Intussusception can be defi ned as the invagination of a segment of bowel (the intus- susceptum) into a more distal loop of bowel, the intussuscipiens. There are four different types of intussusception: ileo-colic, ileo-ileal, ileo-ileo-colic, and colo- colic. 90% are ileo-colic and ileo-ileo-colic intussusceptions, 90% have no patho- logic lead point, and 10% have a lead point in children, due to a Meckel’s diverticulum, polyp, other tumors (Burkitt’s lymphoma), or enteric duplication cysts. In contrast, intussusception in adults is commonly associated with a lead point.
The intussusceptum is pulled further into the distal segment of bowel by peristalsis, pulling the mesentery along with it and trapping the vessels. If not reduced, edema, ischemia, and bowel obstruction (usually partial) ensue with necrosis of bowel.
Intussusceptions can be reduced by using positive contrast, i.e., water soluble con- trast like Omnipaque ® or negative contrast (carbon dioxide). Successful reduction is noted by (1) free fl ow of contrast into the terminal ileum or (2) progressive reduction of ileo-colic intussusception to the ileo-cecal valve under fl uoroscopic visualization.
Barium is not used because, if the bowel perforated during the reduction attempt, barium would leak into the peritoneal cavity and form concretions with the bowel contents, a mess to clean up surgically. Contraindications to reduction include perforation and peri- tonitis. If reduction is unsuccessful with enema, the patient will require surgery.
Figure 26.7 shows a single-contrast water soluble enema performed in an attempt to reduce the intussusception. The very end of the intussusception did not com- pletely reduce (black arrow). The patient was taken to surgery and found to have a large Burkitt’s lymphoma of the distal ileum which acted as the lead point for the intussusception to develop and prevented its reduction.
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multicenter studies have shown that CTC is almost as sensitive (98–99% sensitivity) in the detection of polyps greater than 5 mm as optical colonoscopy.
For this type of study, the large bowel is prepped in the same way as for an opti- cal colonoscopy. The patient is placed in the CT scanner and a rectal tube is inserted in the rectum, and the colon is distended with carbon dioxide via a special insuffl a- tion pump. The CT scanner is used to obtain very thin slices through the abdomen and pelvis and images are reconstructed in axial, coronal, and sagittal planes. The patient is then rescanned in the prone position ( Figs. 26.8 – 26.10 ).
The CT images are then reviewed using special software in either 2D mode (axial, coronal, or sagittal) or in 3D mode (“virtual colonoscopy”) or both. Colonic polyps are considered signifi cant if they measure >5 mm from the base of the stalk to the top of the polyp. In general, polyps <5 mm on CTC are not reported, or if they are reported, a recommendation of follow-up colonoscopy (optical or CT) in 5–7 years can be made.
There is some controversy over how polyps measuring between 6 and 9 mm should be managed. Ultimately it is the patient and treating physician preferences and any associated comorbid conditions that dictate how these polyps will be dealt with. In general, if there are 1–2 polyps measuring 8–9 mm and the patient is young,
FIGURE 26.7 - INTUSSUSCEPTION
Single-contrast water soluble enema performed in an attempt to reduce the intussusception. Arrow points out the nonreducing distal end which was a Burkitt’s lymphoma
FIGURE 26.8 - CT COLONOGRAPHY
( a ) This demonstrates a “double-contrast” image obtained by the CT scanner, and is used as a
“road map” during the virtual colonoscopy portion of the study. ( b ) This is a magnifi ed “dou- ble-contrast” view of the cecum. There is a large fi lling defect in the cecum
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optical colonoscopy with polypectomy is recommended. In a young patient with <3 polyps between 6 and 7 mm, follow-up in 3 years by colonoscopy (optical or CT) is recommended. If there are >3 polyps, polypectomy is recommended, no matter what the age of the patient. Polyps >10 mm at any age should be removed by optical colonoscopy and sent for pathology evaluation.
If the patient is 50 years and CTC is negative for signifi cant polyps or masses, optical colonoscopy is recommended in 5 years. If the patient is 55 years and optical colonoscopy is negative for polyps or masses, follow-up every 10 years by colono- scopy (endoscopy or CT) is recommended.
FIGURE 26.10 - CT COLONOGRAPHY
( a ) Coronal 2D CT image of the colon also shows a polyp in the transverse colon in the same patient ( arrow ) as in Figs. 26.8 and 26.9 . ( b ) This is a 3D CT image of a “virtual colonoscopy”
study in the same patient, demonstrating the polyp in the transverse colon ( arrow ). Biopsy specimen of this polyp came back as benign adenoma
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to Imaging & Technology, DOI 10.1007/978-1-4614-0944-1_27,
© Springer Science+Business Media, LLC 2012
Gas is normally present in the stomach and colon. Small accumulations of gas may be found in the duodenum and upper portion of the jejunum. Scattered collections of gas may be present throughout much of the small intestine in bedridden patients, patients on narcotics for pain relief, and those who swallow large amounts of air habitually. Air can be seen as individual accumulations of rounded or ovoid shaped air. If a single loop of normal intestine can be recognized because of gas fi lling, the shadow is seldom more than 5–8 cm in length. More often, the gas does not form any specifi c loop pattern.