Pocket of Fluid on Leg

A quick scan of my appointment schedule on any given day reveals a litany of the typical problems encountered by pet cats. Interspersed with the well-pet and update-the-vaccinations exams you’ll find “vomiting”, “diarrhea”, “urinating on the rug”, “runny eyes”, “losing weight”… the list goes on. It’s not often I see “pocket of fluid on leg”, so I was particularly curious about this one. 

(Please note, what follows is semi-graphic material (no pictures, just written experience).  Proceed with cation if blood, pus, and ooze makes you queasy.  If you just chuckled at "blood, pus, and ooze," then you'll be fine.)

When I examined Percy, sure enough, there was a noticeable bulge coming off the lateral surface of her left front leg. It was kinda floppy, as if it was filled with some kind of gelatinous material. It didn’t feel watery, like a cyst, and it didn’t feel smooth and solid, like a lipoma (a fatty tumor). I really hadn’t seen anything like this before.

Percy was getting a little cranky during the examination, and she wouldn’t let me feel her front leg as thoroughly as I would have liked. I recommended that we admit her for a few hours, sedate her, and then I could obtain a good quality x-ray, and then insert a needle into the swelling. If it turned out to be a solid mass, I would aspirate the contents into the hub of the needle, and then spray it onto a slide for evaluation by a cytologist. If the swelling contained fluid, I would submit the fluid to our laboratory for analysis. Percy’s owner consented.

We sedated Percy and I shaved the fur off her leg to get a better view of this swelling. (Percy is a long-haired cat and the hair was camouflaging the blob on her arm pretty effectively.) The swelling was centered over the lateral part of the forearm, between the elbow and wrist. The largest area was right in the middle of the arm. The elbow was not involved. The elbow was normal, and then about an inch down from the elbow, the swelling abruptly appears. As you progress down the leg, the swelling doesn’t abruptly go back to normal. It tapers as it approaches the wrist, but it looks like the wrist is not involved. 

The x-ray revealed that the bones are not involved at all. The radius and ulna were normal, and the elbow joint and wrist joint were unaffected. 

I decided to try to drain this swelling. I stuck a needle into it and aspirated. The syringe filled with fluid, but not your normal watery cyst fluid. This fluid was the color and consistency of corn syrup. It was very thick and it filled the syringe very slowly. I touched the syringe onto a microscope slide and squeezed out a drop, and when I pulled the syringe away, a long stringy strand of fluid appeared, connecting the drop to the syringe. This stuff was weird and sticky. I drained about 20 cc of fluid from the mass and saved it in some tubes. I submitted the tubes for analysis by a pathologist.

After I drained the fluid, I felt again. There was no solid mass at the base of the fluid pouch. All that was left was an empty sac. I called one of the surgeons at Blue Pearl Veterinary Partners for another opinion. The surgeon I spoke to confirmed that this was indeed bizarre, and he suggested that this could be some type of mass, like a sarcoma, that is secreting the sticky fluid. There are sarcomas called myxosarcomas that secrete a sticky material that resembles mucus (for lack of better description). Neither of us could come up with much else. He said he’d be happy to look at the cat once the fluid analysis came back, and we could then decide if this was something that was best addressed surgically. Percy woke up uneventfully and I sent her home.

Yesterday the analysis came back. The pathologist is calling this “joint fluid”. When I first aspirated the fluid, I thought it resembled joint fluid, but the swelling didn’t involve a joint! It seemed to begin in the mid-shaft of the forearm. The elbow and wrist weren’t involved. If the joints were normal, joint fluid accumulation would be unexpected. There was no sign of infection, and no signs of cancer, according to the pathologist. 

For now, Percy’s owner is going to just monitor things at home. I’m going to recheck her in a month to see if the fluid as re-accumulated. If it has, I think I will send the cat to Blue Pearl for a surgical consultation. Whether this thing needs to be removed or not remains to be seen. I suppose if it refills but causes no problems for the cat, she can live with a small bulge on her left forearm. If it continues to grow, or if it starts to bother her and affect the way she walks, she’ll probably need some procedure to reduce the size of it. I’m tempted to err on the cautious side and have a surgeon take a look sooner, as surgical removal would be more challenging if the bulge grows too large and starts encroaching on the joints above and below the swelling. In any event, we’ll revisit this puzzling cases in a later blog post, when she comes back for her recheck.

Never a dull moment, I tell ya.