Acute Small Bowel Ischemia (ASBI) is due to a sudden interruption of blood intake in a portion of small bowel; this leads to ischemia of the bowel segment involved,
cellular damage and bowel wall necrosis [1].
Although ASBI represents an uncommon cause of abdominal pain,
with a relatively low incidence (from 0.09% to 0.2% of all the admissions in an Emergency Department) [2-5],
a correct diagnosis and a prompt recognition of intestinal vascular impairment is mandatory,
since ASBI is linked to high morbility and mortality (from 50% to 80%) [6-9].
ASBI is a result of occlusive and non-occlusive forms of ischemia.
Occlusive forms are linked to a vascular obstruction (arterial or venous),
due to thrombo-embolic events,
which are,
in order of frequency,
acute mesenteric arterial embolism (usually involving superior mesenteric artery),
acute mesenteric arterial thrombosis and acute mesenteric venous thrombosis [10-11].
In non-occlusive forms,
mesenteric vessels are not obstructed,
but blood flow through mesenteric circle is not adequate enough to ensure a correct blood provision to the bowel.
This state is generally associated with other kinds of pathologies,
for example it is linked to a low cardiac output syndrome,
consequent to myocardial infarction or various types of cardiopathies; alternatively,
it arises when a low blood flow condition occurs,
associated with a vasoconstriction of bowel's vessels (for instance the vasospasm due to systemic hypotension or drugs) [12].
The two types of ASBI described above can be considered as "primary" forms of bowel ischemia,
since the main problem is represented by a reduced blood intestinal intake.
The other form of non-occlusive ASBI,
which can be defined as a "secondary" clinical entity of bowel ischemia,
is consequent to intestinal strangulation,
which occurs when an intestinal obstruction (due to internal hernia,
adhesions,
volvulus or invagination) is associated with a vascular impairment of the bowel segment involved [12-13].
Finally,
also the forms of bowel ischemia associated with neoplasms,
vasculitis,
inflammatory bowel diseases and traumatic events can be defined as "secondary" non-occlusive ASBI.
Imaging signs of ASBI are similar,
indipendently from the aetiology of the vascular impairment; Computed Tomography (CT),
performed with endovenous contrast medium administration,
has a primary role in the diagnosis of ASBI,
highlighting different alterations consequent to ischemia from various causes.
Diagnostic accuracy of CT in ischemia due to arterial obstruction,
which is the most frequent type of ASBI,
has not been assessed yet.
However,
it has been estimated that CT angiography in the diagnosis of ASBI without an apparent cause,
including both occlusive (arterial and venous) and non-occlusive forms,
has a sensitivity ranging from 64% to 96% and a specificity going from 92% to 100% [14-15].
As concerns every CT indicator of ASBI analized alone,
there are not many data in literature; anyway,
it has been reported that altered bowel wall enhancement and the presence of intramural bowel gas are the only two more sensitive (42%) and highly specific (97%-100%) signs of reduced vascular intake to small bowel wall [15].
Arterial/venous occlusion and air in portal venous system have shown a lower sensitivity (12%-15%) and a higher specificity (94%-100%) [15]; increase in bowel wall thickness and mesenteric fat stranding are more sensitive (85%-88%) but less specific (61%-72%) signs [15].
In the forms of "secondary" ASBI consequent to a bowel obstruction,
CT has a sensitivity going from 83% to 100%,
a specificity ranging from 61% to 93%,
a Positive Predictive Value (PPV) of 72%-88% and a Negative Predictive Value (NPV) of 93-100% [16-19],
even if more recently a lower sensitivity has been reported [20].
Considering CT sings alone,
an absent or reduced bowel wall enhancement and mesenteric fat stranding have resulted the most specific indicators.
Fecal sign is another item reported as indicative of a bowel obstruction [20].
The aim of this study was to evaluate which CT signs related to ASBI are the most reliable indicators of ischemia in 94 patients with surgical evidence of bowel vascular impairment,
especially in cases with primary non-occlusive ASBI,
where CT is not able to highlight a specific aetiology of the reduced blood intake to small bowel.