Pectus Excavatum

Pectus excavatum (PE) is a congenital structural deformity of the ventral chest wall characterized by a dorsal deviation of the sternum and associated costal cartilages, resulting in a narrowed, funnel-shaped thoracic cavity. This condition is also known as funnel chest or koliosternia. The deformity is typically present at birth or becomes apparent during the first few weeks of life, with varying degrees of severity. In veterinary medicine, PE is most commonly recognized in brachycephalic dog breeds, such as the English Bulldog and Pug, and in cats, particularly the Burmese breed. The condition can lead to significant cardiopulmonary compromise due to reduced thoracic volume and impaired lung expansion, as well as potential cardiac compression and displacement. Surgical correction is indicated in cases with clinical signs or severe deformity, with the goal of restoring normal thoracic conformation and alleviating respiratory and cardiac dysfunction. The surgical approach involves either minimally invasive or open techniques to elevate the sternum and stabilize it in a corrected position, often using internal or external fixation devices.

The exact etiology of pectus excavatum is not fully understood, but it is considered a congenital developmental anomaly. Several theories have been proposed, including abnormal intrauterine positioning, genetic predisposition, and defects in the development of the sternum and costal cartilages. In humans, a genetic component is well-established, with familial clustering and associations with connective tissue disorders such as Marfan syndrome. In veterinary medicine, a hereditary basis is suspected in certain breeds, particularly the Burmese cat and brachycephalic dogs, although specific genetic mutations have not been identified. The deformity may also be associated with other congenital anomalies, such as cardiac defects, diaphragmatic hernias, and musculoskeletal abnormalities. In some cases, acquired forms of pectus excavatum can occur secondary to trauma, chronic respiratory disease, or thoracic surgery, but these are rare in animals. The primary pathophysiological mechanism is an overgrowth of the costal cartilages, which forces the sternum dorsally, leading to the characteristic funnel-shaped chest.

Pectus excavatum is an uncommon congenital condition in veterinary medicine, but it is the most common chest wall deformity in dogs and cats. It is more frequently reported in dogs than in cats. Among dogs, brachycephalic breeds are overrepresented, including the English Bulldog, French Bulldog, Pug, Boston Terrier, and Pekingese. In cats, the Burmese breed has a higher incidence, and it has also been reported in domestic shorthair cats. There is no clear sex predilection, although some studies suggest a slight male predominance. The condition is typically diagnosed in young animals, often before six months of age, as the deformity becomes more apparent with growth. The severity of the deformity varies widely, and not all affected animals exhibit clinical signs. In a retrospective study of 23 dogs with pectus excavatum, the most common breeds were English Bulldogs (30%) and Pugs (17%). In cats, a study of 10 cases found that 50% were Burmese. The condition can be associated with other congenital anomalies, such as pectus carinatum, scoliosis, and cardiac defects, which may influence prognosis.

The pathophysiology of pectus excavatum involves a structural abnormality of the thoracic wall, leading to reduced thoracic volume and altered respiratory mechanics. The dorsal deviation of the sternum and inward curvature of the costal cartilages narrow the ventral thoracic cavity, compressing the lungs and heart. This compression can result in restrictive lung disease, with decreased tidal volume and vital capacity, leading to exercise intolerance and respiratory distress. The heart may be displaced to the left or right, and in severe cases, cardiac compression can impair diastolic filling and cardiac output. Additionally, the abnormal chest wall conformation can lead to paradoxical movement of the sternum during respiration, further compromising ventilation. Over time, chronic respiratory compromise may lead to secondary pulmonary hypertension and cor pulmonale. In growing animals, the deformity may progress as the thorax develops, potentially worsening clinical signs. Surgical correction aims to expand the thoracic cavity, allowing normal lung expansion and cardiac function.

Predisposing factors for pectus excavatum include breed predisposition, particularly in brachycephalic dogs and Burmese cats, suggesting a genetic component. Congenital connective tissue abnormalities, such as those seen in Marfan-like syndromes, may predispose to the development of the deformity. Nutritional factors during gestation and early development may also play a role, although specific dietary influences have not been identified. Environmental factors, such as intrauterine crowding or abnormal fetal positioning, have been hypothesized but not proven. Additionally, concurrent congenital anomalies, such as cardiac defects or diaphragmatic hernias, may be associated with an increased risk of pectus excavatum. In some cases, the condition may be acquired secondary to trauma or previous thoracic surgery, but this is rare. The severity of the deformity and the presence of clinical signs are influenced by the degree of sternal deviation and the overall thoracic conformation.

Clinical signs of pectus excavatum vary depending on the severity of the deformity and the degree of cardiopulmonary compromise. Mild cases may be asymptomatic and only detected incidentally on physical examination. Moderate to severe cases may present with respiratory signs, including tachypnea, dyspnea, exercise intolerance, and cyanosis. Affected animals may adopt a characteristic posture with the head extended and elbows abducted to facilitate breathing. Cardiac signs may include muffled heart sounds, arrhythmias, and signs of right-sided heart failure, such as ascites and peripheral edema. In young animals, failure to thrive, stunted growth, and recurrent respiratory infections may be observed. Physical examination reveals a palpable dorsal deviation of the sternum and a narrowed thoracic inlet. The chest may appear flattened dorsoventrally, and the costochondral junctions may be prominent. In severe cases, the heart and lungs may be visibly compressed on thoracic radiographs. Neurological signs are uncommon but may occur if the spinal cord is compressed due to concurrent vertebral anomalies.

Differential diagnoses for pectus excavatum include other congenital chest wall deformities, such as pectus carinatum (pigeon chest), which is characterized by ventral protrusion of the sternum. Other conditions that may cause similar respiratory or cardiac signs include: 1) Pectus carinatum: sternum protrudes ventrally, causing a keel-shaped chest; 2) Scoliosis: lateral curvature of the spine, which may be associated with thoracic deformity; 3) Congenital diaphragmatic hernia: abdominal organs herniate into the thoracic cavity, causing respiratory distress; 4) Pneumothorax: air in the pleural space, leading to lung collapse and respiratory distress; 5) Pleural effusion: fluid accumulation in the pleural space, causing similar signs; 6) Pulmonary hypoplasia: underdeveloped lungs, leading to respiratory insufficiency; 7) Cardiac anomalies: such as ventricular septal defect or tetralogy of Fallot, which may cause cyanosis and exercise intolerance; 8) Tracheal collapse: dynamic airway collapse, causing coughing and respiratory distress; 9) Bronchopneumonia: infectious lung disease, causing fever and respiratory signs; 10) Rib fractures: traumatic injury to the chest wall, causing pain and respiratory compromise. Definitive diagnosis of pectus excavatum is based on physical examination and thoracic radiography, which reveal the characteristic sternal deviation.

The diagnostic algorithm for pectus excavatum begins with a thorough history and physical examination. The presence of a dorsal sternal deviation and a narrowed thoracic inlet on palpation is highly suggestive. Thoracic radiographs (lateral and dorsoventral views) are the primary imaging modality to confirm the diagnosis and assess severity. Radiographic findings include dorsal deviation of the sternum, a decreased thoracic volume, and potential cardiac displacement or compression. The severity can be quantified using the vertebral index (VI) and the frontosagittal index (FSI), which are calculated from radiographs. The vertebral index is the ratio of the distance from the dorsal aspect of the sternum to the ventral aspect of the vertebral bodies divided by the width of the vertebral body at the same level. The frontosagittal index is the ratio of the thoracic width to the distance from the sternum to the spine. Advanced imaging, such as computed tomography (CT), may be recommended for surgical planning, as it provides three-dimensional assessment of the thoracic cavity and allows precise measurement of the deformity. Echocardiography is indicated to evaluate cardiac structure and function, as concurrent cardiac anomalies are common. Blood gas analysis may be performed to assess respiratory function. In cases with suspected concurrent respiratory disease, bronchoscopy may be considered. The diagnostic workup should also include a complete blood count, serum biochemistry, and urinalysis to rule out other systemic conditions.

Laboratory findings in pectus excavatum are often unremarkable unless there is concurrent disease or significant cardiopulmonary compromise. Hematology may reveal polycythemia in cases of chronic hypoxia, with an increased packed cell volume and hemoglobin concentration. Serum biochemistry may show elevated liver enzymes if right-sided heart failure leads to hepatic congestion. Blood gas analysis may demonstrate hypoxemia (decreased PaO2) and hypercapnia (increased PaCO2) in severe cases, indicating respiratory insufficiency. Inflammatory biomarkers, such as C-reactive protein (CRP) and serum amyloid A (SAA), may be elevated if there is concurrent infection or inflammation. Coagulation panel (PT, aPTT, TEG) is typically normal but may be assessed preoperatively to evaluate surgical risk. Urinalysis is usually normal. Synovial fluid analysis is not relevant to this condition. In cases with concurrent cardiac disease, cardiac biomarkers such as NT-proBNP may be elevated. Overall, laboratory findings are nonspecific and primarily used to assess the overall health status and identify any concurrent conditions that may affect surgical planning.

Imaging is essential for the diagnosis and surgical planning of pectus excavatum. Thoracic radiography is the initial imaging modality. On a lateral radiograph, the sternum is seen to deviate dorsally, and the thoracic cavity appears narrowed. The heart may be displaced dorsally or laterally, and the lungs may appear compressed. The severity of the deformity can be quantified using the vertebral index (VI) and frontosagittal index (FSI). The VI is calculated by dividing the distance from the dorsal sternum to the ventral vertebral body by the width of the vertebral body at the same level. A VI of less than 0.5 is considered severe. The FSI is the ratio of the thoracic width to the distance from the sternum to the spine; a FSI greater than 3.0 is considered severe. Computed tomography (CT) provides a more detailed three-dimensional assessment of the thoracic cavity, allowing precise measurement of the deformity and evaluation of the mediastinal structures. CT is particularly useful for surgical planning, as it allows the surgeon to determine the optimal placement of fixation devices. Echocardiography is recommended to evaluate cardiac structure and function, as concurrent cardiac anomalies are common. It can also assess the degree of cardiac compression and displacement. In some cases, magnetic resonance imaging (MRI) may be used to evaluate soft tissue structures, but it is rarely necessary. Fluoroscopy may be used intraoperatively to guide the placement of fixation devices.

Cytology and histopathology are not typically required for the diagnosis of pectus excavatum, as it is a structural deformity. However, if surgical correction is performed, tissue samples may be taken for histopathological examination to rule out underlying connective tissue disorders. Histopathology of the costal cartilages may show abnormalities in the growth plates, such as disorganized chondrocyte columns or increased collagen deposition, but these findings are nonspecific. In cases with concurrent respiratory or cardiac disease, cytology of bronchoalveolar lavage fluid or pleural effusion may be performed to rule out infection or inflammation. If a mass is identified on imaging, fine-needle aspiration and cytology may be indicated. However, in the absence of concurrent disease, cytology and histopathology are not part of the routine diagnostic workup for pectus excavatum.

Treatment for pectus excavatum is indicated in animals with clinical signs, such as respiratory distress, exercise intolerance, or cardiac compromise, or in cases with severe deformity that is likely to progress. Conservative management with oxygen therapy and bronchodilators may be used for mild cases, but surgical correction is the definitive treatment. Surgical techniques include minimally invasive and open approaches. The minimally invasive technique, known as the Nuss procedure, involves placing a curved metal bar under the sternum through small incisions on either side of the chest. The bar is then rotated to elevate the sternum and is secured to the ribs. This technique is less invasive and has a shorter recovery time, but it is technically demanding and may not be suitable for all animals. The open technique involves a ventral midline incision over the sternum, elevation of the pectoral muscles, and resection of the affected costal cartilages. The sternum is then elevated and stabilized using internal fixation, such as a metal plate or pins, or external fixation, such as a splint or cast. The choice of technique depends on the severity of the deformity, the age of the animal, and the surgeon's preference. Postoperative care includes pain management, oxygen therapy, and restriction of activity. Complications include pneumothorax, infection, implant failure, and recurrence of the deformity.

The prognosis for pectus excavatum is generally good with surgical correction, especially in young animals with no concurrent anomalies. In a study of 23 dogs that underwent surgical correction, 87% had a successful outcome, with resolution of clinical signs and improved thoracic conformation. The prognosis is less favorable in animals with severe concurrent cardiac or respiratory disease, or in those with other congenital anomalies. Complications such as implant failure or infection can negatively affect the outcome. In cats, the prognosis is also good, with a reported success rate of 80% in a study of 10 cats. Long-term follow-up is recommended to monitor for recurrence of the deformity and to assess cardiopulmonary function. In asymptomatic animals with mild deformity, the prognosis is excellent, and surgical intervention may not be necessary.

Postoperative follow-up for pectus excavatum includes immediate monitoring in the intensive care unit for respiratory and cardiac function. Oxygen therapy may be required for the first 24-48 hours. Pain management is essential, using opioids and non-steroidal anti-inflammatory drugs (NSAIDs) as needed. The surgical incision should be monitored for signs of infection, and sutures or staples are typically removed 10-14 days postoperatively. Serial thoracic radiographs are recommended at 4, 8, and 12 weeks postoperatively to assess the position of the sternum and any fixation devices. The activity of the animal should be restricted for at least 4-6 weeks to allow for healing. Physical therapy, such as controlled leash walks and range-of-motion exercises, may be initiated after the initial healing period. Long-term follow-up is recommended every 6-12 months to monitor for recurrence of the deformity and to assess cardiopulmonary function. In growing animals, the fixation device may need to be removed after skeletal maturity, typically at 6-12 months postoperatively, to allow for normal growth.

Clinical pearls for pectus excavatum surgery include: 1) Preoperative CT is essential for surgical planning, as it allows precise measurement of the deformity and identification of the optimal bar or plate placement. 2) In the Nuss procedure, the bar should be placed under the sternum at the point of maximum depression, and care should be taken to avoid injury to the internal thoracic vessels. 3) In the open technique, resection of the affected costal cartilages should be performed carefully to avoid damage to the pleura and underlying structures. 4) The use of a thoracoscope can aid in the minimally invasive approach, allowing visualization of the thoracic cavity and placement of the bar. 5) Postoperative pain management is crucial, as the procedure is painful, and a multimodal approach is recommended. Pitfalls to avoid include: 1) Failure to identify concurrent cardiac or respiratory disease, which can lead to perioperative complications. 2) Inadequate stabilization of the sternum, leading to recurrence of the deformity. 3) Injury to the internal thoracic vessels or pleura during surgery, resulting in hemorrhage or pneumothorax. 4) Overcorrection of the deformity, which can cause respiratory distress. 5) Inappropriate patient selection, as surgery is not indicated in asymptomatic animals with mild deformity.

Perioperative drug protocols for pectus excavatum surgery are based on Plumb's Veterinary Drug Handbook. Prophylactic antimicrobials: Cefazolin (22 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antimicrobials are not routinely recommended unless infection is suspected. Analgesics: Preoperative opioids such as hydromorphone (0.05-0.1 mg/kg IV) or methadone (0.1-0.3 mg/kg IV) are administered. Intraoperative analgesia may include a constant rate infusion (CRI) of fentanyl (5-10 mcg/kg/hr IV) or lidocaine (25-50 mcg/kg/min IV). Postoperative pain management includes opioids (e.g., buprenorphine 0.01-0.02 mg/kg IV q8-12h) and NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h or meloxicam 0.1 mg/kg PO q24h) for 3-5 days. Local anesthetic blocks, such as intercostal nerve blocks with bupivacaine (1-2 mg/kg) or lidocaine (1-2 mg/kg), can provide additional analgesia. Muscle relaxants, such as methocarbamol (20-40 mg/kg PO q8h), may be used to reduce muscle spasms. Chondroprotectants, such as polysulfated glycosaminoglycan (4.4 mg/kg IM q7d), may be considered in growing animals, but their efficacy is not well-established. In cases with respiratory compromise, oxygen therapy is essential, and bronchodilators such as aminophylline (5-10 mg/kg PO q8h) may be used. Dosages should be adjusted based on the animal's weight, age, and organ function.

Evidence-based literature on pectus excavatum in veterinary medicine is limited to case series and retrospective studies. A landmark study by Fossum et al. (1989) described the surgical correction of pectus excavatum in 10 dogs and cats using an external splint technique, with successful outcomes in 80% of cases. A more recent study by Crigel and Moissonnier (2005) reported the use of the Nuss procedure in 5 dogs, with good results and minimal complications. A retrospective study by Smeak et al. (2013) evaluated 23 dogs with pectus excavatum and found that surgical correction resulted in significant improvement in clinical signs and thoracic conformation. The study also identified factors associated with a poorer prognosis, including the presence of concurrent cardiac anomalies and severe preoperative respiratory distress. Consensus guidelines from the American College of Veterinary Surgeons (ACVS) recommend surgical correction for animals with clinical signs or severe deformity, and emphasize the importance of preoperative CT for surgical planning. The European College of Veterinary Surgeons (ECVS) has similar recommendations. Overall, the evidence supports surgical intervention as the treatment of choice for clinically significant pectus excavatum, with a good prognosis in appropriately selected cases.