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Abscesses – causes, symptoms, diagnosis, treatment, pathology

September 17, 2019


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 one 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 kinda like like yelling for help and
being heard by the nearby police. In addition to attracting immune cells, the
cytokines also dilate nearby capillaries – which brings more blood to the site, and make the
capillaries more leaky, so that the white blood cells that do show up, can slip out
of the blood and get into the tissue more easily. Often times, the first immune cells at the
scene are neutrophils, which release chemicals and enzymes that kill bacteria and dissolve
pieces of of dead cells, creating a pool of dead material. This is a specific type of acute inflammatory
response called suppurative inflammation, which simply means that pus is created in
the process. From a macroscopic view, this is sometimes
referred to a 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 loculations or pockets of pus within the abscess itself…kinda 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. For abscesses on the skin, they 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 partiularly 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. Often times, there can be a large empty cavity
that remains afterwards, and this can easily get reinfected. 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. Alright, with that in mind, here’s what
you’ve all been waiting for—a video of an abscess on the earlobe being drained, buckle
up.

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