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Rectoanal Diseases – Medical and Surgical Management
1
Craig Ruaux, BVSc (Hons), PhD, MACVSc, DACVIM (SAIM) and Milan Milovancev, DVM, DACVS‐SA 2
1 School of Veterinary Science, Massey University, Palmerston North, New Zealand
2 School of Veterinary Medicine, Oregon State University, Corvallis, Oregon, USA

Rectoanal diseases are frequent reasons for presentation Diagnosis and Medical Management
of companion animals for veterinary attention. Clinical In up to a third of dogs, anal sac adenocarcinoma is
signs and symptoms, such as straining, “scooting,” fecal discovered as an incidental finding on routine examina-
incontinence, and paradoxical diarrhea, are very dis- tion. When clinical signs are present, they may be a result
tressing to owners. An effective approach to recognition of the local mass effect (straining to defecate, constipation
and management of these diseases relies on a thorough due to enlargement of retroperitoneal and intrapelvic
history and clinical examination, including rectal exami- lymph nodes with metastatic disease). In some cases the
nation wherever possible. In smaller patients, and those primary presenting complaint is polyuria and polydipsia
that resent digital rectal palpation, effective sedation is resulting from loss of concentrating capacity due to hyper-
needed to allow this examination to proceed. Diseases calcemia. Routine clinical chemistry panels will often
involving the distal rectum and perineum are often well reveal both total and ionized hypercalcemia, with or with-
characterized by local examination and palpation, but out concurrent hypophosphatemia. A finding of hypercal-
the intrapelvic rectum can be difficult to fully assess, as cemia in a dog undergoing assessment for polyuria and
many important structures (pelvic urethra, cranial polydipsia should prompt thorough anal sac and rectal
prostate in larger dogs, intrapelvic lymph nodes) are dif- digital examination, using sedation if necessary. With
ficult to reach. Diagnostic imaging of this area is also advanced disease and metastasis to the abdominal lymph
challenging in many cases. Contrast‐enhanced CT nodes dorsal displacement of the colon may be visible on
examination is the imaging method of choice for many of plain abdominal radiographs. Abdominal ultrasonogra-
these cases. phy and, if available, computed tomography will usually
In this section, a variety of rectoanal diseases is briefly
discussed. For some diseases, medical management is have a much greater diagnostic yield than plain abdominal
radiography. On diagnosis, complete pretreatment stag-
appropriate, while in others surgical management is the ing calls for either three‐view thoracic radiographs and/or
primary management modality.
computed tomography. Conclusive diagnosis can usually
be obtained by examination of fine needle aspiration
Anal Sac Adenocarcinoma cytology of the mass. In some cases, the cytology may be
interpreted as “hepatoid” but a benign cytologic appear-
ance does not rule out anal sac adenocarcinoma.
Clinical Presentation
Incidental finding or visible perianal mass/swelling, tenes- Surgical Management
mus, polyuria/polydipsia, anorexia or inappetence, leth-
argy, weight loss, constipation, or posterior weakness. Preoperative patient staging for sublumbar lymph node
and/or pulmonary metastasis is mandatory as this infor-
mation influences surgical approach (e.g., determines
Pathophysiology
whether concurrent sublumbar lymph node extirpation
Anal sac adenocarcinoma arises from malignant trans- is indicated). Surgical removal of the affected anal sac is
formation of the secretory epithelium of the anal sacs. performed via closed anal sacculectomy. The size and

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical