Intussusception

An intussusception is a medical condition in which a part of the intestine goes into another, typically the Ileum into the Ascending colon causing a intestinal obstruction.

An easy way to visualize the mechanism is to imagine when you collapse a telescope, that is essentially what happens to the intestines.

Imaging

Bowel-within-bowel appearance: Alternating layers of bowel wall & mesenteric fat
Target appearance in cross section on CT & US
Small bowel intussusception(SBI) features that differentiate it from ileocolic intussusception
Smaller diameter (mean of 1.5 vs. 2.6 cm)
Entrapped lymph nodes less common
More common in periumbilical or left abdomen

Sonographic findings that may indicate need for surgery

Length > 3.5 cm
Findings of small bowel obstruction(SBO) & ascites
Pathologic lead point (but US has low sensitivity)

The part that prolapses into the other is called the intussusceptum, and the part that receives it is called the intussuscepiens (think recipient).

Intussusception is a medical emergency and a patient should be seen immediately to reduce complications up to and including bowel necrosis.

A patient may present with abdominal pain and cramping, especially in an episodic crampy nature. They may have “red currant jelly stool” which is bloody stool seen in late intussuceptions, from resulting hemorrhage.

Sonographically you want scan from RUQ to RLQ and search for a large (2 cm or bigger) target like lesion. The protocol goes on to include the LUQ, LLQ Pelvis, epigastrium and umbilical regions. There will often times be lymph nodes near and within the lesion, this is believed to be one of the causes, large lymph nodes can get trapped with peristalsis leading to the Intussusception

Ileocolic Intussusception Transverse Target/Doughnut sign

Ileocolic Intussusception longitudinal

Ileocolic Intussusception transverse

Intussusception with lymph node

One thing to consider is small bowel intussusception which is a transient intussusception that doesnt require treatment, typically waiting 15 minutes will see it resolve.

Small bowel intussusceptions will be smaller and can be located anywhere in the abdomen. They are a transient self resolving condition and are often found in asymptomatic patients. If you see an intussuception that is small , you should wait up to at least 15-30 minutes, though often less time to see resolution. If not the patient may be rescanned a little later to ensure it has resolved. Small bowel intussusceptions do not require treatment.