What does it mean when cosmetic filler shows its hypoechoic in ultrasound?

Nothing: Really. That is just the appearance of the injected filler. Ultrasound can help a physician sort out what kind of filler was injected when the patient doesn't know. Hyaluronic acid, for instance is "black" or hypoechoic on ultrasound while silicone is "white" or hyperechoic. The real issue is whether the cosmetic result is acceptable.

Echo is bounce back: From an aesthetic standpoint, the echoic appearance of a filler has no consequence other than to inform your new physician what was used in the past especially if there are issues related to the filler. Some fillers will show a whitish appearance, others a cloudy haze and some a blackish area. If getting x-rays/scans of your face, let your dentist, md or radiologist know what you have had done.