The presence of intrauterine gas (a.k.a. pneumouterus) can sometimes be inferred by tiny hyperreflective foci, with dirty reverberation shadows on ultrasound, foci of very low attenuation at computed tomography (CT) or signal voids with susceptibility artifact in MRI. The term encompasses air within the uterine cavity as well as intramyometrial air.
It can arise from a number of situations:
normal postpartum period 1,4: it may be seen in ~ up to 20% of healthy patients in the postpartum period
post intrauterine instrumentation
abnormal fistulous connection with the gastrointestinal tract