Fat injection to the forehead for a rounded appearance——latest techniques and retention rate data for Asians

1. Why it is popular among Asians

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

Specifically, a full, rounded forehead shape without soft tissue deficiency or irregular bone contours, and with left-right symmetry and harmony, is believed to signify not merely beauty, but also prosperity, leadership ability, and social success (Chou 2017).

From an anatomical perspective, the fullness of the forehead plays a crucial role in the overall balance and harmony of the face. In particular, when viewed from the side or at an angle, a smooth forehead with a slight convex contour and no wrinkles imparts three-dimensionality to the entire face and is said to add significant appeal to one's appearance and general image (Chou 2017).

Asians tend to have anatomically flat foreheads or prominent irregularities, so there is strong demand for 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 Asians as a means of smoothing facial contours and achieving 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 concepts and dedicated equipment of MAFT

Previous histological research (Carpaneda et al.) demonstrated that when the radius of transplanted fat parcels exceeds 2 mm (millimeters), blood flow and nutrient penetration from the surrounding tissue do not reach the center, resulting in necrosis of the central fat cells (Chou 2017).

To prevent this central necrosis, the MAFT concept maintains the injection volume per application (parcel size) at less than 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 it more effectively and dramatically improving survival rate (Chou 2017).

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

Three-layer injection approach to the forehead

In MAFT to the forehead, fat is carefully distributed and injected into the following three distinct layers based on anatomical structure (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 application: 1/120 mL = 0.0083 mL) and distribute fat in a fan pattern by sliding over the periosteum of the frontal bone. This layer typically receives 5–10 mL (milliliters) of fat grafting, establishing the basic volume and foundation of the forehead (Chou 2017).
• Middle layer (within the frontalis muscle): Angle the cannula slightly and advance it into the muscle of the frontalis. The intramuscular space has abundant blood flow, providing excellent blood supply to the transplanted fat cells. This layer typically also receives 5–10 mL (milliliters) of fat grafting (Chou 2017).
• Superficial layer (subcutaneous layer / between the dermis and frontalis muscle): The forehead skin is the thickest on the face, with dense septa (connective tissue) running laterally from the dermis toward the frontalis muscle. For this reason, grafting a large volume of fat at once is difficult, and the injection volume to this layer typically remains at 3–5 mL (milliliters) or less. It serves to refine surface smoothness (Chou 2017).

Surgical outcomes and patient satisfaction

In a study of 178 patients (167 women, 11 men, mean age 47.7 years), the average time required for the entire MAFT procedure from fat harvesting to grafting 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 at 4–6 months post-operatively seeking fuller augmentation (Chou 2017).

In a long-term follow-up study with an average of 34 months (8–68 months), no major 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 underwent a single procedure reported satisfactory results (53.2% satisfied, 27.5% very satisfied). Furthermore, patients who underwent two procedures achieved an exceptionally high satisfaction rate of 100% (86.4% very satisfied, 13.6% satisfied) (Chou 2017).

3. Retention rate meta-analysis

In autologous fat injection to the face, the extent to which injected fat ultimately becomes established (retention rate: volume retention rate) is the topic of greatest interest to both surgeons and patients. Quantitative meta-analysis using objective imaging techniques has been performed on retention rates, which had previously been based largely on clinical experience.

Mean retention rate and changes over time

A meta-analysis of 27 studies involving 1,011 patients who underwent fat injection to the face showed that the overall pooled mean retention rate for facial fat grafting was 47% (95% confidence interval 41–53%) (Lv 2020).

The retention rates reported in individual studies varied widely, ranging from 26% to 83%, with follow-up periods averaging 3–24 months (Lv 2020).

The retention rate changes dynamically over time. As time progresses—at 3 months, 6 months, and 12 months post-procedure—the retention rate gradually declines, and it has been established that the maximum volume reduction occurs within the first 3 months after surgery (Lv 2020).

This initial volume reduction is thought to be due to water absorption and the resorption of nonviable cells. Subsequently, it is theorized that the volume stabilizes as surviving mature adipocytes differentiate and proliferate (Lv 2020).

Factors affecting retention rate and complications

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

• Number of injections:A clear trend was confirmed showing higher retention rates with secondary fat injection compared to primary injection. This is thought to be because the tissue in the recipient site becomes enriched by the initial transplant, establishing a foundation for blood flow (Lv 2020).
• Fat processing method:In the processing of harvested fat, methods using centrifugation or filtration (filtration) are suggested to potentially yield more consistent and favorable engraftment results compared to simple sedimentation (Lv 2020).
• Patient indications:A trend toward higher retention rates was observed in patients with congenital facial deformities compared to pure cosmetic augmentation. This is theorized to be because the soft tissue of congenital deformities can provide a loose scaffold that more readily supplies nutrition to the transplanted fat (Lv 2020).
• Fat harvest site:No significant difference in retention rate was 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 retention rates (yield higher values) compared to measurement using 3D scans (Lv 2020).

Among the 1,011 patients included, only 2.8% (28 individuals) experienced complications, which were primarily relatively mild in nature, such as infection, irregular contour irregularities, asymmetry, and overcorrection (Lv 2020).

4. Microfat and nanofat differentiation and selection

In modern fat injection, rather than injecting harvested fat as-is, the approach of precisely processing the particle size (parcel size) of the fat according to the injection site and purpose, and selecting the appropriate type, has become 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 the new standardization technique ITR2 (Injectable Tissue Replacement and Regeneration), fat is divided into the following three types and positioned within the anatomical compartments of the face (Crowley 2021).

• Millifat:A relatively large fat parcel 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 structuring (Crowley 2021).
• Microfat:Fat finely processed to a parcel size of approximately 1.0–1.2 mm (millimeters). It is used to compensate for volume loss in shallow subcutaneous fat compartments positioned above facial muscles and to create surface smoothness for marionette lines and perioral wrinkles (Crowley 2021).
• Nanofat:Liquid fat that has been mechanically emulsified finely by passing it through a special filter multiple times. The parcel size is refined to 400–800 microns (or 500 microns) (Crowley 2021), and in another study it is reported to be less than 100 μm (micrometers) (Wei 2017).

Regenerative medicine effects of nanofat

During the fine emulsification process of nanofat, many mature adipocytes are destroyed; however, in their place, SVF (stromal vascular fraction) and adipose-derived stem cells (ASC) become extremely abundant (Crowley 2021). For this reason, 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 fine needle such as 27-gauge, or it can be introduced to the skin surface using microneedles. Through this, growth factors and cytokines secreted by cells work to promote collagen generation, resulting in remarkable improvements in skin texture, elasticity, pore size, moisture content, and even fine lines and pigmentation (Crowley 2021) (Wei 2017).
• Angiogenesis and improved engraftment rate: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 or microfat, blood can more easily reach the center of the fat graft, and the survival rate (engraftment rate) of the transplanted fat cells can be comprehensively 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 a very devastating and irreversible complication called arterial embolism (AE) if fat is inadvertently injected into a blood vessel due to a lack of anatomical understanding or improper injection technique.

Occurrence and High-Risk Injection Sites

According to a systematic review of 61 patients (53 women, 7 men, 1 transgender individual, 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 amount of fat injected in these embolic 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, with the majority of patients (66.0%, 33/50 people) developing initial symptoms during or within 1 hour after injection (Moellhoff 2023).

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

Facial blood flow is formed by intricately intertwined branches of the internal carotid artery system and external carotid artery system, 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 fat boluses are pushed backward in a retrograde manner 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 people), occlusion of cerebral arteries (CA) such as the anterior or middle cerebral artery in 18.3% (11/60 people), and occlusion of both OA and CA in 23.3% (14/60 people) (Moellhoff 2023).

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

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

Hyaluronic Acid InjectionIf hyaluronic acid injection occurs, blood flow may be restored by injecting hyaluronidase, a dissolving agent (antidote), but 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 cases of embolism, and the prognosis is very poor. Therefore, it is more important to "prevent" embolism rather than "treat" it (Moellhoff 2023).

6. Safety Points

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

Acquisition of Deep Anatomical Knowledge

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

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

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

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

Additionally, the diameter size of the needle or cannula is also important. Larger (thicker) cannulas require more physical force to penetrate arterial walls, so the risk of entering blood vessels is lower compared to using thinner needles. Therefore, cannulas with a thickness of 18 gauge or larger 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 standard to physically prevent intravascular injection (Chou 2017).

Strict adherence to safe injection techniques

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

• Pre-injection aspiration check: It is recommended to gently pull the plunger of the syringe immediately before injecting fat and always confirm that blood does not flow into the syringe (i.e., that the needle tip is not inside a blood vessel) (Moellhoff 2023).
• Low-pressure, micro-quantity, retrograde injection: When injecting fat, strong pressure should not be applied to the syringe; rather, extremely small amounts of fat (aliquots) should be slowly injected in a retrograde manner (withdrawing the cannula from the tissue) (Moellhoff 2023).
• Pressure control using MAFT-GUN: When using a precision device like MAFT-GUN, each trigger press can dispense an extremely small amount of fat—1/120 mL (0.0083 mL)—consistently at low pressure. This makes it possible to almost completely eliminate the risk of fat deposits being pushed back into the internal carotid artery system due to the high retrograde pressure that occurs with manual injection (Chou 2017).

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7. Conclusion

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

With the advent of sophisticated micro-injection techniques like MAFT and the differentiated use of fat based on particle size—millifat, microfat, and nanofat (ITR2)—it is now possible to achieve not only volume restoration but also simultaneous tissue regeneration such as skin quality improvement. Objective meta-analysis also shows that retention rates are maintained at an average of approximately 47%, and more stable long-term results can be expected, especially with second grafting and appropriate centrifugation and filtration processing.

On the other hand, injection into incorrect tissue planes or blood vessels carries the serious risk of fatal arterial embolism (AE), which can cause permanent blindness, stroke, or in the worst case, death. Because fat lacks a dissolution agent like hyaluronic acid, treatment after complications occur is extremely difficult, and the prognosis is hopeless.

Therefore, strict safety standards must be adhered to: thorough knowledge of detailed facial anatomy, selection of 18-gauge or larger blunt-tip cannulas, low-pressure micro-quantity retrograde injection, and precise control utilizing devices like MAFT-GUN. Only by rigorously following these practices can we fully protect patient safety while achieving 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. 2017 DOI
2. Li X, Kubiak C, Yang X, et al. Forehead Fat Grafting: Asian Facial Contouring and Augmentation. Plastic & Reconstructive Surgery. 2019 DOI
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. 2019 DOI
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. 2020 DOI
5. Crowley J, Cohen S, Tirtho R, et al. Injectable Tissue Replacement and Regeneration (ITR2): A Comprehensive Review. Aesthetic Plastic Surgery. 2021 DOI
6. Moellhoff N, Grawammer P, Giunta R, et al. Arterial Embolism After Autologous Fat Grafting to the Face: A Systematic Review. Aesthetic Plastic Surgery. 2023 DOI

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 for Zetith Beauty Clinic as a whole. He specializes in precise aesthetic medicine based on anatomical evidence and pursues natural results tailored to each patient's skeletal structure and tissues.