Chylothorax represents an often missed diagnosis and difficult management problem. In this article, we review the cross-sectional anatomy of the thoracic duct, the predisposing causes for chylothorax, and we discuss the role of imaging in evaluation and management of chylothorax.

Chylous effusions develop as a result of disruption of the thoracic duct, thus presenting a difficult management problem. The diagnosis often is initially missed, as chylothorax is an uncommon entity. Delayed diagnosis and treatment of chylothorax may lead to profound nutritional, immunological, and cardiopulmonary compromise. Imaging of chylothorax may be problematic, and a combination of the lymphangiogram and CT scan are often needed to diagnose and locate a leak from the thoracic duct. Management remains controversial, with proponents of early surgical intervention contending with supporters of conservative therapy and nutritional support.

There has been little literature generated regarding chylothorax, particularly in the radiological journals. A brief review of the anatomy of the thoracic duct, as well as a review of the causes, diagnosis, and management of chylothorax, follows.

Materials and methods

Between 1993 and 1996, we performed a retrospective review of ten patients with chylothorax. The patients (6 male and 4 female) ranged in age from 8 to 81 years, with a mean of 44 years. Lymphangiograms were performed for seven of the ten patients. During the filling or vascular phase of the lymphangiogram, the flow of the contrast was followed under fluoroscopy, and permanent films were obtained. Delayed 24-hour frontal and lateral radiographs were filmed during the storage phase to further identify, localize, and quantify the potential lymphatic leak.

In three of the seven patients for whom lymphangiograms were performed, postprocedural CT scans of the body were obtained. Routine CT scans of the body were obtained in five of the ten patients, either without an associated lymphangiogram or prior to lymphangiography. Serial axial scans through the abdomen or chest and abdomen were obtained using helical scanning with contiguous 10-mm slices. Six of the ten patients had surgery for ligation of the thoracic duct. The remaining four patients responded to conservative measures.

Results

The lymphangiograms demonstrated chylous leaks in each of the seven patients. The actual site of the leak was shown in three of the seven lymphangiograms. No significant complications developed following the lymphangiograms.

CT scans of the patients who had not had recent surgery were helpful, yielding information concerning the underlying process integral to the development of the chylous effusion. A large retrosternal thyroid goiter extending into the retroaortic space caused obstruction of the thoracic duct in one patient. Another CT scan of the chest revealed thickening of the interlobular septa and bronchovascular bundles, consistent with diffuse pulmonary lymphangiomatosis. A third chest CT scan demonstrated diffuse small cysts scattered homogeneously throughout the lung parenchyma, consistent with lymphangioleiomyomatosis. A fourth chest CT scan revealed lymphadenopathy in a patient with lymphangiectasia. The case of idiopathic chylothorax showed an empyema on CT imaging.

Surgical causes for the chylothorax included esophagectomy, nephrectomy, and spinal fusion. Nonsurgical etiologies included thyroid goiter, diffuse pulmonary lymphangiomatosis, lymphangioleiomyomatosis, lymphangiectasia, and idiopathic. The chylothoraces were bilateral in three cases and unilateral (5 left and 2 right) in seven cases. There were associated chylous ascites in three patients and chylopericardium in one patient.

Ligation of the thoracic duct was performed in six of the ten patients. The remaining four patients had conservative therapy consisting of a thoracentesis for one patient and chest tube drainage for the other three patients. In all ten patients, the chosen therapy was successful in treating the chylothorax. One of the ten patients expired secondary to unrelated causes, specifically hemorrhage.

Case 1

A 61-year-old man developed a right chylous pleural effusion following a transhiatal esophagectomy for esophageal carcinoma. Conservative management, which included no oral intake, no jejunostomy tube feedings, and hyperalimentation, was not successful in less-

ening the chylous effusion. A lymphangiogram obtained 14 days following surgery showed a leak of the thoracic duct at a level immediately superior to the carina (figure 1A). Following a thoracotomy for ligation of the thoracic duct, the patient had an uneventful recovery. A follow-up CT scan through the lower chest and upper abdomen showed residual Ethiodol in the retroperitoneum and a dilated thoracic duct proximal to the ligation (figures 1B and 1C).

Case 2

A 52-year-old man with metastatic renal cell carcinoma of the lungs underwent a left radical nephrectomy and secondary lumbar (L2) hemicorpectomy with Ll-L3 anterior spinal fusion for resection of a tumor mass. A left pleural effusion developed eight days following surgery. Thoracentesis yielded 2400 cc of a transudate which was low in triglycerides (40 mg/dl) and devoid of chylomicrons. The patient improved symptomatically, and was subsequently discharged, though his stable chest radiographs showed a small left pleural effusion.

The patient was readmitted five days later for management of his increasing complaints of shortness of breath. A second thoracentesis revealed a left chylous effusion, and a chest tube was placed (figure 2A). Conservative therapy including no oral intake and total parenteral nutrition was initiated. The patient's abdominal girth was increasing, consistent with ascites. A lymphangiogram demonstrated two separate leaks within the abdomen, one in the right para-aortic bifurcation region and the second overlying the left pedicle of L4 (figure 2B). A CT scan three days later demonstrated residual Ethiodol in the retroperitoneum and pleural spaces (figure 2C). The patient developed chylous ascites which ascended transdiaphragmatically. He eventually recovered fully with conservative therapy.

Case 3

A 32-year-old woman underwent a bilateral lung transplant for lymphangioleiomyomatosis. Her preoperative chest radiograph showed bilateral chylous pleural effusions and diffuse interstitial lung disease compatible with lymphangioleiomyomatosis (figure 3A). Bilateral chylous effusions present at the time of the procedure reaccumulated following lung transplantation, along with chylous ascites.

A trial of total parenteral nutrition was unsuccessful. A lymphangiogram was unfruitful in demonstrating the site of the leak, as the dye extravasated into the pelvis. However, diffusely abnormal lymphatics compatible with the patient's underlying lymphangioleiomyomatosis were demonstrated.

Follow-up CT scans of the abdomen and pelvis showed residual Ethiodol in the pleural spaces and retroperitoneum, and ascitic fluid in the lower pelvis (figures 3B and 3C). Pleurodesis of the right pleural space and several treatments of periaortic radiation to fibrose the lymphatics diminished the chylous fluid slightly. A CT scan of the chest showed loculated pleural effusions with residual Ethiodol in the right pleural space (figure 3D). Denver shunts and surgical ligation of the thoracic duct were subsequently performed. This patient expired due to exsanguination from her tracheostomy site.

Case 4

A 32-year-old man presented with idiopathic bilateral chylothoraces. A PA chest radiograph showed bilateral chylothoraces (figure 4A). A left thoracotomy with attempted ligation of the thoracic duct was performed. Six years later, the patient redeveloped a right chylothorax. Subsequent thorascopy and placement of a chest tube was not successful. A right thoracotomy, complete pleurectomy, and rubbing of the diaphragm kept the patient asymptomatic for the next six months. A CT scan of the chest later revealed loculated pleural effusions with attenuation measurements equivalent to water (Hounsfield units of -0.9).

Two years later, a high-resolution CT of the chest was performed for evaluation of the patient's progressive symptoms. In addition to the bilateral chylothoraces and pericardial effusion, CT now showed thickening of the interlobular septa and bronchovascular bundles, compatible with diffuse pulmonary lymphangiomatosis (figure 4B). A lymphangiogram revealed normal pelvic and abdominal lymphatics to the level of the aortic hiatus.

Multifocal spillage into the pleural space and parenchymal tissue was noted in the chest near the confluence of the right internal jugular vein and superior vena cava (figure 4C). The patient then underwent an exploratory laparotomy for ligation of the thoracic duct/cisterna chyli, a pericardial window, and drainage of the left pleural space. Lymph node biopsy performed during the surgery revealed lymphogranulomata and dilated sinuses. Follow-up CT scan of the chest and abdomen showed residual small, loculated pleural, mediastinal, and pericardial fluid collections with persistent Ethiodol (figure 4D).

Discussion

Most commonly, the thoracic duct arises from the cisterna chyli, anterior to the first or second lumbar vertebral bodies. The duct courses cephalad through the aortic hiatus, and continues cephalad just to the right of midline between the aorta and azygous vein. It crosses the midline anterior to the fifth vertebral body, coursing posterior to the esophagus, and continuing cephalad just to the left of the esophagus. The duct then empties into the venous system near the junction of the left subclavian and internal jugular veins (figure 5).1

Thoracic duct anatomy is constant only in its variability. Two or more main ducts are present in up to 50% of patients,2 and each may consist of up to eight separate channels.3,4 In one study, multiple ducts were more common than single ducts, and at the level of the diaphragms, where therapeutic ligation is performed, one-third of thoracic ducts were doubled.5

Disruption of the thoracic duct results in chylothorax or chylous ascites. The thoracic duct crosses from right to left in the mid-dorsal region. Injury of the thoracic duct inferior to the T5-6 level usually produces a right chylothorax, whereas disruption superior to this level results in a left chylothorax.6-9 Bilateral chylothoraces occur in multilevel disease, as seen in diffuse lymphatic anomalies.

Causes of chylothorax are categorized as neoplastic, traumatic, idiopathic, or miscellaneous. Overall, the most common cause of chylous effusion is lymphoma, followed by surgical trauma, in particular coarctation repair and esophagectomy. The cryptogenic variety occurs in the neonatal period, comprising the most common cause of a pleural effusion in this age group. Miscellaneous causes comprise four broad categories: impaired venous drainage, scarring, developmental anomalies, and transdiaphragmatic passage of chylous ascites. Some diffuse lymphatic anomalies producing chylothorax include lymphangioma, diffuse pulmonary lymphangiomatosis, lymphangioleiomyomatosis, and lymphangiectasia.10

Lymphangiomas usually present as discrete, focal masses of abnormal lymphatic channels within the mediastinum or occasionally within the lung. Diffuse pulmonary lymphangiomatosis represents another pathologically distinct lymphatic anomaly, with an increased number of communicating lymphatic channels demonstrating smooth thickening of the bronchovascular bundles and interlobular septa. Associated CT findings include diffuse increased attenuation of the mediastinal fat, mild bilateral perihilar infiltration, and pleural effusions or pleural thickening.11 Lymphangioleiomyomatosis, another lymphatic anomaly, has characteristic CT findings of small parenchymal cysts dispersed uniformly throughout the lungs. Pathologically, there is hamartomatous proliferation of smooth muscle adjacent to pulmonary lymphatics, thought to represent a forme-fruste of tuberous sclerosis. The fourth anomaly, lymphangiectasia, represents dilatation of otherwise normal lymphatic vessels. The imaging of lymphangiectasia by CT has not been described, according to recent literature.

The diagnosis of chylothorax is determined through analysis of the pleural fluid. The hallmark of chylous fluid is a triglyceride level above 110 mg/dl. Another diagnostic feature of chyle is the presence of chylomicrons, which give it a milky appearance; however, during fasting, as in the perioperative state, chyle may appear clear. It is important to expediently identify an effusion as chylous, as continued loss of chyle may result in serious complications including nutritional imbalances, immunosuppression, and cardiorespiratory decompensation.1

Imaging of chylothorax by plain film or CT is often nondiagnostic, as the chylous nature of the fluid cannot be determined. Only a single report noted chyle to be lower in density by CT, apparently due to its fat content.12 However, CT may reveal a mediastinal mass or pulmonary abnormalities that may provide the underlying etiology for the chylothorax. Lymphangiography maintains a useful role in the evaluation of chylothorax, providing information regarding the presence, location, or source of a leak. Lymphangiography also is valuable in delineating the anatomy of the thoracic duct, which may vary considerably, particularly at the level of the diaphragm. Others advocate nuclear lymphangiograms, using technetium-99m antimony colloid as the agent, as a useful diagnostic examination for the identification of the leak.13

Chylothorax is often managed conservatively with cessation of oral intake, chest tube drainage, and total parenteral nutrition administration, sometimes with medium-chain triglycerides to reduce chyle flow. Surgical ligation of the thoracic duct is usually recommended when: (1) drainage exceeds 1500 ml/day for adults or 100 mL/yr-age/day for children greater than 5 years of age, (2) drainage exceeds 14 days, or (3) metabolic complications develop.14 The traditional operative approach is to ligate the thoracic duct at a point approximately 5 cm above the diaphragm through a thoracotomy. Rich collaterals and anastomoses along the course of the thoracic duct allow for safe ligation without sequelae, preventing the development of diffuse lower extremity edema. Alternative therapies include pleurodesis, pleuroperitoneal shunts, mediastinal radiation, intrapleural fibrin glue, and pleurectomy.

A limited number of patients have undergone alternative therapies. Pleuroperitoneal shunts enable lymph to be shunted to the greater absorptive surface area of the peritoneal cavity. The aim of this method of treatment is to decompress rather than to seal the fistulous leak. Pleuroperitoneal shunts provided excellent results in two of the larger series, for 12 of the 16 (75%) and 10 of 12 (90%) pediatric patients, respectively.15,16 Another case report of two patients revealed good results, with shortened hospital stays of several weeks following pleuroperitoneal shunting for chylothorax related to Fontan procedures.17 A single congenital chylothorax and a single chylothorax secondary to filariasis were both successfully treated with pleuroperitoneal shunts.18,19 Three patients were successfully managed as outpatients using external pleuroperitoneal shunts.20

Another larger study revealed success in 12 patients: eight with talc pleurodesis, two with shunting, one with talc pleurodesis and gluing the thoracic duct closed, and one with gluing the thoracic duct closed alone.21 In one study, intrapleural fibrin glue was used successfully in the treatment of chylothorax after pulmonary resection for lung cancer.22,23 Additionally, a premature neonate with massive chylothorax following patent ductus arteriosus repair was successfully managed with fibrin glue.24 There is also a single reported case of chylothorax related to lymphangiomatosis of the bone that was subsequently controlled with parietal pleurectomy and an application of fibrin glue.25

Three reported cases of persistent chylothorax, related to lymphoma,

lymphosarcoma, and thoracic aortic aneurysm, were successfully treated by talc pleurodesis.26,27 Additionally, a single case report of a patient with pulmonary lymphangioleiomyomatosis demonstrated successful treatment of recurring chylothorax using tamoxifen and tetracycline pleurodesis.28 A review of four patients with generalized lymphangiomatosis and chylothorax showed that one of the four responded to surgery (pleurectomy) and tetracycline pleurodesis. The surgeries included a surgical pleurodesis, two pleurectomies, and a decortication.29 Another patient with chylothorax following radical nephrectomy responded to tetracycline sclerosis of the retroperitoneum, with resolution of the chylothorax.30

Chemical pleurodesis with the streptococcal preparation OK-432 is another method that has been shown to be successful in managing postoperative chylothorax.31,32 A single report cited bilateral pleurectomy in addition to thoracic duct ligation as treatment for bilateral chylothoraces associated with intestinal lymphangiectasia.33 Another article describes successful treatment of chylothorax related to lymphosarcoma with radiation to the main masses in the abdomen and lower mediastinum, respectively.34 One patient with metastatic ovarian carcinoma to the mediastinum and secondary chylothorax was initially responsive to radiotherapy, but later died.12

In evaluating chylothorax, lymphangiograms maintain a role in determining the anatomy of the thoracic duct, revealing a leak of the thoracic duct, and possibly locating the source of that leak. In patients with chylothoraces refractory to conservative measures, a lymphangiogram should be performed. CT imaging may be reserved for patients with diffuse lymphatic anomalies detected on lymphangiogram, or for staging purposes of those with suspected lymphoma. AR

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Dr. Knisely and Dr. Kuhlman are with the Department of Radiology at the University of Wisconsin Hospital and Clinics in Madison, WI.