The appendix is the little one-ended tube that’s attached to the cecum of the large
intestine, sometimes it’s called the vermiform appendix, where vermiform means “worm-shaped”,
so, that should paint a pretty clear picture of what it looks like.
This odd, yet kinda cute little worm-like structure’s function is actually unknown,
though some theories suggest it might be a “safe-house” for the gut flora, and some
evidence seems to suggests it plays a part in the lymphatic and immune system; other,
arguably more cynical viewpoints maintain that it’s just a useless vestigial organ
from our ancestors.
Whatever the case, the fact remains, it’s pretty talented at getting inflamed and causing
abdominal pain, a condition known as appendicitis, as much as 10% of the population develops
appendicitis, and it’s the most common surgical emergency of the abdomen.
Since the appendix is a hollow tube, the most common cause of inflammation is something
getting stuck in or obstructing that tube, like a fecalith, a hardened lump of fecal
matter that finds it’s way into the the lumen of the appendix and wedges itself there.
It could also be other things though, like seeds that weren’t digested, or even pinworm
infections, which are intestinal parasites.
Another cause of obstruction, especially in children and adolescents, is lymphoid follicle
growth, also known as lymphoid hyperplasia.
Lymphoid follicles are dense collections of lymphocytes that get to their maximum size
in the appendix during adolescence.
Sometimes this growth can literally obstruct the tube.
Also, when exposed to viral infections like adenovirus, measles, or even after immunizations,
the immune system ramps up and these follicles can grow as well.
Whatever the obstruction is, now this appendix is plugged up, right?
Well, the intestinal lumen, including the appendix, is always secreting mucus and fluids
from its mucosa to keep pathogens from entering the bloodstream and also to keep the tissue
moist.
Even when it’s plugged, the appendix keeps secreting as usual.
When this happens, fluid and mucus builds up, which increases the pressure in the appendix,
and just like when you fill up a water balloon, it gets bigger and physically pushes ons the
afferent visceral nerve fibers nearby, causing abdominal pain.
Along with that, the flora and bacteria in the gut are now trapped, and intestinal bacteria
that are usually kept in check in the gut, like E. coli and Bacteroides fragilis are
now free to multiply.
This causes the immune system to recruit white blood cells and pus starts to accumulate in
the appendix.
This activation of the immune system can be seen in the lab as an increase in the serum
white blood cell count.
Patients might also develop a fever in response to the infection, which in combination with
right lower quadrant abdominal pain at the point roughly where the appendix is, known
as known as mcburney’s point, is a super important sign for identifying appendicitis.
Also, along with fever, other classic symptoms include nausea and vomiting.
Now if obstruction persists, the pressure in the appendix increases even more.
At a certain point, as the pressure keeps growing and it continues to swell up, it pushes
on and compresses the small blood vessels that supply the appendix with blood and oxygen.
Without oxygen, the cells in the walls of the appendix become ischemic and eventually
die.
Since these cells were responsible for secreting mucus and keeping bacteria out, now the growing
colony of bacteria can invade the wall of the appendix.
As more cells die, the appendiceal walls become weaker and weaker and for a small proportion
of patients, to the point where the appendix ruptures.
Rupture of an infected appendix allows the bacteria to escape the appendix and get into
the peritoneum, and patients often experience peritonitis with rebound tenderness, meaning
pain when pressure is taken off, again around mcburney’s point.
Patients might also have some abdominal guarding, where their abdominal muscles tense up when
pressed to try and avoid pain.
The most common complication with a ruptured appendix is pus and fluid gets out and forms
an abcess around the appendix, called a periappendiceal abscess.
Sometimes subphrenic abscesses might also form, these would be tiny abscesses below
the diaphragm but above the liver or spleen.
The standard treatment for appendicitis is appendectomy, which is surgical removal of
the appendix along with antibiotics.
If patients have abscesses these are also important to surgically drain.
Removing the appendix isn’t known to have any negative side effects, and sometimes it’s
removed if the surgeons are already doing an abdominal surgery for some other reason
just to avoid an appendicitis down the road!