Abstract
Chylothorax is an uncommon, potentially life-threatening disease of dogs and cats. Medical records of 12 animals (five dogs and seven cats) undergoing surgical management of chylothorax from 2001 to 2005 were reviewed. All animals received thoracic duct ligation and thoracic omentalization. In some cases, a combination of subtotal pericardectomy and/or pleural stripping was also employed. All animals survived surgery, and none was lost to follow-up. Median survival time for cats was 209 days (range 2 to 1328 days), and for dogs it was 211 days (range 7 to 991 days). Although postoperative mortality was higher than in other recent studies, no complications could be directly attributed to thoracic omentalization. A controlled, prospective study is needed to compare outcomes of this management method to those of other methods.
Introduction
Chylothorax is an uncommon and potentially fatal disease of dogs and cats. Morbidity and mortality occur secondary to the thoracic accumulation of chyle, which results from leakage from the thoracic lymphatic system.1 Many processes can lead to chylothorax, including events such as trauma, heartworm disease, neoplasia, cranial mediastinal masses, venous thrombosis, fungal granulomas, congenital thoracic duct abnormalities, constrictive pericarditis, cardiomyopathy, pericardial effusion, and congenital cardiac disease.2–4 Despite the numerous potential causes, the most common diagnosis is idiopathic chylothorax.5
Chylothorax can be managed medically or surgically. The medical approaches fall into two major categories: 1) therapies that remove chyle from the thorax and 2) treatments that reduce the production of chyle. The former includes thoracocentesis and chest tube placement. The latter includes the use of low-fat diets, medium chain triglycerides, administration of rutin (a nutraceutical that decreases blood vessel leakage and increases absorption of chyle),6 furosemide, antibiotics, octreotide (a somatostatin derivative that is thought to decrease chyle formation), and steroids.1,5,7 Despite the array of therapeutic options, no superior medical protocol has emerged.
Surgical treatment of chylothorax is intended to impede the accumulation of chyle in the chest cavity via occlusion of the thoracic duct. The most commonly reported procedure is thoracic duct ligation (TDL) via thoracotomy.1,2,4,5,8–15 Ligation may be performed with or without the aid of mesenteric lymphangiography to identify branches of the duct.10 Positive-contrast radiographic imaging studies and administration of methylene blue solution or Evan’s blue solution have been evaluated as methods of lymphangiography.4,9,10,16 Preoperative oral administration of cream or a high-fat meal has also been employed to increase intraoperative visualization of the thoracic duct.4 Embolization of the thoracic duct was reported in 1989 as a potential alternative to ligation, but reports of its clinical use are lacking.17
As a solitary procedure, TDL has a reported success rate of about 20% in cats and 53% in dogs.1,11 Utilization of adjunct procedures has become more common in the past several years in an effort to increase the efficacy of disease resolution. The most common additional procedure is pericardectomy; however, ablation of the cisterna chyli, pleural stripping, shunt placement, introduction of diaphragmatic mesh, pleurodesis, and thoracic omentalization have also been described.4,12–14
Omentalization has been used successfully as an adjunct in the surgical treatment of various diseases and conditions such as prostatic abscesses, nonresectable stump pyometra, gastric ulcers, and leaking intestinal anastamoses.18 A few solitary case reports evaluate the successful outcome of thoracic omentalization in combination with TDL in cats and dogs.14,19,20 Debate currently exists regarding the use of omentalization in the surgical management of chylothorax.
The purpose of this study was to evaluate the clinical outcomes of cats and dogs after surgical management of chylothorax via en bloc TDL and thoracic omentalization. Disease-free interval and survival times were used as indicators of outcome.
Materials and Methods
Criteria for Inclusion
Only cats and dogs diagnosed with idiopathic chylothorax were included in this study. Chylothorax was diagnosed if the fluid triglyceride measurement exceeded the serum triglycerides.1 Disease was classified as idiopathic based on the exclusion of other causes by complete medical workup. Cases with parasitic, neoplastic, traumatic, or cardiac abnormalities were excluded from the study. Inclusion also required the animal to have been surgically managed with TDL and thoracic omentalization. Twelve cases (five dogs and seven cats) met the above criteria between 2001 and 2005 [Tables 1A⇓, 1B⇓]. Records were reviewed for signalment, dates of diagnosis, confirmation of diagnosis, abnormalities in hematology and serum chemistry, preoperative treatments, surgical procedures performed, postoperative complications, and long-term follow-up.
Signalment, Procedures, and Survival Times for Study Dogs
Signalment, Procedures, and Survival Times for Study Cats
Preoperative and Anesthetic Protocol
No animal received a preoperative high-fat meal (oil or cream), by preference of the surgeon. Preanesthetic and induction agents were selected on the basis of individual animal needs [Tables 2A⇓, 2B⇓]. All cases were intubated and maintained on isoflurane inhalant anesthesia.
Anesthetic and Pain Management Protocols for Dogs
Anesthetic and Pain Management Protocols for Cats
Surgical Technique
All cases were operated on by a single surgeon (Padgett). Animals were placed in dorsal recumbency, and a combined median sternotomy and midline laparotomy were performed. En bloc TDL was achieved with surgical ligaclips after gross identification of the duct.9 New methylene blue was administered if the duct could not be identified.
In cats with >50% compromised lung tissue from fibrosis (determined subjectively), decortication was performed with dry gauze and careful dissection. For animals receiving subtotal pericardectomy, the pericardectomy was performed via sharp dissection through the thoracotomy.
Intercostal chest tube placement occurred prior to omentalization. Omentalization was performed by first creating a grid incision through the right ventral aspect of the diaphragm to allow passage of the omental flap. The omental flap was created by incising near the dorsal leaf of the omentum transversally to obtain the desired width and then extending longitudinally to allow maximum lengthening [Figure 1⇓]. The flap was then passed through the grid incision and tacked to the ventral thorax with multiple, simple interrupted, absorbable sutures [Figure 2⇓]. Simple continuous absorbable suture was used for apposition of a portion of the grid incision (to avoid thoracic herniation of abdominal contents but allow vascular supply of the omentum to remain intact).
Development of the omental flap. With the dog in dorsal recumbency, the omentum is brought cranially to expose the dorsal leaf where the flap originates.
Placement of omental flap. With the dog in dorsal recumbency, the omental flap is brought up through the diaphragmatic grid incision and tacked to the ventral thoracic wall with simple interrupted sutures.
Closure consisted of nonabsorbable cruciate sutures for apposition of the sternebrae. Subcutaneous, intradermal, and skin closures were performed routinely. Additional procedures performed were decided on an individual case basis [Tables 1A⇑, 1B⇑].
Postoperative Management
Postoperative analgesia was afforded via various combinations of periodic or continuous-rate infusions [Tables 2A⇑, 2B⇑]. Removal of the chest tube occurred between days 2 and 9 based on individual case assessment. Animals were noted as either eating or anorectic; quantity of food intake was not recorded. Respiratory rates were recorded, and respiratory efforts were subjectively assessed.
Results
Of the 12 cases, seven were cats and five were dogs [Tables 1A⇑, 1B⇑]. The median age at time of surgery for cats was 7 years (range 3 to 11 years), and for dogs it was 5 years (range 3 to 5 years). Median durations of clinical signs prior to diagnosis were 60 days for cats (range 8 to 121 days) and 29 days for dogs (range 5 to 190 days). Median times from diagnosis to surgery were 20.5 days for cats (range 7 to 42 days) and 28 days for dogs (range 1 to 84 days). Variable treatment protocols were tried prior to surgery [Tables 3A⇓, 3B⇓]. Medical treatments for chylothorax were discontinued upon admission to the hospital for surgery.
Preoperative Medical Management of Chylothorax for Dogs
Preoperative Medical Management of Chylothorax for Cats
Median survival times were 209 days for cats (range 2 to 1328 days) and 211 days for dogs (range 7 to 991 days). Of the 12 cases, nine were alive at the time of discharge from the hospital. Three cats died in the immediate postoperative period (within 4 days of surgery). Of these, two cats (case nos. 7, 10) had undergone pericardectomy and pleural stripping in addition to TDL and omentalization; the third cat (case no. 9) had only TDL and omentalization. Gross and microscopic pathology for case no. 9 identified fibrinosuppurative and fibrotic pleuritis, mucopurulent bronchitis, and chronic passive lung congestion. Pathological findings for case no. 10 identified aortic thrombosis as the cause of death, although no prior history of cardiac disease was present. Case no. 7 died after the onset of dyspnea and subsequent respiratory arrest; the owner declined necropsy.
Four cases were presented with complications after discharge from the hospital. Case no. 1 was presented 2 days after discharge (6 days postoperatively) with subcutaneous emphysema, elevated heart and respiratory rates, dyspnea, anorexia, and hyperthermia. The dog was rehospitalized, and 20 mL of chylous fluid was withdrawn from the right thorax. The dog went into cardiac arrest approximately 26 hours after presentation. Postmortem examination identified locally extensive atelectasis and fibrosis, lymphoplasmacytic pleuritis, and acute to subacute fibrinopurulent pleuritis.
Case no. 2 was presented 2 days after discharge (6 days postoperatively) for labored breathing. Serosanguineous fluid (300 mL) was aspirated from the thorax. Fluid analysis was consistent with an inflammatory effusion. One year after surgery, this dog was again presented with both peritoneal and pleural effusions. Although chylous effusion was ruled out, no definitive diagnosis was made. The dog was managed medically and at last follow-up (562 days postoperatively) had no clinical signs referable to pleural or peritoneal effusion.
Case no. 11 was presented to the clinic 2 days after discharge (6 days postoperatively) for retained urine and constipation. At the routine 6-month follow-up examination, the cat was asymptomatic; however, radiographs revealed intrathoracic fluid accumulation. Chylous effusion (100 mL) was aspirated from the thoracic cavity. The cat was alive and clinically normal at the time of data gathering, 209 days postoperatively.
Case no. 12 had a previous diagnosis of megacolon and was presented with constipation 15 days after discharge (20 days postoperatively). The cat was managed medically. Total survival time after surgery was 1328 days. Cause of death was unknown, and necropsy was declined.
Discussion
Some of the earliest papers regarding chylothorax in the dog and cat date back to the late 1950s.21 Despite this long history, no definitive treatment for chylothorax has emerged. The most commonly reported method of surgical management is TDL. In recent years, this technique has been combined with subtotal pericardectomy and has resulted in improved clinical outcomes.4,5,11,15 Current studies continue to explore surgical methods such as omentalization and cisterna chyli ablation as adjunct procedures to manage this disease.14,19,20
Thoracic omentalization as an adjunctive therapy for treatment of chylothorax was first reported in 1999 for the management of a 6-year-old dog.19 A second paper reported the use of omentum as a drain in a cat in which pleural fibrosis was so severe that TDL could not be performed.20 Both animals recovered and were alive at the time of publication (16 and 13 months after surgery, respectively).
The actual function of omentalization in the management of chylothorax is unknown. Proposed theories and arguments for omentalization include the following:
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Omentum may function as a physiological drain to prevent the accumulation of chyle in the thoracic cavity while the thoracic duct heals.
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Omentum may play a direct role in the healing of the thoracic duct by providing a source of neovascularization and fibroplasia.14,20
Arguing against omentalization is the fact that while the omentum may absorb the chyle from the thoracic cavity, it does not function to resolve the source of the effusion.14
No direct complications appear to accompany this adjunct procedure. Theoretical complications include abscessation of the omentum, infarction, diaphragmatic herniation, and granuloma formation resulting in lung compression. None of these were noted in the study population, and most complications appeared to result from the chronicity of the primary disease.
Conclusion
This report presents the largest number of chylothorax cases reported to date that were managed through the addition of thoracic omentalization. Long-term clinical resolution is acceptable, although a higher mortality rate may be present in the immediate postoperative period (days 0 to 7). A controlled, prospective study is needed to compare outcomes of this management method to those of other methods.
Acknowledgments
The authors thank S. Adkins, RVT, for preparation of the illustrations of the surgical procedure.
References
