The slit infrahepatic IVC: pathologic entity or normal variant?

A common finding on abdominal ultrasound and CT examinations is variation in the size of the inferior vena cava (IVC). On occasion the infrahepatic IVC even assumes a slit-like appearance. Though commonly related to respiratory change and to the degrees of intra-abdominal pressure, some have claimed the slit-IVC may be an indicator of hypovolemia. To study this phenomenon, we evaluated prospectively the IVC in 26 normal volunteers. These individuals were studied supine by dynamic image ultrasound at end-inspiration, end-expiration, and during the Valsalva maneuver. The size of the IVC was maximal with the patient supine and at end-inspiration (A-P 1.8 cm). The subhepatic IVC decreased in size at end-expiration (A-P 1.2 cm) and frequently collapsed with the Valsalva maneuver (A-P 0.7 cm). Dramatic changes in the size of the IVC with changes in ventilation are normal variants. The use of the slit-IVC to diagnose hypovolemia should be done with caution.