Leukemia (Blood Cancer)

Abscesses

Everyone who has ever had a pimple has had an abscess, even though they’re tiny, they’re still abscesses. An abscess forms when normal tissue, like skin, for example, is split apart and that new space is invaded by nearby pathogens like bacteria. And there are roughly ten bacterial cells for every human cell and they cover every surface of the human body.

So any cut or break in the skin or closed-off area within the body is an invitation for bacteria to dive in and multiply. When that happens the immune system typically responds and a battle ensues with the result being pus - a mixture of bacteria, immune cells, and dead tissue. So, in response to an injury, the tissue releases small chemicals in the local area called cytokines, like tumor necrosis factor, interleukin-1, interleukin-6 and interleukin-17, and chemokines which attract nearby white blood cells which are part of the immune system.

It’s kind of like yelling for help and being heard by the nearby police. In addition to attracting immune cells, the cytokines also dilate nearby capillaries – which bring more blood to the site, and make the capillaries leakier, so that the white blood cells that do show up, can slip out of the blood and get into the tissue more easily. Oftentimes, the first immune cells at the scene are Neutrophils, which release chemicals and enzymes that kill bacteria and dissolve pieces of dead cells, creating a pool of dead material. This is a specific type of acute inflammatory response called supportive inflammation, which simply means that pus is created in the process.

From a macroscopic view, this is sometimes referred to as liquefactive necrosis, because the area of dead tissue turns to liquid. As those immune cells get to a point where they can’t withstand the environment, they die too and become part of that pool. Initially, the debris might be intermixed with healthy tissue, but over time it can coalesce into a single area - a process that is often sped up when more immune cells get involved. Around this pool of pus, a wall of fibrinogen - which is the same protein that holds together blood clots - starts to harden into a barrier. Occasionally sheets of fibrin form septations, creating loculation or pockets of pus within the abscess itself...kind of like an abscess within an abscess...Even though the pus is largely dead material, there are still plenty of live bacteria within the pus, which makes it highly infectious if it gets spread from one place to another.

One of the most common bacteria found in abscesses, especially in the skin or underlying soft tissue, is Staphylococcus aureus. In fact, Staphylococcus aureus releases the enzyme coagulase, which helps speed up the process of building the fibrinogen wall. In contrast to an abscess near the skin, ones that originate deeper in the body often occur in spaces that are already relatively walled off.

For example, in the gallbladder, if a stone blocks bile from flowing out, it essentially becomes a new home for bacteria. Bacteria from the nearby small intestine can easily sneak past the stone, crawl into the gallbladder, and multiply, which causes an inflammatory response, and eventually, an abscess might form. Typically these deep infections are a mix of aerobic bacteria that use up all of the available oxygen, and anaerobic bacteria that can only live in its absence. As far as symptoms go, abscesses typically cause signs of inflammation - which are redness, warmth, swelling, and pain.

Abscesses on the skin, often come to a head over time, where the tissue overlying the abscess breaks down allowing it to drain out by itself. People with weakened immune systems, like newborns and those undergoing chemotherapy treatment for cancer, are at particularly high risk, because they’re not able to “wall off” the infection, allowing the bacteria to get out of the tissue and into the bloodstream. In these situations, symptoms can also include fever and vomiting.

Diagnosing an abscess in the skin or soft tissue is usually done by feeling it or sometimes with an ultrasound of the area. When an abscess is filled with enough fluid it becomes possible to feel the fluid move around - and this is called fluctuance.

A deeper abscess is usually diagnosed through imaging studies like ultrasound, CT, or MRI scans. Intravenous imaging contrast can really stand out around an abscess since the small blood vessels around the abscess remain dilated and leaky due to the constant inflammatory response. This is called ring-enhancement since it lights up the blood vessels around the abscess.

Generally speaking, infections are treated with antibiotics alone, but in order for antibiotics to work, they need to first reach the bacteria, and that’s usually done through the bloodstream. Since abscesses do not have blood vessels inside of them, the antibiotics can only diffuse into an abscess and that’s not very effective especially when dealing with a large abscess; you could imagine it getting those guys close to the edges, but there’s no way it’s getting to the bacteria in the middle. That’s why the most important treatment for an abscess is incision and drainage – in other words, cutting it open and squeezing out or somehow removing everything inside. Doing it thoroughly is important so that all of the septations get removed so that parts of the abscess don’t remain intact. Oftentimes, there can be a large empty cavity that remains afterward, and this can easily get re-infected.

To prevent that, large abscesses that are drained are often packed with gauze to fill in the space, until the tissue heals naturally on its own over time. Deeper abscesses sometimes have to be drained with long needles or surgery, depending on the location.

Finally, antibiotics are sometimes used even after drainage to make sure that there are no additional bacteria are lingering around.