Normal CT appearance of the distal thoracic duct

OBJECTIVE. The aims of this study were to determine how often the distal thoracic duct can be identified on neck CT and to characterize the CT appearance of the duct. MATERIALS AND METHODS. In a review of electronic medical records from January 2001 to January 2003 we identified the cases of 500 patients who had undergone CT of the neck. Because they had confounding factors such as cancer or cervical lymphadenopathy, 199 of these patients were excluded, leaving 301 patients in the study: 131 (44%) male patients and 170 (56%) female patients. The age range was 11-92 years (average age, 46 years). Two head and neck radiologists used strict diagnostic criteria and consensus to identify the distal thoracic duct on both sides of the neck. One half of the images selected at random were flipped left to right. The purpose of randomization was to avoid interpretation bias, because the thoracic duct is known to typically course within the left side of the neck. The configuration of the distal duct was tabulated, and effects of age and sex were statistically evaluated. RESULTS. The left side of the neck was unevaluable in 26 (9%) of 301 patients because of streak artifact. In the other 275 patients, the distal thoracic duct was identified in the left side of the necks of 150 (55%) of the patients. Eleven of these patients (4%) also had a visible duct in the right side of the neck, but a right-sided duct was never identified without a left-sided counterpart. The distal thoracic duct had a tubular configuration in 70 (43%), a flared configuration in 72 (45%), and a long segmental fusiform dilation in 19 (12%) of 161 patients. Patient sex had no significant effect on the appearance of the distal thoracic duct. Older patient age had a slight positive effect on the size of the duct. CONCLUSION. Familiarity with the normal CT appearance of the distal thoracic duct can be helpful in differentiating a normal duct from pathologic lesions of the lower neck, such as lymphadenopathy.