Diaphragmatic Support of a Thoracic Wall Defect in a Dog

Introduction

Repairing thoracic wall defects is a common problem encountered when cancerous or suspect masses are removed from the thoracic wall. The main goals in repairing such defects include establishing an airtight seal, stabilizing the thoracic wall, eliminating dead space, and protecting vital organs.^1,2 Several techniques have been described in an effort to achieve these goals. Options have included the use of autogenous grafts and flaps (e.g., latissimus dorsi muscle, rectus abdominis muscle, external abdominal oblique muscle, pericardium), meshes (e.g., small intestinal submucosa extracellular matrix, polypropylene, polytetrafluorethylene), or diaphragmatic advancement. The type of repair used depends on the size and location of the defect and presence of infection. For example, some defects may be too large to use autogenous grafts. Also, diaphragmatic advancement only works for defects between ribs nine and 13, and synthetic meshes are contraindicated in contaminated wounds.^2–5

This report describes a novel approach to repairing a large thoracic wall defect in an English setter in which the dog’s diaphragm was used to close the defect. This technique is different from diaphragmatic advancement, and, to our knowledge, using the diaphragm to repair a body wall defect has not been previously described in the veterinary literature. This may prove to be an effective alternative method for the repair of caudal thoracic wall defects.

Case Report

A 3-year-old, 26.4-kg, intact male English setter was presented to the Lloyd Veterinary Medical Center at Iowa State University for a recurring mass on the right caudal thorax. The dog had been kicked by a horse approximately 8 months prior to referral and developed a mass-like swelling in the right caudal thoracic region. Due to suspicion of potential abscess, the referring veterinarian initially treated the dog with amoxicillin/clavulanic acid^a (9.6 mg/kg q 12 hours) and enrofloxacin^b (unknown dosage). The swelling had apparently resolved with this treatment. Three months after initial therapy, the swelling returned, and another 4 weeks of amoxicillin/clavulanic acid (14.4 mg/kg per os [PO] q 12 hours) and enrofloxacin (5.2 mg/kg PO) were prescribed. The swelling did not resolve but instead persisted for 4 months after the second round of antibiotic therapy was finished. At that point, surgical exploration of the swelling was performed. A large amount of purulent material was found, and the wound was flushed with diluted iodine. No foreign body was identified at the time of surgery. A swab of the wound was submitted for culture and yielded no microbial growth. The swelling returned 5 weeks after surgery. The owner was concerned, because the swelling had grown in size much more quickly in comparison to the other reoccurrence.

The dog was presented to the Lloyd Veterinary Medical Center soft tissue surgery service on June 9, 2008, for further evaluation of the swelling. This date was approximately 8 months from the original onset of the mass. On physical examination, an approximately 8 cm-diameter mass was palpated in the right caudal thoracic area. The mass was firm except for an approximately 2-cm, soft region in the center. The mass was subcutaneous in nature and firmly adhered to the body wall. The dog had been slightly depressed and anorexic for the 24 hours preceding presentation. The remainder of the physical examination was unremarkable. A complete blood count and serum biochemical analysis were performed on the day of presentation. No abnormalities were noted other than a slight decrease in alanine aminotransferase (23 IU/L, reference range 24 to 105 IU/L). A computed tomography (CT) scan revealed a mass that measured 14 cm long, 14 cm wide, and 7 cm thick. The mass did not appear to invade the thoracic cavity or the directly underlying ribs, but the mass was intimately associated with ribs 10 through 13. Additionally, the external abdominal oblique muscles and musculature between the 11th and 13th ribs were involved. The dog was scheduled for surgical removal of the mass.

Differential diagnoses included abscess, granulomatous disease, and neoplasia. The thoracic cavity was included in the CT, and no lesions or pleural effusion were observed in the thorax, suggestive of metastatic disease.

Preoperatively, the dog received hydromorphone^c (0.1 mg/kg intramuscularly [IM]) and acepromazine^d (0.01 mg/kg IM). Thiopental^e (7.7 mg/kg intravenously [IV]) and lidocaine^f (2 mg/kg IV) were used for induction. Anesthesia was maintained with isoflurane.^g Lactated Ringer’s solution^h was administered throughout surgery, and cefazolinⁱ (22.3 mg/kg IV) was administered every 2 hours throughout surgery.

The dog was placed in left lateral recumbency, and the area around the mass was prepared for surgery. An elliptical incision was made around the mass, and it was carefully removed by blunt and sharp dissection. Hemorrhage was controlled by electrocautery and hemostats. The mass was strongly adhered to the 11th and 12th ribs, and the musculature surrounding the ribs appeared to be necrotic. The 11th and 12th ribs were resected with double-action bone cutters. The dog was placed on a circular rebreathing system at induction and was subsequently ventilated with a respirator in preparation for entry into the thoracic cavity. The mass contained purulent material, and a small foreign body (approximately 8 × 2 mm) suspected to be plant material was identified. Once the mass and foreign body were removed, the area was copiously lavaged with sterile saline. The mass was submitted for histopathology, and swabs of the mass and thoracic wall were submitted for culture. A 24-French chest tube was placed between the seventh and eighth ribs on the right side of the thoracic cavity.

The removal of the mass resulted in a large defect in the caudal thoracic wall [Figure 1]. The diaphragm was used to repair this defect. First, multiple, preplaced stay sutures were used to help approximate the pars costalis of the diaphragm to the edges of the defect. Where possible, sutures were placed cranial to the 10th rib and caudal to the 13th rib to assist with support of the defect. Using horizontal mattress stay sutures, the pars costalis was permanently secured to the thoracic wall defect with 0 Prolene^j [Figures 2, 3]. Although moderate tension was on the diaphragm, this strategy provided an airtight seal for the thoracic cavity and structural support for the thoracic wall defect. No obvious communication into the abdomen was identified at the repair site, and subsequently no omentum was used in the repair of the defect. A substantial amount of dead space was appreciated directly over the reconstructed defect as a direct result of resecting all of the musculature associated with the mass. This prompted the placement of a Jackson-Pratt^k closed suction drain in the area of the rib resection to help prevent seroma formation. A simple continuous intradermal layer was placed using 3–0 Monocryl.^l The skin was closed with 3–0 nylon^m in a cruciate pattern.

For analgesia at the conclusion of surgery, approximately 1.5 mL of bupivacaineⁿ was used in a line block fashion along the incision. Immediately postoperatively, the dog was treated with hydromorphone^c (0.05 mg/kg IV), and a continuous-rate infusion (CRI) of fentanyl^o (4 μg/kg per hour) was initiated for ongoing pain management. The dog was also treated with metronidazole^p (7.6 mg/kg IV q 12 hours) and ampicillin^q (19 mg/kg IV q 8 hours). The chest tube was removed approximately 6 hours after surgery once negative pressure was achieved and maintained. For 7 hours postoperatively, oxygen saturation as measured by pulse oximetry (SpO₂) (range 95% to 98%) was monitored and remained within an acceptable range (95% to 100%). The closed suction drain had only a small amount of fluid (9.6 mL) removed that night, over an approximate 12-hour period.

On the first day postoperatively, the dog was switched to hydromorphone (0.08 mg/kg IV q 4 hours). The CRI was discontinued, and the IV hydromorphone was instead administered for pain. Two days postsurgically, the dog’s appetite had returned. All IV medications were discontinued, and the dog was instead prescribed tramadol^r (2 mg/kg q 8 hours for 10 days), amoxicillin/clavulanic acid^a (14 mg/kg q 12 hours for 10 days), and metronidazole^p (9.5 mg/kg q 12 hours for 14 days). By 4 days postoperatively, the closed suction drain was removed, as fluid production was minimal. The dog was discharged 9 days after surgery. (Discharge could have been earlier, but the owner was unable to pick up the dog until then.)

Histopathological examination of the mass revealed a small, clear foreign body. A diagnosis of focal, chronic, pyogranulomatous, and fibrosing panniculitis and myositis was made. The culture from the mass and thoracic wall grew Fusobacterium spp. and two strains of strictly anaerobic gram-positive rods that were similar to Actinomyces spp. These organisms were susceptible to the antibiotics that the dog was prescribed (i.e., amoxicillin/clavulanic acid^a and metronidazole^p), and no changes to the antibiotic regimen were made.

Follow-up calls to the owner revealed that the dog’s exercise level and attitude were back to normal, and the mass had not returned. The dog competed in a field trial approximately 2.5 months postoperatively, reportedly running non-stop for 30 minutes with no respiratory complications. At the time of this writing (16 months since discharge from the hospital), the dog’s attitude and athletic ability had returned to levels seen before development of the mass.

Discussion

This case report describes a unique approach to repairing a large defect in the thoracic wall of a dog, created as a result of a radical mass excision involving resection of the 11th and 12th ribs. The dog’s diaphragm was used to repair the defect and support the thoracic wall. This procedure allowed for an airtight closure of the thoracic cavity, providing physical support and a good cosmetic appearance without negatively affecting the dog’s athletic performance. Histopathology revealed the mass to be a foreign body abscess with significant necrosis and myositis.

Several criteria need to be kept in mind when repairing a large thoracic wall defect. These include an air-tight seal for the thoracic cavity, protection of the thoracic organs, rigidity and support of the thoracic wall, and elimination of dead space.^1,2,5 Numerous methods and materials have been described for the repair of thoracic wall defects. Unfortunately, no one method is appropriate for repair of all thoracic wall defects. The most common techniques employ the use of autogenous tissues, small intestinal submucosa (SIS) extracellular matrix, and polypropylene mesh (PPM). Other techniques utilize sheep dermal collagen, polytetrafluoroethylene mesh (Gore-Tex), polyglycolic acid (Dexon), chemically cross-linked bovine pericardium (Perigard), polyvinyl sponge (Ivalon), regenerated cellulose fabrics (Fortisan), nylon, silicon polymers, carbon fiber, polyester mesh (Dacron), and polyglactin (Vicryl).^1,2,5–7

Autogenous grafts have the benefit of originating from the animal’s own body, thus eliminating the complication of rejection of foreign material. Many types of autogenous tissues have been used as grafts and flaps in the past. These include pedicle grafts, omentum, peritoneum, rectus fascia lata, latissimus dorsi muscle, rectus abdominis muscle, external abdominal oblique muscle, pericardium, bone, and myocutaneous flaps.^2,3,8,9 Based on the substantial resection performed in this case, it was determined that repair of the defect by use of a graft may have had a higher incidence of complications and morbidity compared to our described technique. A flap technique, such as the use of latissimus dorsi muscle as described by Halfacree et al. (2007), may have been a good alternative since the muscle extends caudally to the 13th rib.⁹ Another procedure that falls into the autogenous category is diaphragmatic advancement. For defects involving the ninth to 13th ribs, the diaphragm can be moved cranially and sutured to the intercostal muscles.^2,3 Diaphragmatic advancement is useful in situations where the caudal-most ribs need to be resected and the diaphragm has to be sectioned as part of an abdominal wall resection. The diaphragm is then resutured in a more cranial position. This diaphragm advancement technique should not be confused with ours, which involved the reconstruction of a caudal thoracic wall defect with the diaphragm. In our situation, resecting the diaphragm from the body wall would have been difficult, and we would have not addressed the defect.⁸

Small intestinal submucosa extracellular matrix meshes are made of acellular collagen.^5,10 One of the properties of collagen, making it a good choice for meshes, is that it is structurally conserved between species; therefore, rejections are not expected.¹⁰ Site-specific tissue (such as organized fibrous connective tissue, muscle, adipose, and bone) is formed when SIS mesh is used.^5,7 Arteries and veins that form in the new growth are also very similar to the native structure.¹⁰ Resistance to infection is another useful property of SIS. Rapid capillary penetration, its relatively quick degradation, and the presence of a small peptide with antibacterial activity all contribute to the SIS’s ability to resist infection.^5,10 Using SIS mesh also results in minimal adhesion formation, as SIS can adapt to normal wound contraction.^5,10 This is important in maintaining lung function. One disadvantage to using SIS mesh in a thoracic wall defect is the perforations, making the formation of an airtight seal difficult. A second disadvantage is its thin structure, which does not lend much support to the thoracic wall or protection to the underlying organs. In our dog’s case, the lack of surrounding soft tissue to help form a seal and protective barrier made the SIS mesh undesirable.

Polypropylene mesh is another widely used material to repair body wall defects. It is easy to handle and can be cut to fit the size of the defect.³ Polypropylene mesh has a low permeability to liquid and gas and can be easily sterilized, helping reduce the risk of infection.^2,3 While PPM will support a rapid ingrowth of vascularized tissue, scar tissue forms instead of site-specific tissue.^2,7 Polypropylene mesh does not contract with wound healing, and problems can be seen with wrinkling of the mesh, leading to irritation and an increased risk of infection. The encapsulated scar tissue that forms around the nonabsorbable mesh also increases the risk of infection.¹⁰ Our surgical site was assumed to be contaminated, so we did not want to use foreign material for fear of an increased chance of infection. Similar to SIS, PPM is thin and has perforations, making it difficult to provide support, protect underlying organs, and obtain an airtight seal. For these reasons, the decision was made not to use PPM to repair the defect in the dog of this report.

The technique chosen for this case (using the diaphragm to repair and support the thoracic wall defect) has several advantages over the other techniques and materials listed. The dog’s own tissue was used, so the risk of rejection was eliminated. The diaphragm was already a healthy, well-vascularized tissue. The defect was immediately repaired with a fully intact tissue that formed an airtight seal of the thoracic cavity. The diaphragm muscle was also thicker than the meshes that could have been used, leading to an increased protection of underlying organs. Eliminating the need for synthetic material is anticipated to decrease the likelihood of adhesions or irritation developing in surrounding tissues and organs.

Possible complications are associated with this technique. The CT scan indicated an intimate association with the 13th rib, and the surgeons chose to spare the 13th rib based on their gross assessment of the rib and lack of obvious necrotic tissue associated with this rib. This decision could have potentially resulted in contaminated tissue being left in the surgical field and perhaps recurrence of the mass. Further, repositioning the diaphragm in this procedure resulted in a decreased thoracic cavity space. This could decrease the ability of the lungs to fully inflate and the animal’s ability to adequately oxygenate. Similar concerns have been expressed with the diaphragm advancement technique. To address this issue when using the diaphragm advancement technique, the caudal lung lobe is sometimes removed.³ The dog of this report was able to adequately oxygenate following surgery (as determined by serial SpO₂), and his athletic ability did not seem compromised according to follow-up conversations with the owner. No change in the respiratory pattern or effort during the dog’s recovery was noted. Two months after surgery, this dog was competing in field trials with no signs of decreased athletic ability compared to his condition before the mass appeared. More cases are needed to fully evaluate the impact of this procedure on oxygenating and future athletic ability.

Conclusion

In summary, the use of the diaphragm to support and repair a caudal thoracic wall defect appears to be a good option. This procedure likely has been performed in the past by other veterinarians in the field; however, to our knowledge, it has not been reported. To have a full understanding of possible complications with this procedure, more cases need to be performed. Using the diaphragm could prove to be a viable alternative for repair of caudal thoracic wall defects resulting from other conditions such as osteosarcoma, chondrosarcoma, and severe trauma.