Typhoon is one of those cross-bred dogs who has enjoyed excellent health for his entire life: Collies have been bred for function rather than appearance, so in general, they tend to be healthier animals than many modern dog breeds.
Last week, Andrew noticed something worrying: a large, fist-sized lump had appeared beneath Typhoon’s left ear. This felt firm, and it wasn’t painful to touch. Andrew knew enough about dog health to realise that this was potentially a serious problem. He had once owned a dog that had developed a lump when she was thirteen years old; it turned out to be cancer, which ended up taking the life of his pet. At eight years of age, Typhoon was a middle aged animal, at the stage of life where certain diseases – including cancer – become more common. For this reason, he brought Typhoon to see me the next day.
When I examined Typhoon, I was as concerned as Andrew had been. The lump was large, and it was not in a place that could be easily explained by reasons other than cancer. It was not a lymph node, or another normal structure of any kind. And when I squeezed it, Typhoon didn’t mind, which meant that it was unlikely to be an abscess or infection. This meant that cancer was high on the list of possibilities.
In this type of situation, there is only one way forwards: a sample of the lump needs to be collected and sent off to the laboratory for analysis. The simplest way of doing this is to take a type of biopsy known as a Fine Needle Aspirate (FNA). This is exactly what it sounds like: a fine needle (just like the type of needle that’s normally used to give an injection) is pushed through the skin, into the swelling. When this is done, some of the cells from the swelling are collected in the needle barrel. The needle is then pulled out, and its contents are squirted directly onto a microscope slide. The slide is then dried, and sent off to a laboratory. A pathologist then uses special stains to treat the slides, and then examines them in detail under the microscope. When cells are examined at a magnification of a hundred times or more, it’s possible to identify them precisely. If the swelling is caused by a cancerous growth, cancer cells can often be seen under the microscope. And if a swelling is caused by a benign process such as inflammation, a different type of cells are present.
The technique is not always 100% effective at diagnosing cancer: not all cancers have cells that can be easily collected and identified. But it’s still the easiest, fastest and cheapest way of carrying out a rapid screen for cancer when a pet develops a suspicious lump.
A Fine Needle Aspirate is usually almost painless, in the same way as a simple injection is barely noticed by most pets. So it’s usually done in a consultation, without needing to admit the patient to the clinic for the day.
So after discussing this with Andrew, I went ahead and took a Fine Needle Aspirate from the swelling beneath Typhoon’s ear. Typhoon sat still while I did this, but something unexpected happened. When I pushed the needle in, a dribble of fluid dripped from the needle. I had thought this was a solid mass, but it now seemed that it contained liquid of some kind.
I attached a large syringe to the needle, and I pushed it in again. This time, I drew the plunger back on the syringe, and to my surprise, I sucked back around 20 ml (four teaspoonfuls) of clear fluid, like water. It was now obvious that the swelling was not solid after all: it was a fluid-filled structure that had been so pressurised that it felt hard.
I continued to suck out the fluid with the syringe until there was no more left, and by this stage, the swelling had completely vanished. So what on earth was the cause? There was no point in sending any sample off to the laboratory: the lump had just contained fluid, without any cells to analyse.
So what could cause a lump filled with clear fluid? In theory, a cyst could develop like this randomly, but that would tend to grow slowly. This had come up quickly, so it was more likely to be something to do with a sudden incident.
I asked Andrew a bit more about Typhoon’s life: how did he spend his time. What sort of exercise did he get? Andrew explained that he had two dogs, and the dogs had occasional tussles with each other. The other dog was bigger and stronger, and he sometimes pinned Typhoon to the ground, gripping him firmly by the neck. There was never any serious aggression, but it was certainly rough play.
This gave me the answer I was looking for: the mass was most likely to be a swelling called a haematoma, or a blood blister. When the other dog had grabbed Typhoon by the neck, a blood vessel under the skin must have burst. The bleeding had caused the swelling to appear, but then the blood had clotted, and all that was left was the fluid component of the blood, called serum. And this was the clear fluid that I had drained.
Now the the mass was empty, there was no need for any other action: as long as the other dog doesn’t grab his neck again, Typhoon’s lump has hopefully been cured for good.