Anatomical Variations Of The Thoracic Duct Question And Answers

Trachea Anatomy

Describe the Trachea under the following headings:

1. Trachea Extent
2. Trachea Relations
3. Trachea Development
4. Trachea Histology and
5. Trachea Applied Anatomy.

Answer:

Trachea under the following headings:

Trachea (syn. windpipe) is 12 cm long, flexible, fibrocartilaginous tube, lying more or less in the midline in the lower part of the neck and superior mediastinum.

Trachea Anatomy

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1. Trachea Extent:

It extends from the lower border of the cricoid cartilage (opposite to the lower border of the C6 vertebra) as a continuation of the larynx to the lower border of the T4 vertebra, where it bifurcates into two principal bronchi.

2. Trachea Relations:

In the neck:

Trachea Anterior

• Skin
• Superficial fascia with platysma and investing layer of deep fascia
• Sternothyroid and sternohyoid muscles
• Isthmus of thyroid gland (opposite 2nd, 3rd, and 4th tracheal rings)
• Anastomosis between superior thyroid arteries
• Pretracheal fascia
• Inferior thyroid veins
• Left brachiocephalic vein (in children only)

Trachea Posterior

• Esophagus
• Recurrent laryngeal nerves
• Lobes of the thyroid gland (one on either side)

Trachea Anatomy

In the thorax:

Thorax Anterior

• Manubrium sterni
• Sternothyroid muscles
• pretracheal fascia
• Left brachiocephalic vein
• Arch of aorta
• Brachiocephalic trunk, left common carotid artery, and Remains of thymus

Thorax Posterior

• Esophagus
• Left recurrent laryngeal nerve
• Vertebral column

Thorax Right side

• Right lung and pleura
• Azygos vein
• Right vagus nerve

Trachea Anatomy

Trachea Left side

• Left common carotid artery
• Left subclavian artery
• Left vagus nerve

3. Trachea Development

• The trachea develops from the laryngotracheal diverticulum (respiratory diverticulum) of the primitive foregut.
• It gets separated from the esophagus by the tracheoesophageal septum.
• The defective development of this septum gives rise to a common congenital anomaly called tracheoesophageal fistula.

4. Trachea Histology

Histologically, the wall of the trachea from within outward consists of 4 layers:

1. Mucosa
2. Submucosa
3. Cartilage, and
4. Adventitia.

1. Mucosa:
   • The lining epithelium is pseudostratified ciliated columnar with few goblet cells (i.e. respiratory epithelium)
   • Lamina propria is made up of loose connective tissue, rich in elastic fibers
2. Submucosa
   • Consists of loose areolar tissue
   • Contains a large number of mixed seromucous glands
3.  Cartilage:
   • Consists of C-shaped hyaline cartilages with their gaps facing posteriorly.
   • Which are filled by smooth muscle (tracheal) and fibroelastic ligament?
4.  Adventitia:
   • Consists of dense connective tissue rich in elastic fibers
   • Contains nerves and vessels

5. Trachea Applied anatomy

• Carina:
  • Carina is a sharp ridge-/keel-shaped process seen during bronchoscopy at the tracheal bifurcation.
  • Carina is situated 25 cm below the incisor teeth. It is a useful clinical landmark.
  • The mucous lining of the carina is highly sensitive and the cough reflex is usually initiated here.
• Tracheostomy:
  • Tracheostomy is a life-saving surgical procedure in which an opening is made in the trachea to insert a tracheostomy tube in cases of respiratory obstruction.
• Tracheoesophageal fistula:
  • Tracheoesophageal fistula occurs due to failure of separation of the trachea from the esophagus following defective development of the tracheoesophageal septum.
  • In most of the cases (85%), the lower segment of the esophagus communicates with the trachea.

Trachea Clinical Presentation

• The infant vomits after every feed given to him/her.
• Presence of air in the fundus of the stomach (a diagnostic sign of tracheoesophageal fistula).

Enumerate the differences between right and left principal bronchi. Discuss its applied anatomy.
Answer:

Differences Between Right And Left Principal Bronchi:-

The differences between the right and left principal bronchi are given in the Table below.

Trachea Anatomy

Differences between Right and Left Principal Bronchi:

Right and Left Principal Bronchi Applied Anatomy

Inhaled foreign bodies usually enter into the right principal bronchus because it is shorter, wider, and lies more or less in line with the trachea.

Question 4. Describe the Thoracic Duct under the following headings:

1. Thoracic Duct  Introduction
2. Thoracic Duct  Course and Relations
3. Thoracic Duct  Tributaries
4. Thoracic Duct  Development and
5. Thoracic Duct  Applied anatomy.

Answer:

Thoracic Duct  Introduction

• The thoracic duct is the largest lymphatic channel of the body present in the thoracic region. It drains lymph from the whole of the body except the right upper quadrant, which is drained by the right lymphatic duct.
• Thoracic Duct  extends from the lower border of the T12 to the C7 vertebrae.
• Thoracic Duct  is 45 cm long and beaded in appearance.
• Thoracic Duct  commences from the cranial end of the cisterna chyli and terminates at the root of the neck by opening in the angle between the left subclavian and left internal jugular veins.

Thoracic Duct  Course and relations

• After arising from the cranial end of the cisterna chyli, it enters the thoracic cavity through aortic orifice of the diaphragm on the right side of descending thoracic aorta and on the left side of the azygos vein.
• At first, it ascends in the posterior mediastinum behind the esophagus. Then, it crosses behind the esophagus from the right to the left at the level of the T5 vertebra. Then, it ascends along the left border of the esophagus in the superior mediastinum and neck until it reaches the level of the transverse process of the C7 vertebra.
• In the neck at the level of the C7 vertebra, it arches laterally on the left side behind the carotid sheath and in front of the vertebral system to terminate by entering into the junction of the internal jugular and subclavian veins.

Thoracic Duct  Tributaries

1. In the abdomen: Descending thoracic lymph trunks from the lower six intercostal spaces.
2. In the thorax: Lymph trunks from
   • Upper six intercostal spaces
   • Posterior mediastinum
   • Upper lumbar region
3. In the neck:
   • Left jugular lymph trunk
   • Left subclavian lymph trunk
   • Left bronchomediastinal lymph trunk

Thoracic Duct  Development

• Thoracic Duct  develops from two longitudinal lymph channels present by the side of the primitive vertebral column.
• They get connected by a transverse channel at the level of T5 vertebra.
• The right longitudinal channel above the communicating transverse channel and left longitudinal channel below the transverse channel disappear and give rise
  to the thoracic duct.

Thoracic Duct  Applied anatomy

• Obstruction of the thoracic duct may be caused by microfilariae parasites (Wuchereria bancrofti) or surrounding tumors.
• This may lead to the accumulation of chyle in the thorax, peritoneal cavity, and tunica vaginalis, leading to chylothorax, hemoperitoneum, and cephalocele, respectively.
• Inadvertent damage of the thoracic duct in block dissection of the neck causes leakage of the chyle, which may lead to chylothorax.

Question 5. Write a short note on the Azygos Vein.
Answer:

Azygos Vein

• The azygos vein is an unpaired (‘azygos’ = single/without companion) vein, situated on the posterior thoracic wall in the upper lumbar region.
• Azygos Vein connects the superior and inferior vena cava. It drains the venous blood from the thoracic wall and upper lumbar region.

Azygos Vein Formation

Azygos Vein is formed by the union of

• The right subcostal vein, and
• Right ascending lumbar vein at the level of the T12 vertebra.

Azygos Vein Course

• After formation, it ascends to enter the thoracic cavity through the aortic orifice of the diaphragm (in the aortic opening, the abdominal aorta is on the left side, the thoracic duct in the middle, and the azygos vein is on the right side).
• In the thorax, it ascends up to the T4 vertebra where it arches forward over the root of the right lung to terminate in the superior vena cava at the level of the right second costal cartilage.

Azygos Vein Tributaries

• Right superior intercostal vein (formed by union of the 2nd, 3rd, and 4th right posterior intercostal veins)
• The 5th to 11th right posterior intercostal veins
• Accessory hemiazygos vein (at the level of the upper part of the T8 vertebra)
• Hemiazygos vein (at the level of the lower part of the T8 vertebra)
• Right bronchial vein (near the termination of azygos vein)
• Esophageal veins
• Mediastinal veins
• Pericardial veins

Azygos Vein Applied anatomy

In the case of superior or inferior vena cava obstructions, the azygos vein serves as an important channel to establish collateral circulation.

Question 6. Write a short note on the lobe of the azygos vein.
Answer:

The Lobe of the Azygos Vein

• In 1% of the population, the apex of the right lung splits into medial and lateral parts by a fissure.
• The bottom of the fissure contains the arch of the azygos vein suspended by a fold of pleura called pleural septum/mesoazygos.
• The medial part of the split apex of the right lung is called the lobe of the azygos vein.
• It is caused by the upward development of the apical bronchus, medial to the azygos vein (note normally it develops lateral to the arch of the azygos vein).

Lobe of the Azygos Vein Applied anatomy

• The lobe of the Azygos vein presents as a small dense shadow close to the right sternal angle in-plane X-ray chest PA view.
• It may be confused to the enlarged mediastinal lymph node.