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 Table of Contents  
CASE REPORT
Year : 2018  |  Volume : 4  |  Issue : 2  |  Page : 55-57

A Rare Bilateral Variation of The Anterior Belly of Digastric Muscle


1 Assistant Professor, Department of Anatomy, IGIMS, Patna, India
2 Additional Professor, Department of Anatomy, IGIMS, Patna, India
3 Professor, Department of Anatomy, IGIMS, Patna, India

Date of Web Publication10-Dec-2020

Correspondence Address:
Avanish Kumar
Additional Professor, Dept. of Anatomy, IGIMS, Patna, Bihar
India
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Source of Support: None, Conflict of Interest: None


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  Abstract 


The digastric muscle is a suprahyoid muscle which consists of two bellies: anterior & posterior. Above the hyoid bone these two bellies are connected by an intermediate tendon, which is anchored to the hyoid bone by a fascial sling of investing layer of deep cervical fascia. The variations of the anterior belly of digastric muscle are uncommon. In the present case, we found a bilateral symmetric variation in the anterior bellies of digastric muscle in a 58 year old female cadaver. Both accessory bellies were present bilaterally medial to the anterior digastric muscles. Each accessory bellies consisted of two segments: anterior and posterior. Both segments crossed each other & looked like the letter "X". Both accessory bellies originated from the digastric fossa & inserted to the anterior digastric muscle. In the midline these accessory bellies were attached to each other by dense connective tissue that also connected these bellies to the mylohyoid muscle superiorly. Anatomical variations of the digastric muscle may affect the mastication as well as deglutition. Moreover, the accessory digastric muscles also affect the different diagnostic imaging and therapeutic procedures in the region of head and neck. Therefore this type of variations must be considered in procedures involving this area.

Keywords: Digastric muscle, accessory belly, anatomical variation, hyoid bone


How to cite this article:
Akhtar MJ, Kumar B, Sinha RR, Kumar A, Kumar V. A Rare Bilateral Variation of The Anterior Belly of Digastric Muscle. J Indira Gandhi Inst Med Sci 2018;4:55-7

How to cite this URL:
Akhtar MJ, Kumar B, Sinha RR, Kumar A, Kumar V. A Rare Bilateral Variation of The Anterior Belly of Digastric Muscle. J Indira Gandhi Inst Med Sci [serial online] 2018 [cited 2021 Dec 4];4:55-7. Available from: http://www.jigims.co.in/text.asp?2018/4/2/55/302959




  Introduction: Top


The anterior belly of the digastric muscle is attached to the digastric fossa, present on the internal surface of the mandible. The posterior belly arises from the digastric groove, which is present in between the styloid process & the mastoid process of the temporal bone. The floor of the mouth is formed by the mylohyoid & geniohyoid muscles along with the anterior belly of the digastric muscle[1]. The anterior belly of the digastric muscle is superficial to the mylohyoid and deep to the platysma muscle. The paired digastric muscles when act together, it either depress the mandible or elevate the hyoid bone. They help in the process of deglutition by elevating the hyoid bone and in mastication by depressing the mandible. The anterior belly of the digastric & the mylohyoid muscle both develop from the first branchial arch, whereas the posterior belly of digastric muscle develop from the second arch. Since these two bellies are derived from the mesenchyme of two different branchial arches, so they are innervated by two different nerves[2]. Thus, the anterior belly of digastric muscle is innervated by the mandibular nerve, a branch of trigeminal nerve & the posterior belly by the facial nerve. The variations of the anterior belly of digastric muscle are quite uncommon. Accessory bellies of the digastric muscle may alter the movements of the mandible & the hyoid bone. They even cause difficulties in the clinical diagnosis of the different pathological masses in the submental area and also interfere with successful surgeries in the anterior neck region.


  Case Report: Top


During routine dissection of head & neck, in the department of Anatomy, Indira Gandhi Institute of Medical Sciences, Patna, Bihar, we came across a bilateral symmetric variation in the anterior bellies of digastric muscle in a 58 year old formalin preserved female cadaver. During dissection, we removed the skin, superficial fascia, platysma and deep fascia of neck and exposed the digastric muscle which consisted of anterior and posterior bellies. Posterior belly originated from the mastoid notch of the temporal bone and ended as intermediate tendon and then the intermediate tendon continued with the anterior belly which was inserted to the lateral half of the digastric fossa presents on the internal surface of the mandible. In addition, there were two accessory bellies of the digastric muscle found. Both accessory bellies were situated bilaterally medial to the anterior digastric muscle. Each belly of the accessory muscles consisted of two segments: anterior & posterior. Both segments crossed each other and appeared as the letter "X". Both accessory bellies originated from the digastric fossa and attached with the anterior digastric muscle. In the midline these accessory bellies were attached to each other with dense connective tissue and the mylohyoid muscle [Figure 1]. These accessory bellies were also supplied by the mylohyoid branch of the inferior alveolar nerve.
Figure 1: Dissection of the anterior neck region showing the accessory bellies of anterior digastric muscle

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  Discussion: Top


In the present case, we reported bilateral variation of the anterior bellies of digastric muscle. In a cadaveric study, by De-Ary-Pires et al.[3] the variations of the anterior bellies of digastric muscle were classified into 5 different types: In type 1 to 4; anterior belly consist of one, two, three & four bellies associated with some extra slips respectively and mentohyoid muscle described as type 5. They reported 18% cases of accessory bellies in their study. Fujimura et al.[4] reported the variations in anterior bellies in 24.1% of cases. Sarikcioglu et al.[5] described a case of triplication of anterior belly of digastric. Celik et al.[6] found quadrification of anterior belly of digastric. While, some authors reported complete absence of the anterior bellies[7],[8],[9]. Kyung DS et al.[10] described a bilateral variation of digastric muscle in a Korean male cadaver. They reported two accessory bellies. These accessory bellies originated from the medial side of the normal bellies. Then, it merged & attached at the mylohyoid raphe of the mylohyoid muscle. They measured the bellies & reported that right & left were approximately 30 and 32 mm in length respectively, and both were 7 mm in width. The anterior as well as accessory bellies were innervated by the nerve to mylohyoid on each side. They also reported a third accessory belly originated from the right intermediate tendon and continued for 15 mm further horizontally. It fused with the right lower bundle of the right accessory belly and finally inserted at the mylohyoid raphe. It was also innervated by the nerve to mylohyoid & it had no any connection with the left digastric muscle. They found submental artery supplied the muscles on each side. Mascaro MB et al.[2] found an accessory anterior belly of the digastric muscle during routine dissection classes of the submental region of an approximately 40 year old Brazilian male. Those were presented bilaterally medially to the anterior digastric muscles. They also found the bellies looks like the letter X. On the left side the long segment was 20 mm in length & 6 mm in width while the short was 10 mm in length & 9 mm in width. On the right side the long segment was 20 mm in length & 9 mm in width while the short was 12 mm in length & 7 mm in width. In the midline these accessory bellies were also fused to each other by dense connective tissue. Singh Z, Kaur G, Kaur A[11] described a case in which on the right side the anterior belly of the digastric muscle was absent while a bilateral symmetrical accessory bellies of anterior digastric muscle was present. These accessory bellies were present superficial to the mylohyoid muscle on the right side and superficial to the anterior belly of the digastric muscle on the left side. These were supplied by nerve fibers coming from the nerve to the mylohyoid.

Occurrence of supernumerary muscles may be due to the abnormal development of the muscle primordium. The anterior belly of digastric arises from the first branchial arch. Any abnormalities of the neural crest cells which belong to the first branchial arch may results in the additional or accessory bellies of anterior belly of digastric[12]. The detail knowledge regarding anatomic variations of the anterior belly is clinically important during surgeries in the anterior neck region. The anterior belly of digastric is commonly used during the plastic surgeries for the functional restoration of the lower lip in cases of facial nerve palsy[13].


  Conclusion: Top


Accessory bellies of the digastric muscle may alter the movements of the mandible & the hyoid bone. They even cause difficulties in the clinical diagnosis of different pathological masses in the submental area and also interfere with successful surgeries in the anterior neck region. Therefore this type of variations must be considered in procedures involving this area.



 
  References Top

1.
Standring S, Borley NR, Collins P, Crossman AR, Gatzoulis MA, Healy JC, et al. Gray's Anatomy: The Anatomical Basis Of Clinical Practice. 40thed, London: Elsevier Ltd., 2008: 435-41.  Back to cited text no. 1
    
2.
Mascaro MB, Picoli LC, Santos FM, Bonsi AB, Souza MR, Prosdocimi FC. Anatomical variation of the anterior belly of the digastric muscle: case report and clinical implications. J Morphol Sci 2011; 28(1): 72-5.  Back to cited text no. 2
    
3.
De-ary-pires B, Ary pires R, Pires neto MA. The human digastric muscle: patterns and variations with clinical and surgical correlations. Ann Anat 2003; 185(5): 471-9.  Back to cited text no. 3
    
4.
Fujimura A, Onodera M, Feng XY, et al. Abnormal anterior belly of the digastric muscle: a proposal for the classification of abnormalities. Anat Sci Int 2003; 78(3): 185-8.  Back to cited text no. 4
    
5.
Sarikcioglu L, Demir S, Oguz N, Sindel M. An anomalous digastric muscle with three accessory bellies and one fibrous band. Surg Radiol Anat 1998; 20(6): 453-4.  Back to cited text no. 5
    
6.
Celik HH, Aldur MM, Ozdemir B, Aksit MD. Abnormal digastric muscle with unilateral quadrification of the anterior belly. Clin Anat 2002; 15(1): 32-4.  Back to cited text no. 6
    
7.
De-Ary-Pires, B., Ary-Pires, R. and Pires-Neto, MA. The human digastric muscle: patterns and variations with clinical and surgical correlations. Annals of Anatomy 2003; 185(5): 471-9.  Back to cited text no. 7
    
8.
Larsson, SG. and Lufkin, RB. Anomalies of digastric muscles: CT and MR demonstration. Journal of Computer Assisted Tomography 1987; 11(3): 422-5.  Back to cited text no. 8
    
9.
Ozgursoy, OB. and Kucuk, B. Unique variation of digastric muscle: a confusing landmark for head and neck surgeons. Acta oto?laryngologica 2006;126(8):881-3.  Back to cited text no. 9
    
10.
Kyung DS, Lee JH, Lee YP, Kim DK, Choi IJ. Bilateral variation of the head of the digastric muscle in Korean: a case report. Anat Cell Biol 2011; 44: 241-43.  Back to cited text no. 10
    
11.
Singh Z, Kaur G, Kaur A. A variant digastric muscle. International Journal of Anatomical Variations 2011; 4: 120-122.  Back to cited text no. 11
    
12.
Loukas M, Louis RG, Kapos T, Kwiatkowska M. A case of a bilateral accessory digastric muscle. Folia Morphol (Warsz) 2005; 64(3): 233-6.  Back to cited text no. 12
    
13.
Tan ST. Anterior belly of digastric muscle transfer: a useful technique in head and neck surgery. Head Neck 2002; 24(10): 947-54.  Back to cited text no. 13
    


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