Chest wall resection What’s all the fuss about?
Referring vet resources Chest wall resection Case Study
BVSc MRCVS DECVS
Diplomat of the European College of Veterinary Surgeons
Specialist in Small Animal Surgery
6 years old, Female Neutured, German Shepherd
Sasha was presented to her regular veterinary team for assessment of a large, thoracic wall mass which had only become apparent 2-3 days prior. Sasha was not showing any clinical signs associated with this mass.
An aspirate of the mass performed at the referring practice revealed a spindle cell proliferation, with a concern for osteosarcoma. Sasha was referred for staging and further diagnostics.
Sasha was referred to GARS internal medicine team for further investigations prior to treatment.
Grading and Staging: What’s all the fuss about?
Whenever presented with a mass, information about underlying cell type, local and distant behaviour is extremely helpful in both planning definitive treatment and prognosticating (disease free interval and survival time). Together this helps achieve ‘well informed choices’ by pet owners.
Information gained from grading/staging prior to treatment also optimises treatment strategies from the outset, leaving less room for surprises down the road.
Cytology is achieved from a fine needle aspirate. Almost always the first port of call, we encourage everyone to perform these routinely when confronted with a mass. FNA is minimally invasive, is economical, and generally does not require sedation/ anaesthesia and in many cases can determine the tumour cell type. However, it has limited information on behaviour, and some tumours (mesenchymal cells in particular) may not exfoliate readily and the sample may be non-diagnostic. Especially regarding locations that are challenging to deal with, tumour type and behaviour can be extremely important information as it influences decision to treat and what surgical dose is required.
Grading is achieved by collecting a larger piece of tissue (typically wedge, Trucut, Jamshidi etc) which allows the pathologist to more accurately assess tumour type and predict its behaviour (*propensity to recur and spread). Grade for most tumours closely correlates with survival times. However, for some tumours, grade can be underestimated from a biopsy and tumours should still be submitted for histopathology following definitive removal for assessment of grade and margins. This helps to determine if further treatment is required (wider cut, chemotherapy etc).
When performing an incisional biopsy, there are two important considerations for where to sample:
- Where the sample is taken with respect to the margins of the mass: Take a biopsy from the junction of the mass with normal tissue. Sampling directly in the centre of the mass risks sampling a necrotic core, particularly for large masses and suspected sarcomas.
- Resection margins: Following an incisional or punch biopsy, the biopsy tract is considered contaminated and so needs to be resected. Therefore, prior to performing the biopsy, it is critically important to consider what margins may be needed, the orientation of the tension lines, and how the defect may need to be closed. These considerations ensure that the biopsy tract is kept within the margin of resection to avoid seeding cells and contaminating surrounding healthy tissue, and making the procedure much larger than it needs to be.
Staging is an assessment of the patient to determine whether we are dealing with only local disease (the tumour and immediate surrounds), or whether there is distant disease as a result of metastasis. Most tumour types require some form of staging, but it is not always exactly the same process and requires assessment of the organs each tumour is most likely to metastasise to. It is incredibly valuable in planning tumour resection and is also a good prognosticator of survival times for many tumours.
Staging can be performed using combinations of imaging modalities, including radiographs, ultrasound, MRI, CT and Scintigraphy and sampling of any abnormalities. The modalities selected are based on local disease site and distant site(s) to survey. Ability plus sensitivity/specificity of respective modalities also needs to be balanced with economics and is generally ‘case by case’ driven.
What about Sasha’s grading/staging?
Sasha underwent a contrast CT of her chest. This revealed an aggressive, monostotic mass in the ventral extent of the 6th rib. The main features which indicated it was an aggressive lesion were presence of osteolysis of the rib cortex, with invasion of soft tissue attenuating tissue into the medullary canal. The mass also had a mixed attenuation with soft tissue and mineral attenuating regions. The mass was localised to the rib, with no extension to the 5th or 7th ribs; we look for periosteal reaction in the early stages and invasion of the bone if the mass is a lot closer to the adjacent ribs. The main differential diagnoses following the CT scan were: chondrosarcoma, osteosarcoma, fibrosarcoma, other spindle cell tumours.
An incision biopsy was performed which confirmed a well-differentiated chondrosarcoma.
Reported survival times for chondrosarcomas that have not grossly metastasised which are removed with clean margins vary from 3-5years, to a median survival time not being reported in one study due to the length of time. The prognosis following resection with clean margins is very good.
Understanding the disease and expected outcomes, Sasha’s owners elected to pursue surgery to remove the mass. She underwent definitive surgery via a thoracic wall resection to remove the mass plus a healthy tissue margin (best chance of avoiding local recurrence). The resection margin for a chondrosarcoma is 3cm, and one unaffected rib on either side of the mass. For this patient, this meant that the resection involved ribs 5, 6 and 7, with at least a 3cm margin circumferentially.
Intercostal nerve blocks were performed at the dorsal aspects of spaces 4-8 to help provide perioperative analgesia. Fentanyl and ketamine continuous rate infusions were also required intraoperatively, and mechanical ventilation was maintained throughout the procedure (*manual or mechanical ventilation is required whenever the chest loses negative pressure).
Closure options in this area included:
- Latissimus dorsi muscle transposition
- Latissimus dorsi myocutaneous flap transposition (including overlying skin)
- Synthetic graft (prolene mesh)
- Autogenous Biologic graft (thorocolumbar fascia graft)
- Xenogenic Biologic graft (Porcine Small Intestinal Submucosa)
A thoracodorsal axial pattern flap was not considered an option as it would not provide the deeper muscular tissues for closure of the thoracic wall. An external abdominal oblique muscle flap can be considered for more caudal thoracic wall masses. Meshes can be considered but unfortunately have a high infection rate, so the patient’s own tissues are preferred where possible.
Following aseptic preparation of the thoracic wall, the margins of the mass and the biopsy tract were marked to determine the incision margins. The movement of the skin was also assessed to determine the best closure options.
Given the lack of invasion of the mass into the superficial muscles and the skin, a coned approach was considered to preserve the skin and superficial muscles as much as possible for closure. The skin incision was performed 3cm from the edges of the biopsy tract (green line in schematic) and then widened to include tissues 3cm from the edges of the mass (red lines in second schematic indicate this “coned” incision and dissection). NOTE: Schematic only, not to scale. The muscles were transected, and the ribs transected dorsally and ventrally at the margins marked, with a sagittal oscillating saw. Once removed, a thoracic drain was placed to monitor for pulmonary leakage, and to achieve negative pressure.
The latissimus dorsi was then elevated bluntly and the perforating vessels cauterised. The dorsal attaching fascia was transected, and once an appropriate length of muscle was elevated, it was rotated into the defect, attaching to remaining ribs, with subcutaneous tissues and skin apposed.
Sasha recovered under the GARS specialist critical care team and was discharged 24hrs following surgery once her chest drain was no longer productive.
Histopathology confirmed a well differentiated chondrosarcoma, with 0 mitoses per 10 HPF with clean margins.
No further treatment is recommended for Sasha.
Monitoring for patient following this procedure involves repeat CT scans at 3, 6, 12, 18 and 24 months post-operatively. Depending on the patient, evidence of metastasis and surgical margins, chemotherapy would be considered.