Arathi Vinayak VCA West Coast Animal Emergency and Specialty Hospital, Fountain Valley, CA, USA Anal sacs are paired sinuses consisting of a fundus and neck with a duct that opens on the anocutaneous junction at the 4 and 8 o’clock positions sandwiched between an external striated anal sphincter muscle and an inner smooth anal sphincter muscle. Non‐neoplastic disease of the anal sacs occurs commonly in dogs with an incidence of 12.5–15.7% and is less common with an incidence of 0.4% in cats.1–3 This non‐neoplastic disease can be broadly divided into three categories of impaction, inflammation, and abscessation with all being on a continuum of the same disease process.4,5 Impaction refers to a non‐painful condition where the contents of the anal sac cannot be expressed. Inflammation, commonly referred to as anal sacculitis, is a swollen, painful condition that sometimes is associated with pyrexia. Abscessation refers to a painful swelling of the anal sac region associated with pyrexia and purulent and/or bloody discharge. Predisposing factors identified in a recent study included certain dermatological conditions, diarrhea, certain dog breeds (predilection in small dog breeds), male cats, and obesity in dogs.1 Other factors identified include diet, pudendal nerve dysfunction, perianal fistulas, and inflammatory bowel disease.6 Impaction appears to be the most common refractory problem.1 While medical management is the mainstay for non‐neoplastic conditions, anal sacculectomy is considered for refractory cases or if the client no longer wants to pursue medical management. Surgery remains the mainstay for dogs and cats with neoplasia of the anal sacs. In dogs, apocrine gland anal sac adenocarcinoma (AGASACA) is the most common malignancy seen in this region.7 As the name suggests, neoplastic transformation occurs in the glandular epithelial cells of the apocrine glands within the anal sacs.8,9 While cure is seldom achieved, long‐term survival can be achieved in early stages of disease and in dogs with small tumors, underscoring the importance of routine rectal examinations. Spaniel breeds are over‐represented with Cocker Spaniels having a mean relative risk estimate of 7.3.10 Other predisposed breeds are German Shepherds, Alaskan Malamutes, Dachshunds, and Golden retrievers.10–12 AGASACA is typically seen in middle‐aged to older dogs with a median age of presentation is 9–11 years.10–14 The more recent literature shows a relatively equal male and female prevalence.10–14 Clinical signs associated with the tumor include perianal swelling, bloody discharge, scooting, misshapen stools, straining during defecation, and urinary incontinence.9–16 Paraneoplastic hypercalcemia seen with this malignancy is due to production of parathyroid hormone‐related protein (PTHrP) by the tumor. PTHrP functions in a manner like endogenous parathyroid hormone (PTH) by binding to receptors on renal tubular cells and osteoblasts, increasing the renal reabsorption of calcium and resorption of bone.17 The resultant elevations in ionized and total calcium lead to inhibition of antidiuretic hormone as the mechanism behind the polyuria and polydipsia.16 Hypercalcemia is noted in 27–53% of dogs with AGASACA.11,12,16–19 The more recent studies in veterinary patients do not show hypercalcemia to be a negative prognostic indicator in the face of treatment.11,20 Other malignancies of the anal sac and perianal region include malignant melanoma, squamous cell carcinoma, perianal adenoma, perianal adenocarcinoma, lymphoma, mast cell tumor, and hemangiosarcoma.10–14,21–26 Malignant anal sac melanoma (MASM) is an uncommon but very aggressive malignancy in dogs.21 Bloody anal sac discharge and perianal licking are the most common presenting signs. Anal sac tumors have different prognoses depending on benign versus malignant status, tumor type, stage of disease, and treatment chosen. An in‐depth discussion of the many tumor types, stages, and prognoses is not possible for the scope of this chapter, and discussion will be limited to brief discussions on prognosis after surgical excision. Anal sac tumors in cats are uncommon and include AGASACA and squamous cell carcinoma.27–31 Discharge and perianal ulceration were the most common clinical signs noted in cats with AGASACA and may lead to a delay in diagnosis, as the signs are similar to anal sac impaction/anal sacculitis/abscessation.28,29 A thorough rectal examination with fine needle aspiration is warranted in cats with this presentation.29 Paraneoplastic hypercalcemia has been reported in 1 of 5 cats in one study, and 3 of 27 cats in another study, but whether the mechanism of this hypercalcemia is due to elevated PTHrP production by the tumor is yet to be elucidated.28,29 Squamous cell carcinoma of the anal sac in cats is a very rare disease with report of only two cats in the veterinary literature. Thus, there is little information on tumor behavior and prognosis in cats. Only one of the two cats was treated with surgery and adjuvant radiation and chemotherapy with local recurrence reported 236 days after surgery and euthanasia at 552 days post‐surgery. The other cat in the report was euthanized 28 days following medical management with anti‐inflammatories.31 Infections, impactions, and draining tracts need to be treated in advance of surgery to decrease the risk of complications postoperatively.1 Untreated infection/inflammation can obscure visualization and lead to intraoperative complications, such as incomplete excision of the sac or duct, contamination of the surgical field with infection, and/or iatrogenic rectal perforation. In cases where anal sac tumors are suspected, diagnosis is confirmed with a fine needle aspiration of the mass. If malignancy is confirmed, staging must be performed prior to proceeding with surgery. Staging diagnostics are similar for malignancies of the anal sacs in dogs and cats. Bloodwork consisting of a complete blood count, serum chemistry, urinalysis, and/or ionized calcium if total calcium is elevated is recommended. If ionized hypercalcemia is noted, PTH and PTHrP evaluation is recommended to differentiate primary hyperparathyroidism from hypercalcemia due to malignancy. Thoracic and abdominal imaging is recommended, as metastasis to the medial iliac, internal iliac (formerly known as hypogastric), and sacral lymph nodes occurs in up to 96% of affected AGASACA dogs.11,12,20,32,33 The most recent computed tomography (CT) staging study for AGASACA revealed iliosacral lymphadenopathy in 71% and pulmonary metastasis in 11%.34 Other less common sites of metastasis include liver, bone, and spleen.11–13 Markedly enlarged lymph nodes in the iliosacral or sublumbar region are more likely to be consistently detected on abdominal radiographs due to significant ventral displacement of the colon, opacity in the retroperitoneal space caudally, and lack of clear delineation of the ventral iliopsoas muscle.35 The sensitivity and specificity of abdominal radiographs in the detection of iliosacral lymphadenopathy for general practitioners, radiology residents, and board‐certified radiologists were 81/70%, 94/81%, and 75/100%, respectively.35 Mild to moderate enlargement of the iliosacral lymph nodes may be missed on radiographs, necessitating the need for advanced imaging. Abdominal ultrasonography is routinely used for staging in veterinary medicine but has limitations, as caudally‐located lymph nodes within the pelvis (such as the sacral nodes affected with anal sac malignancies) will likely be missed. When ultrasound was compared to CT for AGASACA staging, ultrasound correctly identified all affected nodes in only 30.8% of affected dogs but was able to identify at least one enlarged node in all affected dogs.36 Another comparative study evaluating ultrasound and magnetic resonance imaging (MRI) showed that while MRI identified all abnormal lymph nodes, ultrasound only detected abnormal nodes in 33% of dogs (two of six affected dogs).37 Thus, CT or MRI should be considered for more accurate staging for malignancies. Fine needle aspiration of any concerning findings that have the potential to represent metastasis is performed using imaging guidance for cytology. Cytology, in addition to imaging, will help identify stage, prognosis, and treatment options prior to surgery. Other tumors of the anal sacs are also staged similarly. Open, closed, and modified closed techniques have been described.6,38,39 The open technique is seldom used and not advocated, as this technique has a 13.67 times higher long‐term complication rate when compared to a closed technique.38 A modified closed technique pioneered by the late Dr. Phil Hobson at Texas A&M University was recently described and published.40 The modified closed technique has an advantage over the traditional closed technique in that the entirety of the duct, including its anocutaneous opening, is excised in the case of neoplasia, thus ideally minimizing chances of tumor recurrence. Regardless of the technique chosen, care should be taken to minimize damage to the adjacent rectal wall, external anal sphincter muscle, caudal rectal nerve (branch of pudendal nerve), and caudal rectal artery (branch of internal pudendal artery).39 If an open technique is used, care must be taken to ensure all of the sac and duct complex is excised. The patient is placed in sternal recumbency with a towel to raise the caudal abdomen to elevate this area. The tail is gently secured cranially; over‐extension of the tail is avoided to prevent nerve damage in the lumbosacral region. The anal sacs are expressed of their contents and flushed with a 22‐gauge catheter, and the terminal rectum is manually evacuated of feces to prevent contamination intraoperatively. Lubricated tampon or gauze is rolled and gently inserted into the terminal rectum, and a pursestring anal suture may be placed additionally cranial to the anocutaneous anal sac duct openings. Enemas are not recommended, as liquid feces may not be contained by the gauze and pursestring suture. The pelvic limbs can be flexed at the stifles and hock such that the entire limb can be secured on the table. Alternatively, the stifle can be extended with the pelvic limbs positioned off the table, but padding between the limb and table is recommended, as there are anecdotal reports of femoral nerve damage and resultant limb paresis in the postoperative period.
35
Anal Sacculectomy in Dogs and Cats
Introduction
Indications/Pre‐op Considerations
Surgical Procedure
Standard Closed Technique
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
