Hygromas are the way your cat’s body may react to protect a bony area where repeated trauma is occurring. When repeated irritation or trauma occurs, the body produces a fluid (serum) encased in a thick capsule of tissue to create a cushion between the skin and a bony prominence. This is most commonly seen in cats at the elbow where they develop as a response to repeated trauma in an area where there is little tissue between the skin and bone. Hygromas can become quite large, interfering with movement if left untreated and trauma continues. Complications arising from hygromas can include ulceration and infection. If your cat develops a hygroma you should consult your veterinarian for treatment.

Hygromas in cats present as a slowly enlarging fluid-filled swelling.

Hygromas are caused by a buildup of serum or fluid in a sac at the site of a bony prominence where the skin is thin and there is little tissue protecting the bone. Causes of this are:

Your veterinarian will perform a physical exam on your cat to determine the nature of the swelling. The location of the swelling at a joint with a bony prominence will be an indicator of hygroma. Your vet may perform radiographic tests (x-ray, scans) to rule out fracture or joint disease. In addition, a sample of fluid may be taken by fine needle aspiration to rule out abscess (infections) and neoplasia (tumor). If a hygroma is diagnosed and requires surgical intervention, your vet may perform routine blood and urinalysis to check the general health of your pet prior to surgery.

Treatment varies depending on the size of the hygroma. Small hygromas may be treated with padding over the area to protect the area from continued pressure and allow the hygroma to shrink on its own. If this occurs, further more invasive treatment may not be required.

If the hygroma is large, and especially if it becomes infected (which is common), your veterinarian will need to surgically drain the fluid and, if necessary, treat the infection with antibiotics. Depending on the area and extent of swelling, a drain may be sutured in and left in place temporarily to allow drainage to continue over a period of time. If the hygroma is especially large, skin grafting may be required to repair damage caused in the removal of the hygroma.

Bandaging and padding of the area will be required postoperatively to ensure no further trauma or irritation occurs during healing that would result in a recurrence of the hygroma.

Treatment will also involve identifying the trauma or traumas responsible for the hygroma and ensuring that your cat is no longer exposed to the cause, for example lying on a hard surface or repeatedly getting stuck in a small space.

There is a high risk of complications from surgical excision and this is not usually recommended for treatment of hygromas. 

Prognosis is good unless complications such as ulceration or infection have occurred which will require further intervention, medication and treatment.

Recovery is usually straightforward. Your cat may need cage rest if a drain is temporarily placed, to prevent the drain coming out prematurely, and an Elizabethan collar to prevent them tearing at drain, sutures, or bandaging. If sutures are in place they will need to be removed by your veterinarian.

Identifying and removing the trauma responsible will prevent reoccurrence of the hygroma. Your pet should not be allowed to lie on a hard surface, they should be given a padded bed with adequate bedding during and after recovery. 

You should monitor your pet for signs of complications during recovery, including continued irritation, ulceration, rupture of sutures, infection, or drain coming out prematurely.