title: Value of frontal caval measurement in the placement of inferior vena cava filters.
abstract: OBJECTIVE
  Inferior vena cavae (IVC) can be of unusual geometry, often having odd shapes and being oriented (in long axes) away from the horizontal plane. However, after insertion of a filter, most IVC adopt a circular cross-section. The objective of this study was to determine if the IVC diameter estimated by frontal measurement (cavogram equivalent) reflects the true circular diameter of the infrarenal vena cava. Diameter estimation is clinically important in the correct selection of a filter, because mega cavae (diameter 28 mm or greater) require a particular filter.
  
  
  METHODS
  The infrarenal IVC was measured on computed tomographic (CT) scans in 136 patients. The frontal diameter was recorded as that which would be obtained by a cavogram. Corrected circular diameter was obtained by mapping the circumference of each cross-section on CT to a straight line and calculating diameter from circumference.
  
  
  RESULTS
  The average frontal caval diameter was 20.5 (standard deviation 3.7) mm, whereas the average corrected circular diameter was 23.0 (standard deviation 3.4) mm. By frontal measurements, 6 IVC diameters were 28.0 mm or greater. Similarly, by corrected circular diameter, 6 IVC diameters were 28.0 mm or greater. However, of the 6 mega cavae extrapolated to cavograms, only 3 corresponded to mega cavae when corrected for true circular diameter. Yet, of the 6 mega cavae identified by corrected circular diameter measurement, 3 were not identified by frontal diameter assessment. Of the 6 patients with true mega cavae, 2 were being evaluated for right lower quadrant pain, 2 for lymphoma, 1 for a pelvic mass, and 1 for staging of a head and neck cancer.
  
  
  CONCLUSIONS
  Cavograms can over- or underestimate the true diameter of an IVC, and may thus lead to incorrect filter choice. It is recommended that a sonogram or CT scan be obtained to visualize the IVC in cases of suspected mega cava, and that true circular diameters be used for selection and placement of IVC filters.
authors.affiliation: Department of Diagnostic Imaging, Foothills Hospital, Calgary, Alta. deepak.kaura@crha-health.ab.ca
authors.forename: D R
authors.initials: DR
authors.lastname: Kaura
authors.forename: R R
authors.initials: RR
authors.lastname: Gray
authors.forename: D J
authors.initials: DJ
authors.lastname: Sadler
authors.forename: C B
authors.initials: CB
authors.lastname: So
authors.forename: J C
authors.initials: JC
authors.lastname: Saliken
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D016306:Vena Cava Filters; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging*