Hi Linh,
This is a common question I am asked,
The way I define a cord lipoma is when I find some fat within the inguinal canal which is not reducible and does not increase in volume when the patient strains. It may move slightly during straining but not far as it is attached to the spermatic cord. The fat will also have a beginning and end point as you scan along the canal (think of it as a small egg shaped piece of fat living in the canal)
A hernia on the other hand (direct or indirect) is generally reducible, it grows in size and moves freely along the canal when the patient strains and it has no end point at the origin end (in other words it is still present as it passes into the deep ring or through the posterior wall depending if it is indirect or direct respectively)
So I think they are quite different.
If you are seeing a small piece of fat at the superficial ring that is only slightly mobile into the distal canal and there is no defect in the posterior wall and it can not be reduced through the deep ring and it has a beginning and end point within the canal and it does not increase in size / volume during straining you have found a cord lipoma!
Steve