ANATOMY
Irrigation of the intestinal tract depends on three branches of the abdominal aorta: the celiac trunk,
the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA).
The first and second portions of the duodenum are irrigated by the gastroduodenal artery,
which most commonly arises from the common hepatic artery of the celica trunk.
The third portion of the duodenum receives arterial blood from the inferior pancreaticoduodenal branches of the SMA.
The jejunum,
ileum and caecum are irrigated by the AMS,
as well as the ascending colon (by the right colic artery) and the transverse colon (by the middle colic artery).
Finally,
the descending colon,
the sigma and the upper portion of the rectum are irrigated by the IMA and its branches the left colic artery,
sigmoid branches and superior hemorrhoidal artery respectively.
ETIOLOGY
AMI occurs because of an inadequate blood supply to the bowel,
due to many different causes,
that can be divided into occlusive or not occlusive.
In the first group,
the occlusion can be either arterial (the most frequent of both) or venous; for the former,
the most frequent cause is thromboembolism (40-50% of the cases),
followed by thrombosis (20%),
dissection (5%),
arteriosclerosis,
postsurgical complications,
vasculitis and fibrous dysplasia,
while the latter is mainly caused by venous thrombosis,
hypercoagulability states,
infiltrative tumors,
inflammation or abdominal infections.
For the second group,
non-occlusive reduced intestinal blood flow may be caused by systemic low blood flow due to systemic shock,
cardiac failure,
dehydration,
stress,
drugs or pheochromocytoma,
or it can be caused by mechanical causes,
such as bowel strangulation or marked abdominal distension.
An inadequate blood supply to the bowel may also occur after irradiation,
trauma,
immunodepression,
chemotherapy,
tumors or abdominal inflammation like pancreatitis,
appendicitis,
diverticulitis and peritonitis…
FISIOPATHOLOGY
The first layer of the bowel wall that is affected by ischemia is the mucosa.
At this point,
the lesion is reversible and can cure without significant consequences.
If the ischemia continues,
the necrosis will affect the submucosa and the muscular layer,
and in this case,
residual fibrosis may develop after the ischemic process is resolved.
Lastly,
the necrosis process may reach the serosa,
affecting the whole intestinal wall (transmural necrosis).
This is an emergency,
which requires urgent surgery.
CLINICAL AND ANALYTICAL FINDINGS
The prevalence of AMI increases with age so it should be suspected on elderly patients with cardiovascular risk factor (arteriosclerosis,
arrythmia,
DVT,
etc.).
Symptoms and signs are often nonspecific,
such as acute abdominal pain,
abdominal distension,
gastrointestinal bleeding (resulting in anemia),
leukocytosis with neutrophilia,
increased D-dimer...
The elevation of alkaline phosphatase,
LDH,
amylase or lactic acidosis is indicative of established intestinal necrosis.