1 Introduction
The submental island flap (SIF) has emerged as a valuable reconstructive option for head and neck defects following oncologic resection. First described by Martin et al. in 1993
[1], the SIF has gained widespread acceptance in contemporary reconstructive surgery due to its unique advantages. Compared to free tissue transfer, the SIF offers several distinct benefits including elimination of microvascular anastomosis, excellent color and texture match between donor and recipient sites, high success rates, and favorable cost-effectiveness
[2,
3].
However, the reliability of pedicled flap reconstruction is intrinsically dependent on consistent arterial supply and unimpaired venous drainage. While the submental artery is generally considered to have a relatively constant origin, anatomical variations have been documented in cadaveric studies
[4]. Notably, the course of the submental artery between the anterior belly of the digastric muscle and the mylohyoid muscle after its origin demonstrates considerable variability. A comprehensive understanding of the spatial relationship between the submental artery and these anatomical structures is crucial for minimizing the risk of inadvertent vascular injury during flap elevation. Furthermore, the venous drainage pattern of the submental region exhibits substantial heterogeneity, with venous outflow potentially directed toward the internal jugular vein, external jugular vein, or anterior jugular vein
[5]. In patients requiring cervical lymph node dissection, preservation of the dominant venous drainage pathway becomes paramount for ensuring flap viability.
Given that contrast-enhanced computed tomography (CT) is routinely performed for preoperative evaluation of head and neck malignancies without imposing additional clinical burden, we hypothesized that systematic preoperative CT analysis could facilitate prediction of individual vascular anatomy, thereby optimizing surgical planning and flap design. Despite the clinical significance of preoperative vascular mapping, limited data exist regarding standardized CT interpretation protocols for submental flap vasculature assessment.
This study aimed to develop a systematic approach for preoperative CT evaluation of submental flap vascular anatomy through retrospective analysis of 109 patients with various head and neck conditions (including benign tumors, malignant tumors, congenital diseases, and other pathologies). Specific objectives included: (1) establishing practical techniques for identifying target vessels on contrast-enhanced CT images; (2) characterizing common anatomical patterns of submental artery origin and its spatial relationships with the anterior digastric and mylohyoid muscles; and (3) delineating the predominant venous drainage pathways (external jugular vein, internal jugular vein, or anterior jugular vein). The reliability of this CT-based assessment protocol was preliminarily validated through selective intraoperative observations in a subset of cases.
2 Materials
The study population consisted of inpatients admitted to the Department of Head and Neck Surgery at the Eye & ENT Hospital of Fudan University between January 1, 2024, and June 30, 2024. Contrast-enhanced CT images of the head and neck region were analyzed for 109 patients, yielding 218 sides for evaluation.
Inclusion criteria: Patients aged 18 years or older; complete medical records available; standardized contrast-enhanced CT scanning protocol, including: Scanning parameters: dual-source CT scanner with high-resolution thin-slice contrast-enhanced neck CT acquisition; scanning baseline for the parotid region at the orbitomeatal line; scanning baseline for the pharyngolaryngeal and cervical regions at the vertical line through the laryngeal ventricle; slice thickness of 3.0 mm, rotation time of 0.28 seconds per revolution, contrast agent (iohexol injection) volume of 50–75 mL, intravenous injection rate of 3 mL/s, and scanning initiated 40 seconds post-injection. Post-processing technique: soft tissue window settings with a window width of 250 Hounsfield units (HU) and window level of 50 HU; reconstruction thickness of 1.0 mm.
Exclusion criteria: History of head and neck trauma, radiotherapy, or surgery; congenital head and neck malformations; parapharyngeal space mass lesions or infectious processes.
3 Imaging Review Methodology
3.1 Image viewing software and parameter adjustment
Carestream Vue Motion software was utilized for image interpretation. Window width and window level were adjusted to optimize visualization of vascular structures and soft tissues. The window width was adjusted within a range of 200–600 HU, and the window level within a range of 0–150 HU.
3.2 Submental artery course identification protocol
3.2.1 Localization of the submental artery origin
Two methods were employed to localize the origin of the submental artery: (1) On axial images, the inferior border of the mandible was first identified, followed by visualization of the mylohyoid muscle and submandibular gland medial to the mandible. Within the triangular region bounded by these three structures, the origin of the submental artery from the facial artery could be identified. This anatomical landmark was designated as the “submental artery triangle” (Figure 1a). The submental vein frequently drains into the facial vein within this triangle; however, arterial structures typically exhibit a more tortuous course, which facilitates differentiation. (2) The submandibular gland can also serve as a landmark for localizing the facial artery. The facial artery typically courses immediately adjacent to or penetrates through the submandibular gland. Therefore, once the submandibular gland is visualized, scrolling through 3–5 adjacent slices superiorly or inferiorly usually reveals the facial artery. Subsequently, the vessel is traced distally until reaching the “submental artery triangle”.
3.2.2 Determination of submental artery course and its spatial relationship with adjacent muscles
A dual-pane window interface was activated within the software, enabling synchronized viewing of axial and coronal images. After localizing the submental artery origin on axial images, the corresponding point was identified on coronal images. This reference point was closely monitored while progressively advancing through anterior coronal slices. The position of the reference line displayed on axial images facilitated orientation during this process. Throughout the sequential evaluation of image slices, the course of the submental artery and its spatial relationships with the mylohyoid muscle and digastric muscle were meticulously documented (Figure 2a).
3.3 Submental venous drainage assessment protocol
The drainage pattern of the submental-facial venous system can generally be determined from axial CT images. First, the facial vein was identified anterior to the masseter muscle. The facial vein is characteristically larger in caliber than the facial artery, allowing differentiation by scrolling through several adjacent slices. The facial vein was then traced proximally until reaching its drainage vessels. When the facial vein primarily drained into the external jugular vein, careful review was performed to identify any communicating branches draining toward the anterior jugular vein. In such cases, the anterior jugular vein was first localized at the level of the thyroid cartilage (Figure 1b), and then traced distally to identify branches extending toward the submental region (Figure 1c). When the facial vein demonstrated drainage to both the anterior jugular vein and external jugular vein, the vessel with larger caliber was designated as the dominant drainage pathway according to Professor Fang's classification system
[6].
4 Observation Parameters and Adjudication Protocol
4.1 Observation parameters
The spatial relationships of key anatomical structures were classified as follows. For the submental artery origin, its position was categorized as either deep or superficial to the mylohyoid muscle. The main trunk of the submental artery was classified according to its relationship with the digastric muscle: superficial to the digastric muscle, lateral to the digastric muscle (Figure 2b), deep to the digastric muscle (Figure 2c), or penetrating through the digastric muscle (Figure 2d). Additionally, the facial vein drainage pattern was classified according to Fang's classification system (Figure 3a): Type I, drainage into the internal jugular vein (Figure 3b); Type II, drainage into the external jugular vein (Figure 3c); and Type III, drainage into the anterior jugular vein (Figure 3d).
4.2 Adjudication protocol
Images were independently reviewed by two head and neck surgeons (with 8 and 5 years of clinical experience in submental island flap reconstruction, respectively). When both reviewers reached concordant conclusions, the results were directly recorded. In cases of discordant interpretation, a diagnostic radiologist was consulted for adjudication, and the consensus opinion among all three reviewers was documented. Cases where unanimous agreement could not be achieved were designated as indeterminate.
4.3 Statistical analysis
Data were analyzed using IBM SPSS Statistics version 25 software package. Categorical variables were expressed as frequencies and percentages, with intergroup comparisons performed using Pearson's chi-square test. All tests were two-tailed with a significance level of α = 0.05.
5 Results
5.1 Inter-reader agreement assessment
Both reviewers independently evaluated the same cohort of patient images, comprising 109 patients (218 sides). Initial concordance was achieved in 73 cases, while 36 cases demonstrated discordant interpretations. Following consultation with the diagnostic radiologist, consensus was reached in 30 of the 36 discordant cases, with 6 cases remaining indeterminate. Consequently, concordant interpretations were obtained for 94.5% (103/109) of patients, which were included in subsequent statistical analysis (Table 1).
5.2 General clinical characteristics
Among the 103 patients included in the analysis, 69 were male and 34 were female. Patient age ranged from 19 to 80 years, with a mean age of 57.02 ± 14.56 years. The distribution of diagnoses was as follows: laryngeal carcinoma (n = 35), thyroid carcinoma (n = 24), hypopharyngeal carcinoma (n = 21), thyroglossal duct cyst (n = 14), tonsillar carcinoma (n = 7), and benign parotid tumors (n = 2) (Table 2).
5.3 Submental artery
5.3.1 Spatial relationship between submental artery origin and mylohyoid muscle
The origin of the submental artery was located superficial to the mylohyoid muscle in all 206 sides examined.
5.3.2 Spatial relationship between main trunk of submental artery and anterior belly of digastric muscle
The main trunk of the submental artery was positioned deep to the anterior belly of the digastric muscle in 64 sides (31.1%), superficial to the anterior belly of the digastric muscle in 68 sides (33.0%) and penetrating through the anterior belly of the digastric muscle in 74 sides (35.9%) (Table 3).
5.4 Submental vein
According to Fang's classification system, Type I drainage pattern (facial vein draining into the internal jugular vein) was observed in 116 sides (56.3%). Type II drainage pattern (primary drainage into the external jugular vein) was identified in 67 sides (32.5%), and Type III drainage pattern (primary drainage into the anterior jugular vein) was present in 23 sides (11.2%) (Table 3).
5.5 Communicating branches between drainage veins
Among the 116 sides with Type I drainage pattern, collateral drainage to the external jugular vein was identified in 6 sides (5.2%). Among the 67 sides with Type II drainage pattern, collateral drainage to the anterior jugular vein was observed in 29 sides (43.3%). Among the 23 sides with Type III drainage pattern, collateral drainage to the external jugular vein was identified in 5 sides (21.7%) (Table 4).
5.6 Anatomical feature distribution by gender, tumor laterality, and side
Intergroup comparative analysis revealed no significant differences in the distribution of submental arteriovenous anatomy or drainage characteristics between the tumor-bearing side in malignant cases and the non-malignant side. Similarly, the spatial relationship between the submental artery and the digastric muscle showed no significant differences between male and female groups. Notably, however, the direction of submental venous drainage demonstrated statistically significant differences between sexes. The distribution of Type I, Type II, and Type III drainage patterns was 65.20%, 23.90%, and 10.90% in males, compared to 38.20%, 50.00%, and 11.80% in females, respectively (χ2 = 15.454, p < 0.001) (Table 5).
Among 103 patients (206 sides), no significant difference was observed in the distribution of submental artery types (χ2 = 0.808, p = 0.668) or facial vein drainage patterns (χ2 = 4.399, p = 0.111) between the left and right sides. For the submental artery, bilateral concordance was found in 46 patients (44.7%), with a Kappa value of 0.170 (poor agreement). For facial vein drainage, 75 patients (72.8%) showed bilateral symmetry, with a Kappa value of 0.522 (moderate agreement) (Table S2).
6 Discussion
The submental island flap (SIF) occupies a central position within the upper and lower neck region, functioning as a versatile reconstructive option for head and neck defects. It offers distinct advantages including low technical demands, cost-effectiveness, and high success rates
[3,
7]. The flap can be transposed superiorly for reconstruction of oral cavity and oropharyngeal defects
[8,
9]. When transposed inferiorly for laryngopharyngeal reconstruction, the tissue volume can be adjusted according to the size of the defect, thereby avoiding the bulkiness characteristic of pectoralis major myocutaneous flaps
[10]. Furthermore, for reconstruction of adjacent tissue defects, such as those involving the parotid gland or facial region, the SIF provides excellent color, texture, and skin quality match with the recipient site
[11]—advantages not shared by other regional flaps such as the supraclavicular flap. In recent years, numerous investigators have developed modified applications of the SIF, including de-epithelialized submental flaps, composite flaps incorporating mandibular bone segments, and reverse submental flaps for reconstruction of more distant defects
[9,
11,
12].
Reliable arterial perfusion and stable venous drainage are fundamental prerequisites for flap survival. The submental artery is widely recognized as the principal arterial supply to the SIF, while the facial vein, which receives drainage from the submental vein, serves as the primary venous outflow pathway
[5,
13]. The submental artery has a relatively small caliber and originates from a deep anatomical location. In the absence of adequate experience and without preoperative prediction of its course, the main arterial trunk is susceptible to inadvertent injury during both antegrade and retrograde flap dissection. Facial vein drainage patterns demonstrate considerable heterogeneity. Based on Professor Fang's experience
[6], three principal drainage types can be identified: Type I (internal jugular vein), Type II (external jugular vein), and Type III (anterior jugular vein). Preoperative knowledge of the dominant drainage pathway enables selective preservation of critical venous structures during neck dissection and flap harvest.
Several investigators have advocated preoperative Doppler ultrasonography for localization of flap vasculature
[14]. However, practical application has revealed that although ultrasound can detect the facial artery and vein in the submandibular region, the compression exerted during probe manipulation itself causes vascular displacement. Moreover, the presence of the submandibular gland prevents accurate depth assessment based on surface markings. Additionally, surface markings obtained under ultrasound guidance undergo positional shifts due to changes in surgical positioning, thereby limiting their utility for intraoperative vascular management. In contrast, CT imaging provides objective anatomical landmark-based localization, with osseous structures offering particularly reliable positional references. Admittedly, identification of the submental artery on contrast-enhanced CT remains technically challenging, as the mean diameter at its origin ranges from only 1.02 to 1.80 mm, with progressive tapering along its course. Consequently, clear visualization is achievable primarily at its origin from the facial artery. Fortunately, our analysis of 206 sides revealed that this location demonstrates considerable consistency, situated within what we term the "submental artery triangle", bounded by the mandible, submandibular gland, and mylohyoid muscle. This position lies approximately 5.0 mm from the inferior mandibular border and 23.8 mm from the mandibular angle
[4], and can be accurately identified with appropriate adjustment of window width and window level settings. Complete visualization of the submental artery throughout its entire course is not achievable on contrast-enhanced CT. Within the mandibular and submental triangle regions, the submental artery is typically accompanied by 1–2 submental veins
[15], with the submental vein averaging 2.2 mm in diameter
[16], thereby providing superior contrast enhancement. Therefore, the technique we have developed for tracing the submental artery essentially involves tracking the most closely associated submental vein. This intimate anatomical relationship has been consistently observed during our clinical flap harvest procedures.
In the field of otolaryngology-head and neck surgery, the majority of SIF procedures do not require complete vascular skeletonization to increase pedicle length or mobility. Conversely, some investigators recommend incorporating the mylohyoid muscle within the flap to ensure arterial supply reliability. Indeed, our analysis of 206 sides revealed that although larger branches may penetrate the mylohyoid muscle to supply the floor of mouth, the main trunk of the submental artery consistently courses superficial to the mylohyoid muscle. Disruption of this muscular barrier at the floor of mouth is generally not recommended; however, in cases of substantial tissue defects in the recipient site (such as the auriculotemporal region or parapharyngeal space), the tissue volume of the flap can be augmented by incorporating part of the mylohyoid muscle along with the submandibular gland. Regarding whether the ipsilateral anterior belly of the digastric muscle should be included within the flap, careful image analysis is imperative. Our data demonstrate that in 31.1% of cases, the main trunk of the submental artery courses deep to the digastric muscle, and in 35.9% of cases, the submental artery penetrates through the anterior belly of the digastric muscle. In these cases, complete incorporation of the anterior belly of the digastric muscle is necessary to prevent vascular injury. In 33% of cases, the submental artery courses superficial to or does not intersect with the digastric muscle; in such instances, meticulous dissection enables harvesting of a thinner flap without incorporating the digastric muscle. However, for surgeons with limited experience, inclusion of the anterior belly of the digastric muscle within the flap substantially reduces the risk of vascular injury. We have observed that the terminal branches of the submental artery can be readily identified at the mentum attachment point of the digastric muscle on imaging studies, where anatomical landmarks are relatively constant. Based on practical experience, we recommend initiating flap dissection at the digastric muscle attachment site guided by preoperative imaging. This retrograde approach offers two advantages: (1) vascular structures are more readily identifiable at this location, enabling safer flap dissection using the vessel as a landmark; and (2) these vessels represent terminal branches, such that inadvertent injury at this level typically does not compromise overall flap viability (Figure 4).
Certain head and neck malignancies necessitate cervical lymph node dissection, which subjects the cervical venous system to substantial risk. Complete preservation of the dominant drainage vein is recommended. Our analysis revealed that 65.2% of male patients and 38.2% of female patients demonstrated facial vein drainage into the internal jugular vein (Fang Type I). Although 5.2% of this subgroup exhibited communicating branches to the anterior or external jugular veins, the decision to utilize the SIF requires careful consideration in patients requiring radical neck dissection. When superior alternatives are unavailable, meticulous image review should assess communicating pathways between the segment of facial vein distal to the submental vein confluence and the anterior branch of the retromandibular vein. If imaging demonstrates an intact pathway comprising the facial vein–anterior retromandibular vein–posterior retromandibular vein–external jugular vein, the common facial vein can be divided after completion of the primary flap harvest, with flap color monitored to assess venous drainage adequacy. Normal flap coloration suggests feasibility of continued flap utilization, as craniofacial veins occasionally lack valves or possess small valves permitting retrograde flow. However, this approach is not universally applicable; we have observed substantial venous valves in the facial vein at the mandibular border level (Figure 5). Therefore, pedicle division trial with direct observation is necessary. If superior retrograde drainage proves inadequate, a hybrid flap with venous anastomosis remains an option
[17]. Furthermore, consistent with Professor Fang's observations, when facial vein drainage follows Type II or Type III patterns, communicating branches between the external jugular vein and anterior jugular vein are frequently present. Our imaging analysis detected such communications in 37.8% of cases, suggesting that flap design in this subgroup should favor greater flap width.
This study has several limitations. First, direct surgical validation was not performed. Although our cohort comprised patients who subsequently underwent surgery, only a subset received SIF reconstruction, and retrospective retrieval of detailed intraoperative vascular documentation was insufficient for systematic correlation. Second, formal inter-observer reliability assessment using kappa statistics was not conducted. Our protocol relied on consensus adjudication for discordant cases rather than independent blinded evaluation, which may have introduced bias. These methodological limitations—lack of surgical correlation and absence of standardized reproducibility metrics—will be addressed in a planned prospective study incorporating systematic intraoperative documentation and formal inter-observer agreement analysis.
In conclusion, CT imaging-based preoperative assessment and individualized surgical planning can effectively mitigate risks associated with anatomical variations, providing reliable assurance for the safe application and successful reconstruction with the SIF.
The Author(s) 2025. This article is available under open access at journal.hep.com.cn.
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