Page 49 - VetCPD Jnl Volume 7, Issue 4

VETcpd - Surgery
to poor sample collection or misdiagnosis of the tumour as inflammation, and so
all samples should be sent to an external laboratory (Cohen et al. 2003; Bacon et al. 2017).Where a cytological diagnosis
is not made, or if the cytology report doesn’t reflect the clinical appearance of the mass, such as rapid growth, biopsy is required for histopathological diagnosis. Similarly, biopsy is imperative if knowing the grade of the tumour will influence
the surgery performed, or if the surgery may be associated with high morbidity, for example deciding whether to amputate
a limb or perform a surgery with muscle resection and/or advanced reconstructive procedures (Figure 1).
Options for biopsy include needle, core,
or wedge biopsy (using a scalpel or
biopsy punch). Regardless of technique,
the location of the biopsy should not
compromise the planned excision, and
the biopsy tract should be located so two weeks previously. The mass is firmly adherent to underlying muscle. An incisional wedge biopsy (arrow)
Figure 1: Soft tissue sarcoma on the cranial thigh of a dog. The mass was present when the dog was rescued has been performed as radical surgical excision is planned.
Subscribers
that it can be readily excised with the tumour.The needle core biopsy is quicker to perform and easier for subcutaneous masses (Figure 2), but it is harder to obtain
a sample from small masses and it yields with a low mitotic index, whereas Grade less tissue than wedge biopsies, even if 3 (high-grade) sarcomas are poorly
multiple samples, typically 6-10, are taken. differentiated, with a high mitotic index
The three methods have similar accuracy and >50% necrosis.
compared to excisional biopsy, although Only
over- and under-interpretation of tumour
grade may occur (Perry et al. 2012).
Under-interpretation may occur in up
to 30% of biopsies of soft tissue sarcomas,
so some caution should be exercised in a
report of a low-grade tumour of a biopsy
specimen (Perry et al. 2012).A biopsy
report of a high-grade tumour will be
Most soft tissue sarcomas seen in first- opinion practice are low-grade and have low metastatic potential, but staging a tumour for spread to local lymph nodes and distant organs remains important, particularly if a large surgery is planned. Metastasis to local lymph nodes is much less common than pulmonary metastasis
incorrect in only approximately 10% cases. (Kuntz et al. 1997). However, given there
Figure 2: Core biopsy of a subcutaneous mass. Surgical Treatment
The main problem traditionally cited with soft tissue sarcomas is that they are locally invasive and have the potential to recur after resection. Unfortunately, it is not possible to predict what size margin of normal tissue should be resected lateral and deep to a soft tissue sarcoma to prevent recurrence occurring.Traditional recommendations are to take a 3-cm
skin and lateral tissue margin and a clean deep fascial margin (Ehrhart 2005), as some studies report that recurrence and survival times are related to completeness of excision (Kuntz et al. 1997; McSporran 2009). Despite the size of these margins, some tumours recur. More recent studies have suggested that the extent of resection does not affect recurrence or survival,
Histopathological subtype will be described by the pathologist, as it is important to distinguish soft tissue sarcomas from other sarcomas with different biological behaviours, e.g. histiocytic sarcoma.There are also some differences in outcomes within the
‘soft tissue sarcoma’ group, for example perivascular wall tumours have a lower
rate of recurrence than fibrosarcomas (Kuntz et al. 1997). Immunohistochemistry may be recommended to further aid
in differentiating histopathological subtype. Soft tissue sarcomas are
graded histopathologically as 1-2-3 (low-intermediate-high grade) based on degree of cell differentiation (how well the cells and their growth reflect the tissue of origin), mitotic index and percentage tissue necrosis. Grade 1 (low-grade) soft tissue sarcomas are well differentiated
is the potential for metastasis, local lymph nodes are aspirated for cytology, even
if they are not palpably enlarged. This
is easier for the limbs, where regional lymph nodes are typically palpable and are clearly defined (the superficial cervical or axillary nodes \[thoracic limb\] and the popliteal or inguinal nodes \[pelvic limb\]), but is less easy to determine in other locations, such as the trunk, where the draining lymph node is not defined and palpation maybe difficult. It is not known whether cytology of lymph nodes has good diagnostic accuracy.
Pulmonary metastasis is assessed using three- or four-view inflated thoracic radiography, or computed tomography. Pulmonary metastasis is more common in high-grade sarcomas (41-44% incidence) than low or intermediate-grade sarcomas (≤13% combined).
VETcpd - Vol 7 Issue 4 - Page 45