Functional closure of the femoral canal revealed by computed tomographic scanning.

The lacuna vasorum contains, as well as the external iliac vessels, a space called the femoral canal which allows pulsation and other changes in the diameter of the two vessels. The canal is closed by a connective tissue septum which is too weak to prevent a herniation alongside the vessels. The functional closure of the canal was investigated by artificial augmentation of the intraluminal pressure of the vein in five specimens and by computed tomographic (CT) scanning during a Valsalva manoeuvre in ten normal persons. In the abdomen the intraluminal and extraluminal pressures are raised in parallel, with no consequence for the diameter of the vessels. In the area of the lacuna vasorum the intravenous pressure is conveyed down to the first competent valve which is located 0.5 cm distal to the inguinal ligament, while the extraluminal pressure is reduced to normal. At each rise of the intra-abdominal pressure the vein will therefore bulge and exactly fill the empty space of the femoral canal thus preventing herniations by an on-demand mechanism. By CT scanning it was found that the vein in the femoral canal increased its diameter 2.5-3.0 times during the Valsalva manoeuvre.