1

Introduction

Differential diagnosis of a neck mass is important and challenging to many otolaryngologists. When patients present with a lateral neck mass, we consider a differential diagnosis including branchial cleft cyst, benign lymph node disorders and metastatic malignancy. When the patients describe a lateral neck mass on swallowing which disappears after swallowing, the problem is more complicated and is usually diagnosed as an omohyoid muscle syndrome. A review of English language articles showed that omohyoid syndrome is commonly listed in a differential diagnosis for lateral neck mass . The mechanism and pathophysiology of this syndrome are unknown, and the action of the omohyoid muscle is variable. Some authors say it depresses the hyoid bone and others say it has an association with phonation and swallowing . It must certainly relax when the hyoid bone has an upward movement and contract when it moves downward. However, it works paradoxically in rare conditions. There are several reports in the literature demonstrating this, and they are described as omohyoid syndrome, omohyoid muscle syndrome, or omohyoid sling syndrome. What is generally known is that omohyoid syndrome was first described by Zachary et al. in 1969 . Three authors reported omohyoid syndrome after an initial report in Lancet . These patients complained about severe pain at the affected site, and after several hours the pain subsided spontaneously. In physical examination, local tenderness along the omohyoid muscle was detected. These patients were treated with an analgesic or a maneuver which decreased tension in the omohyoid muscle .

The sternohyoid muscle is a long, thin muscle which is located bilaterally along the length of the front of the human neck, lateral to the trachea. The muscle originates on the medial end of the clavicle and the sternum, and inserts with tendonous fibers to the hyoid. Due to its location, it is useful for several functions including depression of the hyoid bone, head and neck movement, and speech. The sternohyoid muscle’s main function is the depression of the hyoid bone. The hyoid bone is located below the mandible, and is a “U” shaped bone that is partially responsible for tongue movement and the action of swallowing. [The sternohyoid is one of a pair of muscles responsible for this action.]

In this study, we reviewed abnormal findings of the sternohyoid muscle presenting as a lateral neck mass, and we called it sternohyoid syndrome. Apparently, there are no previous reports about this in the literature. Our clinic experienced a sternohyoid syndrome appearing as an omohyoid syndrome in two individual patients and after investigating the pathophysiologies, we report the findings here.

1.1

Clinical presentations

Two patients in our clinic were initially diagnosed with omohyoid syndrome. They presented with a left neck mass at swallowing, mild dysphagia with pain, and foreign body sensation in their throat for the past six months, to several years. They were concerned about the possibility of cancer. However, they had no aspiration or choking difficulties, nor was there any associated medical history or prior head and neck surgery, or any cervical injury.

Physical examination showed no positive finding when the patient was not swallowing. However, a soft lump appeared in the left neck over the junction of cervical vertebrae three and four. The mass was next to the anterior border of the sternocleidomastoid muscle. It rose up simultaneously with laryngeal elevation during swallowing, and disappeared after swallowing. The elevation of the mass during swallowing was from the anterior portion of the hyoid bone to the midportion of the clavicle. The neck was photographed at rest and during swallowing ( Fig. 1 ). The mass appeared near the intersecting point of the sternohyoid muscle and sternocleidomastoid muscle. Neck computed tomography (CT) showed no abnormal finding around the hyoid area and the muscle’s midportion. However, abnormal attachment to the mid-clavicle area of the left sternohyoid muscle was noted ( Fig. 2 ). We initially diagnosed these as an omohyoid syndrome, as the mass only appeared with swallowing. Abnormal sternohyoid attachment was an additional consideration for the diagnosis. The bellies of the sternohyoid, omohyoid and sternocleidomastoid muscles were obvious, thus it may not have been a true mass.

Neck photograph of the resting state (A, C) and swallowing (B, D). X-shaped mass showed more medial to omohyoid muscles (B, D: white arrow head).

Enhanced neck computed tomography. Normal anatomy was shown near the hyoid bone (A). Slightly thick sternohyoid muscle was noted on the left side (B) (white arrow). Normal sternohyoid (Right: blue arrow head) and abnormal attachment to midportion of clavicle (white arrow) were noted (C).

1.2

Operative findings

One patient had an operation under general anesthesia. In the operating field, a horizontal skin incision was made on the left lateral neck. After incising the platysma muscle, the sternocleidomastoid muscle below appeared normal. The omohyoid muscle showed no abnormal findings after retraction of the sternocleidomastoid muscle. The superior and inferior belly and intermediate tendon of the omohyoid muscle were normal. However, the sternohyoid muscle originated from an abnormal site in the midportion of the clavicle ( Fig. 3 ). We also found an abnormality of the left sternohyoid muscle, the color was a dark red, and the fascia covering the muscle was denuded. After dissection, horizontal cutting of the sternohyoid muscle was done at the midportion. The patient had no mass or foreign body sensation immediately after the surgery. Three-month follow-up revealed no recurrence of neck mass or discomfort ( Fig. 4 ).

Abnormal sternohyoid and normal omohyoid muscle are shown. Denuded fascia and reddish color of sternohyoid muscle are noted and normal intermediate tendon of omohyoid is noted. (A) Cutting of the abnormal sternohyoid muscle was completed. It was clamped with mosquito forceps superiorly and inferiorly. (B) The sternohyoid muscle is inserted to the midportion of the clavicle. (C) Normal omohyoid muscle was noted in (D).

Postoperative photograph of anterior neck. X-shaped mass disappeared after three months (A: resting state; B: swallowing state).

2

Discussion

Sternohyoid syndrome has not been reported before, but it is very similar to omohyoid syndrome. In this report, the sternohyoid muscle extended and protruded during swallowing, noted as a neck mass. When the neck is extended or turned to one side, the sternohyoid muscle may be noted as a neck mass. With omohyoid muscle syndrome, Ye first reported this syndrome in Chinese literature in 1978, and in English journals in 1980 . He said that more than ten patients were treated via operation and no recurrence was seen. The operating challenge was cutting the omohyoid muscle horizontally near the intermediate tendon. The resection of the superior belly of omohyoid muscle was done. No recurrence was reported. There is an Eastern Asian prevalence of this condition, but the reason is unknown. In this report, we also diagnosed two patients initially as an omohyoid muscle syndrome. But we had doubts after observing the muscle direction during swallowing. It ran straight from the hyoid bone to the midportion of clavicle, without a curve. The superior belly of omohyoid muscle is directed inferiorly to the midportion of the sternocleidomastoid muscle, inferolaterally on the upper neck, and the inferior belly of omohyoid muscle is directed more posterolaterally to the scapula on the lower neck. Thus, the omohyoid muscle is contoured more posterolaterally during swallowing on the lower upper neck.

The diagnosis of a sternohyoid syndrome is through symptoms and history taking. The patients have dysphagia or a palpable mass during swallowing, the same as with omohyoid syndrome . Yet, reviewing the literature, omohyoid syndrome typically shows multiple symptoms. Four patients felt pain (15%), nine patients felt an abnormal sensation (34%), and seventeen patients revealed a neck mass (65%). There are also minor symptoms like voice change (3%), choking (3%), and dysphagia (7%). The important thing for omohyoid syndrome is a visible protruding mass or pain, or a pulling sensation when one is swallowing. We suspect that patients with sternohyoid syndrome demonstrate symptoms similar to omohyoid syndrome. Dynamic CT scan and real-time ultrasonography also provide useful information about strap muscles . CT scan showed no abnormal finding of the sternohyoid and omohyoid muscles, which indicates that CT and ultrasound cannot be definite diagnostic tools of sternohyoid or omohyoid syndromes. Kim et al. also revealed that needle electromyography showed no abnormal findings .

We suspect that there are two mechanisms of pathophysiology for this syndrome, one anatomical and the other physiological. The first is an anatomical variation of the sternohyoid muscle, with abnormal insertion to the clavicle. Normally, the muscle is connected by tendons to the hyoid bone at the superior end, and to the posterior manubrium and medial clavicle at the inferior end. However, the patients in this report revealed that the lower part of sternohyoid muscle was connected mainly to the midportion of clavicle at the lower end. We found this abnormality grossly and intraoperatively. The second proposed mechanism is a denuded fascia of the midportion of the sternohyoid muscle. When the hyoid bone is elevated with swallowing, the midportion of the sternohyoid muscle bulges through the denuded fascia. The overlying sternocleidomastoid muscle then lifts upwards and out. Simultaneously, the left sternohyoid muscle is contracted abnormally when the hyoid bone is elevated with swallowing; the reason why is unknown. Another anatomical mechanism suggested is an additional belly of the omohyoid muscle. Guo-Hua et al. demonstrated a doubled omohyoid muscle as a cause of omohyoid syndrome . They reported that a doubled omohyoid muscle arose from the clavicle and inserted to the lateral hyoid. Below the anomalous muscle there were a normal superior belly and intermediate tendon of the omohyoid muscle. After separation of this anomalous muscle, no recurrence of symptoms was seen during four months of follow-up [ ]. Miura et al. also demonstrated that the superior belly of the omohyoid muscle was merged with the sternohyoid muscle and Rai et al. also reported a similar case with a cadaver [ ]. Hatipoglu et al. revealed an anomalous muscle from the clavicle to the hyoid, designated as a cleiodohyoid muscle [ ]. However, our patient in this report had no omohyoid muscle problems. We found a normal omohyoid muscle intraoperatively, but with a problematic left sternohyoid muscle.

Another issue of the sternohyoid muscle is why it would contract during swallowing or laryngeal elevation. Normally, the main function of this muscle is the depression of the hyoid bone and lowering of the larynx. We reviewed possible mechanisms from the suggested pathophysiologies for omohyoid syndrome. One proposed mechanism is caused by degeneration of the muscle, or muscle atrophy. Ye demonstrated that the omohyoid muscle showed hyaline degeneration and a decreased number of nuclei . Makino et al. reported myogenic atrophy as a cause of omohyoid syndrome . Degeneration of omohyoid muscle fibers can cause a failure of the muscle to lengthen. When the muscle is relaxed, for example with swallowing, this limits upward movement of the hyoid bone and results in tightening of omohyoid muscle tissue and the overlying sternocleidomastoid muscle. Therefore, an x-shaped mass appeared in the lateral neck. However this mechanism is not always applicable to all cases. Shibusawa et al. revealed that pathology results of a resected omohyoid muscle showed no specific changes in the muscle specimen . A second proposed mechanism is due to a bony obstacle of the muscle. Caswell et al. reported that in certain conditions, such as turning the head to the right or swallowing, excruciating pain developed and radiated toward the left shoulder [ ]. Patients gained relief by resting with their neck flexed and turning their chins toward the left. By this maneuver, they concluded that the superior belly of the omohyoid muscle had hooked on to the greater horn of the thyroid cartilage and had gone into spasm. Shibusawa et al. also stated that the superior belly of the omohyoid muscle was attached to the hyoid bone medially and hooked onto the laryngeal eminence in the operating field . A third proposed mechanism is failure of the fascial tissue surrounding the muscle. Mechanical trauma, anatomical variation or a congenital developmental disorder may contribute to this mechanism . Zhang et al. analyzed 50 examples of autopsies and two cases with patients . In their report, restriction of the intermediate tendon sheath during contraction of the omohyoid muscle was observed. They suggested an abnormal or deep cervical fascia connected to the intermediate tendon of the omohyoid muscle as a cause of pain. Kim et al. proposed that loosened fascial attachment of the intermediate tendon allows relatively free motion of the omohyoid muscle and also elevates the overlying sternocleidomastoid muscle .

Treatment of sternohyoid syndrome is elimination of the triggering factor. If the sternohyoid muscle is hooked on the greater horn of the thyroid cartilage and goes into spasm, any maneuver which relaxes the sternohyoid muscle is a treatment option. This could include neck flexion and turning the chin towards the affected side, thus preventing too much extension and spasm of the muscle. Kim et al. reported that head tilt to the lesion side relieves symptoms and signs of omohyoid syndrome . We also believe that education is important, as the condition is not cancerous. Su et al. used botulinum toxin injection for spasmodic omohyoid muscle, as well . In fact, the neck mass decreased completely and the foreign body sensation disappeared within three months after the injection. However, botulinum toxin injection of affected muscle has only a temporary effect on muscle paralysis and the cost is high. The duration of relief is only from six to nine months. Repetitive injection requires the patient’s tolerance and a high cost. A permanent and definite treatment method of sternohyoid syndrome is an operation. Ye first introduced horizontal cutting of the omohyoid muscle . The mass caused by omohyoid muscle syndrome had shown no recurrence for four years [ ]. Shibusawa et al. also resected the superior belly of the omohyoid muscle attached to the laryngeal prominence [ ]. Guo-Hua et al. found a doubled omohyoid muscle in their 42-year-old patient, and resected the anomalous muscle segmentally . It arose from the hyoid and ran into the direction of the clavicle. However, they did not follow up to find the actual terminus of the muscle.

In summary, our patients had a normal omohyoid muscle and sternocleidomastoid muscle. Variations of the omohyoid muscle were not observed at all. There was an intermediate tendon of the omohyoid muscle, which was attached normally from the superior belly to inferior belly of the omohyoid muscle. A sternohyoid muscle arose from the midportion of the clavicle and ran towards the hyoid, but the fascia around the sternohyoid did not exist and the color of the muscle was a dark red. The muscle lost its elasticity when contracted, when the hyoid bone was elevated with swallowing, resulting in tenting of the overlying sternocleiodomastoid muscle. We diagnosed this as sternohyoid syndrome, which appeared as a lateral neck mass in these patients. When a neck mass has been noted on the lateral neck during swallowing with no pathologic findings, this has been previously described as an omohyoid muscle syndrome in all literature to date. However, we introduce sternohyoid muscle syndrome as another syndrome and here describe its symptoms as similar to omohyoid syndrome.