Chronic Pyothorax resulting in Severe Right Sided Pleuropneumonia
By Dr. Alice Lam, Surgical Intern CityU PAVC

A three year-old female spayed Domestic Short Haired cat was presented to the Emergency Department at City U PAVC for investigation of anorexia and increased respiratory effort. Thoracic auscultation revealed reduced respiratory sounds ventrally. Subsequent thoracic radiographs revealed a bilateral pleural effusion. A thoracocentesis was performed and 120ml of grossly purulent exudate was drained. Culture of the fluid revealed a growth of Pasteurella multocida. The pyothorax was initially medically managed; through the placement of bilateral thoracostomy tubes, regular thoracic lavage and antibiosis. Following an initially good recovery the cat was discharged from the hospital, however her clinical signs returned approximately one week later.

Following readmission to the hospital the case was internally referred to the Surgery Department. Clinical examination revealed tachypnea and significant dyspnoea. There was a near complete absence of respiratory sounds on auscultation of the right hemithorax. Further investigation was initiated including a contrast enhanced CT examination of the thorax and an abdominal ultrasound scan. The abdominal ultrasound scan did not reveal any significant concerns. The CT-scan revealed a moderate pleural effusion with marked pleural thickening in the right hemithorax consistent with constrictive pleuritis. In addition, there were areas consistent with abscessation in the cranial mediastinum, middle mediastinum caudal to the cardiac silhouette, ventral to the accessory lung lobe and in the dorsolateral aspect of the tracheobronchial region. Lastly, there was sternal, cranial mediastinal and tracheobronchial lymphadenopathy.

Given the marked changes identified on the CT scan and the recurrence of the disease, the owners elected to proceed with surgical intervention. A right fifth intercostal thoracotomy was performed. Markedly thickened and constrictive pleura were noted, and the right cranial and middle lung lobes appeared collapsed and potentially necrotic. These lobes were resected using the Covidien DST series TA 30 V3 stapling system. The pleura was also carefully dissected from the thoracic wall and the accessible lymph nodes were resected. Bilateral Mila thoracostomy tubes were placed in a routine fashion. Culture of the resected tissue revealed growths of Brevibactrium spp., Micrococcus luteus and Fusobacterium nucleatum. Histopathological examination of the resected lung lobes concluded that there was pleuropneumonia with extensive haemorrhage and pulmonary parenchyma collapse, examination of the resected lymph nodes was consistent with lymphadenitis.

Post-operatively the thorax was lavaged several times per day, and the cat was treated with antibiotics (amoxicillin clavulanic acid) on the basis of culture and sensitivity results. Cytological examination of the drained thoracic fluid was regularly performed. Four days post-operatively the cytology appeared quiescent and therefore the thoracostomy tubes were removed. Following a further 36 hours of observation the cat was discharged on continued antibiotics and analgesia.

The cat was closely monitored following discharge. Happily, three months post-operatively no concerns were identified clinically or on repeated thoracic radiological examination. The owners also report that at home the cat has gone from strength to strength and has returned to her bright mischievous self.

In recent months we have seen an increasing number of cats with severe pyothorax necessitating multiple lung lobectomies and in some cases complete unilateral pneumonectomies. The aetiology of the pyothorax is sometimes not identified, however in general the route of infection into the pleural space can be classified into three main groups: Firstly, extension from adjacent structures, including; bronchopneumonia, parapneumonic spread, oesophageal rupture, mediastinitis or sub-phrenic infection. Secondly, direct inoculation of pathogens including from penetrating trauma and migrating foreign body. Lastly, haematogenous or lymphatic spread from distant septic foci [1]. In one study, penetrating bite wounds and abscesses that ruptured towards the thoracic cavity, causing bacterial contamination and ultimately pyothorax were the most common route of infection [1]. The bacteria isolated were commonly gram-negative (Pasteurella spp., Pseudomonas spp., Actinobacillus spp.), facultative anaerobic rods and obligate anaerobic bacteria [1,2]. However, other studies have suggested that aspiration of oropharyngeal flora with parapneumonic spread could be the most common cause of feline pyothorax [2].

Pneumonectomy is associated with a high risk of perioperative morbidity and mortality in human medicine, with a reported postoperative complication rate of 38-59% and mortality rate of 3-12% [3]. There is limited information on the cardiopulmonary adaptations after pneumonectomy in dogs and cats. Reported post-operative complications of pneumonectomy include; acute pulmonary insufficiency, cardiac and gastrointestinal complications [4]. Crawford et al., documented four cats with chronic pyothorax which underwent pneumonectomy and all cats survived to discharge with excellent quality of life on long term follow up [5]. Majeski et al., reported 94% of dogs and 86% of cats survived to discharge following pneumonectomy [3].

Our experiences with pneumonectomy in HK cats (both right and left sides) have been overwhelmingly positive, with an excelent quality of life achieved following the procedures.

It is unclear if the current increase in the number of cats suffering with severe pyothorax will continue however it is vital that the veterinary community is alert to the potential of this life-threatening disease.

We are fortunate enough to have two Specialist Surgeons, Dr. Nicolas Woodbridge and Dr. Jonathan Speelman leading the Surgery Department here at CityU PAVC. If you would like to refer a case, please do not hesitate to contact us.

[1] Barrs, V.R., & Beatty, J.A.: Feline pyothorax – New insights into an old problem: Part 1. Aetiopathogenesis and diagnostic investigation. Veterinary Journal 2009: 179: 163-170
[2] Walker, A.L., Jang, S.S., Hirsh, D.C.: Bacterial associated with pyothorax of dogs and cats: 98 cases (1989-1998). Journal of the American Veterinary Medicine Association 2000: 316 (2): 359-363
[3] Majeski, S.A., Steffey., M.A., Mayhew, P.D., et al: Postoperative respiratory function and survival after pneumonectomy in dogs and cats. Veterinary Surgery 2016: 45:775-781
[4] Liptak, J.M., Monnet, E., Dernell W.S., et al: Pneumonectomy: four case studies and a comparative review. J Small Animal Practice 2004: 45:441-447
[5] Crawford, A.H., Halfacree, Z.K., Lee, K.C. et al: Clinical outcome following pneumonectomy for management of chronic pyothorax in four cats. J Feline Med Surg 2011: 13:762-767