Snow storm appearance on an ultrasound is seen in:

Ultrasound done in a patient with complete hydatidiform mole demonstrates the uterus to be filled with innumerable tiny cysts described as a snowstorm appearance in the first trimester because of its multiple echogenic foci. There will be no evidence of fetal pas. In the case of a paial mole, a fetus can be identified and the placenta will show paial molar changes. In an ectopic pregnancy, ultrasound shows and empty uterus and an adnexal mass. Free fluid in the pouch of douglas may be noticeable. In an ectopic pregnancy, a tubal ring is seen ( Doughnut or Bogel sign). Ref: Fundamentals of Diagnostic Radiology edited by William E. Brant, page 982.