Idiopathic chylothorax is a rare condition with unclear cause. It can develop as a result of ruptured of dilated thoracic duct, with or without proximal occlusion, or as a result of rupture of diaphragmatic or intercostal lymphatic collaterals, or as a result of pulmonary lymphangiomyomatosis . Patients who failed to thoracic duct ligation tended to be obscure and difficult cases, requiring accurate identification and location of the chylous leakage.
Lymphoscintigraphy is performed by injecting technitium-99 m labeled Sb2-S3 colloid or labeled human albumin into the interdigital space of the foot or hand. By employing semiquantitative transport index, a 92% sensitivity and nearly 100% specificity can be achieved in diagnosing lymphedema [13, 14]. Since lymphoscintigraphy is a functional study, we performed LAG with non-contrast CT to define lymphatic anatomy and the site of lymphatic leak.
Recently, the feasibility of MR lymphography has been established by performing multistation imaging of the lower extremities with three-dimensional spoiled gradient echo sequences after a cutaneous injection of gadodiamide. It has proved to be a safe, noninvasive, high-resolution technique for depicting lymphatic abnormalities without using ionizing radiation . Evaluation of abdominal and retroperitoneal lymphatic abnormalities, including lymphatic leaks, has also been described through MR lymphography through heavily T2-weighted fast spin-echo sequences . Despite these advances, conventional LAG remains the gold standard in the evaluation of chyle leaks due to its ability to opacify the lymphatic channels and highlight the presence of lymphatic fistulae or leakage .
Although bipedal LAG is recommended to demonstrate the anatomy of the thoracic duct and to indicate the cause of the chylothorax , the diagnostic capabilities of unilateral pedal LAG has also been demonstrated. Fistulas can often be identified by way of crossover channels that divert lymphatic flow from the contralateral lymphatics toward the fistula . Koga et al. reported lymphatic vessels crossing from the injected to the uninjected side occurred in all 106 patients with chyluria. The direction of flow in the lymphatic channels, being a closed circulation system with a positive pressure, will converge to the point where the integrity of the channels has been breached. So unilateral LAG can detect chyle leakage even when it is on the side opposite that where contrast is injected . The advantages of unilateral over bilateral LAG are that it is easy to identify crossover channels, and there is less discomfort for the patient because of fewer incisions and quicker procedure .
In our study, all 24 patients received monopedal LAG with their thoracic or abdominal lymphatic vessels being shown well. LAG detected thoracic duct leaks in 33.3%, extensive pleural leakage in 4.2%, intra- or retroperitoneal lymphatic leaks in 37.5% and no abnormality in 25% of patients as the origins. This result indicated that the majority of idiopathic chylothorax with thoracic duct ligation failure could be intra- or retroperitoneal leaks, which was different to previous reports .
The number of conventional LAGs has declined markedly since the introduction of cross-sectional imaging techniques. Nevertheless, LAG has a high potential as a reliable method to visualize and directly occlude lymphatic leaks. In nearly 79% of patients, the location of the leak could be detected, and surgical intervention could be planned when therapeutic LAG failed . Due to the irrigating effect of Lipiodol, the lymphatic leak could be completely occluded in 70% of patients when the lymphatic drainage volume was less than 500 mL/day. Even when lymphatic drainage was higher than 500 mL/day, therapeutic LAG was still successful in 35% of the patients. The overall success rate in patients with failed conservative treatment was 51% . The speculated mechanism of attenuation of chyle leakage was thought to be as follows. Firstly, Lipiodol infused during lymphangiography accumulated at the point of leakage outside the lymphatic vessel. Secondly, a regional inflammatory reaction occurred in the soft tissue adjacent to the area of Lipiodol retention. Thirdly, the point of leakage of the lymphatic vessel was obstructed. Finally, Lipiodol retention inside the lymphatic vessel on the distal side of the point of leakage played a role as a therapeutic embolic agent [5, 6].
In our series, LAG with non-contrast CT detected and located chyle leaks in 75% of patients. Its finding could provide important information in decision of treatment. In cases with underlying causes other than thoracic duct lesions by LAG with CT, non-operative management with thoracentesis had a better cure or improve rate than thoracic duct ligation (87.5% vs 25%, P = 0.02). We suggest that unilateral pedal LAG with non-contrast CT is valuable to determine underlying lymphatic vessel leak and localize the leakage site for surgical therapy. It could also indicate those patients suitable for non-operaitve treatment to avoid unnecessary surgical interventions.
Infection and pain are the most common complications seen with LAG, but serious complications have also been reported, including intra-alveolar hemorrhage, allergic reactions to Lipiodol or methylene blue, extravasation of contrast into the deep tissues of the foot, and oil emboli to the lungs, brain, kidney, and liver [3, 5, 8, 18–20]. Fortunately, there was no detectable complication in our series.
The limitation of this study is the limit number of patients with no randomized control comparison, predominantly due to the rarity of idiopathic chylothorax. A multicenter, randomized control study with large number of patients is necessary to investigate the exact value of unilateral pedal LAG with CT in the location and management of idiopathic chylothorax.