Fat injection to the forehead for a rounded appearance—Latest techniques for Asian patients and engraftment rate data

1. Why it's popular among Asian people

In Asian cultural spheres, the shape of the face, particularly the forehead (frontal region), is believed to have a significant influence on personal impression, social evaluation, and even one's fortune.

Specifically, a full, rounded forehead shape with no soft tissue deficiency or irregular bone contours, symmetrical and harmonious, is not merely a symbol of beauty but has long been believed to signify prosperity, leadership ability, and social success (Chou 2017).

From an anatomical perspective, forehead fullness plays a very important role in the overall balance and harmony of the face. Particularly in the silhouette as viewed from the side or at an angle, a smooth, slightly convex wrinkle-free forehead is said to add three-dimensionality to the entire face and greatly enhance the general appeal of a person's appearance (Chou 2017).

Asian people tend to have flatter foreheads or more pronounced irregularities due to skeletal structure, and many seek a rounder, more feminine and youthful appearance. Against this cultural background and aesthetic awareness, autologous fat injection to the forehead (fat grafting) has become extremely popular among Asian people as a means to smooth facial contours and achieve a youthful and attractive appearance (Chou 2017).

2. MAFT Technique

MAFT (Micro-autologous fat transplantation) is a precision injection technique developed to overcome the low engraftment rate in conventional fat injection and complications such as nodule formation, enabling predictable and consistent results (Chou 2017).

Basic concept and specialized equipment of MAFT

Prior histological studies (Carpaneda et al.) demonstrated that when the radius of transplanted fat parcels exceeds 2 mm (millimeters), blood flow and nutrient diffusion from the surrounding area cannot reach the center, causing necrosis of central adipocytes (Chou 2017).

To prevent this central necrosis, the MAFT concept maintains the volume injected per procedure (parcel size) below 1/100 mL (0.01 mL). A spherical fat parcel with a volume of 0.01 mL has a radius of approximately 1.3 mm (millimeters), allowing blood flow to reach all areas and dramatically improving survival rate (Chou 2017).

To perform this extremely minute injection accurately and continuously, a specialized patented precision device called MAFT-GUN is used. With this instrument, surgeons can precisely control fat injection volume in microunits such as 1/60, 1/90, 1/120, 1/150, 1/180, and 1/240 mL, enabling consistent micrograft procedures (Chou 2017).

Three-layer injection approach to the forehead

In MAFT to the forehead, based on anatomical structure, fat is carefully dispersed and injected into the following three different layers (Chou 2017).

• Deep layer (behind the frontalis muscle / on the periosteum of the frontal bone): Set the MAFT-GUN dial to 120 (injection volume per procedure: 1/120 mL = 0.0083 mL) and apply fat in a fan pattern by sliding over the periosteum of the frontal bone. Normally 5–10 mL (milliliters) of fat is transplanted in this layer, creating the basic volume and foundation of the forehead (Chou 2017).
• Middle layer (within the frontalis muscle): Advance the cannula slightly at an angle into the frontalis muscle tissue. Since muscle tissue has very abundant blood flow, transplanted adipocytes receive excellent blood supply. Normally 5–10 mL (milliliters) of fat is transplanted in this layer (Chou 2017).
• Superficial layer (subcutaneous layer, between dermis and frontalis muscle): The skin of the forehead is the thickest in the face, with dense septa (connective tissue) running laterally from the dermis toward the frontalis muscle. Therefore, transplanting large amounts of fat at once is difficult, and injection volume in this layer is normally kept to 3–5 mL (milliliters) or less. It serves to refine surface smoothness (Chou 2017).

Surgical results and patient satisfaction

In a study of 178 patients (167 women, 11 men, average age 47.7 years), the average time for the entire MAFT procedure from fat harvesting to transplantation was 52 minutes (Chou 2017).

The average injection volume to the forehead was 10.2 mL (milliliters), and some patients (12.6%, 22/178) underwent a second touch-up procedure 4–6 months postoperatively to achieve fuller augmentation (Chou 2017).

On long-term follow-up averaging 34 months (8–68 months), no serious complications such as neurovascular injury, skin necrosis, abscess, nodule formation, fibrosis, calcification, or asymmetry were recorded (Chou 2017).

In the final patient satisfaction assessment, 83.1% of patients who received one procedure reported good results (53.2% satisfied, 27.5% very satisfied). Furthermore, among patients who received two procedures, an extremely high satisfaction rate of 100% was confirmed (86.4% very satisfied, 13.6% satisfied) (Chou 2017).

3. Engraftment rate meta-analysis

In autologous fat injection to the face, the extent to which injected fat ultimately survives (engraftment rate: volume retention rate) is a topic of highest interest to both surgeons and patients. Quantitative meta-analyses using objective imaging techniques have been conducted on engraftment rates, which previously relied largely on physician experience.

Average engraftment rate and temporal changes

A meta-analysis of 27 studies including 1011 patients who received fat injection to the face demonstrated that the overall pooled mean engraftment rate for facial fat grafting was 47% (95% confidence interval 41–53%) (Lv 2020).

The engraftment rates reported in individual studies ranged widely from 26% to 83%, with a mean follow-up period of 3–24 months (Lv 2020).

The graft retention rate changes dynamically over time. As time progresses to 3 months, 6 months, and 12 months post-operatively, the retention rate gradually decreases, with the maximum volume reduction occurring in the first 3 months after surgery (Lv 2020).

This initial volume reduction is thought to be due to water absorption and absorption of cells that did not survive. Subsequently, it is hypothesized that the volume stabilizes as surviving mature adipocytes differentiate and proliferate (Lv 2020).

Factors affecting retention rate and complications

This meta-analysis also conducted subgroup analyses on various clinical factors that may affect graft retention rate (Lv 2020).

• Number of injections:A clear trend was confirmed showing higher retention rates with secondary fat injection (secondary) compared to primary injection (primary). This is thought to be because the tissue in the recipient site becomes enriched by the initial graft, creating a foundation for blood flow (Lv 2020).
• Fat processing method:In the processing of harvested fat, methods using centrifugation or filtration suggest the possibility of delivering more consistent and favorable graft results compared to simple sedimentation methods (Lv 2020).
• Patient indication:A tendency toward higher retention rates was observed in patients with congenital facial deformities compared to purely cosmetic enlargement. This is presumed to be because the soft tissue in congenital deformities can provide a loose scaffold that more easily supplies nutrients to the transplanted fat (Lv 2020).
• Fat donor site:No significant differences in retention rate were found based on differences in donor sites for fat harvesting, such as the abdomen or thigh (Lv 2020).
• Impact of volume measurement method:It has been found that volume measurement using CT scans may overestimate (calculate higher) retention rates compared to measurement using 3D scans (Lv 2020).

Among the 1011 patients studied, only 2.8% (28 people) experienced complications, which were primarily relatively mild, such as infection, irregular contours, asymmetry, and overcorrection (Lv 2020).

4. Microfat and Nanofat differentiation

In modern fat injection, rather than injecting harvested fat as-is, the approach of precisely processing the fat particle size (parcel size) according to the injection site and purpose, and using different types accordingly, has become the mainstream. This makes it possible to simultaneously achieve natural volume restoration and skin regeneration.

Characteristics and application sites of each fat type based on ITR2

In ITR2 (Injectable Tissue Replacement and Regeneration), a new standardization technique, fat is divided into the following 3 types and placed in facial anatomical compartments (Crowley 2021).

• Millifat:Relatively large fat particles with a parcel size of 2–2.4 mm (millimeters). It is suitable for areas requiring structural support and is used for replacement of deep fat compartments, augmentation over bone (onlay graft), ligament support, and lip structure formation (Crowley 2021).
• Microfat:Fat processed to approximately 1.0–1.2 mm (millimeters) in parcel size. It is used to compensate for volume loss in shallow subcutaneous fat compartments located above the facial muscles and to create surface smoothness for marionette lines and perioral wrinkles (Crowley 2021).
• Nanofat:A liquid fat mechanically emulsified to a fine consistency by passing it multiple times through a special filter. The parcel size is refined to 400–800 microns (or 500 microns) (Crowley 2021), while another study reports it to be less than 100 μm (micrometers) (Wei 2017).

Regenerative medicine effects of Nanofat

During the emulsification process, many mature adipocytes in nanofat are destroyed; however, in their place, SVF (stromal vascular fraction) and adipose-derived stem cells (ASC) become extremely abundant (Crowley 2021). Therefore, it is used not as a "filler" to provide volume, but for the purpose of "regenerative medicine."

• Skin rejuvenation (skin rejuvenation):Because nanofat is extremely smooth, it can be injected directly into the dermis or subcutis using a thin needle such as 27-gauge, or introduced into the skin surface using microneedling. This allows growth factors and cytokines secreted from cells to function, promoting collagen production, and significantly improving skin texture, elasticity, pore size, hydration, and even fine lines and pigmentation (Crowley 2021) (Wei 2017).
• Angiogenesis and improved graft retention:The SVF contained in nanofat promotes rapid angiogenesis (formation of new blood vessels) in the surrounding tissues where it is transplanted. When used in combination with millifat and microfat, blood flow reaches more easily to the center of the fat graft, and the overall survival rate (engraftment rate) of transplanted fat cells can be improved (Wei 2017).

5. Arterial Embolism Risk

Although autologous fat injection into the face is generally considered a safe and effective procedure, there is a risk of causing a devastating and irreversible complication called arterial embolism (AE) if fat is inadvertently injected into a blood vessel due to lack of anatomical understanding or improper injection technique.

Incidence and High-Risk Injection Sites

According to a systematic review of 61 patients (53 women, 7 men, 1 transgender, mean age 33.56 ± 11.45 years) with arterial embolism following fat injection, the injection sites where AE occurred most frequently are as follows (Moellhoff 2023).

• Glabella or multiple facial regions: 26.2% each (16/61 patients) (Moellhoff 2023).
• Temple: 16.4% (10/61 patients) (Moellhoff 2023).
• Forehead: 14.8% (9/61 patients) (Moellhoff 2023).

The average volume of fat injected in these embolism cases was 21.5 ± 21.5 ml (milliliters), ranging from 0.5 ml to 70 ml (Moellhoff 2023).

Symptoms and Pathophysiology

The onset of symptoms from embolism is extremely rapid; in the majority of patients (66.0%, 33/50 patients), initial symptoms appeared during injection or within one hour after injection (Moellhoff 2023).

The most commonly reported symptoms were "visual symptoms" such as vision loss and eye pain (41.4%, 24/58 patients), followed by "neurological symptoms" such as loss of consciousness, hemiplegia, and aphasia (34.5%, 20/58 patients), or symptoms affecting both vision and neurology (22.4%, 13/58 patients) (Moellhoff 2023).

Facial blood flow is formed by branches of the internal carotid artery system and external carotid artery system intertwined in a complex manner, creating abundant anastomoses (networks). When injecting into the glabella or forehead, embolism can occur when fat is directly injected into branches of the internal carotid artery system such as the supratrochlear artery or supraorbital artery, or when a bolus of fat is pushed backward retrogressively by high injection pressure. Additionally, even when fat is injected into branches of the external carotid artery system, emboli can migrate to the internal carotid artery system through anastomoses (Moellhoff 2023).

Severe Outcomes and Management Limitations

Analysis of occluded vessels showed occlusion of the ophthalmic artery (OA) in 43.3% (26/60 patients), occlusion of cerebral arteries (CA) such as the anterior cerebral artery or middle cerebral artery in 18.3% (11/60 patients), and occlusion of both OA and CA in 23.3% (14/60 patients) (Moellhoff 2023).

These outcomes are extremely serious and significantly affect the patient's life.

• 100% (26/26 patients) of patients with ophthalmic artery (OA) occlusion experienced permanent blindness (Moellhoff 2023).
• The majority (80%, 8/10 patients) of patients with cerebral artery (CA) occlusion were left with permanent neurological deficits such as paralysis (Moellhoff 2023).
• 63.6% (7/11 patients) of patients with occlusion of both OA and CA experienced blindness (Moellhoff 2023).
• Furthermore, 6 patients died as a result of fat embolism (Moellhoff 2023).

Hyaluronic Acid InjectionIn the case of hyaluronic acid injection, blood flow can potentially be restored by injecting hyaluronidase, a dissolving agent (antidote); however, no such dissolving agent exists for autologous fat. Therefore, conservative treatment, pharmacotherapy, and surgical decompression are performed, but there is no established treatment algorithm with confirmed effectiveness in the event of embolism, and the prognosis is extremely poor. Therefore, rather than "treating" embolism, "preventing" it is of paramount importance (Moellhoff 2023).

6. Safety Points

To completely avoid the catastrophic arterial embolism risks of blindness and stroke mentioned above and to safely perform fat injection to the forehead, there are critical safety points (preventive measures) that surgeons must strictly adhere to.

Acquisition of Deep Anatomical Knowledge

An absolute prerequisite for enhancing safety is that the surgeon has a deep understanding of the anatomical structure of facial blood vessels and their three-dimensional course of distribution (Moellhoff 2023).

Dangerous blood vessels such as the supratrochlear artery and supraorbital artery exist in the forehead and glabella. To avoid these vessels, the tissue layer (layer), depth, and direction of the cannula being injected must be appropriately adjusted (Moellhoff 2023).

Selection of Appropriate Equipment (Use of Blunt-Tip Cannulas)

To minimize the risk of penetrating blood vessel walls, the use of blunt-tip cannulas (rather than sharp needles) is strongly recommended (Moellhoff 2023).

Additionally, the diameter size of needles and cannulas is important. Larger-diameter (thicker) cannulas require more physical force to penetrate arterial walls, resulting in lower risk of entering blood vessels compared to using thinner needles. Therefore, cannulas of 18 gauge or larger in diameter are considered safe (Moellhoff 2023).

In fact, even in the MAFT technique, which is highly regarded for its safety, the use of an 18G blunt-tip cannula with a diameter of 1.2 mm (millimeter) is the standard to physically prevent intravascular injection (Chou 2017).

Thorough safe injection technique

In addition to device selection, the following principles must be observed in the actual injection procedure.

• Pre-injection aspiration check:Immediately before injecting fat, it is recommended to gently pull the plunger of the syringe to confirm that blood is not drawn into the syringe (i.e., the needle tip is not inside a blood vessel) (Moellhoff 2023).
• Low-pressure, micro-volume, retrograde injection:When injecting fat, strong pressure should not be applied to the syringe; instead, a very small amount of fat (aliquot) should be slowly injected in a retrograde manner (withdrawing the cannula from the tissue) (Moellhoff 2023).
• Pressure control using MAFT-GUN:When using precision equipment such as MAFT-GUN, each trigger delivers an extremely micro amount of fat—1/120 mL (0.0083 mL)—at a consistently low pressure. This essentially eliminates the danger of fat boluses being pushed back into the internal carotid artery system due to the "high retrograde pressure" that often occurs with manual injection (Chou 2017).

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7. Summary

Fat grafting to the forehead is a highly popular aesthetic medical procedure among Asians for balancing facial proportions and creating a harmonious, youthful, and attractive appearance.

The advent of sophisticated micro-injection techniques such as MAFT, combined with differentiated use of fat based on particle size—millifat, microfat, and nanofat (ITR2)—has made it possible to achieve not only volume restoration but also tissue regeneration, including skin quality improvement, simultaneously. Objective meta-analysis has demonstrated that the graft retention rate is maintained at approximately 47% on average, and with second grafting procedures or appropriate centrifugation and filtration processing, even more stable long-term results can be expected.

However, injection into incorrect planes or blood vessels carries the serious risk of fatal arterial embolism (AE), which can lead to permanent blindness, stroke, or in the worst case, death. Because fat has no dissolving agent like hyaluronic acid, treatment after complications occur is extremely difficult, and the prognosis is bleak.

Therefore, strict safety standards must be observed: thorough familiarity with detailed facial anatomy, selection of 18-gauge or larger blunt-tip cannulae, low-pressure micro-volume retrograde injection, and precise control using equipment such as MAFT-GUN. Only by adhering rigorously to these measures can we fully protect patient safety while delivering long-lasting, highest-level aesthetic results.

References

1. Chou C, Liao H, Lin T, et al. Micro-Autologous Fat Transplantation for Forehead Volumization. Aesthetic Plastic Surgery. 2017DOI
2. Li X, Kubiak C, Yang X, et al. Forehead Fat Grafting: Asian Facial Contouring and Augmentation. Plastic & Reconstructive Surgery. 2019DOI
3. Kang G, Hsiao Y, Huang J, et al. Aesthetic Durable Forehead Contouring in Asians With Fat Grafting and Botulinum Toxin. Annals of Plastic Surgery. 2019DOI
4. Lv Q, Li Y, Fan Y, et al. Fat Grafting for Facial Rejuvenation: A Systematic Review and Meta-analysis of Volume Retention. Aesthetic Plastic Surgery. 2020DOI
5. Crowley J, Cohen S, Tirtho R, et al. Injectable Tissue Replacement and Regeneration (ITR2): A Comprehensive Review. Aesthetic Plastic Surgery. 2021DOI
6. Moellhoff N, Grawammer P, Giunta R, et al. Arterial Embolism After Autologous Fat Grafting to the Face: A Systematic Review. Aesthetic Plastic Surgery. 2023DOI

About the author of this article

Hiromitsu NakamuraPhysician

Zetith Beauty Clinic Ginza / Osaka / Fukuoka

He has a track record of presenting research at domestic and international academic conferences and is involved in technical guidance and education across Zetith Beauty Clinic. He specializes in precision aesthetic medicine based on anatomical evidence and pursues natural results tailored to each individual's skeletal structure and tissues.