Variations and thicknesses of anterior belly of the digastric muscle: an ultrasonographic study.

PURPOSE: This study aims to evaluate the anatomy and anatomical variations of the anterior belly of the digastric muscle. METHODS: Hundred and fifty one ultrasonographic images of the digastric muscle pairs were evaluated in Near East University Faculty of Dentistry Department of Dentomaxillofacial Radiology. Morphological variations were recorded using the classification of the digastric muscle into 12 types by Kim et al. For the analysis, the Mann-Whitney U test and Chi-square test were used, and for the correlational analysis, Spearman's rho test was applied. P < 0.05 was considered statistically significant in all tests. RESULTS: Seventy female and 81 male patients aged 19-60 years were evaluated. Type 1 digastric muscle was observed in 145 of 151 patients, Type 2 in 3 patients, and Type 7 in 3 patients. The thicknesses of the right and left digastric muscles were measured, and a statistically significant difference was observed between the groups when the genders were compared. It was observed that both right and left digastric muscle thicknesses were higher in males than females. There was a statistically significant positive high correlation between right and left digastric muscle thicknesses (p = 0.000; r = 0.736). No statistically significant difference was found between genders (p = 0.596) in terms of anatomical variations. CONCLUSION: Considering that the variations of the digastric muscle may have a clinical significance role, the normal anatomy and variations of this muscle should be well known by maxillofacial surgeons and radiologists.

Comparison between botulinum toxin type A injection on masseter muscle only and additional injection on anterior belly of digastric muscle in sleep bruxism patients: A clinical trial.

OBJECTIVE: This study aims to evaluate the effects on bite force and muscle thickness of the botulinum toxin (BoNT) injection for patients with sleep bruxism (SB) by comparing injections into the masseter muscle only and both the masseter and the anterior belly of the digastric muscle (ABDM) in a clinical trial. METHODS: Twelve SB patients received BoNT-A injections using US-guided techniques into the masseter muscle only (Group A), while the remaining 12 SB patients received injections into both the masseter and ABDM (Group B). Bite force and muscle thickness were measured before injection, as well as 1 and 2 months after injection. RESULTS: The bite force and masseter muscle thickness decreased in both Group A and Group B before injection, and at 1 and 2 months after injection. However, there was no significant difference (p > .05, repeated measures analysis of variance) between the two groups, and there was also no significant difference in ABDM thickness (p > .05, repeated measures analysis of variance). CONCLUSION: This study is the first to assess the short-term effects of BoNT injected into ABDM for SB control. Results show no influence on SB reduction, suggesting the need for further research on BoNT's effectiveness in controlling intense ABDM contractions during sleep and assessing suprahyoid muscle potential impact on rhythmic masticatory muscle activity occurrence.

Double Chin Concerns after En Bloc Mandibular U-Shaped Osteotomy: Submental-Cervical Soft Tissue Changes and Anterior Belly of Digastric Muscle Assessment.

OBJECTIVE: To assess submental-cervical soft tissue changes after en bloc mandibular U-shaped osteotomy and examine alterations in the anterior belly of digastric muscle (ABDM). METHODS: A retrospective study analyzed 20 patients who underwent en bloc mandibular U-shaped osteotomy from 2018 to 2023. Preoperative (Tp) and long-term follow-up (Tf) CT data were collected for analysis, measuring mandibular volume, soft tissue thickness at menton (Mes) and cervicale (C), and ABDM parameters (length, cross-sectional area (CSA), volume, distance from centroid point to the mandibular margin). Correlation analyses were performed to investigate the connection between soft tissue thickness changes, ABDM changes, and mandibular osteotomy volume. RESULTS: Long-term follow-up revealed a significant increase in soft tissue thickness at the Mes and C points after U-shaped mandibular osteotomy, especially at the C point. The adaptive length of ABDM decreased, CSA increased, and volume decreased, but the ABDM centroid point shifted downward relative to the mandibular margin, indicating drooping protrusion. The increment of soft tissue thickness was moderately positively correlated with the amount of osteotomy, and the decrement of ABDM length and volume were slightly positively correlated with the amount of osteotomy. CONCLUSION: The degree of soft tissue relaxation after U-shaped osteotomy is related to the extent of osteotomy. Notably, the protrusion of ABDM relative to the mandibular margin affects submental-cervical contour aesthetics. Prior to U-shaped osteotomy, it is crucial to assess the soft tissue condition of the patient's lower face, and the individualized design of the osteotomy volume should be carried out cautiously and safely. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Sihler's staining of the anterior belly of digastric muscle for botulinum toxin injection.

PURPOSE: The anterior belly of the digastric muscle (ABDM) is the target of botulinum toxin injection; however, anatomical considerations related to the injection point are absent. This study used Sihler's staining to analyze the intramuscular nerve distribution of ABDM to identify the most effective botulinum toxin injection points. METHODS: We used 12 specimens from 6 embalmed cadavers in this study. The specimens were manually dissected to preserve the mylohyoid nerve and subjected to Sihler's staining. From the gnathion to and hyoid bone, the ABDM was divided into three equal parts, distinguishing the anterior, middle, and posterior thirds. RESULTS: Only a branch of the mylohyoid nerve entered the ABDM, and its entry point was located in the middle-third region in all cases. The nerve endings were concentrated in the middle third (100%), followed by the anterior third (58.3%) and were not observed in the posterior third. CONCLUSION: The landmarks used in this study (gnathion and hyoid bone) are easily palpable on the skin surface, allowing clinicians to target the most effective injection site (middle third of ABDM). These results provide scientific and anatomic evidence for injection points, and will aid in the management of ABDM injection procedures in clinical practice.

More than two - A cadaveric study on the morphometry and classification of the digastric muscle in a selected kenyan population.

BACKGROUND: This study aims to elucidate anatomical variations of the digastric muscle in the Kenyan population. METHODS: A total of 41 bilateral neck dissections were performed whereby morphologic observations and morphometric measurements were carried out to characterize and classify the various presentations of the muscle. RESULTS: All cadavers presented with bilateral anterior (ABDM) and posterior (PBDM) bellies of the digastric muscle. Accessory ABDM was observed in 68.3% of cadavers with De-Ary-Pires et al.'s Type II (one accessory belly; 48.8%) and Type III (two accessory bellies; 34.1%) being the most common variations. Unilateral accessory ABDM (43.9%) was more common than bilateral accessory ABDM (24.4%). Two cadavers presented with a mentohyoid muscle. In addition, variations that have not been previously reported, namely fusion of ABDM to the midline and insertion of accessory ABDM into the hyoid bone were observed in one case each. Variation of the PBDM was less prominent, observed at 12.2% of sides dissected. Duplication of PBDM was observed on 4 sides with origin at the mastoid process. The PBDM was longer than the ABDM, but narrower in width. The mean length and width of the ABDM were 4.29±0.72cm and 1.52±1.07cm. The mean length and width of the PBDM were 5.64±1.31cm and 1.07±0.28cm, with the right side being statistically larger than the contralateral side. CONCLUSION: Variations of the digastric muscle are a common finding, with a high incidence at the ABDM. Two new variants were discovered.

Unilateral asymmetrical anterior bellies of the digastric muscle in coexistence with accessory muscle bundles in the submental triangle: A rare case report.

A three-headed anterior belly of the digastric muscle (ABDM) on the right side of a 54-year old Greek male cadaver coexisted with two accessory muscle bundles (AMB) in the submental region. The left ABDM was typical. Typical ABDM was attached to the digastric fossa, while the accessory right anterior bellies to the lower border of the mandible. A muscle bundle arising from the attachment of the left ABDM to the hyoid bone was also observed fusing with the AMB of the ipsilateral side. It is of extreme importance to be aware of the submental region anatomical variations during surgery, imaging interpretation or differential diagnosis of neck masses.

Unilateral hypoplasia with contralateral hypertrophy of anterior belly of digastric muscle: a case report.

Anomalies of the anterior belly of the digastric muscle (DM) are uncommon. We present a case of hypoplasia of the anterior belly of the left DM with hypertrophy of the anterior belly of the contralateral DM. The importance of recognizing this finding is to differentiate hypoplasia of the anterior belly of the DM from denervation atrophy, and not to confuse contralateral hypertrophy with a submental mass or lymphadenopathy. In denervation atrophy of the anterior belly of the DM, associated atrophy of the ipsilateral mylohyoid muscle is present. Hypertrophy of the anterior belly of the contralateral DM can be differentiated from a submental mass or lymphadenopathy by recognizing its isodensity on computed tomography and isointensity on magnetic resonance imaging to other muscles, without abnormal contrast enhancement.

Functional Reconstruction of a Hemiglossectomy Defect With an Innervated Musculocutaneous Submental Artery Island Flap.

This report presents the use of an innervated musculocutaneous submental artery island flap (MSAIF) for the functional reconstruction of a hemiglossectomy defect, with the aim of preserving the volume and mobility of the reconstructed tongue to facilitate swallowing and intelligible speech. A 30-year-old male patient diagnosed with T3N0 stage squamous-cell carcinoma of the tongue underwent hemiglossectomy and ipsilateral I-IV selective neck dissection. For reconstruction, an innervated MSAIF with a 9x4 cm skin paddle, including the left submental vessels, ipsilateral anterior belly of the digastric muscle, mylohyoid muscle, and mylohyoid nerve, was harvested and inserted into the tongue defect. Postoperative healing at both donor and recipient sites proceeded without complications. At a three-year follow-up, the MSAIF has maintained its volume, mobility, and contractility. The patient remains disease-free and reports satisfaction with his swallowing and speech capabilities. The innervated MSAIF represents a reliable and cost-effective reconstruction approach for hemiglossectomy defects, showing favorable results in both swallowing and speech.

A clinical perspective on the anatomical study of digastric muscle.

One of the suprahyoid muscles is the digastric muscle which comprises anterior and posterior bellies joined by an intermediate tendon. Because of its close relationship with the submandibular gland, lymph nodes, and chief vessels of the neck, detailed knowledge about the morphometry of the digastric muscle is essential. The objective of the current cross-sectional evaluative study is to record morphometry along with the digastric muscle's origin, insertion, and variability. Forty human cadavers (25 males and 15 females) were dissected, and the head and neck regions were studied in detail. The attachment of the digastric muscle anterior belly to the digastric fossa of the mandible was noted, and the distal attachment of the posterior belly to the mastoid notch was traced. The length of the anterior belly from the digastric fossa to its intermediate tendon and the length of the posterior belly from the intermediate tendon to its mastoid attachment were measured. There is a fair correlation between the length of the neck and the length of the anterior and posterior belly. The study also identified two cases of bilateral accessory bellies of the anterior belly of the digastric. Normal morphometric data is provided by this study on details of the digastric muscle. It is significant from a clinical and surgical point of view as the muscle lies in proximity to the important structures of the neck.

Lower lip depressor reanimation using anterior belly of digastric muscle transfer improves psychological wellbeing in facial palsy patients.

The authors previously published positive peer-reviewed (21 raters using the Terzis scale) and photogrammetric (Emotrics) outcomes in patients who had undergone two-stage lower lip reanimations up to 2018. Other series have published surgeon and peer-rated results, but we know of only two (n=12) that have assessed patients' views using patient satisfaction surveys. This paper presents patient-rated outcomes (PROMS) in an 11-year series of both single and two-stage anterior belly of digastric muscle (ABDM) lower lip reanimations. Demographics, paralysis characteristics, operative details, and complications were recorded. Patients were telephoned and requested to complete the Glasgow Benefit Inventory (GBI) to assess patient-rated outcomes. Thirty-two patients were eligible (mean age 36.4 years). Twenty-one (63.6%) completed the GBI (mean score +33.3). More patients reported benefit than detriment (95.2% vs 4.8%). Complications were infrequent and included three cases of superficial infections and one of dermatitis. Four patients (12.5%) underwent minor revisions, mostly lipofilling of lip notches. The median (range) duration of follow up was 2.8 (0.3 - 8.5) years. ABDM transfer for lower lip reanimation is a safe, low morbidity procedure that enhances the psychological wellbeing of patients with facial palsy.

Staged upper and lower lip reanimation following facial palsy: Peer-reviewed, patient-rated and objective outcomes.

BACKGROUND: One approach to reanimating both upper and lower lips following facial palsy is through staged surgery: cross-face nerve grafting at stage I, free gracilis muscle transfer to levators at stage II and pedicled anterior belly of digastric muscle transfer (ABDMT) to depressors at stage III. The results of this approach were hitherto unquantified. METHODS: This study retrospectively assessed peer-reviewed, patient-rated and objective outcomes following staged reanimation in adults between 2010 and 2020. Demographics, palsy characteristics and surgery details were recorded. Pre- and postoperative videos were rated by independent assessors using Terzis' aesthetic and symmetry scale. Photographs were analysed using Emotrics and patients completed the Glasgow Benefit Inventory (GBI) patient-rated outcome measure. RESULTS: Ten patients [mean age = 34 (SD = 12.48)] were eligible. All regained lip elevation and depression. All markers of symmetry improved after gracilis transfer. All markers were also improved after ABDMT except for lower lip height when smiling with teeth showing (p > 0.05). Five patients (50%) responded to the GBI (mean score = +39.44). No patients reported detriment from the reanimations. Mean Terzis' scores preoperatively and after stages II and III were 1.5, 2.26 and 2.39, respectively (p < 0.05). Nine patients underwent aesthetic refinements [lipofilling to lower lip notches (n = 5), debulking of gracilis bulk (n = 6), repositioning of muscle insertion (n = 5) and facelifts (n = 2)]. CONCLUSION: The outcomes were positive objectively and as judged by peers and patients themselves. Aesthetic refinements may also be required to enhance these results.

Asymmetry of the Accessory Anterior Digastric Muscle Bellies: The Clinical Significance in Facial and Neck Surgery.

The anterior digastric muscle belly (ADMB) may present significant variations of substantial surgical importance. We present an unusual complex bilateral asymmetry of an accessory ADMB found when dissecting the submental area in a 72-year-old Greek male cadaver. A rare variant was recognized in the submental area constituted by a combination of bilateral asymmetry of the ADMB with unilateral absence of the intermediate tendon. The complex variant caused an obvious morphological asymmetry in the submental area. Such muscular variations may alter the surgical approach to the submental region. Clinicians involved in the treatment of this area should be aware of any possible variant, particularly when dealing with neck mass patients.

Anatomical variations in the digastric muscle.

The aim of this study was to investigate anatomical variations in the digastric muscle. Anatomical dissections of the head and neck region were performed in 15 cadavers at the Anatomy Department during a gross anatomy course. Three cadaver heads revealed anatomical variations in the anterior belly of the digastric muscle. The positional relationships among the accessory muscle bundles, the anterior belly of the digastric muscle, and the mylohyoid muscle were examined. Innervating branches from the mylohyoid nerve were also investigated. The remaining 12 cadaver heads without accessory muscle bundles were used for comparison. Of the three heads with accessory muscle bundles, one head (male) had two muscle bundles of the unilateral type, one head (male) had symmetrical muscle bundles of the crossover type, and one head (female) had a mix of unilateral and crossover types. The likely explanation for these and various other anomalies reported in the literature is the complex morphogenesis of the first branchial arch. Therefore, clinicians should be aware of these anatomical variations of the submental region when performing surgical procedures involving the head and neck and when using computed tomography and magnetic resonance imaging for interpretation or differential diagnosis of neck masses.

Botulinum toxin A injection into the anterior belly of the digastric muscle increased the posterior width of the maxillary arch in developing rats.

BACKGROUND: The purpose of this study was to evaluate the effects of botulinum toxin A (BTX) injection into the anterior belly of the digastric muscle on a growing rat. METHODS: Ten Sprague Dawley rats were used in this study. When the rats were 13 days old, 0.5 units of BTX was injected into the anterior belly of the digastric muscle for the experimental group (n = 5). For the control, the same volume of normal saline was injected (n = 5). The rats were sacrificed at 60 days old, and the skulls were harvested for micro-computed tomography (µCT) analysis. RESULTS: In anthropometric analysis, the zygomatic arch and mandibular bi-condylar width were significantly lower in the experimental group than those in the control group (P = 0.025 and 0.027, respectively). The maxillary point width was significantly higher in the experimental group than that in the control group (P = 0.020). CONCLUSION: BTX injection into the anterior belly of the digastric muscle had effects on the maxillofacial bony width in growing rats.

Cross-over type of supernumerary digastric muscle.

A cross-over type asymmetric anomaly of the anterior belly of the right digastricmuscle was observed during a cadaveric dissection of the submental region.Three irregularly-shaped supernumerary muscle bundles were found between theanterior bellies of the digastric muscles. Although the anomalies of the digastricmuscles are often observed, this complicated pattern has not been previouslyreported. Our findings and previous reports illustrate the morphogenetic complexityof the anterior belly of the digastric muscle, and their potential importancein confounding clinical evaluation or complicating surgical procedures in thesubmental region.

Anatomy and variations of digastric muscle.

The digastric muscle consists of the anterior belly and the posterior belly connecting the mandible, hyoid bone and temporal bone. Its unique morphology, structure and variations have drawn genuine interests in this muscle from anatomists, scientists and physicians for a long time, and the variations of the digastric muscle have been documented since the 18th century. As the usage of computed tomography and magnetic resonance imaging in the neck has become ever increasing, recognizing the variations of the digastric muscle can be a great value since it helps physicians to make better treatment plans and avoid unnecessary invasive procedures in the neck. Although the variations of the digastric muscle do not necessarily cause clinical symptoms, they still have important clinical applications. This article discusses the anatomy, embryology, descriptions of the morphological variations and clinical significance of the digastric muscle.

Anatomical variations of the anterior belly of the digastric muscle / Variaciones anatómicas del vientre anterior del músculo digástrico

A routine dissection of the digastric muscle reflected that it originated by two muscle bellies namely. the anterior and posterior belly which are connected by an intermediate tendon (IT). These bellies originated from the mastoid process of the temporal bone and the digastric fossa of the mandible respectively. The digastric muscle serves as an important surgical landmark in surgical interventions involving the submental area however, accessory bellies may interfere with surgical intervention in this area. Therefore, this study aimed to document the occurrence of the anatomical variations in the anterior belly of the digastric muscle (ABDM) in a selected number of cadaveric samples. Ten bilateral adult cadaveric head and neck specimens (n = 20) were macro-dissected in order to document the morphology of the digastric muscle. The accessory bellies in the ABDM was observed in 60 % of the specimens. Unilateral and bilateral variations were observed in 20 % and 30 % of the specimens, respectively. These accessory bellies originated in the digastric fossa, ABDM, IT and hyoid bone, and inserted into the mylohyoid raphe, mylohyoid muscle and hyoid bone. In addition, an anomalous main ABDM was observed in 10 % of the specimens inserting through a transverse tendon into the hyoid bone. Variations in the digastric muscle are common especially the accessory bellies, therefore, a comprehensive understanding of these anatomical variations could be of clinical importance to the surgeons during head and neck radiological diagnosis and surgical interventions.

Una disección de rutina del músculo digástrico refleja que se éste originaba por dos vientres musculares, anterior y posterior conectados por un tendón intermedio (IT). Estos vientres se originaban a partir del proceso mastoide del hueso temporal y de la fosa digástrica de la mandíbula, respectivamente. El músculo digástrico sirve como un hito quirúrgico importante en las intervenciones que involucran el área submental. Sin embargo, los vientres accesorios pueden obstaculizar la intervención quirúrgica en esta área. Por lo anterior, este estudio tuvo como objetivo documentar observaciones de las variaciones anatómicas en el vientre anterior del músculo digástrico (VAMD) en un número seleccionado de cadáveres. Las muestras consistieron en 10 cabezas y cuellos cadavéricos de individuos adultos, estudiadas bilateralmente (n = 20). Estas muestras fueron disecadas para documentar la morfología del músculo digástrico. Los vientres accesorios en el VAMD se observaron en el 60 % de los casos. Se observaron variaciones unilaterales y bilaterales en el 20 % y el 30 % de las muestras, respectivamente. Estos vientres accesorios se originaban en la fosa digástrica, VAMD, IT y hueso hioides, y se insertaban en el rafe milohioideo, el músculo milohioideo y el hueso hioides. Además, se observó un VAMD principal anómalo en el 10 % de las muestras que se insertaban a través de un tendón transversal en el hueso hioides. Las variaciones en el músculo digástrico son comunes, especialmente los vientres accesorios, por lo tanto, un conocimiento completo de estas variaciones anatómicas podría ser de importancia clínica durante el diagnóstico radiológico de cabeza y cuello y en las intervenciones quirúrgicas de la región.

Accessory Heads of Anterior Belly of Digastric Muscle in Korea / 계명의대학술지

The digastric muscle has two bellies and it has various variation in submental region. During dissection of a 79-year-old Korean female cadaver, bilateral variations at the anterior belly (AB) of the digastric muscle in submental region were shown. Two accessory bellies originated medial to the origin of the two normal ABs of the digastric muscle. They run medially and combined each other anterior to the median raphe of the mylohyoid muscle. In left side, AB of the digastric muscle was divided into two muscular bellies. Therefore, five bellies of ABs of the digastric muscle were found. This novel variation has not been described in the literature and this appearance will guide clinicians during surgical interventions and radiological diagnosis.

Bilateral variations of the head of the digastric muscle in Korean: a case report.

The digastric muscle, as the landmark in head and neck surgery, has two bellies, of which various variations have been reported. In the submental region of a 72-year-old Korean male cadaver, bilateral variations were found in the anterior belly of the digastric muscle. Two accessory bellies, medial to the two normal anterior bellies of the digastric muscle, ran posterior and medially, merging and attaching at the mylohyoid raphe of the mylohyoid muscle. The 3rd accessory belly originated from the right intermediate tendon and ran horizontally, merging the right lower bundle of the right accessory belly and inserted together. These accessory bellies had no connection with the left anterior belly. This unique variation has not been reported in the literature previously, and this presentation will guide clinicians during surgical interventions and radiological diagnoses.

Variations in the anterior belly of diagastric.

The anterior belly of diagastric is highly variable. Variation in anterior belly is most common amongst the submental region variations. We observed 6 such variations in the anterior belly of diagastric among 15 cadavers dissected (40%). Unilateral and bilateral variations were seen in equal number of cases. Accessory belly frequently cross midline and attached over the mylohyoid muscle. Knowledge of such variations is of significant importance while planning for surgeries in submental region and during staging of tumors.