An unusual variation of infrahyoid musculature and its clinical implications

Eva Maria Gonzalez-Soler; Arantxa Blasco-Serra; Francisco Martinez-Soriano; Alfonso A Valverde-Navarro

doi:10.4103/JASI.JASI_219_19

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CASE REPORT

Year : 2021 | Volume : 70 | Issue : 1 | Page : 55-57

An unusual variation of infrahyoid musculature and its clinical implications

Eva Maria Gonzalez-Soler, Arantxa Blasco-Serra, Francisco Martinez-Soriano, Alfonso A Valverde-Navarro
Department of Human Anatomy and Embryology, Faculty of Medicine and Odontology, University of Valencia, Valencia, Spain

Date of Submission	08-Nov-2019
Date of Acceptance	08-Aug-2020
Date of Web Publication	07-Apr-2021

Correspondence Address:
Dr. Arantxa Blasco-Serra
Department of Human Anatomy and Embryology, Faculty of Medicine and Odontology, University of Valencia, Avd. Blasco Ibáñez, 1546010 València
Spain

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JASI.JASI_219_19

Abstract

Knowledge of the anatomy of musculoskeletal system of the anterior neck region is crucial for the good practice of health personnel. In this area, both muscular and vascular systems are closely related, and the anatomical variations that may occur could alter blood conduction or hinder medical and surgical maneuvers. This study reports a case of unilateral duplicated omohyoid muscle and its merger with an anomalous sternohyoid muscle with an intermediate tendinous formation and discusses its clinical importance. This alteration might have represented a problem at a surgical reconstruction of diverse neck structures, in case of having specified one. Besides, a large-flow collateral vein system has been observed, which could also have played an important role in the consequences of this anatomical muscle variation. Thus, it is considered as of importance to report on the anatomical variations found in human dissections, both for basic science researchers and for professionals dedicated to clinical science.

Keywords: Anatomical variations, human dissection, infrahyoid musculature, omohyoid, sternohyoid

How to cite this article:
Gonzalez-Soler EM, Blasco-Serra A, Martinez-Soriano F, Valverde-Navarro AA. An unusual variation of infrahyoid musculature and its clinical implications. J Anat Soc India 2021;70:55-7

How to cite this URL:
Gonzalez-Soler EM, Blasco-Serra A, Martinez-Soriano F, Valverde-Navarro AA. An unusual variation of infrahyoid musculature and its clinical implications. J Anat Soc India [serial online] 2021 [cited 2023 Feb 4];70:55-7. Available from: https://www.jasi.org.in/text.asp?2021/70/1/55/313159

Introduction

Over the last decades, interest has grown in the study of anatomical variations of the infrahyoid musculature, given its clinical relevance.^[1],[2],[3] Infrahyoid musculature is composed of sternothyroid (ST), thyrohyoid (TH), omohyoid (OH), and sternohyoid (SH) muscles.^[4] These are embryologically formed from a muscle primordium occurring in the anterior cervical area: ST and TH come from the deep layer of this primordium, and SH and OH come from the superficial layer, specifically from a degeneration of the splenius spread, which is a characteristic of human species.^[1],[5]

In the case presented in this paper, a unilateral duplicated inferior belly of the OH muscle merging with SH has been found. Besides, a tendinous formation in this SH muscle happened at the same time, and both muscles were found on the right side of the neck. This is a rare case, so it has been considered that it could have significant clinical interest for healthcare professionals.

Case Report

During a regular anatomy dissection of a female cadaver in 2018, a duplicated inferior belly of the OH muscle merged to an anomalous SH muscle with a tendinous formation in its middle (dividing it into two parts) on the right side of the neck was found [Figure 1].

Figure 1: Deep dissection of the right side of the neck of a female cadaver showing the infrahyoid musculature. Note the variations on the omohyoid and sternohyoid muscles. Structures to be valued have been highlighted. SOH: Superior omohyoid muscle, SOHt: tendon of superior omohyoid muscle, IOH: Inferior omohyoid muscle, SSH: Superior sternohyoid muscle, ISH: Inferior sternohyoid muscle, SHt: tendon of sternohyoid muscle, IJV: Internal jugular vein, EJV: External jugular vein, LFCV: Large-flow communicating vein, TG: Thyroid gland

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In this case, we found the following duplication variation of the OH muscle: The superior OH muscle showed a typical appearance of the normal superior and inferior bellies with an intermediate tendon in between. The duplicated inferior belly of the OH muscle was similar to the superiorly positioned muscle, without intermediate tendon, and was united with SH muscle at the medial part of the clavicle, next to an intermediate tendon found on SH. The location of the attachment and the innervation for the duplicated inferior belly of the OH muscle were the same as superior OH muscle. This abnormality could belong to two classifications: Type I (double OH) and Type II (as inferior OH merges with SH). Both are innervated by the ansa cervicalis. This classification of anatomical OH variations has classical roots and is presented as follows: (1) OH muscle is present and has an intermediate tendon (Type V); (2) attached to the superior border of the scapula (Type IV); and (3) supplied by the ansa cervicalis.^[1]

Regarding the anomaly of the SH muscle, an intermediate tendon was found at the level of the medial part of the clavicle and the thyroid gland. It is here that the duplicated inferior belly of the OH muscle appears to be attached [Figure 2]. This merging happens very close to the internal jugular vein (IJV). The intermediate tendon divided SH into a superior and an inferior part.

Figure 2: Photograph showing in detail the tendon of superior omohyoid muscle. Structures to be valued have been highlighted. SOH: Superior omohyoid muscle, SOHt: tendon of superior omohyoid muscle, IOH: Inferior omohyoid muscle, SSH: Superior sternohyoid muscle, ISH: Inferior sternohyoid muscle, SHt: tendon of sternohyoid muscle, IJV: Internal jugular vein, EJV: External jugular vein, LFCV: Large-flow communicating vein, TG: Thyroid gland

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An anterior jugular vein (AJV) was also found (which was eliminated to continue with the management of dissection), and the anastomosis between AJV and the external jugular vein was through a large-flow communicating vein (LFCV).

Discussion

The clinical relevance of alterations of the anterolateral neck musculature has attracted the attention of many anatomists over recent years, given its surgical importance. Actually, neck surgery is, to this day, one of the basic principles of neck cancer therapy. Therefore, not only surgeons but also all health personnel related to clinical treatment of this region must have an unbeatable anatomical base of the anterolateral region of the neck, bearing in mind the possible anatomical variations that could be found, and what complications and risks they could cause.

OH is an anatomical landmark to identify the levels III and IV lymph node metastases of head-and-neck cancers; it has been studied for the treatment of a bowed vocal fold by transpositioning and for the restoration of vocal cord abduction.^[6] In the presented case, a duplicated inferior belly of the OH muscle is merged to the abnormal intermediate tendon of the SH muscle. Based on previous studies, it can be hypothesized that this fusion would have confused the level of classification of metastasis and thus alter postoperative therapy and prognosis by altering these anatomical landmarks.^[6]

Several authors have theorized a genetic reason of alterations in this musculature: Since TBX1 gene regulates the myogenic differentiation and cellular fate within the mesoderm, inactivation or deletion of this gene leads to alterations in the morphology of neck muscles.^[7] Changes in TBX1 gene are responsible for many of the features of 22q11.2 deletion syndrome, which has a heterogeneous presentation, including congenital anomalies, such as palatal, gastrointestinal, cardiovascular, and genitourinary abnormalities.^[8] In the case presented, both OH and SH muscles presented anatomical variations. These two muscles originate from the superficial layer of the infrahyoid premuscular band, whose development depends on this TBX1 gene; moreover, a highly marked scoliosis [Figure 3], a discreet micrognathia, and bilateral polycystic kidneys [Figure 4]a and [Figure 4]b, as well as bilateral dilated megaureters with signs of vesicoureteral reflux [Figure 4]c and [Figure 4]d and an abdominal aortic aneurysm [[Figure 4]d] have also been found.

Figure 3: Photograph of backbone variations. The marked scoliosis has deviated great arteries and venous vessels of the posterior mediastinum, as well as the esophagus; notice how the azygos vein has been completely displaced towards the left. AA: Aorta artery, AV: Azygos vein, VS: Vertebral soma

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Figure 4: Photograph of urinary system abnormalities. (a and b) Both kidneys can be observed. Notice the cystic formations as well as the remarkable size and morphologic differences. (c and d) The megaureters formation. AAA: Aorta artery aneurism, C: Cyst, IMA: Inferior mesenteric artery, LK: Left kidney, LMU: Left megaureter, RK: Right kidney, RMU: Right megaureter

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Intermediate OH tendon is directly adhered to the anterior wall of IJV, connected to it through a thin lamina of the pretracheal layer of the cervical fascia, so the contraction of OH muscle has a direct effect on the lumen of this vessel.^[4] The presented case also showed an AJV and an LFCV. The existence of this collateral vein system plays an important role for the insertion of port catheters, pacemaker leads, or other types of central devices, when there is a problem with other accesses considered as more common.^[9]

Anomalies on the SH muscle are very uncommon; in fact, the variation of the SH muscle observed in the present case has not been previously reported. Kim et al., in 2015, found in vivo human cases in which SH muscle arose from the mid-portion of the clavicle and ran toward the hyoid, without fascia and an abnormal muscle color; from a bioscopic perspective, it was presented as a lateral neck mass, and subjects reported symptoms such as mild dysphagia with pain and foreign body sensation in their throat for a long time, with no choking difficulties. These cases were registered under the name of “SH syndrome.”^[10]

It is important to report these anatomical variations from basic research to clinical fields for the management of diverse interventions, such as neck-and-head surgery. The existence of multidisciplinary clinical-basic work teams is very positive and brings us closer to the understanding of the morphology, physiology, and development of the human body.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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