Introduction

• The two most common reported malformations of the chest in kittens are pectus excavatum ("funnel chest") and flat chested kitten syndrome (FCKS). 
• Pectus excavatum (PE) is a congenital malformation of the sternum and costochondral cartilages causing narrowing of the chest ventrodorsally or sternal depression. Chest compression may reduce pulmonary and cardiac function. 
• In FCKS, the ribcage angles sharply at the costochondral junction and the chest is flattened ventrally. In some breeds there is likely to be a genetic basis behind the syndrome: 
  • The chest flattening seen in FCKS may be a final common pathway associated with a number of underlying defects as the outcome for similar levels of flatness seems to be different between breeds. 
• The two conditions may occur concurrently; in Burmese cats FCKS kittens have an increased incidence of PE. 
• Kittens with weak, splayed legs, are often referred to as "swimmers"   . Swimmer kittens can also have flat chests but it is unclear whether this is cause or effect. Swimmers can also have other chest deformities such as PE or relatively normal chest shape. Print off the owner factsheet Flat chested kitten syndrome (FCKS) and pectus excavatum (PE) to give to your client.

Pathogenesis

Etiology

FCKS

• Unknown. 
• Genetic basis is likely in Burmese although pattern of inheritance is complex; possible associations with coat color have been made. 
• Several kittens in a litter may be affected, rarely all kittens are affected although to different degrees. 
• As this is a syndrome other etiologies are possible and some may be associated with in utero events.

PE

• Unknown occurrence, seems to be random and sporadic but there does appear to be a genetic background.
• Congenital.
• Has been associated with FCKS in Burmese. 

Predisposing factors

FCKS

• The expression of FCKS appears complex and it is unclear why certain kittens or litters develop FCKS and others do not. 
• Events during pregnancy may influence expression and would include nutrition, increased levels of stress, excessive heat during pregnancy - suggestions that pregnant queens using radiator beds frequently are at higher risk.

PE

• Suggested causes of pectus excavatum include congenital predisposition, abnormal intrauterine pressure, abnormal ligament development (ie shortened central diaphragmatic tendon or thickened substernal ligament), deficient muscular components derived from the septum transversum of the diaphragm, congenital thickening of the musculature of the cranial portion of the diaphragm, thickening of substernal ligament, abnormal osteogenesis and chondrogenesis, arrested sternal development. 
• Pectus has also been reported associated with mucopolysaccharidosis (VII) Storage disease in a cat.
• May also be secondary to upper respiratory obstruction (as a result of negative intrathoracic pressure), environmental factors, and posturing difficulties. 

Pathophysiology

FCKS

• Unknown but FCKS can occur rapidly and sometimes also resolve quickly.
• Weakness of costochondral muscles and diaphragm has been postulated.
• Reduced lung capacity due to reduced thoracic volume ± reduced thoracic muscle strength.
• Heart will adopt an abnormal position that may affect cardiac function and/or thoracic blood flow. 

PE

• Role of negative intrathoracic pressure supported by the over-representation of pectus excavatum in brachycephalic breeds. 

Timecourse

FCKS

• Usually apparent within first 10 days of life. 
• Flat chests in mild to moderately affected animals will often resolve spontaneously, especially if nutritional intake is adequate, sometimes to the point where it is hard to detect the abnormality in the adult: 
  • If they survive, even severe cases will improve over time although kyphosis is unchanged.

PE

• Age at presentation will depend on severity of abnormality and clinical signs associated with it. 
• Mild cases are often incidental findings on thoracic radiography. 
• Pectus excavatum will not resolve spontaneous and may progress: 
  • Secondary pulmonary hypertension Pulmonary arterial hypertension (PHT) can develop with signs progressing relatively rapidly.

Diagnosis

Treatment

Outcomes