Veterinary Medicine - September 2008 - (Page 502)

A challenging case PEER-REVIEWED after thoracic duct ligation and partial pericardiectomy. Previous reports of cats with chylothorax that had a thoracic duct ligation without a partial pericardiectomy had a < 40% success rate. Thoracic duct ligation likely allows abdominal lymphaticovenous anastomoses to form, which will transport chyle to the venous system. Thus, the thoracic duct is bypassed, and the pleural effusion can resolve.1 Other surgical options, which are not recommended over thoracic duct ligation and partial pericardiectomy, include passive pleuroperitoneal shunting and active pleuroperitoneal or pleurovenous shunting.2 Before the thoracic duct is ligated, it is often located at surgery by performing a dye study. In our case, the lymphatic and blood vessels dorsal and lateral to the caudal thoracic aorta were ligated en bloc, and then dye was injected to ensure no lling occurred in the thorax. Mesenteric lymphangiography, which requires placing a catheter into a mesenteric lymphatic vessel and infusing methylene blue, can be dif cult to perform in cats. This technique helps identify the branches of the thoracic duct before ligation and identify whether the branches were successfully ligated. Another technique, which was used in this case, is to inject methylene blue directly into a mesenteric lymph node. With either of these approaches, and although it was not done in this case, it is recommended to administer a highfat meal before surgery (withhold food for 12 hours before surgery but feed 1 to 2 ml/kg cream or corn oil hourly for three hours before surgery) to increase lymphatic ow to make it easier to identify the lymphatics. Cranial mediastinal cysts At least 17 cases of cats with cranial mediastinal cysts have been reported; thymic branchial, parathyroid, thyro- glossal, and idiopathic cysts have been described.6 Of the 17 cats with cranial mediastinal cysts, 13 were considered asymptomatic. The four symptomatic cats presented with dyspnea, but only one had pleural effusion. In a recent report of cats with cranial mediastinal cysts, eight of nine cats had follow-up and were asymptomatic from three to 45 months after diagnosis.6 The cysts in that report were drained once with ultrasound-guided aspiration, and none were surgically removed.6 In this case, the cyst appeared to be of thymic origin but was not consistent with a thymic branchial cyst because it was formed by an irregular lining of brous tissue and lacked any epithelial lining. A small cluster of thyroid follicular epithelial cells was present in one area of the cyst. In a previously reported thymic branchial cyst in a cat, thyroid follicles and parathyroid structures were noted within the cyst.7 In this report, the cyst

Table of Contents Feed for the Digital Edition of Veterinary Medicine - September 2008

Veterinary Medicine - September 2008 Contents Leading Off Practical Matters Idea Exchange A Challengin Case: Thymic Cyst and Recurrent Chylothorax in a Cat 10 Life-Threatening Behavior Myths CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - September 2008

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