1. General Considerations

   1. 1. The anal sacs of dogs and cats are paired structures located between the muscles of the internal and external anal sphincters at about 4 and 8 o’clock positions. In dogs, they open at the mucocutaneous junction of the anus, and in cats at a prominence located about 0.25 cm lateral to the anus. The sacs of dogs and cats are lined by thin stratified squamous epithelium. Sebaceous glands line the neck of the anal sacs, while apocrine glands line the fundus. The content of the sacs is usually expressed passively during defecation, but they can also be actively expressed via contraction of the internal and external anal sphincters.

1. 2. Reported incidences of non-neoplastic anal sac diseases in dogs range from 1.5% to 12.5%. These cases were diagnosed in general practice and referral institutions from many parts of the world, which can explain the broad range. The incidence in cats has not been reported but it is believed that cats are less affected by non-neoplastic anal sacs diseases than dogs.
   3. Factors considered to have an impact in the development of anal sac diseases include stool quality, diet type, body condition score, skin disease, and breed.
   4. The pathogenesis of inflammatory anal sac disease is not fully understood. It is speculated that an initial anal sac impaction occurs followed by bacterial overgrowth, which ultimately leads to a local inflammatory reaction.

2. Anal Sac Diseases and Clinical Signs

   1. Primary anal sac disease is classically divided into four clinical entities as described below. Except for neoplasia, these disorders are considered a continuum and differentiation between them is poorly defined.
      1. Impaction – It is a common anal sac problem of dogs, but it is rare in cats. There is no sex or age predilection; however, it appears to occur more often in small breeds and obese dogs. Overfilling and distention of the anal sac may be due to inflammatory bowel disease, diarrhea, obesity, change in the character of the secretion, excess glandular secretion, or change in the anal sphincters muscle tone. Clinical signs subside after expression of the impacted content, but relapses are common.
      2. Inflammation/infection – It is believed to occur because of chronic or recurrent impaction. Other suggested reasons include fecal contamination, obesity, low tail carriage and chronic intestinal diseases. Neutrophils and intracellular and extracellular (more often) bacteria are found in the contents of normal anal sacs making it difficult to separate an infected from a normal sac based on cytological examination. Criteria that have been used, but not validated in studies, are the presence of more than 10% of the microscopic fields (100x) showing intracellular bacteria and red blood cells. Moreover, the presence of blood and pus in the anal sac content and suggestive clinical signs support a diagnosis of anal sacculitis.
      3. Abscessation – It occurs because of chronic infection associated with some degree of impaction. The sac eventually ruptures, and its content extends to the peripheral tissue resulting in cellulitis and ultimately fistulation.
      4. Neoplasia – The most common neoplasia of dogs is apocrine gland anal sac adenocarcinoma (AGASAC), which often metastasizes to regional lymph nodes but can also spread to the lungs and other internal organs. English cocker spaniel was overrepresented in one study. Dogs may have paraneoplastic hypercalcemia and associated polyuria and polydipsia. AGASAC is uncommon in cats. Squamous cell carcinoma has also been reported in dogs and cats, and melanoma, papillary cystadenoma, soft tissue sarcoma combined with AGASACA and mast cell tumor in dogs. A mass or swelling in the perianal area and tenesmus and constipation may be present but some tumors may only be diagnosed via rectal palpation.
   2. Clinical signs
      1. Signs of anal sac impaction and inflammation/infection are similar and include scooting and licking or biting at the anus and perianal region. These signs, however, are not pathognomonic and can be seen with atopic dermatitis, food allergy, perivulvar dermatitis, psychogenic anal licking, tail fold dermatitis, and perianal fistulas.

1. 1. 2. In cases of cellulitis due to abscessation and rupture of the anal sac, perianal swelling, erythema and eventually the formation of sinus tracts will be seen. Pain is present in those cases and typically, only one anal sac is involved. Affected animals are often pyrexic and lethargic.

1. 1. 3. Anal sacs with thicken walls and/or distension due to any of the mentioned causes can be palpated on either side of the anal canal at about 4 and 8 o’clock positions.
      4. The normal anal sac content of dogs and cats is described as pale yellow or straw-colored, serous, clear to translucent, slightly viscous, granular and often having small brownish flecks. A pungent odor is characteristic.
      5. The abnormal content color varies from greenish yellow (pus) to red (blood) to brown to clay to black.
         1. Infected anal sacs often are associated with an opaque, thick, red or yellowish/ greenish-colored material, which have a fetid odor.
         2. Impacted anal sacs are typically characterized by clay- or black-colored contents that are dry or pasty and have minimal odor. The thick and pasty content often has a ribbon-like pattern when expressed.

3. Diagnosis

   1. The diagnosis is based on the pet’s history, suggestive clinical signs, careful rectal palpation of the anal sacs, and macroscopic and microscopic examination of the anal sacs content.
      1. In cases of impaction, the sacs will feel firm and enlarged and the content may be difficult to express.
      2. In cases of abscessation, the anal sac itself and the surrounding tissue are very painful, and sedation may be required for a thorough and proper examination of the patient.
   2. Macroscopic findings highly suggestive of inflammation/infection are the presence of blood and pus. In cases of impaction, the content is tick, dry to pasty and has a tubular to ribbon-like shape.
   3. The microscopic exam of normal anal sac content reveals epithelial cells, a few neutrophils and bacteria (typically extracellular). Many leukocytes, red blood cells and numerous bacteria, especially intracellular, indicate diseased anal sacs. However, as mentioned before, criteria that can be used to differentiate normal from infected anal sacs are the presence of more than 10% of the microscopic fields (100x) with intracellular bacteria and red blood cells. These criteria need to be validated in studies.
   4. Bacterial culture and susceptibility should be performed to select the systemic antibiotic to treat cellulitis.
   5. In the presence of a mass, fine-needle aspiration and/or biopsy should be performed to rule out neoplasia.
   6. Imaging of the abdomen and thorax is indicated in cases of AGASAC.

4. Treatment

   1. Impaction:
      1. Gentle expression of the anal sacs content is mandatory. In cases where the content is hard to express, a ceruminolytic agent can be instilled into the sacs to help soften the content and allow its adequate removal.
      2. Feline anal sac impaction typically occurs without infection and may not recur after expression for a long period. In contrast, in dogs, impaction may recur in 19% to 80% of the cases within 3 days to 3 weeks after expression.
      3. To reduce the frequency of recurrences, regular manual expression for a period of time and diet changes may be beneficial.
      4. Surgical removal, if frequent recurrences, is an option to offer owners.
      5. Look for concomitant dermatoses and treat them appropriately.
   2. Inflammation/Infection:
      1. Treat locally as follows:
         1. Express gently the anal sacs content using a gloved, lubricated finger.
         2. Cut a Tom Cat catheter [3.5 French x 51/2 inch (14 cm)] approximately in half at a right angle. Lubricate the catheter and flush the sacs with saline by gently inserting the catheter into the anal sac opening and through the anal sac duct. Thereafter, attach a 6 mL syringe to the catheter and flush the anal sac until the content comes out clean.
         3. Instill an ointment or solution containing an antimicrobial and a glucocorticoid into the sacs until the product overflows. The authors typically use ear ointments that contains an antibiotic, antifungal and glucocorticoid.
         4. Repeat the procedure every 2 to 3 weeks until the sacculitis is resolved. In general, at least three local treatments are needed.
         5. Sedation is recommended to facilitate the procedure.
      2. The authors do not recommend using systemic antibiotic to treat anal sacculitis because it is not an effective treatment. In contrast, local treatment is very effective because the concentration of antimicrobials at the site of infection is significantly higher than the MIC needed to inhibit the bacteria.
      3. Surgical removal, if frequent recurrences, is an option to offer owners.
      4. Look for concomitant dermatoses and treat them appropriately.
   3. Abscessation:
      1. If the abscess is not ruptured, hot pack the affected area several times a day until the abscess is ready for drainage.
      2. The abscess then is lanced and the content thoroughly expressed.
      3. The anal sac duct must be open, often requiring cannulation.
      4. When the abscess has ruptured or has been surgically opened, it should be flushed with 10% povidone iodine, diluted hydrogen peroxide and/or chlorhexidine daily until closed.
      5. In cases of cellulitis, systemic antibiotic therapy should be administered based on culture and susceptibility.
      6. If the tissue does not heal with medical therapy, surgical excision of the anal sac is indicated.
      7. Look for concomitant dermatoses and treat them appropriately.
   4. Neoplasia:
      1. Consult with or refer to an oncologist for appropriate treatment.

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