Molly is a seven-year-old, female spayed labrador retriever who was referred to Dr Katherine Steele at Brisbane Veterinary Specialist Centre (BVSC) with a large intra-thoracic mass. She had a one-month history of coughing. Physical examination at her primary care veterinarian revealed tachypnoea and thoracic radiographs revealed a large soft tissue opacity mass within the left craniodorsal thorax.
On physical examination at BVSC a 7cm diameter firm mass was palpable along the external lateral thoracic wall just caudal to her shoulder joint. The owner was advised that a primary rib tumour such as osteosarcoma or chondrosarcoma was the most likely diagnosis and computed tomography (CT) was recommended to further define the mass.
Pre- and Post-IV contrast CT study of the thorax was performed and revealed a 10x13cm, irregular, partially mineralised mass encompassing the middle section of ribs 3,4,5 and 6 (Figure 1, over page). The trachea, bronchi and heart were displaced to the right hemithorax and multiple lung lobes were collapsed and atelectic. There was no evidence of pulmonary or thoracic lymph node metastasis.
After discussion with the owner, Molly was taken straight to theatre for wide surgical resection of the mass. A vertical skin incision was made over the mass extending from level of epaxial muscles dorsally and past the costochondral junction ventrally. The subcutaneous and cutaneous trunci muscle were retracted to expose and allow transection of the origin of the latissimus dorsi muscle along the thoracolumbar vertebral fascia. The latissimus dorsi flap was retracted cranially and an intercostal approach to the thorax was made between ribs 7 and 8. Respiration was controlled with intermittent positive pressure ventilation following penetration into the thorax. The mass was palpable within the thorax but was not adhered to any underlying viscera. The mass was removed en-bloc with ribs 2-7, taking 3cm margins along rib ventrally and abutting the epaxial musculature dorsally (Figures 2 & 3). Haemoclips were used for vessel ligation, bupivacaine local block for nerves and rib cutters for osteotomy of each rib.
The latissimus dorsi muscle flap was inspected and deemed viable for closure of the chest wall defect (Figure 4). The muscle flap was trimmed and stretched taut before being secured to the pleural and muscle edges along the defect using 0 polydioxanone mattress and circumcostal sutures deep and 2/0 polydiaxanone simple continuous superficially (Figure 5). The overlying subcutaneous and skin layers were closed routinely. A thoracostomy tube was placed entering intercostal space 9 and secured externally with finger trap suture before draining to negative pressure. The mass was submitted to QML pathology for histopathology and margin assessment.
Molly remained in hospital for two days post-operatively. The thoracostomy tube was removed the day following surgery. She was discharged home with fentanyl patch and meloxicam oral analgesia when she was stable and comfortable. She revisited twice in one week post-operatively and was recovering well. At two weeks post-operatively she developed a pleural effusion consistent with post-operative inflammation that required therapeutic and diagnostic thoracocentesis. The pleural effusion resolved without further intervention following two days of hospitalisation and monitoring. She was seen again three weeks post-operatively and was well. The surgical site and underlying muscle flap had healed without complication.
The two most common rib tumours are chondrosarcoma and osteosarcoma. Both tumors are locally aggressive and surgical resection with ≥3cm margins of normal tissue along the rib and 1 rib cranial and caudal is the recommended treatment. The resultant chest wall defect is rarely able to be closed with primary repair and large chest wall defects can be reconstructed with a variety of techniques.3,4 Autogenous techniques include muscle or myocutaneous flaps, omental pedicle flap and diaphragmatic advancement.3 If an autogenous technique cannot be used to completely fill a large chest wall defect then prosthetic mesh can be used. Autogenous muscle flaps or combination of autogenous techniques with prosthetic mesh are associated with a low rate of complication.3
The latissimus dorsi muscle flap, as used in this case, is an ideal candidate for chest wall reconstruction. The large muscle has good location and arc of rotation to cover most areas of the chest wall. Flap survival is excellent due to the type 5 dual blood supply from the thoracodorsal artery and intercostal/thoracodorsal pedicles. When muscle alone is used to reconstruct defects ≥3 ribs wide then paradoxical respiratory movement of the flap can occur; however, ventilation does not appear to be compromised by this.5
Molly’s final diagnosis was grade 1 chondrosarcoma with complete excision. The prognosis for chondrosarcoma treated with surgical resection alone is excellent, with reported median survival times over 1000 days.1,2
1. Ehrhart N, Withrow S, Straw R et al: Primary rib tumors in 54 dogs. Journal American Animal Hospital Assoc 31:1, 1995
2. Liptak J, Kamstock D, Dernell W et al: oncologic outcome after curative-intent treatment in 39 dogs with primary chest wall tumors (1992-2005). Veterinary Surgery 37:5, 2008
3. Liptak J, Dernell W, Rizzo S et al: Reconstruction of chest wall defects after rib tumor resection: a comparison of autogenous, prosthetic and composite techniques in 44 dogs. Veterinary Surgery 37:5, 2008
4. Matthiesen D, Clark G, Orsher R et al: En bloc resection of primary rib tumors in 40 dogs. Veterinary Surgery 21:3, 1992
5. Halfacree Z, Baines S, Lipscomb V et al: Use of a latissimus dorsi muocutaneous flap for one-stage reconstruction of the thoracic wall after en bloc resection of primary rib chondrosarcoma in five dogs, Veterinary Surgery 36:6, 2007
Dr Katherine Steele, BVSc MVS MVSc MANZCVS DipECVS, Small Animal Surgery Specialist
Dr Katherine Steele, a board certified small animal surgeon, graduated from the University of Queensland in 2008. She completed a rotating and surgical internship in Brisbane prior to relocating to Victoria for a residency at Melbourne University in a small animal surgery. She completed a Masters of Veterinary Studies in 2016 and a Masters of Veterinary Science in 2017. Her interest in oncology led her to Brisbane Veterinary Specialist Centre.