Published 10 October 2026 · Reviewed by Dr Sin Yong
Hyaluronidase is the enzyme that breaks down hyaluronic acid filler. Without imaging, the injection relies on surface landmarks and palpation alone. With ultrasound, the filler can be seen before the enzyme is placed. Used with ultrasound, it becomes a targeted procedure. Dr Sin Yong scans the area first, sees where the filler sits, how deep it is and what is next to it, and places the enzyme into the filler itself. This page explains what the scan shows, how the dose is chosen, and why the face is not refilled on the same day.
Short answerUltrasound shows hyaluronic acid filler as a distinct pocket, with its depth and its relationship to vessels. Dr Sin Yong places a small test dose of hyaluronidase into the mapped filler and reviews at about 48 hours; further doses are titrated to effect, in line with published guidance (King 2018), and he waits at least two weeks before any refilling. The aim is to dissolve only the excess; the scan is what makes targeting possible.
Hard lumps after filler or skin boosters, and only offered surgery? Get assessed first: cutting filler out leaves a scar and can cause dents or nerve injury. Find out how Dr Sin Yong treats them without surgery.
Why image before injecting
Hyaluronic acid filler persists far longer than is commonly assumed. MRI studies have found it in the mid-face years after the last injection (Master, Plast Reconstr Surg Glob Open 2024). A lump, a puffy under-eye or an overfilled cheek may be old filler, new filler, fluid, or something that is not hyaluronic acid at all. Ultrasound shows which it is likely to be, before anything is injected.
Under the eye the layers are thin, so where the filler sits decides what it looks like and how it is treated. Schematic, not to scale.
What the scan shows
On high-frequency ultrasound hyaluronic acid filler appears as a dark, well-defined pocket. The scan shows how deep it sits (under the skin, in the fat, or on the bone), how large it is, and whether it is one pocket or several. It also shows the vessels next to it, which matters both for the hyaluronidase injection and for any future filler. Biostimulator response and fat look different from HA, which is how a mixed history is sorted out. See the glossary entry.
Depth decides the dose and the needle path.Illustrative image — not a patient.
Dose, test, titrate, wait
The UK guideline on hyaluronidase in aesthetic practice recommends, for non-urgent correction, a small test dose and titration to effect rather than a fixed number of units (King, J Clin Aesthet Dermatol 2018). Dr Sin Yong reviews at about 48 hours and waits at least two weeks before any refilling, since the enzyme continues to act and the tissue needs to settle. A later guideline adds a modified high-dose protocol for vascular emergencies, which is a different situation entirely (Murray 2021). Dr Sin Yong follows the conservative route for cosmetic correction: enough enzyme to target the excess he can see, and no more.
Why not dissolve everything?
Blanket dissolving can leave the face hollow and remove filler that was doing its job. With the pocket mapped, the enzyme goes into the excess only. If a hollow remains once the face has settled, it is reassessed after the two-week interval, not refilled on the day. Global consensus on filler complications supports this staged approach (Signorini, Plast Reconstr Surg 2016; Snozzi 2018; Urdiales-Gálvez 2018).
Ultrasound-guided or landmark-guided hyaluronidase: what changes when the filler can be seen
Hyaluronidase works the same way whether or not the filler has been imaged; what changes is where the enzyme goes and how much is needed to reach it. The table compares the two approaches point by point, from locating the pocket to deciding whether to refill, and ends with what neither approach can do.
I would rather see the pocket and put the enzyme into it than flood a cheek and hope the right part dissolves.— Dr Sin Yong
Question
Ultrasound-guided
Landmark-guided
Where is the filler?
Seen as a dark, well-defined pocket, with its depth, size and whether it is one pocket or several
Inferred from palpation, surface contour and the injection record, if there is one
Is it hyaluronic acid at all?
Hyaluronic acid, biostimulator response and fat look different on the scan
Cannot be told apart; a biostimulator lump injected with enzyme does not change
How much enzyme?
A small test dose into the mapped pocket, reviewed and titrated to effect
Dosing across the whole area to be sure of reaching it, with more over-correction risk
What is next to it?
Vessels beside the pocket are seen, which guides the needle path and any later filler
Vessels are assumed from anatomy
Dissolve all or part?
The excess only; filler that is doing its job is left
Harder to be selective, so faces can end up hollow
What neither can do
Act on Sculptra, Ellansé, Radiesse, PDLLA or fat; those are mapped and managed with Time Freeze Laser LCLR®
The same limit
Dr Sin Yong performs the scan and the injection himself in the same visit. The published guidance on test dosing and titration is cited below; the wider correction options are on filler correction and the glossary entry.
The scan shows what a lump is likely made of; it does not prove it, and where something does not look like filler, further tests are arranged. On each of these pages, what the scan shows decides the plan:
Filler granuloma: whether a firm lump is a filler deposit, a granuloma around filler or a granuloma with no filler left. That decides the order: what is dissolved, what is treated without an incision, and the few that need an operation.
Filler migration: where filler has moved to and how far it reaches, so that hyaluronic acid is dissolved where it now sits.
Silicone filler lumps: whether silicone sits as a defined deposit or is spread through the tissue, and where it has reached, which is not always where it was injected.
PMMA filler lumps: where the acrylic beads sit, mapped before Dr Sin Yong uses the Sculpting mode of Time Freeze Laser LCLR®, without an incision.
The Tyndall effect: how close to the surface the filler sits, so that only the superficial deposit is dissolved.
Risks
Bruising and swelling at the injection site; over-correction if too much is used, which is why dosing is staged; and, rarely, allergy to the enzyme, which is why a skin test is always done first. Vascular compromise after filler is an emergency that uses a different, high-dose protocol and is not what this page describes; if your skin turns pale, dusky or mottled, or pain is getting worse after filler, get urgent assessment by the doctor who injected you, or at A&E, now.
Fee factors
The number of areas scanned and treated, the number of sessions the titration needs, and whether the scan finds something other than hyaluronic acid. Set out in writing after assessment. How fees are quoted.
Your next step
1. MessageWhatsApp +65 8023 7170 with what is bothering you. A reply comes from the clinic, not a bot.
2. AssessmentDr Sin Yong examines you himself on Orchard Road, with ultrasound where earlier filler is involved.
3. A plan in writingWhat he would do, what he would not, the fee factors, and the option of no treatment.
Every treatment is performed by Dr Sin Yong personally. Singapore Medical Council registered · invited to share his clinical expertise internationally as a Key Opinion Leader for CLASSYS, DEKA, HIRONIC, FOTONA, ALMA, LUTRONIC and ILOODA · HSA-registered devices · ultrasound-guided correction
Lumps that are not hyaluronic acid alone are covered with other filler complications.
Frequently Asked Questions
It is aimed at the deposits causing the problem rather than the whole area. Whether to dissolve everything or only part is decided at the consultation, after the scan has shown where the filler sits and how much of it remains.
Because it shows where the filler is, how deep, how much, and what is next to it. That lets the enzyme go into the filler rather than across the whole area, so the enzyme is directed at the excess.
For non-urgent correction, a small test dose first, then a review at about 48 hours; further doses are titrated to effect, in line with published guidance. No fixed number is used.
Dr Sin Yong waits at least two weeks, and never refills on the same day. The face is reassessed once it has settled.
No. Those products are not hyaluronic acid. Ultrasound still helps, because it shows what the lump is likely made of; the treatment for non-HA over-stimulation is Time Freeze Laser LCLR®.
Yes. Dr Sin Yong performs the scan and the injection himself in the same visit on Orchard Road.
References
King M, Convery C, Davies E. The use of hyaluronidase in aesthetic practice (v2.4). J Clin Aesthet Dermatol. 2018;11(6):E61-E68. PMID 29942426. source
Murray G, Convery C, Walker L, Davies E. Guideline for the safe use of hyaluronidase in aesthetic medicine, including modified high-dose protocol. J Clin Aesthet Dermatol. 2021;14(8):E69-E75. PMID 34840662. source
Master M, Azizeddin A, Master V. Hyaluronic acid filler longevity in the mid-face: a review of 33 magnetic resonance imaging studies. Plast Reconstr Surg Glob Open. 2024;12(7):e5934. doi:10.1097/GOX.0000000000005934. source
Signorini M, Liew S, Sundaram H, et al. Global Aesthetics Consensus: avoidance and management of complications from hyaluronic acid fillers. Plast Reconstr Surg. 2016;137(6):961e-971e. doi:10.1097/PRS.0000000000002184. source
Snozzi P, van Loghem JAJ. Complication management following rejuvenation procedures with hyaluronic acid fillers — an algorithm-based approach. Plast Reconstr Surg Glob Open. 2018;6:e2061. doi:10.1097/GOX.0000000000002061. source
