PFOs are very common, but not all PFOs are identical or carry the same risk. Individuals who have PFOs can be grouped according to many PFO characteristics such as large PFOs 0.6–1 cm, versus small PFOs less than 0.6 cm and associated anatomic structures.
The diagnosis of a stroke caused by the presence of a PFO is fraught with danger in the absence of defined thrombi in the veins of the lower limbs and the vena cava that return blood to the right atrium. The investigative techniques for detecting important PFO characteristics and assessing risk of embolic stroke are not clear and require intensive research. Kerut et al. appropriately stated ‘‘the challenge that remains is to determine which PFO and clinical contexts confer an increased risk of significant disease.’’
The diagnosis of PFO as a cause for cryptogenic stroke creates a dilemma for neurologists and patients. It is certain that errors in diagnosis are made based on the presumed association of PFO and stroke.
In addition some neurologists often advise aspirin for the prevention of stroke in patients with PFOs. This advice lacks logic because clots that embolize through a PFO must originate in the venous system and such clots are not prevented significantly by the use of aspirin. Anti¬coagulants such as warfarin are advisable and superior to aspirin in patients who have sustained a TIA or stroke proven to be caused by paradoxical emboli via a large PFO. Warfarin is also advised in patients with a large PFO with well-defined characteristics that is accompanied by proven thrombi in the venous system seen negotiating the foramen, a rare scenario (see Fig. 4).

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