Chest Wall Tumors

Chest wall tumors are neoplasms arising from the structural components of the thoracic wall, including the ribs, intercostal muscles, connective tissues, and occasionally the sternum or vertebrae. They can be primary (originating from the chest wall itself) or secondary (metastatic from distant sites or direct invasion from adjacent thoracic structures). Primary chest wall tumors are predominantly malignant, with osteosarcoma and chondrosarcoma being the most common in dogs, while fibrosarcoma and others occur less frequently. In cats, fibrosarcoma and osteosarcoma are also seen, often associated with injection sites. These tumors present significant surgical challenges due to the need for wide resection, chest wall reconstruction, and maintenance of respiratory mechanics. The surgical approach involves en bloc resection of the affected chest wall segment with adequate margins, followed by reconstruction using synthetic mesh, autogenous tissue, or a combination to restore thoracic integrity and prevent paradoxical breathing.

The etiology of chest wall tumors varies by tumor type. Primary tumors often arise spontaneously without a known cause, but certain factors may contribute. For osteosarcoma, genetic predispositions and previous radiation exposure have been implicated. Chondrosarcoma may arise from benign cartilaginous lesions. Fibrosarcoma in cats is strongly associated with injection sites, particularly vaccines and other injectable medications, leading to the term 'injection-site sarcoma'. These tumors are thought to develop from chronic inflammation and fibrosis at the injection site, with malignant transformation of fibroblasts. Other potential causes include trauma, chronic irritation, and environmental carcinogens. Metastatic tumors to the chest wall originate from primary neoplasms elsewhere, such as mammary gland carcinoma, pulmonary carcinoma, or hemangiosarcoma, spreading via hematogenous or lymphatic routes. Direct invasion can occur from lung tumors, mediastinal tumors, or pleural neoplasms.

Chest wall tumors are relatively uncommon in small animal practice. In dogs, primary chest wall tumors account for approximately 5-10% of all primary bone tumors, with osteosarcoma being the most frequent (about 50-60% of primary chest wall tumors), followed by chondrosarcoma (20-30%), and fibrosarcoma (10%). Large and giant breeds, such as Golden Retrievers, Labrador Retrievers, Rottweilers, and Great Danes, are overrepresented for osteosarcoma, typically affecting middle-aged to older dogs (median age 7-9 years). Chondrosarcoma also occurs in similar breeds but may have a slightly older median age. In cats, fibrosarcoma, particularly injection-site sarcoma, is the most common chest wall tumor, with a median age of 8-10 years. There is no strong sex predilection, though some studies suggest a slight male predominance for osteosarcoma. Metastatic chest wall tumors are more common than primary tumors, especially in older animals with known primary malignancies.

The pathophysiology of chest wall tumors involves local invasion and destruction of thoracic wall structures, leading to pain, respiratory compromise, and systemic effects. Primary malignant tumors, such as osteosarcoma and chondrosarcoma, arise from bone and cartilage cells, respectively, and grow expansively, causing cortical bone destruction and periosteal reaction. As the tumor enlarges, it invades adjacent soft tissues, including intercostal muscles, pleura, and sometimes the lung parenchyma. This invasion can lead to pleural effusion, pneumothorax, or direct pulmonary involvement. The tumor may also compress intercostal nerves, causing neuropathic pain. Metastatic spread occurs hematogenously, most commonly to the lungs, but also to other bones and organs. The systemic effects of malignancy, such as cachexia, anemia, and hypercalcemia (particularly with osteosarcoma), can further compromise the patient. In cats with injection-site sarcomas, the tumor is often aggressive, with local recurrence rates high due to incomplete excision and a tendency to infiltrate along fascial planes.

Predisposing factors for chest wall tumors include breed and genetic susceptibility, particularly for osteosarcoma in large and giant breeds. Previous radiation therapy for other conditions can increase the risk of secondary sarcomas. In cats, the administration of vaccines (especially rabies and feline leukemia virus) and other injectable drugs is a well-documented risk factor for injection-site sarcomas, with the risk increasing with the number of injections and the use of adjuvanted vaccines. Chronic inflammation or trauma to the chest wall may also predispose to tumor development, though this is less clearly defined. Age is a factor, as most primary tumors occur in middle-aged to older animals. Additionally, animals with a history of other malignancies may be at higher risk for metastatic chest wall tumors.

Clinical signs of chest wall tumors are often insidious and may include a visible or palpable mass on the thoracic wall, which may be firm, fixed, and sometimes painful. As the tumor grows, it can cause lameness if it involves the forelimb or shoulder region, or respiratory signs such as dyspnea, tachypnea, or coughing if it compresses the lungs or pleura. Pleural effusion can lead to muffled heart and lung sounds. Systemic signs include lethargy, anorexia, weight loss, and fever. In advanced cases, neurological deficits may occur if the tumor invades the spinal canal or brachial plexus. Pain may be elicited on palpation of the mass or the surrounding area. In cats with injection-site sarcomas, the mass may be located at a previous injection site and can be rapidly growing, often with a broad base and infiltrative borders.

Differential diagnoses for chest wall tumors include: 1) Abscess or cellulitis: presents with acute swelling, pain, fever, and leukocytosis; imaging shows soft tissue swelling without bone lysis; responds to antibiotics. 2) Hematoma: history of trauma, fluctuant swelling, resolves over time; ultrasound or CT shows fluid-filled cavity. 3) Rib fracture with callus: history of trauma, focal swelling, radiographs show fracture line and callus formation. 4) Osteomyelitis: chronic infection, draining tracts, bone lysis with periosteal reaction; culture and histopathology confirm. 5) Primary lung tumor with chest wall invasion: respiratory signs, mass in lung parenchyma with extension to chest wall; CT and histopathology differentiate. 6) Pleural neoplasia (mesothelioma): diffuse pleural thickening, effusion, cytology and biopsy. 7) Metastatic neoplasia: known primary tumor, multiple lesions, imaging and biopsy. 8) Cystic lesions (e.g., bronchogenic cyst): well-defined fluid-filled mass, benign course. 9) Granulomatous disease (fungal or mycobacterial): systemic signs, positive serology or culture. 10) Lipoma: soft, mobile, benign; ultrasound or CT shows fat density.

The diagnostic algorithm for chest wall tumors begins with a thorough history and physical examination, including palpation of the mass and assessment of respiratory effort. Thoracic radiographs (three views) are essential to evaluate the mass, identify bone lysis or proliferation, and check for pulmonary metastases. If the mass is suspected to involve the chest wall, advanced imaging with CT is recommended to assess the extent of the tumor, involvement of adjacent structures (lung, mediastinum, spine), and to plan surgical resection. CT is superior to radiography for evaluating bone destruction and soft tissue invasion. Ultrasound can be used to guide fine-needle aspiration (FNA) of the mass for cytology, though histopathology is required for definitive diagnosis. A biopsy (incisional or core needle) should be performed to determine tumor type and grade, which guides treatment and prognosis. If metastatic disease is suspected, abdominal ultrasound and possibly lymph node aspiration are indicated. Preoperative staging includes a complete blood count, serum biochemistry, urinalysis, and thoracic imaging. If the tumor is osteosarcoma, a bone scan may be considered to rule out other skeletal lesions.

Laboratory findings in chest wall tumors are often nonspecific. Complete blood count may reveal anemia of chronic disease, leukocytosis due to inflammation or infection, or thrombocytopenia if there is disseminated intravascular coagulation. Serum biochemistry may show hypercalcemia, particularly in dogs with osteosarcoma, due to paraneoplastic secretion of parathyroid hormone-related protein. Alkaline phosphatase may be elevated in osteosarcoma. Other abnormalities may reflect organ dysfunction if metastases are present. Urinalysis is usually unremarkable. Coagulation panel (PT, aPTT, platelet count) is important for surgical planning, as some tumors may cause a hypercoagulable state. Inflammatory biomarkers such as C-reactive protein (CRP) may be elevated. For cats with injection-site sarcomas, feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) testing may be recommended. Synovial fluid analysis is not typically performed unless there is joint involvement.

Radiography: Thoracic radiographs may show a soft tissue mass with or without bone involvement. Rib tumors often cause osteolysis, periosteal reaction, and pathological fractures. The mass may be extrapleural, with smooth borders and displacement of the pleura. Radiographs are also used to screen for pulmonary metastases. Ultrasonography: Ultrasound can be used to evaluate the internal architecture of the mass, guide FNA, and assess for pleural effusion. It is less useful for bone evaluation. Computed Tomography (CT): CT is the imaging modality of choice for chest wall tumors. It provides detailed three-dimensional information about the extent of the tumor, bone destruction, soft tissue invasion, and involvement of the lung, mediastinum, or spine. CT is essential for surgical planning, as it allows accurate measurement of the tumor and determination of resection margins. Magnetic Resonance Imaging (MRI): MRI is superior for evaluating soft tissue extension, particularly into the spinal canal or brachial plexus, and for assessing bone marrow involvement. It may be used when neurological signs are present. Angiography/Fluoroscopy: These are rarely needed but may be used to assess vascular invasion or for embolization in highly vascular tumors.

Cytology: Fine-needle aspiration of chest wall masses can provide a preliminary diagnosis. Osteosarcoma may show pleomorphic spindle cells with osteoid production, but cytology is often nondiagnostic and cannot differentiate between sarcoma types. Histopathology: A definitive diagnosis requires biopsy. Incisional biopsy (wedge or core needle) is preferred to obtain a representative sample. Histopathological features vary by tumor type. Osteosarcoma shows malignant osteoblasts producing osteoid or bone. Chondrosarcoma is characterized by malignant chondrocytes in a cartilaginous matrix. Fibrosarcoma consists of spindle cells with collagen production. Injection-site sarcomas in cats are often fibrosarcomas with marked inflammation and necrosis. Histopathology also provides tumor grade, which is important for prognosis. Surgical margins should be evaluated for completeness of excision. Special stains (e.g., immunohistochemistry) may be used to differentiate tumor types, such as vimentin for mesenchymal origin.

The primary treatment for chest wall tumors is surgical resection. The goal is en bloc resection of the tumor with wide margins (at least 2-3 cm of normal tissue) to reduce the risk of local recurrence. The surgical approach involves making an elliptical incision around the tumor, extending through the skin, subcutaneous tissue, and muscles. The affected ribs are identified, and the intercostal muscles are incised. The tumor is removed along with the affected ribs and associated soft tissues. If the tumor involves the sternum or vertebrae, a more extensive resection may be required. After resection, chest wall reconstruction is necessary to restore thoracic integrity and prevent paradoxical breathing. Reconstruction options include: 1) Primary closure if the defect is small (<5 cm) and the chest wall is stable. 2) Synthetic mesh (polypropylene or polytetrafluoroethylene) to bridge the defect, often combined with muscle flaps (e.g., latissimus dorsi, external abdominal oblique) or omental pedicle grafts. 3) Autogenous tissue flaps alone for larger defects. The mesh is sutured to the surrounding tissues with non-absorbable sutures (e.g., polypropylene) in a tension-relieving pattern. A thoracostomy tube is placed to evacuate air and fluid postoperatively. Adjuvant therapy: For osteosarcoma, adjuvant chemotherapy (e.g., carboplatin) is recommended to delay metastasis. For chondrosarcoma, surgery alone may be curative if complete excision is achieved. For fibrosarcoma, radiation therapy may be considered if margins are incomplete. In cats with injection-site sarcomas, aggressive surgical resection with wide margins (3-5 cm) is crucial, and radiation therapy may be added to improve local control.

The prognosis for chest wall tumors depends on tumor type, grade, and completeness of excision. For chondrosarcoma, the prognosis is good with complete surgical excision, with median survival times exceeding 3 years. Osteosarcoma has a guarded prognosis due to high metastatic potential; median survival times with surgery and chemotherapy are around 10-12 months, with 1-year survival rates of 40-50%. Fibrosarcoma has a variable prognosis, with local recurrence being a significant issue; median survival times are around 1-2 years. In cats with injection-site sarcomas, the prognosis is poor if incomplete excision, with high recurrence rates; with aggressive surgery and radiation, median survival times can be 2-3 years. Negative prognostic indicators include incomplete margins, high tumor grade, tumor size >5 cm, and presence of metastasis at diagnosis.

Postoperative follow-up is essential to monitor for complications and recurrence. Thoracic radiographs are recommended at 1, 3, 6, and 12 months postoperatively, then every 6 months thereafter to screen for pulmonary metastases. Physical examination should be performed at each visit to assess the surgical site for any signs of recurrence. If a thoracostomy tube was placed, it is typically removed within 24-48 hours postoperatively. Activity restriction is advised for 4-6 weeks to allow healing of the chest wall reconstruction. Pain management is continued as needed. Adjuvant chemotherapy protocols require regular monitoring of blood counts and renal function. For cats with injection-site sarcomas, close monitoring for local recurrence is critical, and any new mass should be biopsied promptly.

Pearls: 1) Always obtain advanced imaging (CT) before surgery to accurately plan resection margins and identify any extension into the thoracic cavity. 2) Use a generous elliptical incision to ensure wide margins; do not compromise on margins to facilitate closure. 3) When reconstructing the chest wall, ensure the mesh is taut to prevent paradoxical breathing, but not so tight that it restricts ventilation. 4) Consider using a muscle flap (e.g., latissimus dorsi) to provide additional soft tissue coverage and vascularity to the mesh. 5) Place a thoracostomy tube before closing the thorax to manage postoperative pneumothorax and effusion. Pitfalls: 1) Inadequate margins leading to local recurrence; always aim for at least 2-3 cm margins. 2) Failure to recognize tumor invasion into the lung or mediastinum, leading to incomplete resection. 3) Closing the chest wall without reconstruction, causing respiratory distress. 4) Not placing a thoracostomy tube, resulting in undetected pneumothorax. 5) Underestimating the need for adjuvant therapy in high-grade tumors.

Perioperative antimicrobial prophylaxis: Cefazolin (22 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antibiotics are not routinely needed unless contamination occurred. Analgesia: Preoperative opioids (e.g., hydromorphone 0.05-0.1 mg/kg IV, or methadone 0.1-0.2 mg/kg IV) and postoperative continuation for 24-48 hours. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) are used for 3-5 days postoperatively, provided renal function is normal. Local anesthesia: Intercostal nerve blocks with bupivacaine (1-2 mg/kg, maximum 2 mg/kg) can provide intraoperative and postoperative analgesia. Constant rate infusion (CRI) of lidocaine (25-50 mcg/kg/min) and ketamine (0.1-0.5 mg/kg/hr) may be used for multimodal analgesia. For chemotherapy in osteosarcoma: Carboplatin (300 mg/m² IV every 3 weeks for 4-6 cycles) is commonly used. Dosage adjustments are made based on neutrophil counts. For cats with injection-site sarcomas, doxorubicin (1 mg/kg IV every 3 weeks) may be used, but its efficacy is limited. Supportive care: Gastroprotectants (e.g., omeprazole 1 mg/kg PO q12h) if NSAIDs are used long-term. Antiemetics (e.g., maropitant 1 mg/kg IV q24h) if chemotherapy is administered.

Several studies have evaluated the outcomes of chest wall tumor resection in dogs and cats. A retrospective study by Liptak et al. (2008) reported that dogs with chondrosarcoma had a median survival time of 3.5 years after surgical resection, while those with osteosarcoma had a median survival of 10 months with surgery and chemotherapy. Another study by Buracco et al. (2011) found that the use of polypropylene mesh for chest wall reconstruction resulted in acceptable complication rates and good functional outcomes. In cats, a study by Martano et al. (2012) demonstrated that aggressive surgical resection with wide margins (3-5 cm) for injection-site sarcomas improved local control, with median disease-free intervals of 16 months when combined with radiation therapy. The ACVS consensus statement on surgical oncology recommends that chest wall tumors be managed with en bloc resection and reconstruction, with adjuvant therapy based on tumor type and grade. Overall, the evidence supports that complete surgical excision is the most important prognostic factor, and that advanced imaging (CT) is essential for surgical planning.