Associate Professor (Surgical Oncology), Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
An incisional biopsy is indicated to determine the tumor type prior to chest wall resection. This can be done as a wedge incisional biopsy or with a Tru-Cut biopsy (needle core biopsy) technique. The advantage of the wedge biopsy is that a larger biopsy can be obtained. The advantage of the Tru-Cut biopsy technique is that it is a faster procedure that may not require general anesthesia with less disruption of the tissue planes. Regardless of technique, the biopsy should be planned so that the entire biopsy tract can be easily removed at the time of definitive surgery. The biopsy should be taken centrally over the tumor with only one incision. There should be minimal disruption of tissue planes deep and lateral to the biopsy incision.
Three-view thoracic radiographs are a good starting point to evaluate a mass over the thoracic wall. This will serve to determine the intrathoracic extent of the lesion and to evaluate for pulmonary metastasis. With chondrosarcomas in particular, the palpable mass on the exterior of the thorax may be a small percentage of the total mass. It may not be possible to correctly determine the origin or extent of disease based on radiography alone. If the tumor is of rib origin, radiographs may indicate the degree of bone lysis or production. This has not been found to help distinguish between OSA and CSA (Liptak). Computed tomography is the imaging modality of choice to evaluate chest wall tumors. It allows the accurate evaluation of the origin of the tumor and the other structures that are involved in the thorax. The length of rib involvement and extent of soft tissue involvement can also be accurately assessed for surgical planning. The lungs can also be evaluated for evidence of metastatic disease with the CT.
Nuclear scintigraphy should be considered in cases of osteosarcoma to determine if there is evidence of metastatic disease or if the rib mass is a metastatic site. If nuclear scintigraphy is not available, long bone survey radiography should be considered as an alternative method to evaluate for other bone lesions. Abdominal ultrasound is recommended for staging in certain tumor types. This test should be performed in cases of known hemangiosarcoma or when a pleural effusion accompanies the clinical signs associated with the thoracic wall mass.
Description of Surgical Procedures
I. Rib Tumors
Rib tumors are usually sarcomas and aggressive resection is critical to successful treatment. Completeness of surgical excision has been shown to have a significant effect on survival and disease-free interval in dogs with chest wall tumors (Ehrhart; Liptak). The planned margins of resection should include one rib cranial and one rib caudal to the lesion (Liptak; Baines). Dorsal and ventral margins should be 3 cm along the ribs (Liptak; Baines). One school of thought is that the entire rib should be removed by disarticulating the rib with the vertebra and sternum. However, this does not appear to be necessary if adequate margins from the tumor are removed dorsally and ventrally. The reported maximum number of ribs that can be resected is 6 (Slatter; Liptak; Pirkey-Ehrhart). Anecdotally, 7 ribs have been successfully removed (Ehrhart; Withrow, personal communication). However, the removal of 7 or 8 ribs increases the risk of causing severe respiratory compromise and dysfunction. The location of the tumor may determine the ability of the surgeon to remove more than 6 ribs. This is better tolerated in the caudal thorax, where diaphragmatic advancement is possible. In the cranial thorax, the creation of a flail chest with the removal of more than 6 ribs may cause ventilatory failure. Even the removal of 5 ribs can cause respiratory compromise in some patients in the cranial thorax (Ehrhart, personal communication). In general, skin is not resected en bloc with tumors arising from the rib. This is contrary to a recent paper that utilized en bloc resection and a myocutaneous flap for reconstruction of primary rib chondrosarcoma in 5 dogs (Halfacree). There may be exceptions to this if there is extensive invasion in the soft tissues lateral to the rib seen on CT. The common rib tumors such as OSA and CSA tend to remain somewhat encapsulated within the periosteum. This concept is similar to the resection of distal radial osteosarcomas that spare surrounding soft tissues in a limb spare procedure. The overlying muscle also serves as another plane that is a barrier to extension of the tumor into the subcutaneous tissue and skin. The three-dimensional imaging should serve as a guide for whether or not skin resection is necessary. Another rule of thumb is to assess the mobility of the skin over the mass. If the skin is mobile over the mass, the need for resection is less likely. If a biopsy is performed, the biopsy tract will need to be resected with the tumor. The latissimus dorsi muscle can also be spared if appropriate based on imaging and its mobility. The latissimus dorsi muscle is an important source of autogenous tissue for reconstruction of the defect. For cranial rib resections, care must be taken to avoid the brachial plexus. Most importantly, the origin of the nerve roots that make up the radial nerve can be found coursing around the first rib. Resection including the 1st rib has been reported to be successful with no impairment of limb function (Liptak).
II. Invasive Soft Tissue Masses of the Tissues Lateral to the Ribs
In general, these tumors are invasive soft tissue sarcomas. They should be removed using the same principles as with sarcoma removal anywhere on the body. As with rib tumors, these tumors require three-dimensional imaging for appropriate presurgical planning. On three-dimensional imaging, these masses would involve the soft tissues from the subcutaneous tissue and skin medially to the chest wall. If there is not a fascial plane between the tumor and the chest wall, these tumors require a true en bloc resection from skin through the chest wall.
Although it is rarely reported in veterinary medicine (Munday; Ferreira), lung or chest wall tumors may penetrate the chest wall at the level of the brachial plexus. Such tumors may require lung and chest wall resection combined with forequarter amputation. The same principles of en bloc resection are followed.
III. Reconstruction After Thoracic Wall Resection
There are several options for reconstruction of the thoracic wall defect after rib resection or true en bloc resection. These options include the use of prosthetic mesh implants such as Marlex, Gore-Tex, and Vicryl. Marlex is the most commonly reported implant used in veterinary and human thoracic wall reconstruction techniques. Local tissue flaps have also been reported either alone or in combination with prosthetic mesh. The most commonly used local tissue is a latissimus dorsi flap, either alone or as a myocutaneous flap (Liptak; Halfacree; Raffoul; Mansour).
For tumors of the caudal chest wall, diaphragmatic advancement can be used to decrease the size of the thoracic defect to be closed or completely close the defect. This is performed by detaching the diaphragm from its attachments laterally and ventrally to allow mobilization of the diaphragm. The diaphragm is then advanced and sutured to the remaining chest wall to allow for an airtight, rigid fixation. A partial or complete caudal lung lobectomy may have to be performed concurrently to prevent atelectasis of the affected hemithorax and subsequent V/Q mismatch (Slatter). This is best performed with a TA stapling device. The amount of the lung lobe resected depends on the degree of diaphragmatic advancement.
Liptak et al. recently compared autogenous, prosthetic and composite methods of chest wall reconstruction. They found that the complication rate was higher for prosthetic and composite techniques compared with autogenous reconstruction, with complications being 12.8x more likely to occur with prosthetic techniques and 3.0x more likely to occur with composite techniques compared with autogenous tissue reconstruction (Liptak). The current recommendation for chest wall reconstruction is to use a latissimus dorsi flap when possible and to add Marlex mesh if necessary to augment the repair.
Masses of the sternum can be approached in much the same way as masses in other areas of the thoracic wall. Incisional biopsy for tissue diagnosis and three-dimensional imaging will guide preoperative planning. The decision to include skin in the resection will be based on the same logic as with rib tumors. The overlying pectoral muscle may be resected with the tumor. The amount of sternum resected will depend on the amount of bone involved on CT imaging. Three-centimeter margins should be taken cranial and caudal to the tumor. The ribs are cut 3 cm from the sternal mass. The sternum is cut using an oscillating bone saw and the ribs are cut using bone cutters. The segment of the chest wall is removed en bloc.
The defect is reconstructed using Marlex mesh, a Marlex mesh PMMA sandwich, heterogenous bone and mesh, spinal plates or an autogenous muscle flap. The pectoral muscle can be used in the reconstruction if it has not been removed with the en bloc resection. The amount of rigidity required depends on the size and location of the defect. If many ribs are removed and/or if the manubrium is resected, an effort should be made to restore rigidity to the reconstruction. This can be done with a Marlex mesh-methylmethacrylate sandwich and autogenous tissue. There was an increased incidence of early complications seen in sternal resections and reconstruction in dogs in a recent retrospective study (Liptak). This may indicate that this location is less forgiving in terms of reconstruction techniques.
Patients require intensive care post operatively for pain management and to monitor for respiratory dysfunction. These patients require 24-h care in an intensive care unit. Pain should be managed using opioid analgesics in combination with NSAIDs (if not contraindicated). Ketamine and lidocaine CRIs can also be considered. A chest tube should be placed intraoperatively to monitor for and manage pleural effusion, should it occur. Nasal oxygen will be helpful in some cases because chest wall resection will create some degree of hypoventilation postoperatively due to pain and due the change in the conformation of the chest wall. Blood gas analysis should be part of the postoperative monitoring plan to evaluate for potential respiratory complications such as hypoventilation, V/Q mismatch and aspiration pneumonia. An indwelling urinary catheter should be considered to allow strict rest of the patient for 12–24 h and to allow the clinician to monitor urine output. All patients should be on intravenous fluids until they are eating and drinking. In a large thoracic resection, fluid loss from hemorrhage and evaporative losses intraoperatively can be substantial. Careful monitoring of the patient's hydration status in the postoperative period is important.
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