Anal sac ultrasound in dogs: a case of emphysematous anal sacculitis
Amazingly (actually maybe it’s not amazing :/) there appears to be just one published study on ultrasonography of canine anal sacs. This reflects a general lack of enthusiasm for anyone getting to grips with pathological conditions of the AGs. And it’s a sad state of affairs since they’re easy and rewarding to scan.
That one ground-breaking study is:
Diagnostic imaging features of normal anal sacs in dogs and cats
Technique is straightforward: a linear probe gives best results and i usually scan in a transverse plane from a point ventral to the anus with the beam directed dorsally and about 20 degrees angled cranially.
The present patient has a history of chronic anal irritation unresponsive to various antibiotics, glucocorticoids or oclacitinib.
On sonography of the perianal area:
This is really not normal. The left anal gland is OK but on the left the anal gland lumen is gas filled.
Cytology of right anal gland secretion revealed large numbers of degenerate neutrophils and bacteria: some of which were intracellular.
About 10% of ‘normal’ asymptomatic dogs have neutrophils in their anal gland secretions. However, they tend to be <10 per HPF and non-degenerate:
J Vet Med A Physiol Pathol Clin Med. 2004 Jun;51(5):249-53.
Gross and cytological characteristics of normal canine anal-sac secretions.
At the time we theorised that this might be an emphysematous anal sacculitis (not that such a thing has ever been reported to the best of our knowledge…but it seemed like a reasonable explanation). On this basis 3 weeks of co-amoxiclav were dispensed: to no noticeable effect.
Although, on re-examination post-antibiotic the gas had vanished from the right gland:
However, the perisaccular soft tissue remains patchily hyperechoic and the contents are hyperechoic compared to the left gland:
Bilateral anal sacculectomy was performed. Histopathology:
‘The epithelial lining of the sac is extensively ulcerated and there is a mixed inflammatory reaction surrounding the wall with occasional lymphoid follicles’
On culture a mixed growth was present in samples from both glands. That from the right gland featured a heavy growth of Staph pseudintermedius sensitive to most antibiotics including co-amoclav.
This is all interesting on several fronts: firstly, I can’t find any other reports of ultrasonographic appearance of anal sacculitis in dogs. Secondly, emphysematous anal sacculitis may be a previously-undescribed entity. I find it easy to imagine that an anal gland full of gas might be painful. Thirdly, a 3 week course of an apparently appropriate antibiotic filed to eliminate an apparently sensitive Staph from the anal gland.