, and to look at patients with “high risk” PFO characteristics.

In all, 2680 subjects were included. Thaler et al. found a significant association between PFO and large, superficially-located strokes; conversely, those without PFO were more likely to have smaller, deeper, more chronic infarcts. Those with a PFO were not found to be associated with previous strokes or multiple infarcts; this was thought to be age-related, as those with PFO tended to be younger. There was no association between “high risk” PFO features and imaging characteristics.

This is the largest study to look at the imaging characteristics of those with cryptogenic stroke, limited mainly by the imaging assessments of the component databases. This work strengthens some of the traditional associations between PFO-related strokes and neuroimaging; however, as the authors caution, it is not always easy to distinguish between embolic and local disease. Also, conventional stroke risk factors may in fact contribute to stroke risk in those cryptogenic strokes appearing as small and deep infarcts. Therefore, neuroimaging characteristics should augment, not replace, clinical judgment in the quest to better characterize cryptogenic strokes.