Figure 1

An 84-year-old man underwent percutaneous patent foramen ovale (PFO) closure for repeated attacks of ischemic strokes with unknown origin. The transesophageal echocardiogram performed prior to the intervention showed a small fibrous structure at the lower edge of the septum secundum (SS) of the typical thickness of the septum primum (SP) (Figure 1, arrow in the left lower corner). This structure was also visible radiographically (Figure 1, arrow).

Figure 2

The primitive sinuatrium is separated into right atrium (RA) and left atrium (LA) by the down-growth of the septum primum. Numerous perforations form in the anterosuperior portion of the septum primum before the septum secundum (SS) begins to develop to the right of the septum primum (Figure 2). The coalescence of these perforations creates the ostium secundum (OS) that should be covered by the septum secundum. The gap between the two septa (foramen ovale) is supposed to close physiologically and then fuse anatomically after birth by a change in pressures of left and right atria. Yet, it remains open as a PFO in a minority of people.

The swordfish septum secundum, named after its appearance, consists of a remnant portion of the septum primum protruding from the tip of the septum secundum (Figures 1 and 2, arrow). It represents an anatomical curiosity without clinical significance. It does not interfere with device closure of the PFO which was successfully accomplished with an Amplatzer PFO occluder (Figure 1, 25 mm/18 mm diameters of the right- and left-sided discs, respectively).