Anal Sac Adenocarcinoma

Signalment

Have only been confirmed in dogs although they may occur in cats. Predisposed breeds include:

• 

  English Cocker Spaniels

• 

  Springer Spaniels

• 

  Daschunds

• 

  Alaskan Malamutes

• 

  German Shepherds

and mixed-breed dogs

• Mainly older bitches (90%)

Description

A highly malignant neoplasia that readily metastasizes to the medial iliac lymph nodes. May also lead to paraneoplastic hypercalcaemia due to parathyroid hormone-related peptide. The tumours can be between 1 and 10cm in size and 50% of them will metastasize.

Diagnosis

History and Clinical Signs

See Anal Sac Disease - General

Also:

• Flattened stools
• Pernieal swelling
• Hypercalcaemia signs including polydipsia and polyuria.

Biochemistry

To assess:

• Calcium
• Phosphate
• Renal function

Thoracic radiographs

At least two views to check for thoracic metastases.

Abdominal imaging

Caudal abdominal radiographs or abdominal ultrasound to assess the medial iliac lymph nodes for metastases.

Treatment

The treatment of choice is surgical excision if the patient is normocalcaemic without any metastases. The success will depend upon the size of the mass.

Treatment of Hypercalcaemia

High fluid rates of 0.9% saline to diurese calcium. Furosemide should be administered (2mg/kg intravenously) once the patient in normocalcaemic.

Prognosis

Potential postoperative complications include infection, wound dehiscence, faecal incontinence and in 25% of cases, local recurrence. Hypercalcaemia reoccurs in 35-50% of cases due to metastases. Serum calcium levels should therefore be reguarly along with evidence of mass regrowth. Post-op survival ranges between 2 and 39 months with the average being 8 months

References

Hall, E.J, Simpson, J.W. and Williams, D.A. (2005) BSAVA Manual of Canine and Feline Gastroenterology (2nd Edition) BSAVA

Merck & Co (2008) The Merck Veterinary Manual