Estimated reading time: 6 minutes
Clyde is a five-year-old 65kg bull-mastiff who stole all our hearts. He was seen by his referring veterinarian after a week-long history of lethargy, tachypnoea and inappetence. Thoracic radiographs were performed and showed a fluid/soft tissue opacity that obscured the majority of the lung fields and cardiac silhouette. Thoracocentesis was performed and one litre of chyle-like fluid was removed.
The removed fluid was submitted for evaluation and revealed a lymphocyte-rich effusion with triglyceride levels higher than in serum. Clyde was referred to the Adelaide Veterinary Specialist & Referral Centre, Medicine Department for investigation.
Differential diagnoses for chylothorax included: pericarditis/cardiac disease, intrathoracic mass e.g. thymoma, or cranial mediastinal neoplasia; thoracic duct occlusion, thromboembolic disease, inflammatory disease and idiopathic chylothorax.
A diagnostic plan included thoracic ultrasound and echocardiogram with a view to performing a CT scan if there was no pathology evident on the ultrasound examination. Right-sided congestive heart failure can contribute to increased venous return and hence pleural effusion. A small degree of tricuspid valve disease was noted on the ultrasound examination but not considered significant, particularly in light of there being no supporting clinical signs.
No specific causes could be found on a CT scan and therefore an idiopathic diagnosis was made. Ultrasound-guided thoracocentesis was performed from the right thorax and additional chyle removed. Clyde was monitored over the following 12 months and after initial resolution developed recurrent episodes of coughing and dyspnoea with an acute life-threatening episode of chylothorax where four litres of chyle was removed.
Emergency thoracocentesis was performed on the patient in sternal recumbency. Using local anaesthetic and a small skin cut down, large 14 G over the needle catheters were inserted dorsal to the costochondral junction at the 8th intercostal space. Fluid was then removed using extension tubing attached to a 3-way stop cock and 50ml syringe.
If back pressure was encountered, gently tilting Clyde to the dependant side and manipulating the catheter’s trajectory into the chest allowed for maximal flow. Medical management including low-fat dietary modification helps, and patients occasionally resolve spontaneously but idiopathic forms often require thoracic duct ligation to stop the effusion. Chronic effusion has also been shown to increase the risk of fibrosing pleuritis which causes dyspnoea, so Clyde’s owners elected to proceed to surgery.
Pre-operative CT lymphangiography can help visualise the various branches of the thoracic duct. This may be performed by injecting Iohexol contrast agent into either the popliteal, mesenteric lymph nodes or an iodine contrast agent subcutaneously around the anus. Intraoperative mesenteric lymphangiography and fluoroscopy has also been described. A practical technique and one used in this case involved diluted methylene blue injected into a lymphatic or intranodally. This is very helpful in identifying all branches of the thoracic duct helping to ensure complete ligation.
Clyde was positioned in left lateral recumbency and a right-sided ninth intercostal thoracotomy was performed after he was placed on a ventilator. A local block was carried out at the two ribs cranial and caudal to the thoracotomy using Bupivacaine. A further 200ml of chyle was suctioned and the chest lavaged with saline.
The pleura was thickened on its reflection at the mediastinum. The aorta, sympathetic chain and azygos vein were identified. A para costal incision was made and after exteriorising a loop of duodenum, an attempt at catheterisation of an efferent lymphatic for lymphangiography was made. The lymphatics were very friable and after two attempts at catheterisation this was abandoned.
A lymph node at the ileocolic mesentery was then injected with 0.5ml of methylene blue. Five minutes later, the thoracic duct and its associated branches could be clearly visualised in the right mediastinum. Three large ducts could be seen in the peri aortic tissue and three 10mm liga clips were applied. A 2cm incision was made dorsal to the aorta and a number of smaller ancillary branches were seen.
An encircling 2/0 Prolene ligature was passed through the mediastinum and used to ligate these en bloc. A right-sided subtotal pericardectomy was performed by making a T-shaped incision ventral to the phrenic nerve and extending to the apex of the heart, thereby removing a triangular area of thickened pericardium. The chest and abdomen were lavaged with copious amounts of warm saline and a chest drain placed.
Layered closure of the thoracotomy and para costal incision was performed.
After surgery, Clyde was closely monitored by a dedicated hospital team overnight, then spent a few days with our emergency and critical care team. Clyde has done extremely well post operatively and at three months has no further symptoms.
Useful facts about chylothorax:
- Chyle is fatty lymphatic fluid circulated from the intestine to the cranial vena cava.
- Any factors that increase flow or decrease drainage may dilate the lymphatics causing lymphanioectasia.
- Any disease that increases systemic venous pressure can cause chylothorax.
- A history of coughing is often the first symptom later followed by dyspnoea.
- Radiographs are a useful diagnostic tool.
- Chyle is typically white or pink and occasionally red in colour.
- Suspected chylous effusions should be submitted in an EDTA tube for evaluation.
- Diagnostic characteristics include triglyceride content (higher than simultaneously collected serum) and cytology (predominant cell type is lymphocytes or non-degenerative neutrophils).
- CT lymphangiography can be useful but not essential in diagnosis and treatment.
- If the underlying disease is diagnosed and treated appropriately, many cases resolve.
- Surgery is warranted where the underlying cause is unknown (idiopathic) and effusions become chronic.
- Low fat diets are non-curative.
- Surgical treatment involves TD ligation and pericardectomy (commonly performed, often done simultaneously). Pericardectomy is thought to lower right-sided venous pressure normalising venous pressure and lymphatic flow.
- Success rate with TDL and subtotal pericardectomy is around 80%.
- Cisterna Chyli ablation and less commonly TD glue embolisation and active pleuro peritoneal shunting are also described. V
(Reference – Small Animal Surgery 5th Edition, Theresa Welch Fossum, 2018, CV Mosby Publishing)
Dr Bruce Meyers MMED Vet (Small Animal Surgery)
Adelaide Veterinary Specialist and Referral Centre
Dr Meyers qualified as a veterinarian in 1993 and completed his master’s degree in Small Animal Surgery in 2008 at the University of Pretoria (Onderstepoort).
Dr Meyers is registered as a specialist veterinary surgeon with the South African Veterinary Council, and he established St. Helier Veterinary Hospital and Specialist Centre in Durban, before he relocated to Adelaide in January 2022 with his wife, daughter and their three dachshunds.
