Not All Dark Masses are Tumors

Joanne Lynn Intile, DVM, MS, DACVIM
Updated: April 22, 2014
Published: November 07, 2012
Share this:

Trixie’s owners sat stone-faced across from me in the exam room. They were a middle-aged couple filled with worry for their beloved 14-year-old tabby cat; they had been referred to me for evaluation of a tumor in her chest. Trixie was like a child to her owners — this became evident within the first few minutes of the appointment when they would finish each other’s sentences while describing how she played fetch with her toys or how she begged for food like a dog or how they picked her out from a litter of seven other kittens at their local animal shelter. 


Their tone became solemn as they described how Trixie had developed a slight cough over the past few weeks, which did not resolve with treatment with antibiotics and anti-inflammatory medications. Her primary veterinarian performed radiographs (X-rays) of her chest the week before their appointment with me and saw a suspicious area within the cranial (front) part of her chest cavity. She was very worried about a tumor as a cause of the chronic cough, and so she referred Trixie and her owners to the oncology service at my hospital for further testing and treatment options.

Prior to meeting with Trixie’s owners, I reviewed her radiographs and saw exactly what her veterinarian was troubled about. I too was concerned about what I saw on the films. There was an irregular mass located in the normally tiny space between the left and right topmost portion of Trixie’s lungs, sitting just in front of her heart. From a purely logical standpoint, the odds weren’t in Trixie’s favor. She was a geriatric cat, and some statistics suggest that more than 50 percent of pets over the age of ten will develop cancer.

I know the most common types of tumors that grow in the chest include lymphoma, thymomas, tumors of the thyroid or parathyroid glands, or even tumors that spread from another area in the body, none of which were options offering a good long-term prognosis. The mass was also quite large, which added another negative for Trixie, due to concern that it could be invading into regional blood vessels and/or nerves. I also know chest tumors can often cause fluid to build up within the space around the lungs, which further restricts expansion of these vital organs, causing a reduction in ability to oxygenate blood, which could ultimately prove fatal. Despite all of these undesirable outcomes, I also knew we didn’t have an actual diagnosis of cancer, which meant there was a chance the abnormality seen on the radiographs represented something completely benign. Further testing was necessary in order to provide an accurate prognosis. As I always tell owners, nothing makes me happier than to tell them their pet actually doesn’t have cancer, and I was really hoping to be able to do that for Trixie.

I sat before Trixie and her owners and explained my concerns about the possible causes for the mass. My recommendation was to perform an ultrasound of the mass to try to better clarify its location in relation to other organs within the chest, to gain some information as to whether the mass was attached to any vital structures, and most importantly, to attempt to obtain a sample of the cells comprising it, using what is known as a fine needle aspirate procedure. No matter what I said, Trixie’s owners remained absolutely grim and teary-eyed with concern over her welfare. Nothing I could offer would console them that there could possibly be a good outcome. They asked me many questions about the different types of cancer it could be, and expressed they were not likely to pursue surgery or radiation therapy or chemotherapy, should those treatment options be recommended based on the outcome of the ultrasound. However, after much deliberation, they wanted to know more about what the mass was, and they agreed to perform the scan.

Trixie was positioned on her back and a small region of fur was clipped away from the side of her chest. The radiologist swabbed a small amount of bright blue gel along the bare skin and changed a few settings on the ultrasound machine. He gently placed the probe on her side and we both stared attentively at the screen, while swirls of blacks and whites and shades of gray appeared at first in a rather haphazard manner, then slowly taking form into more recognizable structures: the rhythmic beating of her heart, the bright contrast of a rib bone, the rippled shadows of the lung tissue, and there it was, the mass itself, sitting right in front of the heart and between the lungs.

Knowing the typical ultrasonographic appearance of tumors, I anticipated seeing a solid form of gray tissue, but instead I found myself staring at a screen filled with blackness, surrounding by a thin rim of brightness. At first none of the images made sense, but after a few seconds, I turned to the radiologist and we both exclaimed our thoughts at the same time: "It’s a cyst!"

The swirling blackness on the screen was no mirage. It represented fluid, which meant the ominous mass seen on the radiographs was nothing more than a large liquid-filled sac known as a cyst. Cysts arise when the cells lining various structures within the chest cavity begin producing excessive amounts of fluid, which accumulates slowly, similar to a water balloon. Over time this can cause compression of the surrounding organs. To be absolutely sure of the diagnosis, we elected to introduce a small needle into the structure and withdrew some of the fluid. It appeared colorless and without cells, confirming our diagnosis. Trixie did not have cancer!

When I told her owners the great news, they were relieved and thrilled. They started tearing up again, but this time out of sheer happiness. We discussed the different ways to manage her cyst, and since Trixie wasn’t really showing any clinical signs associated with her diagnosis at this point, we did not need to intervene at this time. Rather, we would be able to monitor her condition with repeat imaging tests to assess growth of the cyst over time.

Although her owners were overcome with emotion, and although I felt so happy to report that her prognosis was now excellent for long-term survival, Trixie, like a typical feline, seemed otherwise unimpressed with the day’s events, and she scowled at the three of us from the depths of her pet carrier, gently thrashing her tail from side to side in protest of her lack of breakfast.

Trixie is a good example of why it is important to take the extra step to pursue additional tests to confirm a diagnosis, even when there is a great deal of suspicion that an animal’s signs are due to cancer. When I discuss various additional diagnostics with owners, sometimes it is a struggle to communicate the reasoning behind my recommendations, especially when they may perceive the tests as redundant or unnecessary or invasive. Experience allows me to have just enough breadth to recognize the many non-cancerous conditions that can mimic cancer and it is my goal to be able to provide owners with all available options, which I can only really accurately do when I am certain of a diagnosis. In my opinion, this is especially true when owners are not inclined to pursue definitive treatments for cancer, as I strongly feel they should make such a decision with as much information as possible.

Trixie continues to do well, and although she may cough from time to time, I am happy to report that she remains cancer-free and continues to provide her owners with joy and companionship — and the occasional tail thrash on the days she has her recheck appointments. I don't take it personally though — we all take it as a sign of her continued good health and we look forward to her visits each month.

Dr. Joanne Intile

Image: Emma’s Xray by Jason Pierce / via Flickr