A pathological lesion can be identified at the leadpoint of intussusception
in about 6% of episodes. Occasionally, general manifestations of an underl
ying disease indicate the specific cause of an intussusception (e.g., perio
ral pigmentation in Peutz-Jeghers syndrome), but usually the clinical featu
res provide no clues as to the aetiology. Neonatal intussusception may be c
aused by a duplication cyst or Meckel's diverticulum. Beyond 12 months, the
proportion of intussusceptions due to a pathological lesion at the leadpoi
nt increases with age. There is an identifiable lesion in the majority of c
hildren over 5 years of age. Postoperative intussusception accounts for bet
ween 0.5% and 16% of intussusceptions, although it has a variety of causes;
it typically follows retroperitoneal dissection. It is unusual for an intu
ssusception due to a pathological lesion at the leadpoint to be reduced by
enema. If it is reduced, the lesion may be seen at the time of reduction or
fluoroscopy, or subsequently on ultrasonography.