- A seroma is a serous fluid-filled lump that typically forms at or near the site of a surgical incision; non-surgical seromas can also occur
- Post-surgical seromas generally appear 7 to 10 days after a procedure
- Seroma symptoms include no pain on contact, serous drainage from the incision/wound, and slight skin redness
- Many times, treatment consists of monitoring and activity restriction; draining or revision surgery may be recommended in some cases
- If a seroma becomes infected, your veterinarian may prescribe an antibiotic
While finding a fluid-filled lump at the site of your pet’s recent surgery is certainly upsetting, most lumps will typically end up being simple seromas. A seroma in dogs is a common post-surgical complication for our canine companions, and as far as lumps on your pets go, it’s one of the least concerning, That being said, it’s good for pet parents to have an understanding of what seromas are and how to manage them with the help of a veterinarian.
What Is a Seroma?
In dogs, a seroma is a fluid-filled lump that most commonly forms at or near the site of a surgical incision. These swellings contain serous fluid, which is a clear to yellow fluid that is slightly thicker than water. Serous fluid is made of blood plasma and inflammatory cells but doesn’t include actual blood.
It’s normal for healing wounds to have a small amount of serous discharge. When there is dead space (open space between tissue planes) or pocketing in a surgical wound, the serous fluid can accumulate and form a seroma.
Depending on how fluid-filled they are, seromas can feel soft to firm. Squeezing or poking a seroma sometimes feels like squeezing or poking a water balloon. Other fluid-filled lumps like hematomas or abscesses often feel similar, but hematomas contain blood and abscesses contain pus.
Causes of Seromas in Dogs
Formation of a seroma in dogs post surgery is relatively common. Reports vary, but one study showed that 18 percent of dogs developed a seroma after placement of closed suction drains in clean surgical wounds. 
Most post-surgery seromas in dogs appear typically within about seven to 10 days after. Surgical factors can contribute to seroma formation, such as if the surgeon leaves dead space when closing the incision or excessive dissection between tissue planes during the surgery. The dead space or pocketing can lead to serous fluid accumulation.
Seromas often develop when incisions are in high-motion areas of the body or on the underside of your pet. Seromas can also develop in dogs who aren’t adequately rested after surgery. Dogs with surgical incisions should usually have activity restriction for at least 10 days, which means no roughhousing, jumping around, or running. Your dog should be leash-walked after surgery.
Because spay surgery is common, with an incision on the dog’s belly, formation of a seroma after this type of surgery is one of the most common seroma presentations at veterinary clinics.
Seromas can also develop with non-surgical wounds. Examples include traumatic wounds (like from getting hit by a car) or puncture wounds. Like surgical wounds, dead space within these wounds may result in fluid accumulation, causing a seroma.
A dog of any breed or age group can develop a seroma. Highly active dogs, dogs with large incisions, dogs who have incisions in high motion areas, and recently spayed female dogs are more likely to develop seromas.
Symptoms of Seromas in Dogs
A visible, fluid-filled lump near a recent incision is the main symptom, but other symptoms to be aware of can include:
- No pain when touched
- Serous drainage from the associated incision or wound
- Slight skin redness (Seromas don’t usually cause the level of inflammation seen with abscesses or bruising sometimes seen with hematomas.)
Diagnosing Seromas in Dogs
If you suspect your dog has developed a seroma after spay surgery or another procedure, it’s a good idea to have the surgery site checked out by your veterinarian.
Your veterinarian will usually be highly suspicious of a seroma just by knowing your dog had a recent surgery or injury and feeling the lump. Their suspicions can be confirmed by placing a needle into the lump and removing fluid. If serous fluid is removed, it’s likely to be diagnosed as a seroma.
In some cases, the veterinarian may look at the fluid under a microscope to rule out infection. If the veterinarian is concerned that there may be a hernia, they may recommend an X-ray of the area or an ultrasound of the bump prior to placing a needle in to ensure that the swelling is just fluid and not organs.
How to Treat Seromas in Dogs
In many cases, seroma treatment in dogs simply requires patience and monitoring on your part. A lot of seromas resolve on their own over time. The body’s resorption of the seroma may take several weeks.
If you and your veterinarian determine that waiting to see if the body handles the seroma on its own is the best option, your veterinarian may recommend placing a heat pack on the seroma for 10 to 15 minutes several times per day. The heat will encourage the vessels to dilate, which can encourage fluid resorption.
Your pet should be activity restricted while you’re monitoring the seroma. Again, activity restriction in dogs generally means no rough play, no jumping or running, and short leash-walks only, though your veterinarian may have additional activity restriction recommendations.
If the seroma is particularly large or bothersome to your pet, the veterinarian may recommend draining the fluid. Unfortunately, a lot of seromas will refill after a one-time draining.
For particularly pesky seromas that don’t want to resolve, the veterinarian may recommend placing a temporary drain that removes fluid or undergoing a revision surgery to tack down dead space.
Some seromas can become infected and lead to abscess development, so your veterinarian may prescribe antibiotics, such as cephalexin, to prevent infection.
How to Prevent Seromas in Dogs
Preventing surgical seromas is a joint effort. Your veterinarian works to prevent seromas in tacking down dead space during your pet’s surgery, and you work to prevent seromas by following your veterinarian’s activity restriction recommendations.
However, in some cases, despite everyone’s best efforts, a seroma still develops. Very rarely are seromas dangerous in dogs, and luckily, they’re usually easy to manage with time and patience.