Page 127 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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Anal sac adenocarcinoma (ASAC)
VetBooks.ir Malignant tumour arising from the apocrine epithelial cells in the wall of the anal sac.

Clinical features
• Common in dogs and rare in cats.
• Age: peak incidence between 8 and 12 years in dogs and 6–17 years in cats.
• Approximately half of the tumours present as masses in the perineal area. Others are
directed inwards, and masses may not be visible from the outside, but often palpable
on rectal examination.
• Larger masses can cause difficulties in defecation and can be ulcerated.
• In some cases, ASAC can present with signs referable to anal sac impaction and/or
sacculitis, especially in cats.
• ASAC often has an occult presentation. By the time the diagnosis is made, approxi-
mately 70–80% of the dogs will have local and/or distant metastases. The tumour
most frequently metastasizes to the regional lymph nodes, but occasionally can spread
to other organs, in particular lung, liver, spleen and bone.
• In cats, the presumptive metastatic rate is approximately 16%.
• Over-represented canine breeds: Cocker Spaniel, English Springer Spaniel, Cavalier
King Charles Spaniel, Dandie Dinmont Terrier, German Shepherd Dog.
• Over-represented feline breeds: Siamese cat.

Cytological features
• Cellularity is often moderate to high.
• Background: variably haemodiluted and pale basophilic.
• Neoplastic cells can present as naked nuclei embedded in a pale basophilic background of
cytoplasmic material or as intact cells in cohesive clusters. Variable numbers of rosette-like/
acinoid arrangements are seen.
• Cell clusters might be mildly disorganized and cell crowding and nuclear moulding can be
observed.
• Nuclei are medium to large, round, and have finely stippled to granular chromatin. Occa-
sional hyperchromatic nuclei can be present. Nucleoli can be indistinct. If present, they are
small, round, single or multiple.
• The cytoplasm is scant to moderate, pale basophilic and often has poorly defined margins. It
can occasionally contain small, clear, punctate vacuoles. Rarely, neoplastic cells with a larger
amount of cytoplasm can be seen. In this case, the cytoplasm tends to be pale basophilic to
amphophilic and smooth (without any granularity).
• Anisokaryosis and anisocytosis vary from minimal to occasionally moderate. The N:C ratio
is high. Mitoses can occasionally be observed.
• Low to moderate numbers of inflammatory cells can be present, including activated macro-
phages and granulated mast cells.
• The aspirates can occasionally contain variable numbers of anucleated squamous epithelial
cells and extracellular bacteria, which suggest concurrent anal sac impaction.