Study objectives: To determine normative values for superior vena cava (SVC) length and the utility of radiographic landmarks for identifying the boundaries of the SVC for assisting central line placement.
Design: Cross-sectional study.
Setting: Urban tertiary care medical centers.
Patients: Patients undergoing thoracic MRI scanning for various indications.
Measurements and results: The SVC dimensions and relationship to radiographic landmarks were determined from MRI scans of 42 patients (22 men, 20 women; median age, 57 years). The median length of the SVC was 6.8 cm (range, 4.4 to 10.0 cm) and did not correlate with gender or other measured cardiovascular dimensions. The right tracheobronchial angle was the best radiographic landmark for determining the cephalad origin of the SVC being always caudad and within a median of 1.5 cm (range, 0.1 to 3.8 cm) of the upper SVC. It was always at least 2.9 cm above the atriocaval junction. The right superior heart border was formed by the left atrium in 38% (95% confidence interval, 23 to 53%) of patients and did not reliably identify the atriocaval junction.
Conclusions: The right tracheobronchial angle is the most reliable landmark for the upper margin of the SVC. Venous catheters placed caudad to this landmark and cephalad to the right superior cardiac silhouette or no more than 2.9 cm caudad to the tracheobronchial angle result in catheter tips within the SVC.