Clinical History
A 56-year-old male patient with no personal history of interest presented with a painless palpable left supraclavicular mass and no infectious symptoms.
A contrast enhanced computed tomography (CT) of the neck was performed.
Imaging Findings
CT examination of the neck confirmed the presence of a left fat density lesion without septa, solid poles or contrast enhancement with radiological appearance suggestive of lipoma (Fig. 1).
Incidentally, a soft-tissue mass within the right posterior triangle of the neck was identified. The structure had a similar course to the levator claviculae muscle (Fig. 1 – 2): it originated from the trapezius and was situated anterior to the levator scapulae muscle. Caudally, the muscle followed an anterior and slightly lateral trajectory to be inserted in the middle third of the clavicle, being located superficially in almost all its passage.
Discussion
The levator claviculae or cleidocervical muscle is a rare accessory skeletal muscle located in the posterior triangle of the neck. Despite its unusual reported presence in humans (prevalence 2 – 3 %), the levator claviculae muscle exists in almost all mammals being the atlantoscapularis anterior its possible homolog in primates. [1] Lately, its diagnosis is increasing due to the widespread use of imaging. [2]
This muscle acts as a synergist of the trapezius and the serratus anterior muscle to raise the arm above the horizontal plane of the shoulder and also acts as an auxiliary muscle for respiration. Its disappearance during evolution may be related to the upright posture and the decreased need in humans to raise the arm above the shoulder. [3]
The embryologic origin of the levator claviculae muscle is controversial. A recent review concludes that the levator claviculae and the levator scapulae muscles arise from the same myotome. This myotome partially gives rise to the trapezius and the sternocleidomastoid as well, having the possibility that the levator claviculae fuses with those two muscles in a few rare cases, as it is probably happening in our case. [3]
The levator claviculae muscle has a characteristic course through the neck. It has a tendency to appear on the left side in humans [2, 3], but in other primates, it is always present bilaterally. The presence of the muscle on the right side, as in our case, is much rarer than on the left side. It generally arises from the anterior portion of the transverse processes of the upper cervical vertebrae (C1 - C4, been described until C6, [2]), from where it courses inferiorly and medial to the sternocleidomastoid muscle, and is inserted in the lateral third of the clavicle [1, 3]. Nonetheless, variations in its origin have been described and it may arise from the sternocleidomastoid, anterior scalene and from the trapezius muscle [4], as it happens in this case.
Although it has no clinical significance, on rare occasions – as in gymnasts – it may cause thoracic outlet syndrome [2]. Angulations of the clavicle due to muscular hypertrophy have also been described [5].
Knowledge of this rare accessory vestigial skeletal muscle is important because it may be misidentified as a pathological finding, especially lymphadenopathy. [4]
Teaching Points:
Radiologist should be aware of this normal anatomical variant that may be misidentified as a cervical lymphadenopathy and that may be more prevalent that classical texts say.
Differential Diagnosis List
Right levator claviculae muscle and left supraclavicular lipoma.
Lymphadenopathy
Metastases
Aneurysms
Neurofibromas
Cysts
Venous thrombosis
Sternocleidomastoid muscle
Final Diagnosis
Right levator claviculae muscle and left supraclavicular lipoma.
