A rare bilateral variant of the levator claviculae: a case report

Abstract

Introduction and importance:

The levator claviculae is a rare anatomical variant located in the posterior cervical triangle, typically unilateral and left-sided, with an estimated prevalence of 1–2% of the population. We report a bilateral and asymmetric levator claviculae identified during a cadaveric dissection by first-year medical students. Recognizing this variation is of clinical interest and holds educational value for anatomical training.

Presentation of case:

The muscle was identified on both sides, each with two heads, with a more prominently developed appearance on the right. The short head originated from the transverse process of the third cervical vertebrae, while the long head originated from the transverse process of the second cervical vertebrae. The muscle on the right side inserted onto the posterolateral border of the clavicle, while on the left, it inserted into the middle of the clavicle. Bilateral innervation originated from the second, third, and fourth cervical spinal nerve rami. Blood supply to the right side originated from the transverse cervical artery, while the dorsal scapular artery supplied the left side.

Clinical discussion:

This report highlights the embryological basis and clinical significance of this rare anatomical variant. Clinically, its misinterpretation could affect radiological assessment, medical diagnosis, surgical procedures, and patient outcomes.

Conclusion:

Collectively, understanding rare anatomical variants holds clinical and educational value, shedding light on cadaveric dissection as a valuable tool not only in medical education but also in improving surgical outcomes and clinical assessment.

Introduction

The levator claviculae (LC) is a rare muscular variation with an estimated prevalence of 1–2%. Typically, LC originates from the transverse processes of upper cervical vertebrae and inserts onto the lateral or posterolateral aspect of the clavicle. This muscle tends to appear more often unilaterally on the left side, originating from the transverse process of the C3 vertebra^[1].

Several anatomical variations in the origin and insertion of the LC have been previously reported^[2]. For instance, the muscle has been identified on the right side with insertion on the posterior aspect of the middle clavicle^[3]. Other cases have reported LC originating from the levator scapulae and reaching the serratus anterior and trapezius with insertions onto the sternocleidomastoid muscle^[4]. Besides, the reported length of the LC varies between 5 and 12 cm^[1,3], and its vascular supply commonly originates from branches of the ascending cervical artery^[3–5].

HIGHLIGHTS.

• The levator claviculae, a rare anatomical variation, is typically unilateral and left-sided

• A bilateral and asymmetric presentation was depicted during cadaveric dissection

• Identification of this variant holds clinical significance with direct effects on patient care

The muscle function has been reported to assist in respiration through the ribcage’s elevation, as well as in neck twisting and rotation^[1]. It is innervated by cervical nerves C2–C5⁴ with minor documented variations. In one case, innervation was supplied through a branch of the 4th cervical nerve^[3]. Differences have been noted between the innervation of the upper third of the muscle, innervated directly from the anterior rami of C2 and C3, and between the lower two-thirds, innervated by branches from the loop between C3 and C4. Besides, reports of an anastomosis between the C3 and C4 spinal nerves, forming a single branch that crossed over the C5 nerve and entered the muscle dorsally near its origin, have been described^[2]. This article reports a rare asymmetric bilateral LC, stressing its embryological and clinical importance. Describing this variant holds clinical and educational relevance, particularly in radiological assessment and surgical procedures. This case report has been reported in line with the SCARE checklist^[6].

Case presentation

This rare muscular variation in the posterior neck was identified during routine cadaveric dissection of a 64-year-old female cadaver in the Clinical Anatomy course for medical students.

A muscle consistent with the LC was identified bilaterally, showing asymmetry in size and position. On the right side, the muscle was larger and more anteriorly located, measuring 12 cm in length and 2 cm in width. Its short head originated from C3, whereas its long head originated from C2, inserting onto the posterolateral border of the clavicle. On the left side, the LC had a smaller size (5 cm long and 12 mm wide) and a more posterior location. It originated from C3 and inserted onto the mid-lateral part of the clavicle. Notably, muscles on the two sides shared similar attachment sites, supporting the argument that they represent the same muscle. On the left side, the LC was supplied by the dorsal scapular artery, arising in our case from the transverse cervical artery. The artery pierced the muscle posteriorly near its midline. On the right side, the blood supply originated from the transverse cervical artery. The cervical artery was found running posterior to the LC (Fig. 1).

Figure 1.

(A) Left neck showing levator claviculae (LC) supplied by the dorsal scapular artery (DS), which arises from the transverse cervical artery (TCA). Proprioceptive fibers (P) originating from the anterior rami of C2, C3, and C4 innervate the LC. Note the superior trunk of the brachial plexus (BPsup) and the trapezius muscle (T) for reference. (B) Right neck showing the LC, innervated by nerves (N) C2, C3, C4. T, trapezius; C, clavicle.

Discussion

This case report describes a rare bilateral and asymmetric LC, with differences in origin, insertion, and vascular supply between the two sides, emphasizing the variability of this muscle compared to previous literature reporting its unilateral, left-sided appearance^[1].

The embryological origin of the LC muscle is of evolutionary and clinical significance. It has been regularly observed in evolutionary relatives of Homo sapiens, such as arthropod apes^[3]. In humans, it has been hypothesized to have origins from the trapezius, scalenus anterior, and possibly the longus colli muscles. Notably, Leon et al proposed that it arises from a ventrolateral primordial segmentation^[3].

Based on its anatomical characteristics, specifically, its insertion on the clavicle, the LC is thought to have an inspiratory function, aiding in lifting the ribcage. Originating from the upper cervical vertebrae, it exhibits a contractile direction upwards and backwards. In arthropod apes, considering their forward-leaning posture, this muscle likely aids in inspiration as it lifts the rib cage superiorly and posteriorly to allow for increased inspiration. Whereas, in humans, with a generally upright posture, there is no need for a muscle performing this action, as most of the inspiratory effort involves lifting the ribcage only upwards, reducing the functional necessity of the LC, which could explain the evolutionary regression of this muscle^[2]. It is worth noting that the presence of the LC muscle is among many anatomical variations in human muscles, such as the frequently reported absence of the palmaris longus^[7], or the plantaris muscle, which is missing in 6–8% of individuals^[8].

Clinically, the LC has been misinterpreted in CT scans of patients, sometimes as a lymph node or a collection of lymphatics, which could possibly influence surgical management and treatment choices, as well as tumor staging^[5]. It has also been mistaken for cysts, hemangiomas, aneurysms, and metastatic tumors^[2]. In addition, some cases of the LC muscle have misled physicians due to its location, where a palpable angular deformity of the clavicle is induced by the muscle tendon(s)^[9]. One clinical case involved a gymnast whose LC muscle led to thoracic outlet syndrome^[10]. Otherwise, incidental findings of this muscle in patients have been asymptomatic, but generally pose additional findings that mislead physicians in their radiological diagnoses^[1,2].

Among the numerous anatomical variations in the human body, the LC muscle, identified in this report, is a relatively rare, uncommon anatomical variation. However, as this is a single case, further studies are warranted to identify and document the incidences of these variations, which could aid in updating prevalence, variations, and clinical associations. Enriching such databases with evidence-based reports will contribute to deciphering the complex human anatomy, which holds significant educational and clinical implications.

Conclusion

Recognition of this rare LC variant, and its detailed documentation, enhances the understanding of clinicians, in particular surgeons and radiologists, and directly impacts patient outcomes, highlighting the role of cadaveric dissection in medical education.

Ethical approval

The authors hereby confirm that every effort was made to comply with all local and international ethical guidelines and laws concerning the use of human cadaveric donors in anatomical research.

Consent

Not applicable.

Sources of funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author Contributions

M.Q. and A.C.: writing – original draft; S.K.: Writing-reviewing and editing; G.N., A.H., and J.H.: methodology, writing – reviewing & editing. All authors reviewed the manuscript.

Conflicts of interest disclosure

The authors declare that they have no conflict of interest.

Guarantor

Jihad Hawi.

Research registration unique identifying number (UIN)

Not applicable.

Data availability statement

All data generated or analyzed during this study are included in this published article.

Provenance and peer review

Not commissioned; externally peer reviewed.