Zak is an 8 year old Golden Retriever, who is healthy, full of life, but has developed a small lump on the right tarsus (see attached photo). The lump was first noticed some 3 weeks ago and a fine needle aspirate has been performed by our local vests (report is detailed blow). He has for the last 2 weeks been on reduced activity, just to rule out exercise as an issue. When walking he shows no signs of a limp or any pain. When mobilised the lump does feel as if it is connected to the bone structure (rather than just the skin) and appears to be soft to the touch. The vets report to the layperson is inconclusive and could suggest simple fluid around the joint or a soft tissue sarcoma! From what I have read, if this is a sarcoma, then the aspirate should have been conclusive and we should have received a grading, 1, 2, 3. The vet had 2 attempts to aspirate the lump, the first withdraw was very limited and clear fluid, the second looked just like blood. Might this inconclusive Cytology report be the result of a poorly performed aspirate? Does anyone have any experience of this with their dog and what our next steps should be (repeat the aspirate, conduct a core biopsy, x-ray, CT, etc? REPORT Cytology report: Six submitted smears of aspirates from a soft 2 cm diameter mass over the right tarsus ?sarcoma DESCRIPTION Nucleated cellularity is moderately low and cell preservation is moderate to good. There is a very pale eosinophilic fluid background containing very large numbers of erythrocytes, occasional clumps of platelets and numerous strands of fibrin which entrap a moderate proportion of the nucleated cells preventing evaluation. In areas the erythrocytes are seen windrowing (lining up in row). Nucleated cells are predominantly large mononuclear cells, often with abundant variably vacuolated cytoplasm (activated appearance), with lesser numbers of small lymphocytes. There are low numbers of non-degenerate neutrophils in numbers proportionate to the amount of background blood. In addition, there are occasional aggregates of atypical mesenchymal cells. Individual cells are generally caudate in appearance with wispy indistinct cell borders and a moderate amount of mid to dark basophilic cytoplasm. Nuclei are round to plump oval, ranging in size from 1x up to 3 times RBC diameter with coarse stippled chromatin and up to 7 small variably shaped prominent basophilic nucleoli INTERPRETATION Markedly haemodiluted viscous fluid with moderate mesenchymal proliferation (see comment) COMMENT The cytological appearance of the background fluid is reminiscent of synovial fluid. Given the location an outpouching of the joint capsule or synovial bursa is a consideration. Whilst small numbers of mesenchymal cells can be seen in synovial aspirates reflecting aspiration of synovial membrane the cells are typically quite bland. Here the mesenchymal cells are quite large and display moderate atypia. This is excessive for normal joint capsule. It may possibly reflect highly reactive synovium but I am concerned for a neoplastic mesenchymal population here (sarcoma). In particular, given the nature of the background, a synovial sarcoma.