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The given case scenario and paradoxical elevation of the left dome of the diaphragm on inspiration are suggestive of left phrenic nerve palsy. The left phrenic nerve runs anterior to the scalenus anterior.

The course of the left phrenic nerve:

Cervical region - both phrenic nerves pass,

• Anterior to scalenus anterior muscle
• Posterior to sternocleidomastoid and inferior belly of omohyoid
• Posterior to internal jugular vein, transverse cervical artery, and suprascapular artery
• Posterior to the thoracic duct on the left

Root of the neck - It lies medial to the trunks of the brachial plexus in the neck. At the root of the neck, it runs anterior to the second part of the subclavian artery and posterior to the subclavian vein.

Thorax - The phrenic nerve enters the thorax by crossing medially in front of the internal thoracic artery. Within the thorax, the phrenic nerve descends anterior to the pulmonary hilum between the fibrous pericardium and mediastinal pleura, accompanied by the pericardiacophrenic vessels.

Superior intercostal artery is a branch of the costocervical trunk.

It descends in front of the neck of the first 2 ribs and gives rise to the first two posterior intercostal arteries.

The artery is not constant and is more common on the right. When it is absent, it is replaced by a direct branch from the aorta.

Each of the upper 9 intercostal spaces has 2 anterior intercostal arteries and 1 posterior intercostal artery.

The 10th and 11th intercostal spaces have no anterior intercostal artery and 1 posterior intercostal artery.

Anterior intercostal arteries arise from the following:

• Internal thoracic artery - Upper 6 spaces
• Musculophrenic artery - 7th to 9th spaces

Anterior intercostal arteries anastomose with the respective posterior intercostal arteries and their collaterals. They are shorter than the posterior intercostal arteries.

Posterior intercostal arteries are not branches of the internal thoracic artery, hence there would be no decrease in blood supply through these arteries.

Branches of the internal thoracic artery:

• Terminal branches at the level of the 6th intercostal space:
• Superior epigastric artery
• Musculophrenic artery
• Sternal branches to:
• Transversus thoracis muscle
• Periosteum of the posterior sternal surface
• Sternal red bone
• Anterior intercostal arteries for the first 6 intercostal spaces.
• Perforating branches that pierce and supply pectoralis major and then become direct cutaneous vessels that supply the skin.

Rib notching occurs due to enlargement of the posterior intercostal arteries. This is seen in coarctation of aorta.

There are 11 pairs of posterior intercostal arteries, and these supply up to the costochondral junction. The first 2 pairs are branches of the superior intercostal artery, a branch of

the costocervical trunk. They are distributed to upper 2 intercostal spaces. The lower 9 pairs are branches of the descending thoracic aorta, which lies to the left of the vertebral column. Hence, the right posterior intercostal arteries are longer than those on the left.

Clinical significance:

Coarctation of the aorta is a congenital heart disease, causing narrowing of the aorta. Chest x-ray shows rib notching and enlargement of left subclavian artery.

The blood flow to the lower limb is maintained by intercostal and superior epigastric arteries.

In the post-ductal coarctation of the aorta, an extensive collateral circulation develops from the following sources:

• Axillary artery - The branches involved are:
• Thoraco-acromial
• Lateral thoracic
• Subscapular
• Subclavian artery - The enlarged branches are:
• Suprascapular
• Costocervical trunk (1st and 2nd posterior intercostals)
• Internal thoracic arteries
• Costocervical trunk
• Posterior intercostal arteries
• Inferior epigastric arteries

The internal thoracic arteries give rise to:

• Anterior intercostal arteries that carry blood to the posterior intercostals (3rd-6th) and thence into the descending aorta
• Superior epigastric arteries that anastomoses with the inferior epigastric (in the rectus sheath)
• and sends blood into the external iliac artery and thence towards the lower limb.

High vascularity is observed in the anterior thoracic wall as well as over the posterior thoracic wall especially in the interscapular area.

The scapular anastomosis is opened up and both scapulae become pulsatile.

Radiographic evidence of "rib notching" is seen in the inferior margins of the rib due to greatly enlarged posterior intercostal arteries. Also, the radiographic shadow of the enlarged left subclavian artery is quite evident clinically.

Lower limb may be supplied by the channels:

• Arch of aorta—subclavian artery—internal thoracic artery—superior epigastric artery—inferior epigastric artery—iliac artery—pelvis and lower limb.
• Arch of aorta—subclavian artery—internal thoracic artery—anterior intercostal artery—posterior intercostal artery—descending thoracic aorta—thorax, abdomen, pelvis, lower limb.
• Arch of aorta—subclavian artery—vertebral artery—anterior spinal artery—segmental artery—thoracic and abdominal aorta—thorax—abdomen, pelvis, lower limb.

The left first posterior intercostal vein is not a tributary of the left superior intercostal vein.

On both sides, the first posterior intercostal vein drains into the brachiocephalic or vertebral vein. On the right side:

• The 2nd, 3rd, and often the 4th posterior intercostal veins form the right superior intercostal vein, which drains into the arch of the azygos vein.
• The lower spaces drain directly into the azygos vein.
• On the left side:
• The 2nd, 3rd and sometimes 4th posterior intercostal veins form left superior intercostal vein which drains into the left brachiocephalic vein.
• The 4th or 5th to 8th posterior intercostal veins drain into the accessory hemiazygos vein.
• The 9th to 11th posterior intercostal veins drain into the hemiazygos vein.

The structures marked A are the right and left brachiocephalic veins. The left superior intercostal vein drains into the left brachiocephalic vein.

Tributaries of the brachiocephalic vein:

• Left and right internal thoracic veins
• Left and right inferior thyroid veins
• Left superior intercostal vein drains into the left brachiocephalic vein.

The right superior intercostal vein drains into the azygos vein. Hemizygous vein drains into the azygous vein. (Option A)

Superior thyroid veins drain directly into internal jugular veins. (Option B) Right superior intercostal vein drains into the azygous vein. (Option C)

Superficial epigastric and iliolumbar veins do not help to drain the blood in inferior vena caval (IVC) obstruction as they drain into the IVC itself. Iliolumbar veins drain directly into the IVC and superficial epigastric vein drains via the femoral vein.

In IVC obstruction, the collateral channels open up to drain the blood from the lower limb into the superior vena cava (SVC) and then to the heart.

The main collateral channels are via azygous and hemizygous veins and vertebral venous plexuses. They communicate with the common iliac veins by the ascending lumbar veins and tributaries of the inferior vena cava. Additionally, blood is also drained by inferior epigastric veins gt; superior epigastric veins gt; internal thoracic veins gt; brachiocephalic veins gt; superior vena cava.

In the given case scenario of an inhaled foreign body, it is most likely to lodge into the right bronchus. The right bronchial veins drain to the azygos vein.

Left bronchial veins drain into the accessory hemiazygos vein or left superior intercostal vein.

Clinical significance:

The right principal bronchus is wider, shorter, and more vertical. This is why an inhaled foreign body is more likely to lodge there. Also, the tracheal bifurcation directs the foreign body to the right lung

The hemiazygos vein crosses from the left to the right side at the level of T8 vertebrae.

The mediastinum is divided into superior and inferior by a line joining sternal angle to the T4-T5 intervertebral disc.

The sternal angle lies between the T4 vertebra and the upper half of the T5 vertebra in the majority of adults.

Sternal plane:

• Extent:
• Anteriorly - Manubriosternal joint (sternal angle or angle of Louis) at second costal cartilage.
• Posteriorly- intervertebral disc between the T4-T5 vertebrae
• Separates superior mediastinum from the inferior mediastinum.
• Anatomical landmark for:
• Superior limits of the pericardium
• Bifurcation of the pulmonary trunk
• Origin of the aortic arch
• The site where the superior vena cava penetrates the pericardium to enter the right atrium

The trachea lies in the superior mediastinum.

Thymomas are tumors of the thymus gland and are associated with myasthenia gravis. The thymus occupies the superior and anterior mediastinum.

The esophagus is present in the posterior mediastinum. The esophagus enters the superior mediastinum and lies between the trachea anteriorly and the vertebrae posteriorly. Inferiorly, it continues into the posterior mediastinum, passes through the diaphragm, and opens into the stomach.

Option A - The thymus is present in the superior and anterior mediastinum. Option B - The ascending aorta is present in the middle mediastinum.

Option D - The tracheal bifurcation is present in the middle mediastinum.

The correctly matched structures are -

Structure

A. Left subclavian artery 2.

B. Hemiazygos vein 3.

C. Phrenic nerve 4.

D. Sternopericardial ligament 1.

s

Location

Superior mediastinu m

Posterior mediastin um

Middle mediastinum

Anterior mediastinu m

The given case scenario is suggestive of laryngocele. The defect is present in the saccule, represented by the area marked A in the above diagram.

The structures marked are:

B. Ventricle

C. Vestibular ligament

D. Vocal ligament

The saccule is a pouch that ascends forwards from the anterior end of the ventricle, between the vestibular fold and thyroid cartilage.

It is conical in shape and contains around 60 and 70 mucous glands, sited in the submucosa.

It is separated from the thyroid cartilage by the thyroepiglotticus muscle which compresses the saccule. On compression, the secretions of the saccule are released into the vocal cords (which lack mucous glands) to lubricate and protect them from desiccation and infection.

Clinical significance:

Laryngocele is an air-filled cystic swelling due to dilatation of the saccule. It is seen in trumpet players, glass-blowers, or weight lifters due to raised trans-glottic air pressure. It can be internal, external, or combined.

External laryngocele presents as a reducible swelling in the neck which increases in size on coughing or performing Valsalva maneuver.

Internal laryngocele is managed by marsupialization and surgical excision through an external neck incision done for external laryngocele.

The vestibular ligament is enclosed within the false vocal cords. The lower free margin of the quadrangular membrane is thickened to form the vestibular ligament.

False vocal cords: These are formed by the vestibular folds. They contain the vestibular ligament, a few fibers of thyroarytenoideus muscle, and mucous glands.

True vocal cords: They extend from the middle of the thyroid angle to the vocal processes of arytenoids. They contain the vocal ligament and subepithelial connective tissue.

The upper free margin of the cricovocal ligament/cricothyroid membrane/conus elasticus is thickened to form the vocal ligament.

The given image shows an endoscopic view of the vocal cords.

Thyroarytenoid muscles cause relaxation of the vocal cords and closure of the rima glottidis.

The nerve which is closely related to the course of the superior thyroid artery is the external laryngeal nerve. Injury to this nerve causes paralysis of the cricothyroid muscle. It is the main tensor of the vocal cord and paralysis of this muscle leads to the decreased pitch of voice.

The internal laryngeal nerve pierces the thyrohyoid membrane at a higher level than the superior thyroid artery. Hence this nerve is not injured and the sensation above the level of vocal cords is preserved.

Except for the cricothyroid, other intrinsic muscles of the larynx are supplied by the recurrent laryngeal nerve. Hence they are not paralyzed in the above clinical scenario.

The weight of the upper limb is transmitted to the axial skeleton by coracoclavicular and costoclavicular ligament.

The weight of the upper limb is transmitted as follows:

Upper limb ⇒ coracoclavicular ligament ⇒ clavicle ⇒ costoclavicular ligament ⇒ axial skeleton

(sternum and 1st rib) Manubrium sterni ⇒ Sternoclavicular ligament ⇒ clavicle.

Note:

• Costoclavicular ligament: Transmits weight of the upper limb to the axial skeleton via the clavicle.
• Coracoclavicular ligament: Transmits weight of the upper limb to the clavicle.
• Sternoclavicular ligament : Transmits weight of the upper limb to axial skeleton via clavicle

(inferomedially)

The structure marked A is the intertubercular sulcus (bicipital groove) and the latissimus dorsi is attached to its floor.

The intertubercular sulcus (bicipital groove) lies between the greater and lesser tubercles.

The attachments of bicipital groove are as follows:

• Lateral lip: Pectoralis major
• Medial lip: Teres major
• Floor: Latissimus dorsi

The contents of the sulcus are as follows:

• Long head of the biceps
• ascending branch from the anterior circumflex humeral artery
• MEMORY TIP:

Remember 'Lady between two majors': The lady (latissimsus dorsi), in the intertubercular sulcus, lies between the pectoralis major laterally, and teres major medially.

The sternoclavicular joint is a synovial sellar (saddle, or hyperbolic paraboloid) joint, and not a hinge joint.

It is the only skeletal articulation between the upper limb and the axial skeleton.

As mobility increases, stability is lost in a joint. The glenohumeral joint is the most mobile joint in the body and is very unstable.

The glenohumeral joint is the most frequently dislocated joint in the body. The shoulder dislocation occurs more commonly in adults and is rare in children. Anterior dislocation is much more common than a posterior dislocation.

Teres major has no role in maintaining the stability of the shoulder joint.

The shoulder joint is a ball and socket joint. Since the head of the humerus is larger than the glenoid cavity, it is often prone to displacement. However, the stability of the shoulder joint is provided by the following:

• Rotator cuff: It is formed by blending of tendons of 4 muscles (SITS)-
• Supraspinatus
• Infraspinatus
• Teres minor
• Subscapularis
• Tendon of the long head of biceps: It passes over the head of the humerus and prevents upward displacement.
• Coracoacromial ligament

Degeneration or tear of the above structures leads to instability of the shoulder joint.

The shoulder joint is least protected inferiorly. The capsule is loose and only one muscle crosses the joint inferiorly, i.e. long head of triceps.