As our domesticated pets live longer lives, the potential for diseases to occur in their lifetime also increases. Of the common conditions afflicting our canine companions, lumps and bumps often result in a trip to the vet clinic or are frequently detected at a wellness exam such as the annual vaccination visit. Skin lumps come in all sorts of shapes and varieties and the level of concern that they raise differs depending on the behaviour of the growth.
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The Layers of the Skin
The visible portion of the skin is the epidermis. It acts as the body’s barrier against environmental contaminants and controls the loss of fluid and salts. Below this is the dermis which acts as a support for the epidermis, housing the blood vessels that supply nutrients to the skin. In haired parts of the body, the dermis also contains hair follicles from which fur or whiskers grow up and poke through the epidermis. Associated with hair follicles are sebaceous glands.
Sebaceous glands are oil glands, producing a substance called sebum which naturally conditions the animal’s coat. When your dog or cat licks themselves, they are spreading this sebum across their coat. The sebum produces a natural sheen to the fur and aids with softness, both of which are a sign of a healthy coat. Sebaceous glands occur anywhere there are hair follicles, but they are present in increased concentrations in certain body parts, namely the paws, rump and tail area, the chin, and the back of the neck.
Sebaceous Gland Lumps
Lumps form when tissue (a group of similar cells) becomes inflamed and irritated, or the cells within a particular tissue grow excessively (known as hyperplasia) or abnormally (known as a neoplasm, or tumour). Tumours are categorised as benign or malignant based on their behaviour or anticipated progression. Benign tumours are a localised problem, affecting that region only, without anticipated spread (metastasis) to other body regions. Benign tumours that develop in glands, are known as adenomas; they are named according to the gland of origin. Benign tumours of the sebaceous glands are therefore sebaceous gland adenomas. Some adenomas may be referred to as an epithelioma if they extend deep into the skin.
By contrast, malignant tumours are generally more destructive than benign tumours. They not only are more likely to alter localised tissue, but they are also more likely to metastasise to other body parts. Malignant tumours that develop in glands are adenocarcinomas, and therefore malignant tumours of the sebaceous glands are called sebaceous gland adenocarcinomas.
Sebaceous Gland Adenomas in Dogs
Hyperplasia of the sebaceous gland is the most common type of growth to stem from these glands. Sebaceous gland adenomas are thought to be a progression of this hyperplasia. As such, the names are sometimes used interchangeably although they are distinct conditions. The likelihood of your dog getting one of these growths increases with age and they are more common in miniature schnauzers, poodles, and cocker spaniels. As sebaceous glands are found wherever hair follicles exist, they can occur on any part of the body, however they more commonly occur on the head and torso.
Sebaceous gland hyperplasia, epitheliomas, and adenomas look visibly similar on the surface. They are usually white to pink/purple in colour and have an irregular outline, sometimes looking like a cauliflower head. As they stem from sebaceous glands, they sometimes secrete a white material from the surface which can form a crust.
Due to their appearance, they are sometimes referred to as warts.
Many dogs develop multiple of these growths across their lifetime, but it is not fully understood why they occur. Unlike warts in people, which are caused by a virus, these canine growths are not true warts as they do not have a virus trigger.
As a benign growth, they are generally considered to be of low concern to your dog’s health. However, even benign growths can become problematic. As the growths protrude above the skin surface, they can become traumatised. Clippers used during grooming sessions can catch them and irritate the surface, or they may be accidentally damaged during play or walks. Some dogs also chew or nibble at these growths, causing self-trauma. The result of this is ulceration, inflammation and/or infection of the damaged tissue.
Treatment for Sebaceous Gland Adenomas
Your vet may diagnose these growths by visual appearance alone as they are quite characteristic, although only a biopsy or removal and analysis of the lump itself can give confirmation. The benign behaviour of these growths means that nothing may need to be done if your dog develops them. Your vet can discuss with you the pros and cons of intervention.
Unlike true warts, freezing does not get rid of hyperplasia or adenomas. If the growths are being irritated, your vet may recommend surgical removal. Depending on the size, location and general health of your dog, this would involve either a general anaesthetic or sedation combined with local anaesthetic. In the case of animals with multiple sebaceous gland growths, it may not be possible or advisable to remove all the growths at one time.
If a growth that was initially left alone seems to be changing in appearance or is becoming irritated, a repeat assessment by your veterinary team should be sought. Recommendations for intervention may change if this has occurred. Malignant sebaceous gland adenocarcinomas are far less common than hyperplasia and adenomas. If your vet is concerned with the appearance or behaviour of your dog’s growth, they may recommend more radical surgery.
Conclusion
Skin lumps involving the sebaceous glands, especially hyperplasia, are common in our pet dogs. The vast majority are benign and therefore of no major concern to your pet. However, even benign growths can become bothersome and may need removal. Whenever you find a new lump on your dog, or a previously assessed lump has changed, your vet can advise you on what is the best way to diagnose and treat them in your pet.
Further Reading:
- Moriello, K. (2022) Structure of the skin in dogs.
References:
- Brooks, W. (2023) Benign sebaceous gland tumours.
- Vail, D.M. and Withrow, S.J. (2007) ‘Tumours of the skin and subcutaneous tissue’ in Withrow & MacEwen’s (eds) Small Animal Clinical Oncology (Fourth Edition).
- The National Canine Cancer Foundation (no date) Sebaceous and modified sebaceous gland tumours.
Discussion