대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Normal thoracic duct

Radiologic Findings

Noncontrast (Fig 1) and contrast-enhanced (Fig 2) axial CT scans though the lung apices show a well-defined, elongated non-enhancing soft-tissue density structure. The lateral margin of the structure (Fig 2, arrow) is seen nearby the posterolateral aspect of the venous angle (the junction of the subclavian and the internal jugular veins). Medially, the structure is seen between the left common carotid and left subclavian arteries. At more caudal levels, the structure is seen in cross section on axial CT, appearing as a hypoattenuating dot adjacent to the esophagus (Fig 3-8, arrow). While the structure is located left anterolateral to the esophagus just above the aortic arch (Fig 3-4), it is located left lateral or left posterolateral to it at the levels of the aortic arch (Fig 5-7). At the level of the left atrium, the structure is seen posterior to the esophagus (Fig 8). The course and appearance of this structure are typical for a normal thoracic duct

Fig1

Fig2

Fig3

Fig5

Fig6

Fig7

Fig8

Brief Review

Anatomically, the cisterna chyli is located at the level of the first lumbar vertebra on the right, and the duct then ascends through the right abdomen and chest [1]. At the level of the fourth thoracic vertebra, the thoracic duct crosses to the left and continues superiorly. Above the clavicle, the thoracic duct forms an arch that rises 3-5 cm above the clavicle [2]. The duct then angles forward, running posterior to the left common carotid artery, and terminates in the posterolateral aspect of the left internal jugular vein-left subclavian vein junction).
Kiyonaga et al. have shown that thin-slice axial and MPR CT images can sufficiently depict the lower and middle sections of the thoracic duct and the cisterna chyli [3]. Liu et al. showed that the cervical thoracic duct frequently can be identified on CT. In their observation, the thoracic duct was seen as a simple tubular shape in 70 (43%) of the 161 cases. Flared configuration, whereby the distal duct flared out just before emptying into the venous confluence, was seen in 72 (45%) cases. Segmental fusiform configuration (segmental dilation of the distal duct), as seen in the present case, was noted in 19 (12%) cases [1]. 15 of those 161 ducts had IV contrast reflex into the terminal portion. Knowledge of the normal course and typical appearance of the thoracic duct is essential in differentiating it from pathologic conditions such as an enlarged Virchow's lymph node [1].
In our own experience, stack mode has been helpful identifying the thoracic duct in the axial CT: It can be seen as a low-density spot rotating half-circle around the esophagus (from 2 o'clock direction just above the aortic arch to 7 o'clock direction at the level of the first lumbar spine).
Hayashi et al. performed MR lymphography with a short echo spacing, 3D, half-Fourier, fast spin-echo sequence, successfully depicting the thoracic duct in six healthy volunteers [4].

References

1. Liu ME, Branstetter BF 4th, Whetstone J, Escott EJ. Normal CT appearance of the distal thoracic duct. AJR Am J Roentgenol. 2006;187(6):1615-1620
2. Langford RJ, Daudia AT, Malins TJ. A morphological study of the thoracic duct at the jugulo-subclavian junction. J Craniomaxillofac Surg 1999; 27:100-104
3. Kiyonaga , Mori H, Matsumoto S, Yamada Y, Sai M, Okada F. Thoracic duct and cisterna chyli: evaluation with multidetector row CT. Br J Radiol. 2012 ;85; 1052-1058
4. Hayashi S, Miyazaki M. Thoracic duct: visualization at nonenhanced MR lymphography--initial experience. Radiology. 1999 ;212(2):598-600.

Keywords

Mediastinum,