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Soft tissue sarcoma: case study

An eight-year-old male Labrador presented with ongoing history of lameness. Clinical examination revealed marked swelling of the right elbow. A mass was noted close to the elbow joint and was suspected to affect joint mobility

07 May 2021, at 9:00am

Cytology examination of a synovial fluid sample from the right elbow was performed. This revealed low cellularity composed predominantly of large mononuclear cells (occasionally vacuolated), with lower numbers of small mononuclear cells and spindle cells. Large mononuclear cells (Figure 1A) had round nuclei with prominent single or multiple small nucleoli and moderate amounts of mid-basophilic cytoplasm. There was mild anisocytosis and anisokaryosis and occasional mitotic figures were present (Figure 1B). Occasional binucleated or multinucleated spindle cells were also noted (Figure 1C).

Sampling of structural lesions with biopsy for histopathology examination was advised to rule out neoplasia.

FIGURE (2) Mitotic figures were present on histological samples
FIGURE (2) Mitotic figures were present on histological samples

Biopsies were submitted from joint capsule and adjacent muscle of right forelimb. Throughout the connective tissue there were infiltrates of plump spindle cells forming short interweaving bundles. The cells had oval nuclei with irregular outlines and reticulate chromatin patterns. Cells contained small nucleoli. They had low to moderate amounts of fibrillar cytoplasm with indistinct borders. There was mild anisocytosis and within this population there were mitotic figures (Figure 2). Sections from the joint capsule consisted of dense fibrocollagenous connective tissue with scattered isolated blood vessels and the same plump spindle cells forming interweaving bundles (Figure 3A) or whorls (Figure 3B) and aggregates.

A diagnosis was made of a canine soft tissue mesenchymal tumour (sarcoma) which appears to be of low to intermediate grade. Differentials include fibrosarcoma, perivascular wall tumour or peripheral nerve sheath tumour.

Historically, synovial cell sarcomas have been reported commonly in dogs. However, more recently studies using immunohistochemistry have shown that many different types of mesenchymal tumours can develop in and around joints in dogs. The majority are not of synovial cell origin. This particular tumour was considered to be of connective tissue origin. Soft tissue sarcomas (mesenchymal tumours) tend to behave in the same way regardless of the exact cell of origin. Given the cytological features, mitotic activity and absence of necrosis this may be a low-grade tumour, although on examination of larger areas of the tumour this grade may increase. Such tumours are locally infiltrative and frequently recur following surgery due to difficulty in achieving adequate excision margins at awkward surgical sites and the ability of these tumours to dissect between fascial planes. Metastasis, however, is uncommon or develops late in the course of the disease, often by haematogenous rather than lymphatic spread.

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Veterinary Pathologist at NationWide Laboratories

Sandra Dawson, BSc, BVMS, FRCPath, MRCVS, is a graduate of Aberdeen and Glasgow Universities, gaining a BSc in agriculture in 1991 and her veterinary degree in 1995. Following a term in mixed practice, Sandra became a resident in veterinary pathology at Edinburgh University and lectured in reproductive pathology. After five years in industry where she gained her MRCPath, Sandra joined NationWide Laboratories in May 2006. She works with surgical biopsies and can advise on all aspects of histopathology in a wide range of species.

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Clinical Pathologist at NationWide Laboratories

Alina Bodnariu, DVM, MSc, PhD, FRCPath, MRCVS, graduated from the Faculty of Veterinary Medicine Bucharest in 2004. Following her postgraduate studies, she worked for two years in small animal general practice. In 2010, she undertook a residency in veterinary clinical pathology within a commercial veterinary diagnostic laboratory, with regular training at the RVC. She was awarded her FRCPath in 2016. She enjoys all aspects of clinical pathology, but her particular interests include cytology and endocrinology.

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