Imaging artifacts during ultrasound can sometimes lead to misinterpretation of normal anatomy as pathology. An example of this is given below with some tips to avoid this confusion during abdominal ultrasounds.
Ileo-ceco-colic junction or intussusception? The cross sectional appearance of an intussusception on ultrasound is characterized by concentric rings which gives the appearance of a target or doughnut (Figure 1). There is a hypoechoic ring on the outside of the target which is the section of bowel that serves as the intussuscepiens (the portion of intestines receiving the bowel) and a ring on the inside that is the intussusceptum. Ileo-ceco-colic junction (ICCJ) in cross section can appear very similar to the ultrasound imaging characteristics of an intussusception particularly if there is thickening of the ileum, colon or cecal wall (Figure 2 and 3).
Figure 1: Intussusception in a dog (left) and cat (right).
Figure 2: White arrows indicate ileo-ceco-colic junction. Normal ileo-ceco-colic junction in a cat (left). ICCJ in a cat with ileal wall thickening (right).
Figure 3: ICCJ in a dog with severe ileal and cecal thickening diagnosed via biopsy as lymphoplasmacytic and eosinophilic enterotyphlitis.
TIPS FOR DIFFERENTIATING INTUSSUSCEPTION FROM ICCJ
Tip #1: Look for a hyperechoic rim surrounding the inner “doughnut hole”. You can often see the mesenteric fat adjacent to the internal ring which appears as a hyperechoic crescent or rim around the inner intussusceptum (Figure 4).
Figure 4: These are the same images as in Figure 1: The white arrows point to a crescent shaped area (left) and circumferential area (right) that represents the hyperechoic mesenteric fat of the inner intussusceptum.
Tip #2: View the structure in both longitudinal and cross sectional planes. An intussusception has a distinct appearance in longitudinal section (Figure 5) which is very different from the normal ileocecocolic junction (Figure 6). The longitudinal appearance of intussusception mirrors the cross sectional appearance where the two “tubes” of the intussuscepiens and intussusceptum are visible as well as the hyperechoic mesenteric fat between them.
Figure 5: Appearance of intussusception in dog (left) and cat (right) in log axis.
Figure 6: Examples of longitudinal views of normal ileoceco-colic junction. White arrows indicate the clearly visible junction of the ileum on the right with the colon on the left.