Structure and Function of the Anal Glands in Dogs
Dr. Dawn Ruben
What Are the Anal Glands?
The anal glands (also called anal sacs) are two glands that secrete a pungent fluid. The fluid travels through small ducts that open into the anus. Typically, this fluid is released during defecation or territorial marking.
Where Are the Anal Glands Located?
The anal glands are located on either side of the anus, just under the skin, at the 4 o'clock and 8 o'clock positions. The glands are embedded in the muscle of the anal sphincter and are not readily visible.
What Is the General Structure of the Anal Glands?
The anal glands are small oval shaped sacs lined with tiny glands. The sacs range in size from that of a pea to a hazel nut. Each tiny gland in the sac produces a fluid that passes through a multitude of small ducts and eventually collects in the sac. As feces pass through the anus, the glands are squeezed, and the fluid is released through a small opening in the duct of the sac.
What Is the Function of the Anal Glands?
The only known function of the anal glands is to produce small amounts of secretions, ranging in color from yellow brown to gray. The fluid is watery to pasty in consistency. It is thought that these secretions are used as a way to mark territory and identify the dog to other dogs. The secretions from these glands are very pungent and may also be expressed when the animal is frightened or alarmed.
What Are Common Diseases of the Anal Glands?
Many dogs never develop problems with these glands, and most people are unaware of their presence. In a some dogs, anal gland impactions, infections, abscesses, ruptures and tumors occur. Diseases of the anal glands vary in severity in the signs they produce. Common symptoms of anal gland disease include "scooting" (dragging the rear end across the floor), a foul odor near the anus, and pain, licking or biting at the rectal area.
Anal gland impactions are the most common disorder associated with the anal glands in dogs. For unknown reasons, the fluid produced in the glands becomes too thick to be expressed naturally through the opening of the ducts into the anus. The fluid continues to be produced, resulting in an enlargement of the gland, secondary irritation, and possibly infection.
Anal gland infections are typically bacterial infections that cause local irritation and inflammation. Abscesses develop when an infection worsens and a significant accumulation of pus occurs within the anal gland. The anal gland may be impacted at the same time. The abscess may continue to enlarge until it ruptures through the skin, causing a small draining hole to develop near the anus. Pus may drain from this small hole.
Anal gland tumors in the dog are often malignant and are classified as adenocarcinomas. Sometimes anal gland tumors result in elevated blood calcium levels, which can cause significant organ damage, including kidney failure.
What Types of Diagnostic Tests Are Used to Evaluate the Anal Glands?
Physical examination and rectal palpation are the primary methods of evaluating the anal glands. Rectal palpation is performed by inserting a gloved finger into the rectum to feel the gland. Radiographs (x-ray) and blood work are not typically used to evaluate the anal glands, but blood tests may sometimes suggest the presence of infection, which prompts further examination of these glands. Tumors of the anal glands are confirmed with a biopsy.