Anatomy Kumar Naveen et al. / JPBMS, 2012, 23 (12)

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JOURNAL OF PHARMACEUTICAL AND BIOMEDICAL SCIENCES

Absence of the Superior Belly of the Omohyoid Muscle: A Case Report

Ashwini Aithal P, MSc1., Naveen Kumar, MSc2*., Satheesha Nayak B, MSc, Ph.D3.

1,2,3 Department of Anatomy, Melaka Manipal Medical College (Manipal Campus), Manipal University, Manipal, Karnataka State, India- 576104. Abstract: Background: The omohyoid muscle is one of the infrahyoid muscles of the neck. It has superior and inferior bellies and an intermediate tendon. Variations in the omohyoid muscle are quite rare. Main observations: We report a case where the superior belly of the omohyoid muscle was absent. Its inferior belly originated from the upper border of scapula near suprascapular notch and passed across the posterior triangle, behind the sternocleidomastoid muscle. The muscle then blended with the fascia of the sternocleidomastoid muscle on its posterior surface. It was supplied by the ansa cervicalis. Due to the absence of the superior belly, division of the anterior triangle of the neck was incomplete. Conclusions: The omohyoid is important in radical neck dissections because it is the surgical landmark for level III and IV lymph node metastases. Thus, knowledge of anomalies of this muscle is important to minimize the complications during the surgical procedures of the cervical region.

Keywords: Infrahyoid muscles, omohyoid muscle, absence of superior belly.

Introduction Discussion: Omohyoid is a key muscle of the neck. It consists of two There are several reports of variations of the omohyoid bellies united at an angle by an intermediate tendon. It muscle. Tubbs et al., reported a case where in the superior arises from the upper border of the scapula, near the belly was attached to the transverse process of the C6, suprascapular notch. The inferior belly is a flat, narrow anterior to the scalenus medius [2]. A case of double band, which inclines forwards and slightly upwards across omohyoids, where in there was a duplicated superior belly the lower part of the neck; it then passes behind the of omohyoid with one part inserting into the hyoid bone sternocleidomastoid muscle and ends there in the and one part fusing with the lateral part of sternohyoid intermediate tendon. The inferior belly divides the muscle was reported by Miura et al., [3]. Tamega et al., have posterior triangle of neck into two sub triangles. reported a case of absence of the superior belly of The superior belly begins at the intermediate tendon, omohyoid [4]. Bolla et al., have reported a case of absence of passes almost vertically upwards near the lateral border of inferior belly where in the superior belly was attached to sternohyoid, and is attached to the lower border of the the clavicle [5]. In addition, Hatipoglu et al., have reported hyoid bone, lateral to the insertion of sternohyoid[1]. the presence of an unfamiliar muscle cleido-hyoideus on the left side [6]. Case Report: During routine dissection for medical undergraduate students, we observed a muscular variation on the right side of the neck of an approximately 55 year old male cadaver. The superior belly of the omohyoid was absent (Figure 1). The inferior belly of omohyoid was normal at its origin. It then passed across the posterior triangle and then behind the sternocleidomastoid muscle. The inferior belly was approximately 6.5cm and was situated proximal to the trunks of the brachial plexus. The muscle then blended with the fascia of the sternocleidomastoid muscle on its posterior surface (Figure 2). The superior belly of the muscle was absent leading to the incomplete division of the anterior triangle of the neck. The inferior belly was supplied by the ansa cervicalis. Figure 1. Photograph showing the absence of superior belly of omohyoid and the blending of inferior belly with the fascia on the posterior surface of sternocleidomastoid muscle. 1 Journal of Pharmaceutical and Biomedical Sciences © (JPBMS), Vol. 23, Issue 23 Anatomy Kumar Naveen et al. / JPBMS, 2012, 23 (12) the internal jugular vein is compressed by the omohyoid and this could lead to modifications in the intracerebral venous hemodynamics [9].

Unusual omohyoid forms described by Bergman et al., include: cleidofascialis, which originates from the middle third of the clavicle and inserts into the fascia colli; cleidohyoideus, which originates behind the sternocleiodomastoid muscle and inserts onto the body of the hyoid bone and hyofascialis, which originates from the hyoid and inserts into the omosternoclavicular fascia [10]. Embryologically, the infrahyoid muscles are formed from a muscle primordium occurring in the anterior cervical area. The muscle primordium is 1st divided into shallow and deep layers. Deep layer becomes the sternohyoid and thyrohyoid while the shallow layer gives rise to the omohyoid [11]. The omohyoid is important in neck dissections because it is the surgical landmark for level III [12] Figure 2. Photograph showing a closer view of the variation wherein the and IV lymph node metastases . inferior belly blends with the fascia on the posterior surface of sternocleidomastoid muscle (reflected in the figure) Conclusion: Because of the significance of the omohyoid muscle in The omohyoid muscle is the best landmark for identifying radical neck dissection as well as its close relation to the the internal jugular vein. Thus, variations in this muscle large vessels and brachial plexus, a better understanding of may increase the risk of injuring the IJV during surgeries in the variations of this muscle is of paramount importance to the neck region [7]. Because of the direct adhesion of the head and neck surgeons during the surgical procedures of intermediate tendon to the anterior wall of IJV, the cervical region. contraction of the muscle has a direct effect on the lumen of this vessel [8]. The studies by Patra et al., confirmed that 8. Ziolkowski M, Marek J, Oficjalska-Mlynczak J. The References: omohyoid muscle during the fetal period in man. Folia. 1. Williams PL, Dyson M. Gray’s Anatomy, ELBS and Morphol. (Warsz). 1983;42:21-30. Churchill Livingstone. 38th edition; p807. 9. Patra P., Gunness T. K., Robert R., Rogez J. M., Heloury Y., 2. Tubbs RS, Salter EG, Oakes WJ. Unusual origin of the Le Hur P. A., Leborgne J., Laude M., Barbin J. Y., omohyoid muscle. Clin Anat. 2004;17:578-82. Physiologic variations of the internal jugular vein 3. Miura M, Kato S, Itonaga I, Usuy T. The double surface, role of the omohyoid muscle, a preliminary omohyoid muscle in humans: Report of one case and echographic study, Surg Radiol Anat, 1988, 10(2):107– review of the literature. Okajima Folia Anat Jpn. 112 1995;72: 81-9. 10. Bergman RA, Afifi AK and Miyauchi R. Illustrated 4. Tamega OJ, Garcia PJ, Soares JC, Zorzetto NL. About a Encyclopedia of Human Anatomic Variation: Muscular case of absence of the superior belly of the omohyoid System: Omohyoideus, Sternohyoideus, Thyrohyoideus, muscle. Anat Anz. 1983;154:39-42. Sternothyroideus.1996.http://www.anatomyatlases.or 5. Bolla SR, Nayak S, Vollala VR, Rao M, Rodrigues V. g/AnatomicVariants/MuscularSystem/MuscleGrouping Cleidohyoideus. A case report. Indian Journal for the s/21Infrahyoid.shtml Practising Doctors. 2007; 3(6) :1-2 11. Lewis WH. The development of the muscular system. In: 6. Hatipoglu ES, Kervancioglu P, Tuncer MC. An unusual Manual of Human Embryology, 1st edn (Keibel F, Mall variation of the omohyoid muscle and review of FP, eds). Lippincott, Philadelphia, 1910; p.454-522. literature. Ann Anat. 2006;188:469-72. 12. Robbins KT, Medina JE, Wolfe GT, Levine PA, Sessions 7. Kasapoglu F, Dokuzlar U. An Unknown variation of RB, PruetCW. Standardizing neck dissection Omohyoid Muscle. Clin Anat 2007;20:964-65. terminology. Official report of the Academy’s committee for Head & Neck Surgery and Oncology. Arch Otolaryngol Head Neck Surg. 1991;117:601-05.

Corresponding Author:- Quick Response code (QR-Code) for mobile Mr. Naveen Kumar., user to access JPBMS website Department of Anatomy, electronically. Melaka Manipal Medical College (Manipal Campus), Website link:- www.jpbms.info Manipal University, Manipal. Madhav Nagar, Manipal Udupi District, Karnataka State. INDIA. 576104. Contact no:- +919880548636

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