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International Journal of Recent Scientific Research
Vol. 5, Issue, 1, pp.05-07, January, 2014
International Journal
of Recent Scientific
Research
ISSN: 0976-3031
RESEARCH ARTICLE
UNUSUAL BILATERAL PRESENCE OF THIRD HEAD OF STERNOCLEIDOMASTOID
MUSCLE AND ITS CLINICAL SIGNIFICANCE - A CASE REPORT
Pushpa, MS and Nandhini, V
Department of Anatomy, Bangalore Medical College and Research Institute, Fort, Bangalore,
India- 560002
ARTICLE INFO
ABSTRACT
Article History:
The Sternocleidomastoid is a paired muscle o0f the neck which flexes and rotates the head.
It also serves as an accessory muscle of inspiration, along with the scalene muscles (Hasan,
2011). An accessory head of Sternocleidomastoid muscle was encountered bilaterally during
routine dissection of the head and neck region in a female cadaver around 60 years old.
Embryological basis for the supernumerary clavicular head may be the unusual separation or
division of mesoderm at the sixth branchial arch (Mehta V et al., 2012, Rani et al., 2011).
The Sternocleidomastoid muscle stays as an important landmark for anatomists, dental
surgeons, oncologists, orthopaedicians, neurosurgeons, plastic surgeons and anaesthetists in
many surgical procedures, knowledge of such variations will prevent major complications
during interventions in this region.
Received 12th, December, 2013
Received in revised form 22th, December, 2013
Accepted 11th, January, 2014
Published online 28th, January, 2014
Key words:
Sternocleidomastoid, accessory head, bilateral
variation
© Copy Right, IJRSR, 2014, Academic Journals. All rights reserved.
INTRODUCTION
Sternocleidomastoid is present in the cervical region, descends
obliquely across the side of the neck and serves as an important
landmark in dividing into anterior and posterior triangles (Mehta
et al., 2012). It is thick and narrow centrally, and broader and
thinner at each end. The muscle is attached inferiorly by two
heads.
 The medial or sternal head is rounded and tendinous,
arises from the upper part of the anterior surface of the
manubrium sterni and ascends posterolaterally.
 The lateral or clavicular head, which is variable in width
and contains muscular and fibrous elements, ascends
almost vertically from the superior surface of the medial
third of the clavicle.
The two heads are separated near their attachments by a
triangular interval which corresponds to a surface depression, the
lesser supraclavicular fossa. As they ascend, the clavicular head
spirals behind the sternal head and blends with its deep surface
below the middle of the neck, forming a thick, rounded belly.
Sternocleidomastoid inserts superiorly by a strong tendon into the
lateral surface of the mastoid process from its apex to its superior
border, and by a thin aponeurosis into the lateral half of the
superior nuchal line. The clavicular fibres are directed mainly to
the mastoid process; the sternal fibres are more oblique and
superficial, and extend to the occiput. The direction of pull of the
two heads is therefore different, and the muscle may be classed as
'cruciate' and slightly 'spiralized'.
The muscle is innervated by the spinal part of accessory nerve
along with branches from ventral rami of C2-3 and sometimes
ventral rami of C4 spinal nerves. It is vascularized by the branches
of suprascapular, superior thyroid, occipital and posterior
auricular arteries. Acting alone, the Sternocleidomastoid muscle
flexes the neck laterally and rotates the face to the opposite side.
Acting together, the muscle of two sides flexes the head and neck
forcibly (Williams et al., 1995). A wide mention of
supernumerary and accessory musculature has been made in the
anatomic, surgical, and radiology literatures. In majority of cases,
accessory muscles are asymptomatic and usually incidental
findings at surgery or imaging. However, sometimes accessory
muscles may produce clinical symptoms. These symptoms may
be related to a palpable swelling or compressive effect on
neurovascular structures (Sookur et al., 2008).
MATERIALS AND METHODS
During the routine cadaveric dissection for undergraduate
teaching in the Department of Anatomy, Bangalore Medical
College and Research Institute, Bangalore the presence of third
head or accessory head of Sternocleidomastoid was observed
bilaterally in a female cadaver around 60 years of age.
Case Report
Right Sternocleidomastoid - It had three heads.
1st head / sternal head had a rounded origin from anterior surface
of the manubrium sterni being 1.2 cms wide, got inserted to the
mastoid process and superior nuchal line of occipital bone with 3
cms width.
2nd head / clavicular head originated from superior surface of
medial one third of clavicle, 2.5cms from the sternal end of
clavicle measuring about 1.4 cms in breadth. Before insertion it
merged with deeper surface of the sternal head at a distance of 4
cms from clavicle and got attached to the mastoid and occiput
deep to the sternal head.
3rd head / accessory clavicular head which had its origin from
superior surface of clavicle, 4.5 cms from the sternal end of
clavicle about 0.5 cm wide, it merged with sternal head above the
* Corresponding author: Pushpa, MS
Department of Anatomy, Bangalore Medical College and Research Institute, Fort, Bangalore, India- 560002
International Journal of Recent Scientific Research, Vol. 5, Issue, 1, pp.05-07, January, 2014
clavicular head at a distance of 4 cms from the clavicle, then it got
attached to the superior nuchal line for insertion corresponding to
the fibres of sternal head. At the fusion of the clavicular heads
with the sternal head it was 2.5 cms wide.
attached to the superior nuchal line for insertion corresponding to
the fibres of sternal head. At the fusion of the clavicular heads
with the sternal head it was 2.6 cms wide.
Medial lesser supraclavicular fossa - the depression was between
1st and 2nd heads, base about 1.5 cm and height of about 4.6 cms
on either side. Internal jugular vein was found in the triangle.
Lateral / additional lesser supraclavicular fossa - the depression
was between 2nd and 3rd heads, base about 0.7 cm and height of
about 5.3 cms on either side. Spinal accessory nerve was found
between 1st and 3rd heads on the superficial aspect and 2nd head on
the deeper aspect and supplied the three heads.
Fig 1 Bilateral presence of third head of SCM (SCM –
Sternocleidomastoid)
Medial lesser supraclavicular fossa - the depression was between
1st and 2nd heads, base about 0.8 cm and height of about 3.2 cms
on either side. Internal jugular vein was found behind the second
head.
Lateral / additional lesser supraclavicular fossa - the depression
was between 2nd and 3rd heads, base about 0.6 cm and height of
about 3.6 cms on either side. Spinal accessory nerve was found
between 1st and 3rd heads present superficially and 2nd head on its
deeper aspect and supplied the three heads.
Fig 3 Spinal accessory nerve
DISCUSSION
Variations in the Sternocleidomastoid are seen usually at its
origin, found rare at its insertion. It may cause different clinical
conditions limiting the function of neck. The Sternocleidomastoid
may consist of five parts in two layers (superficial and deep
layers), out of these five parts the superficial layer consists of
superficial sternomastoid, sterno-occipital, and cleido-occipital
parts. Deep layer have sternomastoid and cleidomastoid parts.
Comparative studies in mammals have demonstrated that the
Sternocleidomastoid muscle frequently separated into above five
parts which are arranged in two layers. The fusion of these two
muscles is considered to be a normal feature (Bergman et al.,
1988). In a study, bipartite clavicular attachment of the
Sternocleidomastoid in the neck of an adult male cadaver was
reported. It was observed unilaterally on the left side of the neck,
where the clavicular head of the muscle exhibited two bellies, one
medial and one lateral. While the medial belly was fused with the
sternal head, the lateral belly appeared to blend with the medial.
Cranially, the Sternocleidomastoid attached to the mastoid process
and superior nuchal line. (Mehta V et al., 2012). The accessory
muscle can be confused with soft tissue masses such as
lymphadenopathies and venous thromboses during physical
examination (Fazliogullari Z et al., 2010).
Left Sternocleidomastoid – It had three heads.
1st / sternal head origin was rounded from the anterior surface of
the manubrium sterni measuring about 0.6 cm in width, inserted
to the mastoid process and superior nuchal line of occipital bone
at a breadth of 3 cms.
Fig 2 Left SCM with the supraclavicular fossas. (IJV – Internal Jugular
Vein, MSCF – Medial Supraclavicular Fossa, LSCF – Lateral
Supraclavicular Fossa)
In another study the additional third head originated from the
middle third of the clavicle and joined the normal two heads
(sternal and clavicular) of the muscle in the middle of the neck.
The insertion and nerve supply of the muscle was normal. The
additional head covered the major neurovascular structures in the
subclavian triangle (Cherian SB & Nayak S, 2008). Additional
slip of clavicular head was observed bilaterally creating one more
surface depression, the additional lesser supraclavicular fossa. The
additional slip was also supplied by a branch from the spinal part
of the accessory nerve (Rao et al., 2007). The surgeons should be
aware of the presence of such additional slips while performing
2nd head / clavicular head originated from superior surface of
medial one third of clavicle, 3.7 cms from the sternal end of
clavicle measuring about 0.5 cm in width. Before insertion it
merged with deeper surface of the sternal head at a distance of 7
cms from clavicle and got attached to the mastoid and occiput
deep to the sternal head.
3rd head / accessory clavicular head originated from superior
surface of clavicle, 5 cms from the sternal end of clavicle, it was
0.9 cm wide. Before insertion it merged with sternal head above
the clavicular head at about 7.5 cms from the clavicle, then it got
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International Journal of Recent Scientific Research, Vol. 5, Issue, 1, pp.05-07, January, 2014
References
surgeries in head and neck regions as these can be used as
myocutaneous flaps without disturbing the normal morphology of
muscle (Rani et al., 2011).
1.
Hasan, T. 2011. Variations of the Sternocleidomastoid
Muscle: A Literature Review. The Internet Journal of
Human Anatomy. 1 (1),
2. Mehta, V.; Arora, J.; Kuma, A.; Nayar, A. K.; Ioh, H.
K.; Gupta, V.; Suri, R.K.; Rath, G. 2012. Bipartite
clavicular attachment of the sternocleidomastoid muscle:
a case report. Anatomy and Cell Biology. 45, 66-69.
3. Rani, A.; Srivastava, A. K.; Rani, A.; Chopra, J. 2011.
Third head of sternocleidomastoid muscle. International
Journal of Anatomical Variations. 4, 204-206.
4. Williams, P. L.; Bannister, L. H.; Berry, M. M.; Collins,
P.; Dyson, M.; Dussek, J. E.; Ferguson, M. W. J. 1995.
Gray's Anatomy. 38th ed. Baltimore, Churchill
Livingstone. 804-5.
5. Sookur, P. A.; Naraghi, A.M.; Bleakney, R.R.; Jalan, R.;
Chan, O.; White, L.M. 2008. Accessory Muscles:
Anatomy, Symptoms, and Radiologic Evaluation.
Radiographics. 28, 481–499.
6. Bergman, R. A.; Thomson, S. A.; Afifi, A. K.; Saadeh,
F. A. 1988. Compendium of Anatomic Variation, In:
Muscles. Baltimore, Urban and Schwarzenberg. 32-33.
7. Fazliogullari, Z.; Cicekcibasi, A.E.; Dogan, N.U.;
Yilmaz, M.T.; Buyukmumcu, M.; Ziylan, T. 2010. The
levator claviculae muscle and unilateral third head of the
sternocleidomastoid muscle: case report. International
Journal of Morphology. 28, 929-932.
8. Cherian, S. B.; Nayak, S. 2008. A rare case of unilateral
third head of sternocleidomastoid muscle. International
Journal of Morphology. 26(1), 99-101.
9. Rao, T.R.; Vishnumaya, G.; Prakashchandra, S.K.;
Suresh, R. 2007. Variation in the origin of
sternocleidomastoid muscle. A case report. International
Journal of Morphology. 25, 621–623.
10. Sirasanagandla, S. R.; Bhat, K. M. R.; Pamidi, N.;
Somayaji, S. N. 2012. Unusual third head of the
sternocleidomastoid muscle from the investing layer of
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30(3), 783-785.
11. Kumar, M.S.; Sundaram, S.M.; Fenn, A.; Nayak, S.R.;
Krishnamurthy, A. 2009. Cleido-occipital platysma
muscle: a rare variant of sternocleidomastoid muscle.
International Journal of Anatomical Variations. 2, 9-10.
Embryology
During the development, Sternocleidomastoid and trapezius
muscles share a common premuscle mass from the last two
occipital and upper cervical myotomes. This muscle mass splits
and separates at 9 mm stage of development (Sirasanagandla, S. R
et al., 2012). This myotome segregates into the ventral
Sternocleidomastoid and dorsal trapezius. The trapezius and
Sternocleidomastoid arises from a common pre-muscle mass in
the occipital region just caudal to the sixth branchial arch.
Therefore, occasionally the margins of these two muscles make
contact with each other. Moreover, HOX D4 and somitic
mesoderm contributes to the development of these muscles where
they are connected to skeletal elements only by posterior otic
neural-crest derived connective tissue. Since HOX D4 and
somites contribute muscle cells to branchial neck muscles, these
myoblasts seem to associate with neural-crest derived muscular
connective tissue (Kumar et al., 2009).
Significance
The Sternocleidomastoid has many vital structures lying under its
cover, like the common carotid artery, accessory nerve, brachial
plexus roots, cervical plexus nerves and lymph nodes (Hasan T,
2011). An accurate and appropriate anatomical knowledge for
anaesthetists is mandatory before attempting a central venous
catheterisation approach for internal jugular vein cannulation. The
presence of an additional clavicular belly narrows the minor
supraclavicular fossa of the neck, leading to cumbersome internal
jugular vein cannulation. This difficulty during cannulation can
accidentally puncture the neighbouring neurovascular structures
thereby leading to haematoma formation or resulting in neural
deficits. (Mehta V et al., 2012).
CONCLUSION
Presence of the abnormal muscles in the neck is not very
common. In most cases, these muscles go unnoticed as they do
not produce any symptoms in the individual. These abnormal
muscles may cause functional deficits by compressing the
neurovascular structures. Plastic surgeons, orthopaedicians and
dental surgeons should be aware of these variations while taking
muscle flap in reconstructive surgeries.
Acknowledgements
Authors are grateful to Dr. Priya Ranganath, Professor & HOD
and to all staffs of department of Anatomy, BMCRI, Bangalore.
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