Hi Shane,
I believe it is one of 3 things and I’ll list them from most common to least common.
- Anal gland rupture. The lesion is situated over the anal gland. The anal glands sit on either side of the anus and they produce a stinky liquid that deposits on the poop as it passes out of the dog. There are many reasons why the liquid can get stuck inside the gland and then it gets thick and doesn’t release. It causes inflammation of the gland that is painful. They tend to rub their bum on the floor and lick back there. It can even rupture which can cause an anal gland abscess in dogs and it would look like the picture you provided. I recommend you see your veterinarian so he can feel it and see if anal gland material is coming through the lesion. They would likely clean it, provide antibiotics for infection, recommend frequent anal gland expressions, and offer some medication to reduce the inflammation or pain which is causing your dog to lick at it.
- Perianal adenoma or perianal adenocarcinoma. There are masses that can occur in this area and they can be cancerous. It’s possible for them to split open like this but I would definitely think it is less likely than the anal gland rupture. I would see your veterinarian and if they are concerned that it may not be an anal gland rupture, I believe they will recommend performing a quick ‘fine needle aspirate’ for ‘cytology’. This involves poking the tissue with a needle, collecting cells from it, and putting it on a slide to identify the type of lesion it is. This can be done in under a minute as long as your dog is restrained well or somewhat cooperative.
- Anal fissures. This is a very rare condition where there is an immune reaction in your dog that causes an open lesion in the tissue around the anus. It is a complicated and frustrating condition but it is unlikely. Also, in the picture, it likely wouldn’t occur right over the anal gland like this, it would be more distributed. Performing cytology to confirm it and then treating with a topical ointment known to suppress the excessive immune reaction is the treatment for it. A cream with the medicinal agent cyclosporine for dogs is often chosen but it is quite pricey.
I hope this helps. I would say it is likely the anal gland rupture.
Good luck and thanks for your question.
Dr. Greenway