Anterior Neck & Thorax LabLink

Anterior Neck & Thorax

Dissection Summary

Locate and identify the relevant osteological features

Find these structures:

  • Humerus
    • Crest of greater tubercle
  • Clavicle
  • Scapula
    • Coracoid process
  • Hyoid
  • Sternum
    • Manubrium
      • Suprasternal notch
    • Sternal angle
    • Xiphoid process
  • Cranium
    • Cranial base
      • Jugular foramen
    • Temporal bone
      • Mastoid process

Remove the skin from the anterior thoracic wall

1.) Prepare for the removal of skin and subcutaneous tissue from three areas of the anterior thorax:

Photo 1. Procedural: planned thoracic incision lines

Midsagittal Incision

  • Palpate from the donor’s suprasternal notch to the xiphoid process. Make a midsagittal incision along this line.

Note: The midsagittal incision is unlikely to jeopardize any deep structures (e.g. muscles or neurovasculature), but take caution when performing transverse/oblique incisions not to cut muscle.

Transverse/Oblique Incisions

  • Area One
    • Superior Incision: Incise from the suprasternal notch. Continue laterally along the clavicle to the acromioclavicular joint.
    • Inferior Incision: Incise from the sternal angle (where rib 2 articulates with the sternum), and extend laterally to the midaxillary line

Note: The 2nd rib is the most superior palpable rib. The sternal angle is at the level of the 2nd costal cartilage.

  • Area Two
    • Inferior Incision: Incise from the 5th intercostal space (or more inferiorly to encompass the entirety of the breast), and laterally to the midaxillary line.
  • Area Three
    • Inferior Incision: Incise from the xiphoid process, following the costal margin, inferolaterally to the midaxillary line.

Note: Superficial fascia (hypodermis, subcutaneous tissue) separates the skin from muscles and often contains neurovasculature (nerve, artery, vein, and lymphatics). Depending on the dissection, you may be asked to either remove the skin (‘skinning’), or remove both the skin and subcutaneous tissue.

Photo 2. Procedural: 'skinning'

Note: When removing large areas of superficial tissues, it may be helpful to create an incision in the reflected skin and subcutaneous tissue through which a finger or tool can be inserted (‘button hole’) to facilitate the removal of superficial tissues.

Photo 3. Procedural: removal of both skin and subcutaneous tissue

2.) Dissection of Area One:

Remove the skin and subcutaneous tissue from Area One. Work from the midline laterally. Once reflected, the superior portion of pectoralis major m. should be visible.

Photo 4. Procedural: Area One

Note: Upon removal of the skin and subcutaneous tissue, anterior and lateral cutaneous neurovascular bundles may be seen leaving the muscle and entering the subcutaneous tissue.

Note: Be careful to not damage the cephalic v. in the deltopectoral triangle, superolateral to pectoralis major m.

Note: The deltopectoral triangle is bounded superolaterally by the deltoid m., superomedially by the clavicle, and inferiorly by the pectoralis major m.

Photo 5. Cephalic vein in deltopectoral triangle

3.) Dissection of Area Two:

Make an encircling cut around the nipple and areola down to, but not through pectoralis major m., and leave in situ for future reference. Remove the skin and subcutaneous tissue to further expose the pectoralis major m.

Note: The nipple is typically located at the 4th intercostal space. This landmark can help in orientation for future dissections. If difficult to dissect or to keep in place, the nipple can be removed.

Photo 6. Procedural: nipple and areola

4.) Dissection of Area Three:

Remove the skin and subcutaneous tissue in Area Three. The external oblique m. and aponeurosis and the rectus sheath will be deep. A small portion of the serratus anterior m. should be visible laterally.

Photo 7. Procedural: Area Three

Clean the pectoralis major and serratus anterior mm., and find the cephalic v.

Find these structures:

  • Pectoralis major m.
  • Cephalic v.
  • Serratus anterior m.
  • Long thoracic n.

5.) Remove any remaining subcutaneous tissue and investing fascia from the pectoralis major mm. and the visible portion of the serratus anterior mm. Remove the investing fascia from the muscle via sharp dissection (sharp sharp scissors) at right angles to the muscle fascicles. This will allow the visualization of basic features of a muscle: fiber directions and attachments.

Note: Muscles are covered with investing fascia that is relatively opaque and firmly attached to the muscle. The thickness of this layer varies in different parts of the body.

Photo 8. Investing fascia

6.) Observe attachments of pectoralis major mm. and serratus anterior mm.

Photo 9. Pectoralis major and serratus anterior mm.

7.) Identify the long thoracic n. on the superficial portion of the serratus anterior m.

Note: The long thoracic n. forms from branches of VPRs of C5-C7; it is unique in its course superficial to the muscle, making it prone to injury.

8.) Locate the cephalic v. in the deltopectoral triangle. Keep this vein intact during reflection of the pectoralis major m.

Note: The cephalic v. drains lateral components of the superficial upper limb into the axillary v.

Photo 10. Cephalic vein and deltopectoral triangle

Reflect pectoralis major mm., and identify pectoralis minor mm. and associated neurovasculature.

Find these structures:

  • Pectoralis minor m.
  • Lateral pectoral n.
  • Medial pectoral n.
  • Thoraco-acromial a. (pectoral brs.)

9.) Reflect the pectoralis major mm. from their proximal attachments (clavicle and sternum/costal cartilages). Use blunt dissection to reflect the muscle laterally to protect the deep neurovasculature.

Note: To reflect muscle, cut a portion of a muscle, and fold it back on itself to reveal deep structures. Reflection may be completed by severing the proximal or distal attachments, or by cutting through the belly of the muscle, as specified. Use blunt dissection methods to further reflect the cut muscle.

Photo 11. Procedural: how to reflect a muscle

Photo 12. Procedural: pectoralis major m. incision

Photo 13. Procedural: pectoralis major m. reflected

Note: Neurovasculature lies immediately deep to the clavicular head of pectoralis major m.

10.) Bilaterally identify and clean the pectoralis minor m., lateral pectoral n., medial pectoral n., and branches of the thoraco-acromial a and v.

Note: The medial pectoral n. innervates both the pectoralis major and minor mm. It typically pierces the pectoralis minor m., which can be helpful for differentiating between the 2 nerves. The medial pectoral n. may emerge as two branches (either through or inferolateral to pectoralis minor m.).

Note: The lateral pectoral n. only innervates the pectoralis major m. and is typically located superomedial to the medial pectoral n. If you find the names confusing, keep in mind they reflect the origins of these nerves from the brachial plexus, not their anatomical relationships in this region.

Photo 14. Medial and lateral pectoral nn.

Note: There are numerous branches of the thoraco-acromial a.: acromial, clavicular, deltoid, and pectoral branches. The pectoral branches serve and are found deep to pectoralis major and minor mm.

Photo 15. Thoracoacromial a. and v., pectoral branches and lateral pectoral n.

Reflect pectoralis minor mm. to identify neurovasculature

Find these structures:

  • Medial pectoral n.
  • Thoraco-acromial a.

11.) Reflect the pectoralis minor mm. from their proximal attachments (3rd-5th ribs). Reflect the muscles superolateral (toward the coracoid process of the scapula). Locate any remaining clavipectoral fascia.

Note: Four main structures pierce the clavipectoral fascia superior to pectoralis minor m.: cephalic v., lateral pectoral n., and thoraco-acromial aa. and vv.

12.) Observe pectoral branches of the thoraco-acromial a. and the medial pectoral n.

Photo 16. Pectoralis minor muscle, reflected

Remove the skin from the anterolateral cervical region

Find these structures:

  • Superficial vv.
    • External jugular v.

13.) Remove the skin of the neck from the base of the mandible, posteriorly to the mastoid process of the skull, inferiorly to the clavicle, and medially to the midline. Retain the (deep) subcutaneous layer, and take care not to damage the external jugular v.

Photo 17. Procedural: Planned cervical incisions

Photo 18. How to skin (leaving subcutaneous tissue) with tools

Note: The superficial veins of the neck, named for their relative position to the deep fascia of the neck, are extremely inconstant in size, appearance, and connection.

Note: The external jugular v. (EJV) is typically the most obvious superficial vein of the neck. The EJV is formed by the junction of the posterior division of the retromandibular v. and the posterior auricular v. The EJV runs superficial to the sternocleidomastoid m. (SCM), and drains into the subclavian v. lateral and deep to the SCM.

Photo 19. Superficial veins

Locate the neck muscles and ‘cervical triangles’

Find these structures:

  • Sternocleidomastoid m.
  • Anterior cervical triangle
  • Accessory n. (CN XI)

14.) Locate and carefully clean the sternocleidomastoid (SCM) mm. Palpate the base of the mandible. Using these muscles and skeletal landmark, identify the anterior cervical triangles.

Note: The anterior cervical triangle is bounded medially by the midline, laterally by the anterior border of the SCM, and superiorly by the base of the mandible.

Photo 20. Anterior cervical triangle

15.) Reflect the sternocleidomastoid m. from its attachments to the sternum and clavicles. Reflect the SCM superiorly and laterally to see deeper structures, specifically the accessory n. (CN XI).

Photo 21. SCM reflected, omohyoid intact and cleaned

Note: Trapezius and SCM mm. are both efferently (motor) innervated by the accessory n. (CN XI). The accessory n. is strictly efferent; therefore, afferent supply to these muscles comes from ventral primary rami of cervical nerves (C2-C4). Typically, C2-C3 (sometimes C4) afferently serve the SCM, whereas C3-C4 afferently serve the trapezius. It is likely that C2-C4 also carry some motor fibers.

Photo 22. Accessory n. (CN XI)

Find these structures:

  • Infrahyoid (strap) mm.
    • Sternohyoid m.
    • Omohyoid m.
      • Superior belly
      • Inferior belly
    • Sternothyroid m.
    • Thyrohyoid m.

16.) Palpate the hyoid bone. Locate and carefully clean the superficial infrahyoid (strap) mm. Be careful to preserve branches of the ansa cervicalis, which innervate these muscles.

Note: The hyoid bone is U-shaped and suspended from the styloid processes of the temporal bones via stylohyoid ligaments. It superiorly supports the larynx via the thyrohyoid ligament, and serves as an attachment for muscles of the extrinsic tongue (geniohyoid m., hyoglossus m.), pharynx (middle pharyngeal constrictor m., stylohyoid m.), suprahyoid region (mylohyoid m.), and infrahyoid region (sternohyoid m., thyrohyoid m., omohyoid m.).

Note: Infrahyoid (strap) muscles largely occupy the area inferior to the hyoid, superior to the sternum, and medial to the carotid sheaths (excepting the inferior belly of the omohyoid). The infrahyoids may be classified into two groups: superficial (sternohyoid mm. & omohyoid mm.) and deep (sternothyroid mm. & thyrohyoid mm.). To help in locating individual infrahyoid mm., understand they are named for their attachments.

Photo 23. Superficial infrahyoid (strap) mm.

17.) Relieve the fascial sling connecting the intermediate tendon of the omohyoid m. to the clavicle (on one side only).

18.) Bluntly separate the right and left sternohyoid mm. On the ipsilateral side of the free omohyoid, superiorly reflect the sternohyoid m. to reveal deeper structures.

Photo 24. Deep infrahyoid mm.

Locate the carotid sheath, and examine its contents

Find these structures:

  • Cervical Plexus
    • Ansa cervicalis
  • Common carotid artery
    • Carotid bifurcation
      • External carotid a.
      • Internal carotid a.
  • Internal jugular v.
  • Vagus n. (CN X)

19.) Locate the carotid sheath deep to the sternocleidomastoid m. and lateral to the infrahyoid mm. Locate the ansa cervicalis superficial to (or within) the carotid sheath.

Note: The ansa cervicalis is a delicate loop of nerve consisting of two limbs: a superior limb (C1), and an inferior limb (C2,3). The superior limb is proximally associated with the hypoglossal n. (CN XII), as fibers of the ventral primary ramus of C1 ‘hitchhike’ along the hypoglossal n., before rejoining the superior limb. Keep in mind that nerves are collections of axons in the peripheral nervous system, and that these axons may move among different nerves on their way to or from target tissues. The ansa cervicalis innervates nearly all infrahyoid mm. (excepting the thyrohyoid m.). The thyrohyoid m. is innervated by fibers from C1 that also hitchhike along the hypoglossal n. and exit distal to the superior limb of ansa.

Note: The limbs of the ansa cervicalis lie upon (and sometimes within) the carotid sheath. The ansa may be located by following its branches from the infrahyoid mm. back to the ansa loop, and then carefully (bluntly) dissecting the limbs from the carotid sheath.

Photo 25. Ansa cervicalis

20.) Open the carotid sheath to reveal its contents.

Note: The carotid sheath is a collection of deep cervical fascia surrounding the:

  • proximal portion of the internal carotid a.,
  • common carotid a.,
  • internal jugular v.,
  • vagus n. (CN X),
  • and sometimes the ansa cervicalis.

Note: Areolar connective tissue binds the carotid sheath to adjacent structures and their fasciae, and often may adhere ansa cervicalis to the sheath. The cervical sympathetic chain may be found immediately posteromedial to the carotid sheath.

Note: Within and around the carotid sheath, you may notice deep lateral cervical lymph nodes. These nodes are divided into a superior and an inferior group (named relative to their position to the omohyoid m). The deep lateral cervical nodes are closely associated with the internal jugular v. Lymph is conducted from the superior deep cervical nodes to the inferior deep cervical nodes before entering the jugular trunk.

Photo 26. Superior and deep lymph nodes

Photo 27. Carotid sheath contents

21.) Follow the common carotid a. superiorly to the carotid bifurcation, where the common carotid becomes the internal and external carotid arteries.

Note: The common carotid artery is an important pulse palpation location.

Note: The internal carotid has no branches in the neck. It travels to the cranium, where it is transmitted through the carotid canal, and supplies blood to the brain, orbit, and forehead.

Note: The external carotid a. is the primary source of blood to the face and superficial head.

Photo 28. Carotid bifurcation

Locate the thyroid gland and associated neurovasculature

Find these structures:

  • Thyroid gland
    • Lobes
    • Isthmus
  • Parathyroid glands
  • External carotid artery
    • Superior thyroid a.
  • Inferior thyroid a.
  • Internal Jugular v.
    • Superior thyroid v.
    • Middle thyroid v.
  • Inferior thyroid v.

22.) On the ipsilateral side as the previously dissected sternohyoid m., reflect the sternothyroid m. superiorly, above the oblique line of the thyroid cartilage.

Photo 29. Procedural: reflecting the sternothyroid m.

23.) Clean the pre-tracheal fascia from the thyroid gland, and observe the venous drainage of the gland.

Photo 30.Thyroid gland

Note: The richly vascularized thyroid gland is typically drained via three sets of veins:

  • superior thyroid vv., typically drain into the internal jugular vv.,
  • middle thyroid vv., typically drain into the internal jugular vv., and
  • inferior thyroid vv., typically drain into the left brachiocephalic v.

Photo 31. Thyroid vv.

24.) Locate the superior thyroid a. and follow it to the thyroid gland, noting its branch, superior laryngeal a.

Note: The superior thyroid a. is the first branch of the external carotid a.

25.) Make a midsagittal cut through the isthmus of the thyroid gland. Carefully reflect either lobe of the thyroid gland to locate parathyroid glands and the inferior thyroid artery. Follow the inferior thyroid a. to the thyrocervical trunk.

Photo 32. Inferior thyroid a.

Note: Parathyroid glands may be found in a variety of locations, but are typically on the posterior aspect of the thyroid gland. There are typically four parathyroid glands (a superior pair and inferior pair), but there may be more or fewer. The superior parathyroid glands are the most constant in size and position. These glands may be supplied by either set of thyroid arteries (as determined by location), but typically the dominant supply is the inferior thyroid aa.

Photo 33. Parathyroid glands & inferior thyroid a.