Adult patients of different age groups,
with different pathological entities underwent CTE.
Our protocol includes a 3 day preparation with liquid diet and withhold of food prior to the examination.
In order to succeed bowel distention the patients ingested a total of 1500mL of oral contrast mixture.
The mixture contained 500mL of mannitol solution 20% diluted in 1000mL of water and was consumed every 7 mins,
250mL per time.
At this point the patients needed supervision and encouragement.
Where there was no contraindication antispasmodic agent was administered to the patient intravenously (i.v.) prior to the examination,
in order to minimize bowel peristalsis.
100mL of contrast agent was also administered i.v.
in a 4ml/s rate.
Scanning was performed on a 16 slice multi - detector scanner about 43 minutes after intravenous non-ionic iodinated contrast media injection in an enteric phase.
The imaging studies were performed on a workstation,
in axial plane as well as MRP and MIP reconstructions.
Findings were confirmed by biopsy and clinical results.
Investigation for Crohn’s disease is a common indication for CT enterography. Crohn's disease is an idiopathic inflammatory bowel disease characterized by widespread discontinuous gastrointestinal tract inflammation.
The terminal ileum and proximal colon are the most common sites.
Bowel wall inflammation on CTE is represented by mural enhancement and bowel wall thickening,
although these findings are highly suggestive of Crohn’s disease,
though they are not specific.
Bowel wall thickening is measured only in bowel loops distended by the previously ingested contrast mixture.
The mesenteric border of the small bowel is most severely affected rather than the antimesenteric border,
therefore producing an asymmetric involvement.
Pseudosacculation of the antimesenteric border is also frequent.
Stratification of the bowel wall and target sign with water density reflect submucosal edema,
and ' white target' sign indicates active disease.
The ‘fat halo’ sign is the result of fat infiltration of the submucosa,
and therefore ‘gray target’ sign depicts the chronic stage of Crohn disease (Fig 1,
2,
3).
Fig. 1: Axial CT enterography in a patient who suffers from Crohn disease with 'fat halo' sign in the terminal ileum
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Fig. 2: Axial CT enterography in the same patient who suffers from Crohn disease in a subacute phase.
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Fig. 3: Axial CT enterography in a patient with Crohn's disease showing 'fat halo' sign in the cecum
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Prominent vasa recta (comb sign) shows perivascular inflammation and fibrofatty proliferation,
a sign of active stage in a patient with known Crohn’s disease (Fig 4).
Fig. 4: Axial image depicts a target water sign in peripheral ileum with mural thickening, contrast enhancement of the mucosa, vascular dilatation and tortuosity of the vasa recta (comb sign) giving the acute stage of the disease.
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Strictures are a common complication of Crohn’s disease.
They are subdivided into fibrotic,
(Fig 5,
6,
7)
Fig. 5: Transverse CT enterographic images depict strictures of ileum loops in patients with chronic Crohn's disease
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Fig. 6: Coronal CT enterographic images depict strictures of ileum loops in patients with chronic Crohn's disease
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Fig. 7: Coronal CT images depicting fibrotic- distended jejunum segments in a patient with Crohn's.
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inflammatory and mixed types (Fig 8).
Fig. 8: Coronal CT enterographic images showing acute disease with comb sign Crohn disease
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The morphologic criteria of an upstream dilatation depict the functional significance of the stricture.
Fibrotic small bowel strictures that haven’t benefited from medical agents should be described in detail due to endoscopic or surgical importance.
Active and chronic findings may co-exist in a number of patients.
Ulcerations reflect severe inflammation (Fig 9).
Fig. 9: Axial CT enterographic images of a patient with Crohn disease in an acute stage, with the presence of ulcers
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Sacculations usually occur in the antimesenteric border and may be present in either acute or chronic disease (Fig 10,11) (4).
Fig. 10: Axial CT enterographic image in a patient with Crohn disease shows bowel involvement with mural thickening and ulcers
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Fig. 11: Axial CT enterographic images in patients with Crohn disease show stricture with upstream pseudodiverticula dilatation
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An important complication in this disease is the formation of fistulas.
The multiplanar capability of CTE is essential in detecting the structures involved and the extent of this penetrating form of the disease.
Abscess,
on the other hand is an extra-enteric fluid collection,
with no communication with the bowel lumen,
also a sign of active disease (Fig 12,
13,
14,
15).
Fig. 12: Axial CT enterographic images depict Crohn disease in an acute stage, with small bowel fistulas and an abscess (yellow arrows), asymmetrical mucosal thickening with increase enhancement (green arrow) and comb sign (red arrow).
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Fig. 13: CT enterographic images in a patient with Crohn disease detect ileo-iliac fistulas.
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Fig. 14: Axial CT enterographic image depicts an abscess that is in contact with an ileum loop
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Fig. 15: Coronal CT enterographic image depicts fibrofatty proliferation and perivascular inflammatory infiltration that outline the distended segments of intestine.
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Large bowel,
perianal region and areas of surgical anastomosis are not considered common sites of involvement.
The radiological signs would be the same as small bowel Crohn’s disease.
Ulcerative Colitis,
is another inflammatory bowel disease which in contrary to Crohn’s disease shows a continuous pattern of bowel involvement.
Although it predominately affects the large bowel,
a common complication is ‘backwash’ ileitis.
Colonoscopy remains the gold standard for this disease but CTE can be used to exclude small bowel involvement.
(5)
Tuberculosis (TB) enteritis with an increasing appearance in immunocompromised as well as immunocompetent patients,
is not often encountered in clinical practice,
but should be considered.
The disease spreads through the lymphoid tissue of the submucosa,
through hematogenous spread from another distant infected site or from direct tissue spread from adjacent infected organs.
It is not unjustifiably called a great mimicker as a radiographic image similar to Crohn’s disease is commonly seen and differentiation can be challenging.
The ileocecal junction is most frequently affected followed by the jejunum.
Isolated jejunum disease is rare.
Imaging findings include extensive mural thickening,
which may acquire a mass-like appearance (Fig 16,
17),
Fig. 16: CT enterographic image in a patient with hypertrophic form of TB enteritis with enlarge mesenteric lymph nodes.
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Fig. 17: CT enterographic images in a patient with hypertrophic form of TB enteritis showing mural thickening (yellow arrow) and mass like lesions(red arrow).
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strictures as well as adhesions leading to bowel obstruction.
There is thickening of the ileocecal valve and of the medial wall of the cecum and a retracted conical and shrunken cecum.
It is classified into ulcerative,
hypertrophic and ulcerative-hypertrophic.
(6)
Some helpful features to differentiate Tb enteritis from Crohn’s disease is the duration of symptoms which in Tb is short but in Crohn’s disease is longer.
The presence of ascites favors Tb.
Peritoneal involvement in this case should also be considered.
Tb peritonitis is classified into wet,
dry and fibrotic type.
Ascites loculation may be seen in the wet and fibrotic type.
Due to CTE’s high spatial resolution nodular appearance of the peritoneum is easily detected in the dry type (cake like omentum).
(Fig 18,
19,
20)
Fig. 18: Tranverse CT enterographic section in a patient with history of Crohn disease shows encased fluid in the mesentery
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Fig. 19: Tranverse CT enterographic section in a patient with history of Crohn disease shows omental enlarged lymphadenopathy.
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Fig. 20: Tranverse CT enterographic section in a patient with history of Crohn disease shows omental thickening
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Extra-enteric manifestations should be considered (pulmonary Tb).
Skip lesions,
with ‘comb-sign’,
mural stratification and mesenteric fibrofatty proliferation are more suggestive of Crohn’s disease.
CTE is a reliable method for detection of small bowel neoplasms. GIST predominantly forms an extraluminal mass.
Carcinoid has been reported to be the most common small bowel neoplasm and tends to present as a vividly enhancing polypoid tumor or as a sessile mass with segmental wall thickening.
It is also presented as a mesenteric mass with calcifications.
They are most commonly encountered in the ileum.
The characteristic image of desmoplastic mesenteric reaction helps suggest the diagnosis.
The duodenum hosts most of small bowel adenocarcinomas in the form of a small mass,
a region of annular narrowing of the lumen with shouldered borders or even and ulcerative plaque.
As a result obstruction may occur or intussusception.
Perforation of an ulcerative plaque is not a frequent complication but may be encountered.
Lymphoma occurs in different patterns and shapes and is typically seen in the ileum due to its rich lymphatics.
It usually appears as a thick,
wall-infiltrating lesions which causes aneurysmal or pseudoaneurysmal dilatation of the lumen,
without obstruction.
Nodular fillings defects may be hard to be distinguished from nodular lymphoid hyperplasia,
but lymphoma appears more irregular with larger nodules.
It may also present as a discrete polyp,
as an infiltrating lesion or an exoenteric mass.
Associated splenomegaly and mesenteric or retroperitoneal lymphadenopathy should also prompt suspicion.
(Fig 21)
Fig. 21: Axial CT enterographic image depicts focal thickened of ileum loop (green arrow) with aneurysmal dilated lumen, without obstruction and enlarged nodes (yellow arrow). Histologically this lesion was a lymphoma.
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Another,
frequent problem in clinical practice is the formation of adhesions as a result of surgery,
radiation and inflammation.
These fibrous bands may create chronic discomfort to a patient,
or even the more sever bowel obstruction. They can be divided into three categories: a) entero-enteric (between bowel loops),
b) entero-visceral (between bowel loops and visceral organs) and c) entero-peritoneal/parietal (between bowel and parietal peritoneum).
On CTE bowel loops,
abnormally clustered in one segment of the abdomen,
create the ‘matted bowel’ image,
which in the correct clinical setting is strongly suggestive of adhesions.
Kinking and acute angulation of the bowel loops reflect their fixation to a certain space.
(Fig 22)
Fig. 22: Coronal CT enterographic section show segments of angulated small bowel (arrow) from underlying adhesions due to ipsilateral post inguinal hernia surgery.
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Adhesions,
also cause the loops to come close together,
therefore dismiss the fat planes separating the structures and cause loss of fat planes.
Change in bowel lumen caliber may also occur,
as well as asymmetry in bowel wall thickness.
They can also create the so called fat notch sign,
whereby a band of fat is insinuated at a site of focal stenosis.
The presence of fibrous bands causes increased attenuation of the mesentery as well as mesenteric vascular crowding.
(7)
Internal hernias consist in the herniation of mesenteric fat or bowel loops through an acquired or congenital defect in the peritoneum or in the omentum.
Although they remain silent in case they are easily reducible,
the can produce discomfort and eventually obstruct the bowel lumen and/or bowel blood supply,
causing strangulation and bowel ischemia.
According to the anatomic location of the hernia there are different types,
depending on the foramina and bowel segment involved.
The left and right paraduodenal hernias are the most common types.
Other types are the lesser sac hernia,
pericaecal hernia,
sigmoid mesocolon hernia,
small bowel mesentery internal hernia and internal hernia due to gastric bypass surgery.
Despite the fact they occur in different segments of the bowel,
there are some common features that suggest this diagnosis.
Crowded bowel loops within a hernia sac or in an abnormal location,
upstream dilatation with segmental findings of stasis,
along with twisting and twirling of the mesenteric vessels.
Sclerosing peritonitis is a rare entity which is characterized by chronic fibrotic thickening of the peritoneum.
Its occurrence rises in patients with continuous ambulatory peritoneal dialysis and vetriculoperitoneal shunts.
Other associations include sarcoidosis,
tuberculosis,
gastrointestinal malignancy and luteinized ovarian thecoma.
CT finding include thickening and enhancement of the peritoneum in the early phases.
Progression of the disease leads to calcification formation as well as small bowel encapsulation.
Its antimesenteric border may be affected by the inflammation,
causing thickening and fibrosis.
Gradually this may lead to adhesions between bowel loops and eventually to obstruction (Fig 23) (8).
Fig. 23: Diffuse inflammation of the peritoneum with thickening and enhancement in which the antimesenteric intestinal wall is involved. Abdominal loculated fluid collections and a left ovarian thecoma.
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