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

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.

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.

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.

Duplicated posterior belly of digastric muscle and absence of omohyoid muscle: a case report and review of literature

PURPOSE

We report a unique case of duplicated posterior belly of digastric muscle and absence of omohyoid muscle, review literatures and discuss its clinical importance.

MATERIALS AND METHODS

An abnormal strip of muscle was found during the routine functional neck dissection in a 58-year-old man, who suffered from moderately differentiated squamous cell carcinoma of right tongue. We check the anatomical features and search for similar variations in the past literatures.

RESULTS

The abnormal strip of muscle was attached to mastoid process, passed anteroinferiorly into the infrahyoid muscles. The muscle was as long as, but narrower than the posterior belly of the digastric muscle. So far, only one case of this anomaly was reported. Meanwhile, the omohyoid muscle was confirmed to be absent in the right neck of this patient.

CONCLUSIONS

To our knowledge, report of variations of both digastric muscle and omohyoid muscle, this variation mostly derives from abnormal development of the mesenchyme in the branchial arches. Attention should be paid to such variations, which might influence surgical procedures.

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 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.

Abnormal digastric muscle with unilateral quadrification of the anterior belly

During dissection of the submental region we observed that the anterior belly of the left digastric muscle had four separate insertions. These muscle bands united in a common tendon as they continued with the posterior belly. This is an anatomical variation in the mylohyoid digastric muscle group in the floor of the mouth. When an asymmetry in the floor of the mouth is detected during diagnostic procedures, such as radiologic studies, anomalies of the anterior belly of the digastric muscle should be considered besides other reasons of asymmetry. Additionally, possible occurrence of such anomalies should be remembered during surgical procedures involving the submental region. This unique variation has not been reported in the literature.

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.