Analysis of Craniofacial Microsomia and Facial Asymmetry: Approaches in Facial Feminization Surgery

Abstract

Background

Comprehensive facial analysis among transgender and gender-diverse (TGD) individuals undergoing facial feminization surgery (FFS) has created new opportunities to investigate facial asymmetry in adults. Although craniofacial microsomia (CFM) is typically identified in infancy, milder forms may go unrecognized, leaving gaps in diagnosis and treatment.

Objectives

The authors of this study examine facial asymmetry, including CFM, among TGD patients undergoing FFS and discuss appropriate surgical strategies.

Methods

Adults registered male at birth undergoing de novo FFS from 2020 to 2024 were retrospectively reviewed. CFM was diagnosed in patients with same-sided hypoplasia in multiple features, including skeletal structures, malar soft tissue, nerves, and the external ear. The OMENS classification characterized facial morphology. Descriptive statistics, Fisher's exact tests, and Mann–Whitney U tests were performed.

Results

Among 175 patients with a median age of 28.0 years (interquartile range [IQR], 24.0-34.0 years), 11 (6.3%) were diagnosed with unilateral CFM and demonstrated greater orbital asymmetry, mandibular hypoplasia, ear anomaly, nerve impairment, and soft tissue deficiency compared with their non-CFM counterparts (total OMENS of 5.0 [IQR, 4.0-6.0] vs 0.0 [IQR, 0.0-1.0], respectively, P < .001). Asymmetry in at least 1 facial feature was observed throughout the entire cohort (83.4%). As for surgical maneuvers, to correct chin cants, patients with CFM often underwent osseous genioplasties involving asymmetrical vertical lengthening, whereas patients without CFM underwent symmetrical repositioning (3.3 mm [IQR, 0.0-4.1 mm] vs 0.0 mm [IQR: 0.0 mm], respectively, P < .001).

Conclusions

CFM may be more common than previously estimated. For individuals with CFM seeking FFS, greater vertical chin manipulation with osseous genioplasty may improve symmetry and feminization.

Level of Evidence: 4 (Therapeutic)

Mild facial asymmetry is widely observed in the general population, with studies reporting estimates ranging from 34% to 99%.^1-4 However, the extent of asymmetry across multiple tissue types remains poorly defined, particularly from a surgically relevant lens. Craniofacial microsomia (CFM), the second most common congenital craniofacial condition, is characterized by hypoplasia of the skeleton and overlying soft tissues.⁵ Yet, its reported incidence varies widely, from 1 in 3500 to 1 in 40,000 births.^5-10 These discrepancies are largely driven by the diagnostic emphasis on severe cases in young children and variable phenotypic manifestations. As a result, mild conditions frequently remain undiagnosed even in adulthood, potentially leading to an underestimation and incomplete understanding of CFM. Recognizing these milder manifestations may be particularly useful for craniofacial surgeons performing skeletal and soft tissue reconstruction, where subtle asymmetries may have significant surgical implications.

Although there is a paucity of studies analyzing baseline adult facial anatomy in detail, craniofacial surgeons are optimally situated to assess variations in facial anatomy and function, particularly in adults seeking reconstructive procedures. One such patient population includes transgender and gender-diverse (TGD) individuals undergoing facial feminization surgery (FFS), where comprehensive analysis of the skeletal and soft tissue structures is essential for surgical planning and treating gender dysphoria.^11-16 Our group's experience evaluating hundreds of patients for FFS over multiple years, through both detailed clinical examinations and computed tomography (CT) imaging, has revealed a wide range of craniofacial asymmetries. Furthermore, the integration of modern craniofacial technologies, such as 3-dimensional (3D) surgical planning, into FFS care additionally allows for more precise assessment of skeletal relationships and refinement of surgical techniques to effectively address asymmetry.^17,18 Although it is known that most individuals have some facial asymmetry, few studies describe the various manifestations in adults, especially in the TGD population. Therefore, defining these variations can be helpful not only for optimizing surgical outcomes in FFS but also for improving the recognition and diagnosis of mild CFM in adulthood.

The authors of this study analyze the spectrum of facial asymmetry and CFM in adult TGD patients undergoing gender-affirming FFS. Additionally, we discuss appropriate surgical strategies to improve both facial feminization and symmetry.

METHODS

Patients

All TGD individuals registered male at birth who underwent FFS or completed preoperative 3D surgical planning (3D Systems, Rock Hill, SC) for an upcoming FFS under a single surgeon (J.C.L.) from August 2020 to February 2024 were retrospectively reviewed. Patients with a history of previous facial surgery were excluded. Demographics, craniofacial anatomy, surgical plans, and operative characteristics were collected (UCLA IRB#: 22-001299).

CFM and Asymmetry Characterization

CFM was diagnosed by the primary surgeon (J.C.L.) and characterized according to the OMENS classification system.¹⁹ The OMENS classification was selected because of its comprehensive evaluation of multiple key facial features present in CFM. Each category (orbital asymmetry, mandibular hypoplasia, ear anomaly, nerve impairment, and soft tissue deficiency) was graded from 0 (normal) to 3 (most severe), with a total compiled score ranging from 0 to 15. The OMENS classification system was further applied to patients without CFM to evaluate normal facial asymmetry. Preoperative clinical examinations, photographs, CT scans, 3D surgical plans, and operative notes were reviewed to determine OMENS scores, House Brackmann grade, chin cant and deviation, and nasal deviation (Supplemental Table 1). Upper facial nerve function was not photographed nor documented during the clinical examination; thus, it was not possible to evaluate.

Statistical Analyses

Descriptive statistics were performed to compare characteristics between patients with and without CFM. Fisher's exact tests were utilized to compare facial anatomy and operative characteristics between cohorts. Differences in OMENS scores and surgical measurements were evaluated using Mann–Whitney U tests. All statistical analyses were conducted in SPSS, version 29.0 (SPSS Inc., Chicago, IL) with a significance threshold of P < .05.

RESULTS

Patient Characteristics

Among a total of 175 TGD patients with a median age of 28.0 (interquartile range [IQR], 24.0-34.0) years included in this study, 11 patients (6.3%) were diagnosed with CFM (Table 1). Most patients overall identified as White (58.3%), followed by Latinx (22.9%), Asian (9.1%), and Black (4.6%). Hormone therapy duration varied widely, with a median duration of 2.0 years (IQR, 1.0-4.0 years). There were no statistically significant differences between groups.

Table 1.

Patient Characteristics

Variables	Total	− CFM	+ CFM	P-value
No.	175	164	11
Age at initial consultation, years, median (IQR)	28.0 (24.0-34.0)	28.0 (24.0-34.8)	28.0 (27.0-33.0)	.810
Ethnicity, n (%)				.109
White	102 (58.3)	92 (56.1)	10 (90.9)
Latinx	40 (22.9)	40 (24.4)	0 (0.0)
Asian	16 (9.1)	16 (9.7)	0 (0.0)
Black	8 (4.6)	7 (4.3)	1 (9.1)
Other	9 (5.1)	9 (5.5)	0 (0.0)
Duration of hormone therapy at initial consultation, years, median (IQR)	2.0 (1.0-4.0)	2.0 (1.0-4.0)	2.0 (1.0-4.0)	.649

CFM, craniofacial microsomia; IQR, interquartile range.

CFM Characteristics

The 11 patients diagnosed with CFM demonstrated a median total OMENS score of 5.0 (IQR, 4.0-6.0; Table 2). The laterality of the affected side was evenly distributed. Discrepancies in orbital position were observed in only 3 patients, with 1 patient displaying a relatively superior positioning of the affected orbit and 2 patients presenting with a relatively inferior orbital position. For the mandible, all patients had some degree of mandibular hypoplasia. The majority had a relatively small mandible and glenoid fossa with a short ramus on the affected side. CT analyses of ramus height further confirmed sizable mandibular asymmetry of 6.1 ± 2.7 mm overall. Additionally, 10 patients presented with a chin cant and deviation, whereas 1 patient had chin point deviation alone. Five patients had discernible ear anomalies characterized by mild hypoplasia and cupping with all structures present. Lower facial nerve impairment and House Brackmann Grade II were observed in all patients, specifically involving the buccal branch in 8 patients and the mandibular branch in 4 patients. Furthermore, all patients demonstrated soft tissue deficiency, which was particularly noticeable in the malar regions. Nasal deviation was also observed across the entire CFM cohort, and alar hypoplasia was noted in most cases.

Table 2.

Craniofacial Microsomia Morphological Characteristics

Patients	1	2	3	4	5	6	7	8a	9	10	11
CFM laterality	L	L	L	R	L	L	R	R	R	R	L
Lateral differences in ramus height, mm	6.0	6.6	7.6	6.7	6.1	1.9	3.4	—	12.0	3.9	6.6
Chin
Cant and deviation	+	+	+	+	+	+	−	+	+	+	+
Point deviation alone	−	−	−	−	−	−	+	−	−	−	−
House Brackmann	II	II	II	II	II	II	II	II	II	II	II
Nose
Nasal deviation	+	+	+	+	+	+	+	+	+	+	+
Alar hypoplasia	−	−	+	+	+	+	+	+	+	−	−
OMENS
Orbital asymmetry	O0	O0	O0	O0	O0	O2↓	O2↑	O2↓	O0	O0	O0
Mandibular hypoplasia	M1	M1	M1	M1	M1	M1	M1	M1	M2B	M1	M2B
Ear anomaly	E1	E1	E0	E1	E0	E1	E0	E0	E0	E0	E1
Nerve impairment	N72	N72	N72	N72	N72	N72	N72	N72	N72	N72	N72
Soft tissue deficiency	S1	S1	S1	S1	S1	S1	S1	S1	S1	S1	S1
Total OMENS score	5	5	4	5	4	7	6	6	5	4	6

CFM, craniofacial microsomia; L, left; R, right.

^aNo CT scan available.

Normal Facial Asymmetry Characteristics and Morphological Comparisons

Within our total cohort of 175 patients, 83.4% demonstrated asymmetry in at least 1 facial feature (Table 3). Upon evaluation using the OMENS classification system, patients without CFM displayed a significantly lower median score of zero within each category and for the total composite score compared with patients with CFM (total OMENS score of 0.0 [IQR, 0.0-1.0] vs 5.0 [IQR, 4.0-6.0], respectively, P < .001). Although the majority of patients without CFM did not display asymmetry in any OMENS category, several patients displayed asymmetry in 1 (16.5%) or multiple (11.6%) features. Specifically, a few patients without CFM demonstrated clinically discernible orbital asymmetry (4.3%), mandibular asymmetry (9.8%), ear anomaly (2.4%), nerve impairment (11.0%), and soft tissue deficiency (13.4%). Most patients in the non-CFM cohort with asymmetry received an OMENS score between 1 and 3, whereas only 1 patient received a higher score of 4. Beyond the OMENS classification, chin cants and deviations were less common in the non-CFM cohort compared with the CFM cohort (22.0% vs 90.0%, respectively, P < .001). Chin deviation alone was rarely observed in both groups (7.4% overall). Additionally, the non-CFM cohort demonstrated a lower House Brackmann Grade I compared with the CFM cohort (1.0 [IQR, 1.0-1.0] vs 2.0 [IQR, 2.0-2.0], respectively, P < .001). Only 18 patients without CFM displayed a House Brackmann Grade II (11.0%). Meanwhile, nasal deviation was observed in most patients without CFM (72.0%).

Table 3.

Anatomical Comparisons Between Patients With and Without Craniofacial Microsomia

Variables	Total (n = 175)	− CFM (n = 164)	+ CFM (n = 11)	P-value
Chin, n (%)
Cant and deviation	46 (26.3)	36 (22.0)	10 (90.9)	<.001
Deviation alone	13 (7.4)	12 (7.3)	1 (9.1)	.583
House Brackmann, median (IQR)	1.0 (1.0-1.0)	1.0 (1.0-1.0)	2.0 (2.0-2.0)	<.001
Nasal deviation, n (%)	129 (73.7)	118 (72.0)	11 (100.0)	.069
OMENS classification, median (IQR)
Orbital asymmetry	0.0 (0.0)	0.0 (0.0)	0.0 (0.0-2.0)	<.001
Mandibular hypoplasia	0.0 (0.0)	0.0 (0.0)	1.0 (1.0-1.0)	<.001
Ear anomaly	0.0 (0.0)	0.0 (0.0)	0.0 (0.0-1.0)	<.001
Nerve impairment	0.0 (0.0)	0.0 (0.0)	2.0 (2.0-2.0)	<.001
Soft tissue deficiency	0.0 (0.0)	0.0 (0.0)	1.0 (1.0-1.0)	<.001
Total OMENS score, median (IQR)	0.0 (0.0-1.0)	0.0 (0.0-1.0)	5.0 (4.0-6.0)	<.001
Breakdown, n (%)
0	118 (67.4)	118 (72.0)	0 (0.0)
1	20 (11.4)	20 (12.2)	0 (0.0)
2	12 (6.9)	12 (7.3)	0 (0.0)
3	13 (7.4)	13 (7.9)	0 (0.0)
4	4 (2.3)	1 (0.6)	3 (27.3)
5	5 (2.9)	0 (0.0)	4 (36.4)
6	2 (1.1)	0 (0.0)	3 (27.3)
7	1 (0.6)	0 (0.0)	1 (9.1)

CFM, craniofacial microsomia; IQR, interquartile range.

FFS Characteristics

Among the 155 patients (88.6%) who completed FFS, there were no differences in the frequency of general FFS procedures between cohorts (Table 4). For the entirety of the cohort, the mean follow-up was 10.4 ± 7.5 months. To accurately report complications, we excluded all patients who were followed for <90 days. Among the 130 patients who were included, the mean follow-up was 12.9 ± 6.4 months. Within this cohort, there were 12 complications (9.2%), of which the majority were local wound healing issues (n = 8, 6.2%). Three patients had scar alopecia (2.3%), and 1 patient had an intraoral infection that was treated with oral antibiotics (0.8%). Revisions occurred in 14 patients (10.8%). The majority of revisions were because of scar revisions of the forehead or scalp (n = 6, 4.6%), followed by revision rhinoplasty (n = 5, 3.8%), revision brow lift (n = 3, 2.3%), or additional fat grafting (n = 3, 2.3%). For skeletal maneuvers, there were 2 revisions for mandibular contour abnormalities (1.5%) and 2 for removal of palpable hardware. Two patients required revision of the anterior table of the frontal sinus setback.

Table 4.

Facial Feminization Surgical Procedures

Variables, n (%)	Total	− CFM	+ CFM	P-value
Completed FFS	155 (88.6)	144 (87.8)	11 (100.0)
Skeletal procedures
Genioplasty	138 (89.0)	128 (88.9)	10 (90.9)	1.000
Forehead reconstruction	135 (87.1)	126 (87.5)	9 (81.9)	.636
Gonial angle reduction	127 (81.9)	118 (81.9)	9 (81.8)	1.000
Soft tissue procedures
Fat grafting	146 (94.2)	136 (94.4)	10 (90.9)	.494
Rhinoplasty	123 (79.4)	115 (79.9)	8 (72.7)	.698

CFM, craniofacial microsomia; FFS, facial feminization surgery.

Upon a closer evaluation of FFS surgical maneuvers, there were minor differences in soft tissue reconstruction. The major difference between patients with and without CFM was skeletal reconstruction of the lower face. Preoperative and postoperative photographs of a patient with CFM (Figure 1) and a patient without CFM are provided (Figure 2).

Figure 1.

A 54-year-old female registered male at birth with craniofacial microsomia presented for facial feminization surgery. She underwent a 3 mm Type III forehead reconstruction, coronal brow lift, sliding genioplasty (3.5 mm chin advancement, 3 mm left cant opening wedge, and 1.75 mm right and 3.5 mm left recontouring), septorhinoplasty (osteotomies, tip elevation and rotation, alar base reduction, and dorsal augmentation), and fat grafting to the malar (8 mL bilateral augmentation) and temple regions (6 mL bilateral augmentation). (A, D, G) Preoperative, (B, E, H) 3 month postoperative, and (C, F, I) 1.5-year postoperative photographs are shown. (J–L) Preoperative 3-dimensional reconstructions of the skull and mandible depict the Pruzansky type 2B mandible characterized by a hypoplastic left condyle with temporomandibular joint displacement, a shorter left ramus, and chin deviation.

Figure 2.

A 37-year-old female registered male at birth presented for facial feminization surgery. She underwent a 4.5 mm Type III forehead reconstruction, hairline reduction, brow lift, reduction genioplasty (4.8 mm right and 4.3 mm left reduction), gonial angle reduction (5 mm bilateral reduction), dorsal preservation septorhinoplasty with septal extension graft (bilateral cephalic trim flaps, alar contour grafts, and inferior turbinate reduction), fat grafting to the malar (9 mL right and 8 mL left augmentation) and temple regions (5 mL bilateral augmentation), and lip augmentation with dermal fat graft. (A, C, E) Preoperative and (B, D, F) 1 year postoperative photographs are shown.

Surgical Approach for Soft Tissue Reconstruction

An in-depth evaluation of soft tissue maneuvers revealed that patients with CFM tended to require a slightly greater fat grafting volume in their affected malar side to correct for soft tissue hypoplasia, whereas patients without CFM generally received equivalent malar augmentation bilaterally (Supplemental Figure 1 and Supplemental Table 2). Both cohorts received equivalent augmentation to the temporal regions. Among patients who underwent a rhinoplasty, the entire CFM cohort and the majority of the non-CFM cohort (81.7%) required a septorhinoplasty to correct a deviated septum.

Surgical Approach for Skeletal Reconstruction

To compare differences in skeletal maneuvers, we pooled all patients who had undergone FFS or completed surgical planning for an upcoming FFS (Figure 3, Table 5). Although no differences in forehead reconstruction were detected, there was a perceptible difference in mandibular reconstruction between cohorts. A higher percentage of patients with CFM underwent osseous genioplasties (70.0%) compared with patients without CFM (38.7%) who tended to undergo contouring genioplasties instead. Osseous genioplasties were performed to correct chin cants and deviations, whereas contouring procedures were sufficient for patients with minimal chin asymmetry. Among patients with CFM who required a horizontal osteotomy, chin cant correction involved significantly greater lengthening on 1 side compared with patients without CFM, who underwent symmetrical bilateral manipulation (3.3 mm [IQR, 0.0-4.1 mm] vs 0.0 mm [IQR, 0.0 mm], respectively, P < .001). Given that chin cant and deviation were corrected simultaneously through the horizontal osteotomy, minimal lateral differences in chin contouring were observed in the CFM cohort. Additionally, patients with CFM required unequal gonial angle reduction to address mandibular asymmetries. However, these differences were not significantly different compared with patients without CFM, who also tended to require laterally unequal gonial angle reduction albeit to a smaller degree.

Figure 3.

(A) Feminizing skeletal reconstruction. No statistically significant lateral differences in (B) supraorbital contouring and (C) gonial angle reduction were observed between cohorts, but patients with craniofacial microsomia (CFM) tended to require more unequal mandibular reconstruction. (D) Patients with CFM tended to require an osseous genioplasty to correct chin cants and deviations. (E) The degree of unequal vertical manipulation in a horizontal osteotomy to correct chin asymmetry was significantly greater in the CFM cohort than in the non-CFM cohort. (F) Meanwhile, horizontal chin manipulation using bilateral contouring was similar. Box and whisker Tukey plots are depicted highlighting the median and interquartile range. A bar graph depicts the frequency of an osseous genioplasty.

Table 5.

Feminizing Skeletal Reconstruction Differences

Variables	Total	− CFM	+ CFM	P-value
Forehead reconstruction	162	153	9
Maximum central reduction, mm, median (IQR)	4.0 (3.0-5.0)	4.0 (3.0-5.0)	4.0 (3.0-5.0)	.965
Lateral contouring, mm, median (IQR)
Average	3.8 (3.0-4.6)	3.9 (3.0-4.8)	3.0 (2.9-4.0)	.207
Differences between laterality	0.0 (0.0-0.5)	0.0 (0.0-0.5)	0.0 (0.0-0.1)	.377
Gonial angle reconstruction	160	150	10
Maximum reduction, mm, median (IQR)
Average	5.8 (4.5-7.2)	5.8 (4.5-7.3)	5.5 (4.5-7.3)	.863
Differences between laterality	0.5 (0.0-1.7)	0.5 (0.0-1.5)	1.3 (0.4-2.7)	.135
Genioplasty	165	155	10
Chin reduction type, n (%)				.092
Osteotomy	67 (40.6)	60 (38.7)	7 (70.0)
Contouring	98 (59.4)	95 (61.3)	3 (30.0)
Maximum vertical change, mm, median (IQR)
Average	0.0 (−1.0-0.0)	0.0 (−1.0-0.0)	1.4 (−0.3-2.0)	.065
Differences between laterality	0.0 (0.0)	0.0 (0.0)	3.3 (0.0-4.1)	<.001
Maximum horizontal change, mm, median (IQR)
Average	3.0 (2.3-3.8)	3.0 (2.3-3.8)	3.5 (2.0-3.7)	.642
Differences between laterality	0.8 (0.0-1.2)	0.8 (0.0-1.3)	0.1 (0.0-1.0)	.241

CFM, craniofacial microsomia; IQR, interquartile range.

DISCUSSION

Our study describes our experience characterizing normal facial asymmetry and CFM among adult TGD patients through a multimodal analysis of preoperative clinical examinations, photographs, CT scans, and 3D surgical plans while also discussing strategies to care for individuals with various degrees of facial asymmetry seeking FFS. Our findings were: (1) 83.4% of patients presented with asymmetry in at least 1 facial feature; (2) whereas the majority of patients displayed normal facial asymmetry, 6.3% of the total cohort displayed unilateral multi-level asymmetry and were diagnosed with CFM; and (3) the primary difference in the FFS approach was observed for the chin, with the CFM cohort requiring more asymmetric vertical lengthening in an osseous genioplasty to correct chin cants and deviations.

Previous studies utilizing photographic and 3D analyses have reported a wide range of estimated facial asymmetry in the general adult population. A recent 3D photographic evaluation of 145 White patients registered male at birth by Lum et al found that moderate facial asymmetry defined as 2 to 5 mm was observed in 58.4% of individuals and severe asymmetry >5 mm was observed in 7.7% of individuals.³ Although the authors of the study did not specifically evaluate for CFM, the proportion of severe asymmetry in adults registered male at birth closely corresponds with our findings. In another study, Rohrich et al performed a preoperative photographic evaluation of 100 patients presenting for a primary rhinoplasty and found that 74% had nasal deviation, 66% had chin deviation, 98% had facial height asymmetry, and 99% had facial width asymmetry.⁴ The proportion of nasal deviation closely matches our findings, yet the rate of chin deviation is nearly double in our observations. Overall, the rate of facial asymmetry in the current study is higher than Lum et al and lower than Rohrich et al, but the methodologies differ as we did not evaluate the amount of general facial asymmetry nor measure facial width and height. Upon a closer investigation of each facial feature, Lum et al reported that asymmetry was identified primarily in the orbits, nose, and chin. Other studies utilizing photographic or 3D measurements have also reported that more asymmetry was present around the orbits and mandible.^2,20-22 Meanwhile, in our study, we found that the majority of asymmetry in the non-CFM cohort was localized around the nose, chin, cheeks, and mandible with very few patients displaying orbital asymmetry. Differences in methodology and gender may partly explain this discrepancy. In particular, gender diversity has not been investigated, especially for transgender patients, and previous studies primarily evaluate patients based on gender registered at birth. These differences highlight the novelty of the current study's approach to utilizing a multimodal evaluation of facial anatomy and function, including precise skeletal measurements, for TGD patients registered male at birth on hormone therapy.

Our observation that CFM was present in 6.3% of the total cohort suggests that CFM could be much more common than previously described. The highest estimate of CFM in the literature to date has been ∼0.028%.^5,6,9 This discrepancy could be partly because of the focus on severe manifestations that are readily identifiable in infants and young children.^7-10,23-25 Additionally, the lack of a formal definition and minimal diagnostic criteria complicates its diagnosis.^5,8,24 To that end, the distinct characteristics between patients with normal asymmetry and those diagnosed with CFM in the current study suggest a minimal differentiation involving clinically discernable mandibular hypoplasia characterized by a small mandible and glenoid fossa with a short ramus, as well as same-sided asymmetry in at least 2 other facial features including the orbits, ears, nerves, and soft tissues. Although mandibular hypoplasia has been considered the cornerstone of CFM, the pediatric craniofacial literature presents a much more heterogeneous presentation of CFM that does not always manifest mandibular asymmetry.^19,26 Therefore, this criterion may be more appropriate for identifying adult patients with mild presentations of CFM. The persisting ambiguity between normal facial asymmetry and CFM may serve as a barrier to its recognition in a greater percentage of the population.

Few studies have attempted to estimate the prevalence of undiagnosed CFM. In a prospective cohort study of 100 consecutive children with isolated microtia, the authors identified unsuspected CFM in 40% of patients.²⁷ By combining our findings and the available data, it has been collectively suggested that there are potentially many more individuals with undiagnosed CFM in the general population. One note is that in our study, we only evaluate CFM in TGD patients registered male at birth. There are reports in the literature that CFM occurs more often in individuals registered male at birth, but the authors of several studies have observed no gender differences.^{19,23,24,28-32} Furthermore, the laterality of the affected side in our cohort was evenly distributed. While some studies have stated that CFM has a right-sided predilection, there are contradicting reports.^{19,26,29-31,33} There is certainly ambiguity within the literature, highlighting the need for a more comprehensive and detailed understanding of CFM.

To adequately address CFM for patients seeking FFS, one must combine reconstructive, aesthetic, and gender-affirming surgical principles. In our study, we suggest that for TGD patients with CFM, an osseous genioplasty with a horizontal osteotomy may be more likely required to feminize and balance the chin. We also found lateral differences in gonial angle reduction for patients, regardless of a CFM diagnosis. Patients with CFM, however, tended to require more bilaterally uneven reconstruction to correct for mandibular hypoplasia. These findings underscore the need to incorporate standard craniofacial surgery principles and perform a thorough analysis of skeletal relationships for all patients undergoing FFS. In addition to facial asymmetries, there may be other skeletal discrepancies to consider, such as malocclusion and orbital dystopia, which could require additional surgical correction.

Although our sample size may be a limitation for accuracy in defining prevalence, the identification of patients with CFM despite the relatively small sample size lends support to the claim that the condition may be much more common than previously considered. Previous studies may have underestimated the rate of CFM because of the lack of quantitative skeletal measurements from CT imaging. Additionally, in the current study, the authors did not detect any cases of bilateral CFM, which could be more challenging to identify especially in mild presentations and thereby potentially underdiagnosed in our cohort. Another limitation is that CFM is purely a clinical diagnosis without established diagnostic markers. There have been attempts to identify genetic markers of CFM, such as haploinsufficient variants in SF3B3 and damaging variants of FOXI3.^34,35 However, these genetic etiologies have only been able to explain a small fraction of CFM cases. Classically, Poswillo proposed that embryonic hemorrhage near the first and second branchial arches is the causal mechanism in the pathogenesis of CFM.⁶ However, his findings have not been reflected in humans, suggesting that other factors, such as the combination of genetic and environmental influences, may underlie the condition. Lastly, although we outline the strategies utilized in our FFS practice, the appropriate surgical approach for addressing facial asymmetry may vary based on individual patient needs and surgeon preferences.

CONCLUSIONS

A multimodal analysis of craniofacial morphology among TGD adults registered male at birth reveals that facial asymmetry is generally prevalent. Although the majority can be considered normal facial asymmetry, mandibular hypoplasia in combination with same-sided asymmetry across multiple facial features and tissue types may serve as a hallmark of CFM, which could be much more common than previously described. For individuals with CFM undergoing gender-affirming FFS, various reconstructive strategies can be utilized to improve facial feminization and symmetry simultaneously.

Supplemental Material

This article contains supplemental material located online at https://doi.org/10.1093/asj/sjaf191.

Disclosures

Dr Lee is a medical education consultant for Stryker (Kalamazoo, MI) and is supported by the National Institutes of Health/National Institute (Bethesda, MA) for Dental and Craniofacial Research R01 DE029234. The other authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.

Funding

This work was supported by the Bernard G. Sarnat Endowment for Craniofacial Biology (J.C.L.) and the Jean Perkins Foundation (J.C.L.). All sources of funds supporting the completion of this manuscript are under the auspices of the University of California, Los Angeles, Los Angeles, CA.