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Piccolo – Chylothorax

Piccolo is an 11-year-old female neutered domestic cat that presented for a 1-week history of increased breathing effort. On examination a grade 2 left parasternal systolic murmur was auscultated, lung crackles were audible with reduced lung sounds ventrally. Haematology and biochemistry were performed indicating an increase in creatinine kinase (1297 U/L) and hypertriglyceridemia (1.1 mmol/L), the remainder of the results were unremarkable. TFAST indicated a large volume bilateral pleural effusion and thoracocentesis was performed yielding white milky fluid confirmed to by chyle.

A thoracic ultrasound and ECHO were performed excluding cardiac disease, lung lobe torsion and a diaphragmatic hernia as differentials, however thickening of the pericardium was noted. An incidental mediastinal cyst like structure was also identified and this was confirmed with thoracic CT.
An abdominal CT also identified concerns of early abdominal effusion. Subsequently, a lymphangiogram was performed by injecting contrast into the popliteal lymph node (see images below). The thoracic duct was visible and appeared to end at the level of the left jugular vein with possible leakage in this area. Moppet was referred to the surgery department for management as ongoing thoracocentesis was required to manage the chylous effusion.

Chyle is triglyceride rich fluid that originates from the thoracic duct. Causes of chylothorax include but are not limited to cardiac disease, neoplasia, pericardial disease, lung lobe torsions, thoracic duct rupture or can be idiopathic. Chylous effusion is often idiopathic, which is determined based on exclusion of other differentials. Patients present with inspiratory dyspnoea and tachypnoea secondary to a pleural effusion. A diagnosis of a chylothorax is confirm by thoracocentesis and fluid analysis. If a specific underlying cause is found, therapy may be directed against that. However, in the acute phase we recommend thoracocentesis to alleviate respiratory distress.

Treatment options for chylothorax include both surgical and medical management. Medical options include dietary management (low fat diet), and nutraceuticals e.g. rutin (stimulates macrophage activity that promotes breakdown of protein in lymphatics thereby resulting in improved pleural effusion reabsorption). Unfortunately, there is no solid data to suggest that these options are effective, however, they are safe and can be trialled prior to surgery. Surgery, with the aim of thoracic duct ligation, is recommended if there is no improvement with medical management.

Studies have been performed to assess the benefits of pericardiectomy and cisterna chyli ablation in addition to thoracic duct ligation. In cats, the addition of a pericardiectomy has been shown to increase the success rate (resolution of effusion) in from 40% to 80% (Fossum et al. 2014). It is hypothesised that pericardial thickening is secondary to chyle irritation increasing the right sided venous pressure and impeding the drainage of chyle and increasing thoracic duct leakage. Pericardectomy is through to reduce the venous pressure and reduce leakage. A study in 2018 also compared the survival time of cats surgically managed with or without cisterna chyli ablation. The median survival time of the former was 380 days and the later 774 days (Stockdale et al. 2018). Therefore, thoracic duct ligation and left sided subphrenic pericardectomy was performed for Moppet via a left sided thoracotomy with intra-operative methylene blue lymphangiography to assist with thoracic duct identification.

Moppet recovered well post-operatively and has no clinical signs of recurrence 4-weeks post-surgery. The long-term prognosis is guarded. Some cats may develop ultrasonographic pleural effusion with no clinical signs until months or years later.

Our general experience with idiopathic chylothorax is that some cats will markedly improve with surgery whereas other patients are refractory to both medical and surgical management. These cases can be further managed with repeat thoracocentesis (ideally using an active subcutaneous pleural port) or placement of a pleuroperitoneal shunt.

Recently we had one cat improve with repeat thoracocentesis (via thoracic drains) followed by a prolonged course of rutin (owners elected against surgery) and is currently alive 6 months post diagnosis.

References:

Stockdale, SL, Gazzola, KM, Strouse, JB, Stanley, BJ, Hauptman JG & Mison, MB 2018 ‘Comparison of thoracic duct ligation plus subphrenic pericardectomy with or without cisterna chyli ablation for treatment of idiopathic chylothorax in cats’, Journal of the American Veterinary Medical Association, vol. 252, pp. 976-981.

Fossum, TW, Mertens, MM, Miller, MW, Peacock, JT, Saunders, A, Gordon, S, Pahl, G, Makarski, LA, Bahr, A, Hobson, PH 2004 ‘Thoracic Duct Ligation and Pericardectomy for Treatment of Idiopathic Chylothorax’, Journal of Veterinary Internal Medicine, vol. 18, pp. 307-310

Appendix:

Figure 1: Lymphangiogram: Migration of contrast (blue arrow) from the popliteal lymph node to the thoracic duct