Anatomical study of the human omohyoid muscle: Regarding intermediate morphologies between normal and anomalous morphologies of the superior belly

Abstract

Intermediate morphologies between normal and anomalous morphologies of the superior belly of the omohyoid muscle (Om) were macroscopically and stereomicroscopically observed in 34 cadavers (24 males and 10 females aged between 51 and 97 years; average age 71.0 years) for anatomical practice, which had been preserved in the Department of Morphological Biology, Ohu University School of Dentistry. The intermediate morphologies were classified into four types on the basis of the developmental degree of the muscle fibers and the number and origin of the belly as follows: type 1, the anterior margin of the belly was unclear owing to poor myofiber development; type 2, the superior belly was composed of a posterior large belly and an anterior small belly; type 3, composed of three to five bellies, with the bellies arranged in a roof tile-like morphology; and type 4, the belly was composed of two bellies arranged anterior-posteriorly parallel to each other (the anterior belly was found to be the inferior belly that had developed and reached the superior belly area). For the intermediate morphologies of the Om superior belly observed in the present study, although type 4 was due to the development of an inferior belly, the other three types were considered to be caused by the poor development of the myofibers in the formation process and by the division of the superior belly into two muscles, or secondary lamellar division of the belly with growth.

Internal Jugular Vein Entrapment in a Multiple Sclerosis Patient

“…Its two bellies, superior and inferior, are separated by an intermediate tendon. A number of variations of this muscle are known, including double muscle, missing of one of the bellies, duplication of one belly, and atypical attachment of the bellies [13–18]. This muscle may also—instead of the scapula—originate from the clavicle [19].…”

Pseudodysphagia Due to Omohyoid Muscle Syndrome

“…The etiology responsible for the loosening of this attachment is not known for certain, but anatomical variation or congenital weakness in development [2,4], racial predisposition, chronic fatigue, or trauma [13] may contribute to the development of OMS. The incidence of anomalies of the OH related to the origin and insertion, the course, and the number of bellies and anomalies of the surrounding muscles is high [4,[16][17][18][19]. Also, poor development of myofibers of the superior belly of OH and the unclear internal margin between OH and cervical fascia are frequent [16].…”

“…The first proposed mechanism is that OMS is caused by failure of OH to lengthen due to muscle fiber degeneration [3]. A recent anatomical study [16] regarding morphologies of the superior belly of OH reported that four types of intermediate morphologies were observed in 18 of 67 samples, and four of them were considered to be caused by the poor development of the myofibers (type 1). This then limits the upward movement of the hyoid bone and results in the tenting or lifting upward and outward of the overlying SCM muscle during the laryngeal elevation phase of swallowing.…”

“…The incidence of anomalies of the OH related to the origin and insertion, the course, and the number of bellies and anomalies of the surrounding muscles is high [4,[16][17][18][19]. Also, poor development of myofibers of the superior belly of OH and the unclear internal margin between OH and cervical fascia are frequent [16]. These various anatomical factors and chronic or instant strong force to the OH may increase the pulling force of OH from the cervical fascia and subsequent loosening or detachment can develop.…”

Theory and practice of laparoscopic surgery against omohyoid muscle syndrome

“…The superior belly (SuB) originates from the IT and inserts into the base of the hyoid bone (H). The OM depresses the hyoid bone after it has been elevated during wallowing (1).…”