Bilateral accessory digastric muscles

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.

Bilateral, asymmetric anomalies of the anterior bellies of digastric muscles

Bilateral, asymmetric anomalies of the anterior bellies of digastric muscles were observed during dissection of the submental region. Specifically, four extra muscle bundles were found between the anterior bellies of the digastric muscle. Although anomalies of the anterior bellies of digastric muscles are often observed, this complicated pattern of digastric anomalies has not been previously reported. Our findings and previous observations illustrate the morphogenetic complexity of the anterior belly of the digastric muscle derived from the first pharyngeal arch, which gives rise to jaw musculature such as the mylohyoid muscle.

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.

Bilateral quadrification of the anterior digastric muscles with variations of the median accessory digastric muscles

During dissection of the submental region, the anterior bellies of the right and left digastric muscles were found to have four separate insertions. Two median accessory digastric muscles were located medially to anterior bellies of the digastrics and inferiorly to the mylohyoid and deep in the platysma. The four accessory muscles of the anterior bellies of the digastric muscles originated from the digastric fossa and inserted into the hyoid bone. Two median accessory digastric muscles were located between the anterior bellies of the digastric muscle and inserted into the hyoid bone as well. These muscle fibers formed a muscular floor for the oral cavity similar to the second mylohyoid muscle. When the muscle heads were analyzed, the anterior belly of the digastric muscle appeared to have six heads. These six heads were united by an intermediate rounded tendon, which was attached to the hyoid bone. This finding of a bilateral quadrification of the anterior digastric muscles with variations in the median accessory digastric muscles has not previously been reported. Anatomic variations of the anterior bellies of the digastric muscles can be easily confused on computed tomographic scans and magnetic resonance imaging. The possible occurrence of such anomalies should be kept in mind during surgical procedures involving the submental region.

The cause of the difference in the submental region: aberrant muscle bundles of the anterior belly of the digastric muscle

The aberrant bundles' presence in the anterior belly of the digastric muscle is important in terms of causing asymmetry in the submental region, getting confused with some pathologic cases, radiologic examination, and aesthetic facial surgery. To provide data, aberrant bundles in the submental region were investigated in 30 cadaver heads. During the dissection of the submental region, origin, insertion, shape, and bilaterality of the anterior bellies of the digastric muscles and the aberrant bundles were investigated. The 20 heads with aberrant bundles were classified into two types based on the muscle arrangement: digastric fossa type and crossover type. The aberrant bundles, which did not cross the median line, were classified as being of the digastric fossa type, whereas those that crossed the line were of the crossover type. Fifteen of the heads contained bundles of the unilateral type and five heads contained the crossover type. In three heads, digastric fossa and crossover types coexisted. In this study, a wide range for incidence in the submental region was observed of variations. Some cases were not described in the classification of the previous studies of this muscle. It is also possible that the incidences may vary as a result of the ethnic differences of the populations studied. Bilaterality was frequently observed in this study. Anatomic variations of the anterior bellies of the digastric muscle can easily be confused with the pathologic conditions in ultrasonography, computed tomography, and magnetic resonance imaging; therefore, it is necessary to recognize that variants of the anterior belly of the digastric muscle occur to avoid confusion when diagnosis shows abnormal lesions in the floor of the mouth and submental region. Additionally, the possible occurrence of such anomalies should be remembered during the surgical procedures involving the submental region.

Bilateral abnormal anterior bellies of digastric muscles

During dissection of the submental region of a male cadaver, we encountered an abnormal digastric muscle on both sides. Two muscle bundles, both of which fused with mylohyoid muscle close to the midline, were observed on the right side. The anterior one originated from the digastric fossa and its length and width were 27 and 9 mm, respectively. The posterior accessory belly originated from the right intermediate tendon and it was 32 mm in length and 11 mm wide. On the left side, there was a single accessory bundle that originated from the left intermediate tendon and inserted into the mylohyoid raphe at the fusion point of the right accessory bundles. The length and width of this belly were 29 and 9 mm, respectively. The remaining suprahyoid muscles of both sides were normal. Anatomical variations of digastric muscle have to be considered in the imaging procedures of the soft tissue masses in the submental region.

Bilateral accessory anterior bellies of the digastric muscle and review of the literature

OBJECTIVE

The aim of our paper is discussing anomalies of the anterior belly of the digastric muscle with presenting our case in light literature.

METHODS

During dissection of the submental region of 26 years old Turkish female embedded cadaver, for this educational purpose in 2000, bilateral accessory digastric muscle was observed.

RESULTS

The anterior and posterior bellies of the digastric muscle had their normal origin and course and were joined by an intermediate tendon, the accessory anterior bellies originated from the digastric fossa, and inserted to the hyoid bone, with a common fibrous band. The accessory anterior bellies of the digastric muscle were in the same shape and coursed parallel to each other.

CONCLUSION

Anatomical variations of the anterior bellies of the digastric muscles can be easily confused with pathological conditions in CT and MR imaging, it is necessary to recognize that muscle variants of the digastric muscle occur to avoid confusion when diagnosing abnormal lesions of the floor of the mouth and submental region. In human body, such as these muscle variations have clinical significance.

Median accessory digastric muscle: radiological and surgical correlation

A median accessory digastric muscle was revealed during a dissection of the submental region. The muscle was located between the anterior bellies of the digastrics, external to the mylohyoid and deep to the platysma. It appeared as a flat quadrilateral sheet. Its base arose from the front of the body of the hyoid bone near its upper border. Lower portion of the fibers, at the right base of the muscle, initially traveled perpendicular to the lower fibers of the right mylohyoid. The rest of the muscle had a median course, with the cranial end inserting into the mandible between the digastric fossae. The muscle elevated the hyoid bone and depressed the mandible when appropriate stress was applied. No other morphologic abnormalities were found in this region. Aberrant anterior bellies of the digastric muscles are uncommon and occur bilaterally or unilaterally. This observation of a median accessory digastric muscle has not previously been reported. Knowledge of this variant will help to avoid confusion with pathological conditions of the floor of the mouth and the submental region. It is relevant both for the interpretation of radiological images and during surgical procedures such as dissection of the anterior belly of the digastric for a malignant disease and graft positioning.

An anomalous digastric muscle with three accessory bellies and one fibrous band

During our routine dissection studies we encountered an anomalous digastric muscle with three accessory bellies and one fibrous band in one embedded cadaver. All of these structures were attached to the mylohyoid raphe. This anomaly should be considered during surgical procedures involving this region.

The "pre-anterior belly" of the temporalis muscle: a preliminary study of a newly described muscle

Gross anatomical structures of the human body have been known and taught to students for centuries. However, at times, anomalies or even previously undescribed structures are discovered and subsequently reported. This preliminary report discusses the discovery of either a previously undescribed belly of the temporalis muscle, a previously undescribed muscle of mastication, or simply an anomaly of the temporalis. The somatosensory innervation of this structure was identified and will be presented. Preliminary measurements of this structure will also be provided. Finally, clinical implications of these findings, which may aid in the diagnosis and treatment of temporal and facial pain, will be discussed.

An accessory mylohyoid muscle

During dissection of the submandibular region of a forty year old male a unilateral left accessory mylohyoid muscle was revealed. This muscle was located between the left anterior belly of the digastric and left mylohyoid muscles. It arose from the left mylohyoid line of the mandible and was inserted into the lower portion of the mylohyoid raphe and hyoid bone. This unilateral accessory mylohyoid muscle is a rare anomaly, which is thought to contribute to the functional support of the floor of the mouth.

Oral cavity: anatomy and pathology

The oral cavity and oropharynx comprise the upper portion of the aerodigestive tract. These two regions are distinguished from each other because pathologic processes differ in their presentations, prognoses, and histologic grades. The normal anatomy of the oral cavity, vestibule, and oral cavity proper is discussed and is followed by a discussion of the sublingual and submandibular spaces. The diversity of pathologic processes that occur in these regions is then presented as well as the more common pitfalls.

An abnormal digastric muscle with three bellies

During the gross anatomy dissection of the submental region, an anatomical variation of the right digastric muscle was found. This muscle had three bellies. Whereas the anterior and posterior bellies had their normal origin and course and were joined by an intermediate tendon, the accessory anterior belly originated from the digastric fossa and a thin tendon together with the anterior belly was inserted onto the hyoid bone. This kind of variation can easily be confused with pathological conditions. For this reason, knowledge of the muscular anatomy and variations of the floor of the mouth is helpful when evaluating the base of the skull with CT and MR imaging.

Bilateral accessory digastric muscles

Anomalies of the anterior bellies of the digastric muscles are uncommon. The description of such anomalies do exist in the literature dating from the 19th Century, but recently radiologists have drawn attention to their existence to avoid confusion with abnormal lesions when scanning the floor of the mouth and the submental space. Bilateral accessory muscles crossing the midline are described.