Lymphatics and Lymph Nodes

Etiology

Chyle is a fluid made up of lymph and chylomicrons absorbed by the intestinal lacteals; as a result of digestion, the fluid is high in triglycerides. Chylothorax refers to the accumulation of chyle in the pleural space. Normally, chyle is returned to the systemic circulation by the thoracic duct, which is the continuation of the cisterna chyli. The cisterna chyli receives lymph from the abdominal organs and the pelvic limbs and lies in the dorsal retroperitoneal space adjacent to the aorta and left kidney. The thoracic duct variably consists of many branches lying dorsal to the thoracic aorta and ventral to the azygous vein on the right side of the thorax in the dog. The duct crosses to the left side in the mediastinum at the level of the fifth or sixth thoracic vertebra. The lymphaticovenous junction is associated with the left external jugular vein, its junction with the cranial vena cava, or the jugulosubclavian angle.¹ Chylothorax occurs when the flow of chyle is increased (e.g. increased hepatic production of lymph) or when entrance of chyle into the venous system is impeded (e.g. increased venous pressures or obstruction of the lymphaticovenous junction). Any process that increases the cranial vena caval hydrostatic pressure or causes complete or relative obstruction of the lymphaticovenous junction predisposes an animal to chylothorax.²

Increased systemic hydrostatic pressure may be secondary to cardiac disease or abnormalities of the cranial vena cava. Many disease processes associated with either right heart failure or conditions associated with compression or obstruction of the vena cava, lymphaticovenous junction, or thoracic duct have been reported to cause chylothorax (Table 43-1). Cardiac diseases associated with increased venous pressure cause an increase in lymph production secondary to hepatic congestion and thereby increase the flow of lymph in the thoracic duct.^3,4 Concurrent, increased venous pressure diminishes flow through the lymphaticovenous junction (relative obstruction). Both processes cause the accumulation of chyle within the pleural space. Direct or indirect trauma to the thoracic duct has been associated with the development of small amounts of chylous effusion within the pleural space.⁵ The thoracic duct heals rapidly with linear or transverse trauma or iatrogenic trauma, and the pleural effusion should be short-lived (1 to 2 weeks) with no specific therapy required for resolution.⁶

Although many disease conditions have been associated with chylous effusion, the most common cause of chylothorax is idiopathic. Abnormal lymphatic flow or pressure within the thoracic duct is thought to lead to thoracic lymphangiectasia. Lymph leaks from the dilated, tortuous branches of the thoracic duct, which are most evident in the cranial thorax.⁷ The pulmonary lymphatics may also play a role in cases of idiopathic chylothorax that fail to respond to therapy.⁸ All potential underlying disease processes (Table 43-1) must be ruled out prior to diagnosing the disease as idiopathic, as failure to diagnose an underlying condition will deny the patient definitive therapy.
 

Diagnosis

History and Physical Examination

Any breed of dog or cat of any age may develop chylothorax. The Afghan hound, Shiba Inu, Siamese, and Himalayan breeds may have an increased prevalence of the disease. Afghan hounds tended to develop the disease in middle age; young Shiba Inus, and older cats were more often affected. Both males and females developed the condition equally.⁴

The presence of pleural effusion usually results in ventilatory compromise. The volume and rapidity of fluid accumulation determine the signs present. Chylothorax may result in no significant signs until the patient becomes dyspneic. Coughing may be the first and only sign associated with chylothorax, and occasionally chylothorax is an incidental finding. The etiology of cough with chylothorax may be related to the primary problem (e.g. heart failure, neoplasia) or may be due to inflammation caused by the presence of chyle within the pleural space. The history of chronic chylothorax often includes depression, exercise intolerance, inappetance, and weight loss. If an underlying disease exists, the history may be representative of that condition.

Tachypnea or dyspnea with rapid, shallow ventilation, or a restrictive ventilatory pattern, and decreased pulmonary and cardiac sounds on auscultation are usually present in cases of pleural effusion. Cats may demonstrate a “breath holding” type of breathing pattern in which forceful inspiration is followed by delayed exhalation.⁹ Lung sounds may be present with increased bronchovesicular sounds dorsally. Chylothorax is rarely unilateral. Other findings include thin body condition, pallor, arrhythmias, cardiac murmurs, or other signs associated with a primary disease. Animals with cranial mediastinal mass lesions or thrombosis may exhibit cranial vena cava syndrome (i.e. edema of the head, neck, and forelimbs with jugular venous distention).

Diagnostic Imaging

Radiographic evaluation of the dyspneic patient is not advised in a significantly compromised patient. Oxygen supplementation, minimal handling, and dorsoventral and horizontal beam imaging rather than lateral and ventrodorsal views may decrease the stress of imaging. The index of suspicion for fluid in the pleural space must be considered prior to imaging, as therapeutic thoracocentesis can decrease the risk associated with imaging in these patients. Radiographic signs of pleural fluid include effacement of the cardiac and diaphragmatic silhouettes, retraction of the lung borders from the thoracic wall, “scalloping” of the lung edges, pleural fissure lines, rounding of the lungs, widening of the mediastinum, and obscuring of the other intrathoracic structures.¹⁰ The presence of a large amount of fluid decreases ability to diagnose cardiac, pulmonary, or mediastinal masses and hilar lymphadenopathy. Radiographs should be remade after removal of the thoracic effusion to increase the diagnostic efficacy of thoracic radiographs.

Failure of pulmonary expansion after therapeutic thoracocentesis should alert the clinician to the possibility of fibrosing pleuritis or pulmonary parenchymal disease such as persistent atelectasis, pulmonary neoplasia, or lung lobe torsion. Animals with fibrosing pleuritis often remain dyspneic, despite removal of pleural effusion and confirmation of minimal fluid on thoracic radiographs. Fibrosis of the visceral pleura is thought to be related to the chronic presence of chylous effusion and an alteration in mesothelial cell function, leading to an imbalance in fibrin production and degradation.

Air in the lungs will reflect sound and decrease the generation of ultrasonographic images of intrathoracic structures. Therefore, ultrasound examination of the thorax should be performed prior to removal of all pleural fluid, as the fluid will provide an acoustic window for imaging the mediastinum. Ultrasonography is also used to evaluate cardiac structure and function and to diagnose whether pericardial effusion is present.

Computed tomography (CT) and magnetic resonance imaging (MRI) have been used with success for thoracic evaluation in dogs. Normal anatomic structure has been reported, and CT has been used to evaluate questionable pulmonary and non-pulmonary conditions identified radiographically. Questionable radiographic and ultrasonographic findings should be evaluated with CT to localize and determine the extent of the abnormality. CT has also been used to guide fine needle aspirates (FNA) and percutaneous biopsies of pulmonary and nonpulmonary mass lesions. The complication rate associated with FNA or transcutaneuos biopsy with CT guidance was 43% in one study, and the diagnostic accuracy was 65% for FNA and 83% for biopsy. The main disadvantage of CT and MRI is the need for and risk of general anesthesia in compromised patients. CT and MRI are becoming more available to practitioners, but the cost benefit ratio must be considered prior to their use.

Laboratory Findings

Thoracocentesis with fluid analysis is imperative in every case of pleural effusion. Fluid should be placed in an ethylenediaminetetraacetic acid (EDTA) tube for cell counts and cytological examination. Fluid should also be saved in a serum tube (i.e. “clot tube”) for biochemical analysis and aerobic and anaerobic culture. Chylous effusion is grossly opaque white or white with a red or pink tinge (Table 43-2).^11,12 The fluid is high in lipid, which may interfere with refractometric quantification of protein. The total nucleated cell count is usually less than 10,000/ μL, consisting mainly of small lymphocytes.⁴ Lower numbers of macrophages may be present and filled with lipid. With chronicity, lymphocytes may be depleted due to decreased production in the face of continued cell loss to the effusion, nondegenerate neutrophils then become the primary cell type in the effusion. Neutrophils may also be the primary cell type in patients that have undergone multiple thoracocentesis, which may induce pleural inflammation. If the repeated aspirates of pleural fluid result in secondary bacterial colonization and sepsis, degenerate neutrophils appear in the fluid.
 

The definitive diagnosis of chylous effusion relies on biochemical testing of the pleural fluid and serum. With chylothorax, triglyceride content of the pleural fluid is higher than that of the serum and cholesterol levels in the pleural fluid is less than that in the serum. Other tests, (e.g. ether clearance and Sudan staining for fat) may also be used to diagnose chylous effusion. Concurrent aerobic and anaerobic culture of the fluid are recommended. Psuedochylous effusion, opaque, white fluid devoid of chyle, has been associated with tuberculosis and rheumatoid pleurisy in man but has not been identified in dogs or cats.

Complete blood count, biochemical profile analysis, and urinalysis should be done and may aid in the identification of a primary cause of chylothorax. They may also be useful in monitoring for lymphopenia, hyponatremia, and hyperkalemia, which have been associated with repeated thoracocentesis in the medical management of the condition.¹³ Significant protein and fluid loss due to chronic chylous effusion may also be reflected in the patient’s biochemical profile and urinalysis. Feline leukemia virus (FeLV), Feline immunodeficiency virus (FIV), and heartworm tests are also recommended to rule out primary disease processes.

Differential Diagnoses

Other causes of cough should be included in the initial differential list if cough is present; however, pleural effusion should be identified early in the evaluation of the patient with chylothorax. Other types of pleural effusion (e.g. hemorrhage, transudate, exudate) are ruled out upon fluid analysis. Chylous effusion may be classified as either a modified transudate or exudate, depending on the reference used to characterize pleural fluid types (See Table 43-2). Primary disease processes that cause chylothorax (See Table 43-1) should be ruled out by diagnostic evaluation including thoracic radiography and ultrasound examination, echocardiography, CBC, biochemical analysis, urinalysis, FeLV, FIV, and heartworm testing, and abdominal radiography and ultrasound. If primary disease conditions are eliminated, the diagnosis of idiopathic chylothorax, which is the most common form of chylothorax, is made.

Medical Management

Any primary condition associated with secondary chylothorax should be treated or the effusion may persist. Treatment of the underlying condition may not, however, guarantee diminution of chyle. Resolution may also take time (e.g. months), depending on the primary condition. While treating the primary condition, the accumulation of chyle within the pleural space may be managed with intermittent thoracocentesis as dictated by clinical signs (e.g. dyspnea associated with a restrictive breathing pattern). Fluid balance and electrolytes should be monitored for significant alterations secondary to repeated thoracocentesis (described in laboratory findings) and is of more concern in patients requiring frequent fluid removal.¹³ Fat soluble vitamins should be added to the diet of patients undergoing prolonged medical management of chylothorax due to the continued loss into the pleural space.³ Recurrent thoracocentesis may also result in secondary bacterial infection of the fluid, despite the high lecithin content, which is thought to have a bacteriostatic effect.⁹ Immunodeficiency has also been hypothesized with the removal of protein and cells by repeated thoracocentesis.

Concurrent dietary changes may alter the fat content of the effusion and improve fluid absorption from the pleural space, thereby decreasing the frequency of thoracocentesis. Low fat diets are therefore recommended in the treatment of idiopathic chylothorax. The fat content of commercially available low fat diets is approximately 6%.⁴ Medium chain triglyceride supplementation may not result in improved nutritional status; they may not be directly absorbed into the intestinal venous system as previously hypothesized. Dietary management and fluid removal rarely result in resolution of cases of spontaneous, idiopathic chylothorax.

The addition of different medications has been attempted in an effort to increase the rate of resolution of idiopathic chylothorax. Benzopyrones are compounds extracted from the Brazilian Fava D’anto tree.¹⁴ They have been used to treat lymphedema in people and have been used to treat idiopathic chylothorax in dogs and cats. Their action may decrease vascular leakage, increase protein lysis and absorption, stimulate macrophage function, and increase tissue macrophage numbers. Rutin, a benzopyrone agent (Rutin, Nature’s Plus, Melville, NY), resulted in improvement in two of four cats treated, and has been reportedly associated with resolution of the disease in two other case reports.^14-16 The empiric dose of rutin ranges from 50 to 100 mg/kg PO q 8 h.¹⁴ A large clinical trial of its use in dogs and cats with idiopathic chylothorax has not yet been reported, but it is commonly used as part of the medical treatment of chylothorax.

Octreotide (Sandostatin^®, Novartis Pharma B.V., Arnhem, the Netherlands) is an experimental agent for the treatment of idiopathic chylothorax. The somatostatin analog has been used to treat chylothorax in people and was associated with a more rapid decline in the amount of pleural chyle following experimental transection of the thoracic duct in dogs.¹⁷ The response to octreotide may be due to inhibition of pancreatic, biliary, and gastric secretions, decreased gastric blood flow, decreased intestinal transit time, and constriction of lymphatic vessels.^17,18 A small therapeutic trial of 10 mg/kg SC q 8 h therapy for 10 to 28 days resulted in resolution of signs in two of three cats. Neither of two dogs treated with octreotide showed a response to therapy.¹⁸ Side effects occurred in two patients and consisted of diarrhea and loose stools.¹⁸ The response of dogs and cats to octreotide has not been investigated investigated in a clinical trial.

Corticosteroid treatment to combat fibrosing pleuritis and furosemide administration to decrease chylous effusion have not been evaluated. Furosemide has not been shown to alter the accumulation of chyle in the pleural space. Its use could result in further fluid loss and dehydration, so it is not recommended for treating chylothorax. Likewise, corticosteroids have not been shown to have any beneficial effect in the treatment of chylothorax, and their use should be reserved for underlying conditions requiring corticosteroid therapy.

It is, however, important to monitor any patient undergoing prolonged medical management for the occurrence of fibrosing pleuritis. Chronic exposure of mesothelial cells to chyle may result in altered fibrin production and degradation.⁹ An imbalance of fibrin may result, leading to the deposition of fibrin on the visceral pleura. Fibrosis of the visceral pleura can result in severe lung lobe atelectasis. Radiographic evidence of failure of complete pulmonary expansion following thoracocentesis or dyspnea in the face of minimal pleural effusion should alert the clinician to this problem, which may decrease the prognosis associated with further therapy. Due to the risk of nutritional and fluid imbalance and fibrosing pleuritis, prolonged medical management (beyond 4 to 8 weeks) is not recommended.³

Surgical Management

Many surgical techniques have been developed in an attempt to improve the resolution rate of idiopathic chylothorax in dogs and cats, which indicates that the definitive therapy has not been established. Surgical treatment is usually sought in animals with chronic chylothorax despite proper medical management and in cases in which medical therapy becomes impractical. Surgical techniques include mesenteric lymphangiography in conjunction with thoracic duct ligation and pericardectomy, passive or active pleuroperitoneal or pleurovenous shunting, omentalization, and ablation of the cisterna chyli.^19-22 Resolution rates associated with thoracic duct ligation alone range from 53% to 20 to 53% in dogs and cats, respectively.^11,12,23 Concurrent or subsequent pericardectomy may dramatically improve the success rate of thoracic duct ligation to 90%.² Both thoracic duct ligation and pericardectomy may be performed with video-assisted thoracoscopic surgery (i.e. thoracoscopy).

Chylothorax resolution rates with omentalization and ablation of the cisterna chyli have not been reported in large numbers of dogs, but these procedures may offer future alternatives for therapy. Redistribution of the effusion into the abdominal cavity or directly into the venous system may be required in cases of persistent chylous or non-chylous effusion after surgery has been attempted and has failed.

Surgical Techniques

Mesenteric Lymphangiography

Mesenteric lymphangiography is recommended prior to ligation of the thoracic duct to provide the surgeon with the number and location of thoracic duct branches. Lymphangiography is repeated after thoracic duct ligation to ensure that all branches have been ligated. If patent branches remain, ligation and lymphangiography should be repeated. An abdominal approach is required, and lymphatic catheterization may be difficult, especially in cats and small dogs. The main disadvantage of lymphangiography is prolongation of surgery time. The other disadvantage is that small thoracic duct branches may remain patent but not fill with contrast material during lymphangiography. The small remaining branches could be a cause for the high failure rate associated with thoracic duct ligation.

Cream (1 to 2 mL/kg) may be fed once an hour for 3 to 4 hours prior to surgery to opacify the lymphatics, making them easier to identify. A right paracostal approach to the abdomen is made in dogs; a ventral midline approach may be made in cats in conjunction with a transdiaphragmatic approach to the thoracic duct.⁷ The ileocecocolic region is exteriorized, and the lymphatics evaluated (Figure 43-1). If necessary, a small volume (0.25 to 0.5 mL) of dilute methylene blue dye may be injected into a lymph node to aid in the visualization of efferent lymphatics. Repeated injection of the dye is not recommended, as Heinz body anemia or renal failure may occur.

A 22 to 20-gauge over-the-needle catheter is placed in a lymphatic, secured to the mesentery with suture, and connected to extension tubing preloaded with heparinized saline. The catheter and extension tubing is then sutured to the adjacent segment of intestine to decrease the risk of catheter dislodgement. A three-way stopcock is placed on the end of the extension tubing for contrast injection. Water soluble contrast (1 mL/kg) is diluted 1:1 or 1:0.5 with sterile saline to decrease the viscosity of the solution and ease injection.^2,7,9 Lateral and ventrodorsal radiographs are recommended after injection. Ventrodorsal radiographs should allow visualization of a larger number of thoracic duct branches than lateral views. Alternatively, computed tomography may be done, which allows visualization of the thoracic duct and its branches without superimposition of adjacent structures or further manipulation of the patient.²⁴ Unfortunately, CT is not available within the surgical suite, making re-evaluation after thoracic duct ligation more difficult. The risk of catheter dislodgement is increased if the patient must be moved to an imaging suite for lymphangiography.

The indwelling lymphatic catheter may also be used for embolization of the thoracic duct with cyanoacrylate.²⁵ The advantage of embolization is the lack of a thoracic approach and the use of a simple approach to the abdomen. The disadvantages of embolization include thrombosis of the cranial vena cava and embolization of pulmonary artery branches.²⁵ Positive pressure ventilation may stop migration of cyanoacrylate during its polymerization phase and decrease the risk of embolization of structures other than the thoracic duct.²⁵ The efficacy of embolization can be evaluated with lymphangiography and repeated if necessary. Thoracic duct embolization, however, has not been studied in a large number of clinical cases.

Standard lymphangiography requires laparotomy and prolongs operative time. A simpler method of injection of the mesenteric lymph nodes with 0.22 mL/kg of aqueous contrast did result in a readable lymphangiogram in four of five dogs if images were made within one to two minutes.²⁶ The difference between a pressurized lymphatic injection by a catheter and mesenteric lymph node injection is not known.
 

Thoracic Duct Ligation

Ligation of the thoracic duct causes new lymphaticovenous anastomoses to form, resolving the effusion and its associated clinical signs.^{2-4,7,11-12,23} The thoracic duct should be ligated in the caudal thorax where the fewest number of branches are located. An intercostal thoracotomy is performed on the right side in dogs and on the left side in cats, located at the eighth, ninth, or tenth intercostal space (Figure 43-2). The duct and its branches are located dorsal to the descending aorta and ventral to the azygous vein and sympathetic trunk. The surgeon ligates all branches of the thoracic duct with silk (2-0 or 3-0) or hemostatic clips. As with mesentericlymphangiography,thethoracicductmaybecolored by injecting methylene blue dye into the lymphatic catheter or directly into a mesenteric lymph node. Mesenteric lymph node injection reliably colored the canine thoracic duct within ten minutes and lasted up to one hour in one experimental study.²⁷

An alternative approach to thoracic duct ligation is to ligate all structures dorsal to the aorta and ventral to the sympathetic trunk, including the azygous vein.²⁸ Thoracoscopic ligation of the thoracic duct has also been developed in dogs.²⁹ Portals are placed in the middle of the chest at the ninth intercostal space and at the junction of the dorsal and middle thirds of the chest at the eighth and tenth intercostal spaces.²⁹ Hemostatic clips are applied to the thoracic duct ventral to the cranial lumbar or caudal thoracic vertebrae, prior to the emergence of the azygous vein into the thorax.²⁹ With any method of ligation, the area dorsal to the aorta should be completely evaluated for branches of the thoracic duct, some of which may lie further lateral than previously described.
 

Pericardectomy

Conditions that result in increased hydrostatic pressure may contribute to the accumulation of chyle in the thorax by two mechanisms. Increased hydrostatic pressure may increase the production of lymph in the viscera and caudal body, which will increase the flow of chyle in the thoracic duct.² Concurrently, the increased hydrostatic pressure in the cranial vena cava will impede drainage of lymph from the thoracic duct into the venous system. Pericardectomy may decrease venous hydrostatic pressure, decreasing both causes of fluid accumulation.² Pericardectomy was described in 20 patients (10 dogs and 10 cats) with idiopathic chylothorax.² It was a primary treatment (n=2) or was done in conjunction with thoracic duct ligation in cases with persistent chylous or nonchylous effusion following thoracic duct ligation.²

Pericardectomy with thoracic duct ligation resulted in a 90% rate of resolution of effusion in the clinical cases reported.² All dogs and eight of ten cats were successfully treated with the combination of the two procedures, which is rapidly becoming the mainstay of therapy for idiopathic chylothorax.² Pericardectomy was done by retracting the pericardium into the intercostal thoracotomy used for thoracic duct ligation or by an additional intercostal thoracotomy.² Pericardectomy is described in Chapter 42.

Ablation of the Cysterna Chyli

Ablation of the cisterna chyli was developed in an attempt to force lymphaticovenous anastomosis formation within the peritoneal cavity, rather than in the thoracic cavity.^22,30 Ablation of the cisterna chyli was theorized to relieve the increase in lymphatic hydrostatic pressure caudal to the site of thoracic duct ligation, which is a proposed mechanism for collateral lymphatic formation and persistence of pleural effusion following thoracic duct ligation. Thoracic duct ligation alone allows new lymphaticovenous anastomoses to form with the azygous vein, but in dogs that underwent ablation of the cisterna chyli with thoracic duct ligation, the anastomoses formed with the caudal vena cava or phrenicoabdominal vein, mesenteric root, or azygous vein.³⁰

Thoracic duct ligation is performed as described above. The cisterna chyli is approached through the abdominal ventral midline.^22,30 The peritoneum adjacent to the left kidney is incised, and perirenal fat dissected until the cisterna is identified ventral to the aorta. Sharp excision of all cisternal membranes is recommended. Seven of eight clinical cases responded to the combination of thoracic duct ligation and ablation of the cisterna chyli.²² Pancreatitis complicated one case but no other significant complications were noted.²²

Omentalization of the Thorax

The omentum is an organ that has been used in the treatment of chronic wounds, abscesses, cystic structures. Omentum provides a rich network of blood and lymphatic vessels for healing and presumably a large surface area for the absorption of fluid and obstruction of vascular leakage. The function of the omentum in the treatment of chylothorax is unknown; its lymphatic drainage is via the thoracic duct. Omental advancement through the diaphragm has been associated with a positive outcome in one dog and one cat with idiopathic chylothorax.^20,21

Pleuroperitoneal or Pleurovenous Shunting

Persistent chylous or nonchylous effusion following surgical treatment for idiopathic chylothorax may respond to pleuroperitoneal or pleurovenous shunt placement. (Figure 43-3) A commercially available shunt utilizes a one-way, manually compressed pump to move fluid from the pleural space into the peritoneal cavity or the venous system.¹⁹ Although seemingly more physiologically sound, pleurovenous shunting can cause major venous, right atrial, or right ventricular thrombus formation. Peritoneal fluid accumulation is well tolerated by veterinary patients, so pleuroperitoneal shunt placement is more commonly performed.⁴ Pre-existing peritoneal conditions that could prevent fluid absorption are a contraindication for pleuroperitoneal shunt placement.
 

The shunt catheter consists of an afferent portion, pump chamber, and efferent limb. The entire system is placed in heparinized saline and filled until no air bubbles are present. A small thoracotomy incision is made over the sixth, seventh, or eighth intercostal space.⁴ The afferent limb is placed in the chest, and a tunnel is made in the subcutis through which the efferent limb is passed, allowing the pump chamber to lie over and be secured to the ribs.⁴ Securing the chamber to the adjacent ribs allows postoperative compression of the chamber for pleural evacuation. The efferent limb is introduced into the peritoneal cavity through a small skin incision and pursestring suture in the abdominal musculature.⁴ Alternatively, the efferent limb is tunneled over the shoulder and into the caudal cervical region, and the efferent limb is introduced into the jugular vein. The efferent limb should be inserted no further than the cranial vena cava. Alternate venous insertion sites include the caudal vena cava or azygous vein.

Unfortunately, many complications have been associated with shunting of pleural fluid including obstruction of the catheter by clot or kink formation, dislodgement of the pump chamber from the thorax, severe abdominal distention, pyothorax, peritonitis, and pleural compartmentalization.¹⁹ The pump chamber moves 1mL of fluid with each compression and may cause patient discomfort and poor client compliance due to the amount of care required to maintain pleural evacuation. These complications may result in shunt removal, replacement, or patient euthanasia.¹⁹

Postoperative Care

Patients should be monitored closely for complications associated with thoracotomy and or laparotomy. The need for fluid evacuation postoperatively is dependent on clinical signs and laboratory evaluation of ventilation. Resolution of pleural fluid accumulation following surgery should be monitored, as recurrent chyle accumulation or accumulation of a modified transudate may complicate recovery. Lung lobe torsion has also been associated with chylothorax or other pleural effusions.³¹ Chronic chylous effusion may also result in fibrosing pleuritis and dyspnea despite evacuation of fluid.

References

1. Bezuidenhout AJ: The lymphatic system In Evans HE, ed.: Miller’s Anatomy of the Dog. Philadelphia: WB Saunders Co., 1993, p 717.
2. Fossum TW, Mertens MM, Miller MW, et al.: Thoracic duct ligation and pericardectomy for treatment of idiopathic chylothorax. J Vet Intern Med 18:307, 2004.
3. Birchard SJ, Smeak DD, McLoughlin MA. Treatment of idiopathic chylothorax in dogs and cats. J Amer Vet Med Assoc 212:652, 1998.
4. Fossum TW: Small Animal Surgery. St. Louis: Mosby, Inc., 2002, 788.
5. Holt JC. A review of traumatic chylothorax with a case report of spontaneous remission in a dog. Aust Vet Pract 8:135, 1978.
6. Hodges CC, Fossum TW, Evering W. Evaluation of thoracic duct healing after experimental laceration and transaction. Vet Surg 22:431, 1993.
7. Birchard SJ, Cantwell HD, Bright RMI. Lymphangiography and ligation of the canine thoracic duct: a study in normal dogs and three dogs with chylothorax. J Amer Anim Hosp Assoc 18:769, 1982.
8. Bilbrey SA, Birchard SJ. Pulmonary lymphatics in dogs with experimentally induced chylothorax. J Amer Anim Hosp Assoc 30:86, 1994.
9. Fossum TW. Feline chylothorax. Comp Cont Ed Pract Vet 15:549, 1993.
10. Suter PF. Thoracic Radiography: A Text Atlas of Thoracic Diseases of the Dog and Cat, With Contributions by Peter F. Lord. Wettswil, Switzerland : P.F. Suter, 1984, 683.
11. Birchard SJ, Smeak DD, Fossum TW. Results of thoracic duct ligation in dogs with chylothorax. J Amer Vet Med Assoc 193:68, 1988.
12. Fossum TW, Forrester SD, Swenson CL, et al. Chylothorax in cats: 37 cases (19691989). J Amer Vet Med Assoc 198:672, 1991.
13. Willard MD, Fossum TW, Torrance A, et al. Hyponatremia and hyperkalemia associated with idiopathic or experimentally induced chylothorax in four dogs. J Am Vet Med Assoc. 199:353, 1991.
14. Thompson MS, Cohn LA, Jordan RC. Use of rutin for medical management of idiopathic chylothorax in four cats. J Am Vet Med Assoc 215:345, 1999.
15. Gould L. The medical management of idiopathic chylothorax in a domestic long-haired cat. Can Vet J. 45:51, 2004.
16. Kopko SH. The use of rutin in a cat with idiopathic chylothorax. Can Vet J. 46:72, 2005.
17. Markham KM, Glover JL, Welsh RJ, et al. Octreotide in the treatment of thoracic duct injuries. Am Surg. 66:1165, 2000.
18. Sicard GK, Hardie RJ, Hayashi K, et al. The use of a somatostatin analogue (Octreotide) for the treatment of idiopathic chylothorax in dogs and cats. Vet Surg 32:496, 2003.
19. Smeak DD, Birchard SJ, McLoughlin MA, et al. Treatment of chronic pleural effusion with pleuroperitoneal shunts in dogs: 14 cases (1985-1999). J Am Vet Med Assoc. 219:1590, 2001.
20. Lafond E, Weirich WE, Salisbury SK. Omentalization of the thorax for treatment of idiopathic chylothorax with constrictive pleuritis in a cat. J Am Anim Hosp Assoc. 38:74, 2002.
21. Williams JM, Niles JD. Use of omentum as a physiologic drain for treatment of chylothorax in a dog. Vet Surg. 28:61, 1999.
22. Hayashi K, Sicard G, Gellasch K, et al. Cisterna chyli ablation with thoracic duct ligation for chylothorax: results in eight dogs. Vet Surg. 34:519, 2005.
23. Kerpsack SJ, McLoughlin MA, Birchard SJ, Smeak DD, Biller DS. Evaluation of mesenteric lymphangiography and thoracic duct ligation in cats with chylothorax: 19 cases (1987-1992). J Am Vet Med Assoc. 205:711, 1994.
24. Esterline ML, Radlinsky MG, Biller DS, et al. Comparison of radiographic and computed tomography lymphangiography for identification of the canine thoracic duct. Vet Radiol Ultrasound. 46:391, 2005.
25. Pardo AD, Bright RM, Walker MA, Patton CS. Transcatheter thoracic duct embolization in the dog. An experimental study. Vet Surg. 18:279. 1989.
26. Brisson BA, Holmberg DL, House M. Comparison of mesenteric lymphadenography performed via surgical and laparoscopic approaches in dogs. Am J Vet Res 67:168, 2006.
27. Enwiller TM, Radlinsky MG, Mason DE, Roush JK. Popliteal and mesenteric lymph node injection with methylene blue for coloration of the thoracic duct in dogs. Vet Surg. 32:359, 2003.
28. Orton EC. Small Animal Thoracic Surgery. Baltimore: Williams & Wilkins, 1995, 95.
29. Radlinsky MG, Mason DE, Biller DS, et al. Thoracoscopic visualization and ligation of the thoracic duct in dogs. Vet Surg. 31:138, 2002.
30. Sicard GK, Waller KR, McAnulty JF. The effect of cisterna chyli ablation combined with thoracic duct ligation on abdominal lymphatic drainage. Vet Surg. 34:64, 2005.
31. Neath PJ, Brockman DJ, King LG. Lung lobe torsion in dogs: 22 cases (1981-1999). J Am Vet Med Assoc. 217:1041, 2000.
     

This technique is one of several surgical procedures used in an attempt to disrupt the flow of abdominal lymph drainage through the thoracic duct system in cats; it is specifically aimed at resolving chylothorax when no identified underlying cause can be found. Occlusion of the thoracic duct system results in the formation of alternate abdominal lymphaticovenous communications to return chyle to the circulation.¹ After a ventral midline celiotomy, a left transdiaphragmatic thoracotomy exposes the thoracic duct system for occlusion with hemostatic clips.¹ The procedure allows vital staining and immediate ligation of the thoracic duct system through a single body wall incision. The technical description of the procedure follows.

Surgical Technique

The cat is placed in dorsal recumbency, and the abdomen is prepared for aseptic surgery. A ventral midline incision is made from the xiphoid cartilage caudal to the umbilicus. The jejunum, ileum, and ascending co-Ion are identified and are exteriorized to locate the mesenteric lymph nodes. A more caudal lymph node is selected, usually the right colic, for injection of 1% Evans blue solution (Sigma Chemical Co., St. Louis, MO). Direct puncture with a 25-gauge needle on a 1-mL syringe is used to deliver 0.1 to 0.2 mL of dye into the selected node. A dry surgical sponge is used to contain any leakage of dye on removal of the needle, thus minimizing abdominal contamination. Lymphatic drainage of the injected dye is immediate. By retracting the descending duodenum ventrally and to the left, the stained intestinal lymphatic trunk is easily visualized as it courses through the duodenal mesentery dorsally toward the cisterna chyli. The transparent wall of the intestinal trunk is covered by visceral peritoneum, which can be delicately dissected away to improve the ease of cannulation of the intestinal trunk with a 22-gauge, over-the-needle catheter (Jelco intravenous catheter x 1 inch, Johnson & Johnson, Inc., Arlington, TX). After stylet removal, spillage of dye from the catheter should be contained by capping the catheter either with an injection cap (PRN Adapter, Becton Dickinson Vascular Access, Sandy, UT) or by attaching the 1-mL syringe containing the Evans blue solution. The catheter is fixed to the mesoduodenum with circumferential ligatures of small-diameter suture material (4-0 or 5-0), and the viscera are returned to the abdomen. Gentle manipulation of viscera minimizes disruption of the catheter.

The left side of the diaphragm is identified by retracting the stomach and left liver lobes caudomedi-ally. A left transdiaphragmatic thoracotomy is performed by incising the diaphragm from a point 2 cm dorsolateral to the xiphoid cartilage dorsally toward the left diaphragmatic crus until adequate exposure of the caudal thoracic aorta is achieved. By curving the diaphragmatic incision to parallel the costal arch, the medial portion of the incised diaphragm can more readily be used as a retractor to contain and displace the abdominal viscera caudomedially. Several stay sutures in the medial margin of the diaphragmatic incision are used for retraction.

The left caudal lung lobe is displaced cranially with a moistened sponge to expose the caudal thoracic aorta. The thoracic duct system should be identified in the areolar tissues surrounding the aorta by its staining from the previously injected Evans blue solution. An additional injection through the catheter in the intestinal trunk may be necessary to improve visualization of the thoracic duct branches. The thoracic aorta is dissected from the thoracic duct system just cranial to the aortic hiatus of the diaphragm. The least number of branches of the thoracic duct system is present for ligation at this location.² The aortic dissection is performed by beginning directly along its ventral ad-ventitia to minimize disruption of any of the thoracic duct branches, which are incorporated in areolar tissue dorsally and laterally. A moistened umbilical tape is passed around the aorta, which is then retracted ventrally to expose the stained thoracic duct system completely within the mediastinal tissues. Contraction of aorta occurs during dissection and retraction. Without immobilization of the thoracic aorta by complete circumferential dissection and isolation, complete exposure to the thoracic duct system cannot be achieved consistently.

Multiple hemostatic clips (Hemoclip [medium], Edward Week, Inc., Research Triangle Park, NC) are used to mass ligate any visible thoracic duct branches, without an attempt to isolate individual ducts before ligation. Usually, a single duct arising from the cranial pole of the cisterna chyli abdominally passes through the diaphragm and gives rise to one or two main thoracic branches, which can be identified at this site along with occasional minor collateral branches.² A major thoracic duct branch courses on the left dorsolateral aspect of the thoracic aorta. Looping collateral branches or a major or minor thoracic duct may be identified along the right dorsolateral aspect of the thoracic aorta, and multiple cross-communications between longitudinal ducts usually exist more cranially. The number of cross-communications increases cranial to the preferred site of ligation (Figure 43-4), which is just cranial to the aortic hiatus of the diaphragm (ventral to T13). The paired sympathetic trunks that lie lateral to the thoracic duct system should not be included in the ligation.

After thoracic duct system ligation, a second injection of dye into the intestinal trunk catheter is performed to highlight any collateral branches at the site of ligation that may have been unidentified but require ligation. The moistened sponge on the left caudal lung lobe is removed, and the lobe is reinflated. The thorax is lavaged with warm balanced electrolyte solution, and all fluid is removed from the thorax with suction. The diaphragm is closed in a simple continuous suture pattern dorsally to ventrally with 3-0 monofilament absorbable suture material. Thoracentesis may be performed through diaphragmatic puncture or through a previously placed thoracostomy tube until negative intrathoracic pressure is established. The abdominal lymphatic catheter is removed, and two-layer or three-layer abdominal closure is performed.
 

Postoperative Care

Postoperatively, a thoracostomy tube is maintained for 24 hours or until thoracic effusion becomes minimal. The success of the procedure is determined by resolution of the chylothorax without recurrence. Perioperative antibiotics are indicated and should be continued until after the thoracostomy tube is removed. Frequent short-term follow-up evaluations are indicated to monitor the cat for recurrent thoracic effusion.

References

1. Martin RA, Richards DLS, Barber DL, et al. Sunt E. Transdiaphragmatic approach to thoracic duct ligation in the cat. Vet Surg 1988;17:22-26.
2. Martin RA, Barber DL, Richards DLS, et al. A technique for direct lymphangiography of the thoracic duct system in the cat. Vet Radiol 1988;29:116-121.
    

Indications

Lymph node biopsy is indicated to evaluate persistent lymphadenopathy, determine if a neoplastic process is present, and to aid in the diagnosis of vague clinical signs associated with systemic disease. Lymphadenopathy may or may not be present; normal sized lymph nodes may still be involved in a disease process. The presence of metastasis for staging of disease or for definitive diagnosis of the type of neoplasia, as in lymphosarcoma, are common reasons for lymph node biopsy. Lymph nodes may also be sampled for the diagnosis of infectious disease or immune mediated conditions.^1-3 Non-diagnostic lymph node fine-needle aspirates (FNA) are also an indication for node biopsy. Peripheral lymph node biopsy is a simple and quick procedure with few complications. The information gained outweighs the risk of the procedure, which can be performed by needle, incision, or excision. Lymph node biopsy during open procedures such as laparotomy or thoracotomy rarely increases the risk associated with the approach or primary disease process. The information obtained may be extremely important for cancer staging and providing an accurate prognosis for the owner. For example, the survival time in dogs with bronchogenic carcinoma of the lung is markedly decreased for patients with lymph node metastasis at the time of surgery.⁴ Excisional lymph node biopsy may be indicated to decrease tumor burden prior to adjuvant chemotherapy, (e.g. malignant melanoma), to decrease tumor activity (e.g. insulinoma, mast cell tumor), or if the nodes are causing clinical signs because of their size (e.g. colorectal compression caused by medial iliac lyphadenopaty).

Contraindications and Complications

Contraindications to lymph node biopsy are rare. A complete evaluation of the patient should be performed prior to sedation or general anesthesia for lymph node sampling. Hemorrhage is one potential complication of lymph node biopsy with needle, incisional, or excisional techniques. Animals with coagulopathies should have the disorder corrected by administration of plasma, a blood transfusion, or vitamin K therapy prior to surgery.

Lymph nodes may have a generous blood supply, and vessels should be carefully ligated as necessary during the procedure. Specific lymph nodes such as the medial iliac, hypogastric, and hepatic lymph nodes are anatomically associated with large blood vessels. The external and internal iliac vessels and the portal vein are adjacent to the lymph nodes and trauma to those vessels can lead to significant hemorrhage. Complete excision of the mesenteric lymph node(s) may be difficult due to the risk of compromise to the blood supply of the bowel. Edema is rarely a complication of lymph node biopsy.⁵

Biopsy Techniques

Selecting a Biopsy Site

Physical examination or the anatomic location of disease usually dictates which lymph nodes are selected for biopsy. The superficial lymph nodes are easiest to sample from patients with generalized lymphadenopathy or unexplained systemic illness (Figure 43-5). The popliteal and mandibular lymph nodes are easily palpated and sampled in patients with normal sized lymph nodes. The mandibular lymph nodes may display reactive hyperplasia due to constant exposure to exogenous antigens of the oral cavity and although they are readily palpated and approached for biopsy, they may not be representative of the condition present.⁶ The same is true for lymph nodes draining the gastrointestinal tract. Normal inguinal and superficial cervical, or prescapular, lymph nodes may also be sampled if necessary, but are not as easily approached. A single approach for the lymph nodes draining the head, parotid, mandibular, retropharyngeal areas, has been described for the staging of maxillofacial neoplasms.

The lymph nodes draining an abnormal site or lesion should be sampled in any case requiring lymph node biopsy. Therefore, the regional lymphatic anatomy should be considered prior to biopsy. A detailed description of lymphatic anatomy should be consulted if the anatomy is not readily apparent. Alternative methods of determining lymph node drainage of a particular site include magnetic resonance imaging and computed tomography following injection of contrast material into the affected region.⁷ Advanced imaging methods with coloration of the lymph nodes and scintigraphic identification of sentinel lymph nodes have not been widely used in veterinary patients.

The drainage areas for specific superficial lymph nodes should be considered prior to lymph node biopsy. The parotid lymph nodes drain the nasal planum, skin, and subcutis of the frontal and temporal regions and many of the muscles of the ear and head. Drainage from the parotid lymph nodes is to the retropharyngeal lymph nodes. The mandibular nodes drain the nose, lips, superficial muscles of the head, and parts of the tongue, oral cavity, and pharynx. Efferent lymphatics from the mandibular lymph nodes proceed to the retropharyngeal lymph nodes. The superficial cervical lymph nodes drain the skin and subcutis of the caudal head, thoracic cavity, neck, shoulder, and portions of the thoracic limb. Drainage from the superficial cervical lymph nodes is to the right lymphatic duct, thoracic duct, or directly into the jugular vein. The axillary lymph nodes drain an area similar to but extending more caudal to the drainage area of the superficial cervical lymph nodes. The axillary lymph nodes also drain portions of the thoracic limb and cranial mammary glands. Efferent lymphatics from the axillary lymph node drain to the right lymphatic duct, thoracic duct, tracheal duct, or external jugular vein. The inguinal lymph nodes drain the skin and subcutis of the ventrolateral trunk, pelvic and tail areas, medial and lateral thigh, perineum, and caudal mammary glands. The drainage from the inguinal lymph nodes proceeds to the external iliac lymph node. The popliteal lymph nodes drain the majority of the pelvic limb structures, mostly distal to the location of the lymph node. Efferent lymphatics go to the inguinal and external iliac lymph nodes.^8,9
 

Fine-Needle Aspiration (FNA)

Any of the superficial lymph nodes that can be palpated and stabilized can be aspirated. Sedation or anesthesia is usually not required, nor is skin preparation necessary. The only equipment needed is glass slides, a 10 or 12 cc syringe, and 22 to 25 gauge needle. Two methods of aspiration exist. One technique uses suction generated by the needle and syringe, the other does not. The lymph node is grasped, and the needle placed within the parenchyma. If suction is used, 8 to 10 cc of suction is generated. The needle is carefully redirected within the lymph node and suction reapplied. Discontinue the procedure if blood appears in the hub of the needle. Release suction prior to withdrawal of the needle from the lymph node. The needle should be removed from the syringe, and 5 cc of air is aspirated into the syringe, the needle is replaced on the syringe, and the material in the needle is immediately sprayed onto a clean glass slide.

If suction is not used, stabilize the lymph node by palpation and insert the needle into the parenchyma. The needle is redirected multiple times; discontinue the procedure if blood appears in the hub of the needle. Fivecc of air is aspirated into a 12 cc syringe, the needle is applied to the end of the syringe, and the material is sprayed onto a clean glass slide. With either procedure, the contents of the needle must be sprayed onto a clean glass slide immediately, and a vertical or horizontal squash preparation made. Only gentle pressure is used to make the smears, as lymph node tissue is extremely fragile; cellular and nuclear damage will interfere with interpretation of the cytology. Wright’s stain is applied to evaluate the smears.¹⁰

Tru-Cut Biopsy

Enlarged lymph nodes can be biopsied with a 14 to 16 gauge Tru-Cut needle, which supplies a cylindrical core of tissue. This method may be used for sampling superficial lymph nodes in cases in which a diagnosis is not apparent on fine needle aspiration cytology and can often be performed under sedation. The lymph node is stabilized by hand, and a stab incision made in the skin over one end of the lymph node. The needle is introduced into the lymph node so that the sampling chamber will ideally remain in nodal tissue only during the biopsy process. Automated or manual biopsy needles are available.

Incisional Biopsy

An incisional biopsy requires a surgical approach to the lymph node and removal of a wedge of tissue for biopsy. Incisional biopsies are usually done on lymph nodes that are difficult to completely excise without consequences, as with mesenteric lymph nodes, and are achieved with stabilization of the lymph node. Superficial lymph nodes are approached by a skin and subcutaneous incision and muscular dissection as needed to expose the lymph node. A wedge of lymph node is excised using a number 15 scalpel blade. The wedge is oriented transverse to the long axis of the lymph node and is removed with minimal handling to avoid damaging the architecture of the specimen. The defect is closed with small (3-0 to 4-0) absorbable suture in a horizontal mattress pattern for hemostasis (Figure 43-6). The approach is closed routinely. Impression smears of the biopsy sample can be made prior to placing the sample in formalin.
 

Ideally, the surface is blotted dry with absorbent paper, and the cut surface is lightly pressed against a clean glass slide; care should be taken to not damage the biopsy specimen during any part of the process. Fungal or bacterial cultures may also be obtained prior to fixation.

Excisional Biopsy

Superficial lymph nodes may be excised with heavy sedation and local anesthetic depending on the patient’s temperament and physical status. General anesthesia for superficial lymph node extirpation is recommended in most patients and is required for deep, abdominal, or thoracic lymph node excision. For superficial lymph nodes, the node is palpated and stabilized with external pressure toward the skin surface. An incision is made longitudinally over the lymph node, and blunt dissection is used to mobilize the node. Afferent vessels may or may not require ligation; more frequently hilar vessels are ligated.⁸ Deep, abdominal, or thoracic lymph nodes are evaluated during surgical exploration. Care is taken when dissecting the lymph nodes from surrounding structures, particularly nerves and vessels. Hemostasis is achieved with ligation and electrocautery in most cases, however, collateral damage to the lymph node can occur if cautery is applied close to the nodal surface.

The lymph node should be handled carefully to avoid structural damage. Samples may be collected for fungal and bacterial culture, and the lymph node may be sectioned for impression smears. The sample should be placed in an adequate volume of 10% formalin for processing.

References

1. Manna L, Vitale F, Reale S, et al.: Comparison of different tissue sampling for PCR-based diagnosis and follow-up of canine visceral leishmaniosis. Vet Parasitol 125:251, 2004.
2. Barrouin-Melo SM, Larangeira DR, Trigo J, et al.: Comparison between splenic and lymph node aspirations as sampling methods for the parasitological detection of Leishmania chagasi infection in dogs. Mem Inst Oswaldo Cruz 99:195, 2004.
3. Mylonakis ME, Koutinas AF, Billinis C, et al.: Evaluation fo cytology in the diagnosis of acute canine ehrlichiosis (Erlichia Canis): a comparison between five methods. Vet Microbiol 91:197, 2003.
4. McNiel EA, Ogilvie GK, Powers BE, et al.: Evaluation of prognostic factors for dogs with primary lung tumors: 67 cases (1985-1992). J Am Vet Med Assoc 211:1422, 1997.
5. Soran A, Aydin C, Harlak A, et al.: Impact of sentinel lymph node biopsy on lymphedema following breast cancer treatment. The Breast J 11:370, 2005.
6. Perman V, Stevens JB, Alsaker R, et al.: Lymph node biopsy. Vet Clin North Amer 4:281, 1974.
7. Suga K, Yuan Y, Ueda K, et al.: Computed tomography lymphography with intrapulmonary injection of iopamidol for sentinel lymph node localization. Invest Radiol 39:313, 2004.
8. Fossum TW. Lymph node biopsy In Bojrab MJ, ed.: Current Techniques in Small Animal Surgery. Philadelphia, Williams & Wilkins, 1998, p 703.
9. Rogers KS, Barton CL, Landis M. Canine and feline lymph nodes. Part I. Anatomy and function. Comp Cont Ed Pract Vet 15:397, 1993.
10. Rogers KS, Barton CL, Lnadis M. Canine and feline lymph nodes. Part II. Diagnostic evaluation of lymphadenopathy. Comp Cont Ed Pract Vet 15:1493, 1993.