Thoracic inlet

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Superior thoracic aperture
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The thorax from in front. (Superior thoracic aperture visible at top.)
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Superior thoracic aperture seen from above
Details
Identifiers
Latin Apertura thoracis superior
TA A02.3.04.003
FMA 7566
Anatomical terminology

The thoracic inlet, also known as the superior thoracic aperture, refers to the opening at the top of the thoracic cavity. It is also clinically referred to as the thoracic outlet, in the case of thoracic outlet syndrome; this refers to the superior thoracic aperture, and not to the lower, larger opening, the inferior thoracic aperture.

Thoracic cavity

The thoracic cavity is the chamber of the body of vertebrates that is protected by the thoracic wall. The central compartment of the thoracic cavity is the mediastinum. There are two openings of the thoracic cavity, a superior thoracic aperture known as the thoracic inlet and a lower inferior thoracic aperture known as the thoracic outlet.

Thoracic outlet syndrome vascular disease that is characterized by compression at the superior thoracic outlet resulting from excess pressure placed on a neurovascular bundle passing between the anterior scalene and middle scalene muscles

Thoracic outlet syndrome (TOS) is a condition in which there is compression of the nerves, arteries, or veins in the passageway from the lower neck to the armpit. There are three main types: neurogenic, venous, and arterial. The neurogenic type is the most common and presents with pain, weakness, and occasionally loss of muscle at the base of the thumb. The venous type results in swelling, pain, and possibly a bluish coloration of the arm. The arterial type results in pain, coldness, and paleness of the arm.

Contents

Structure

The thoracic inlet is essentially a hole surrounded by a bony ring, through which several vital structures pass.

The thoracic inlet is bounded by: the first thoracic vertebra (T1) posteriorly; the first pair of ribs laterally, forming lateral C-shaped curves posterior to anterior; and the costal cartilage of the first rib and the superior border of the manubrium anteriorly.

Thoracic vertebrae vertebrae between the cervical vertebrae and the lumbar vertebrae

In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical and lumbar vertebrae; they increase in size going towards the lumbar vertebrae, with the lower ones being a lot larger than the upper. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, as well as facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. By convention, the human thoracic vertebrae are numbered T1–T12, with the first one (T1) located closest to the skull and the others going down the spine toward the lumbar region.

Rib long curved bone surrounding the chest

In vertebrate anatomy, ribs are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax. In some animals, especially snakes, ribs may provide support and protection for the entire body.

Costal cartilage bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax

The costal cartilages are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs, providing medial extension.

Relations

The clavicle articulates with the manubrium to form the anterior border of the thoracic inlet. Superior to the thoracic inlet is the root of the neck, and the superior mediastinum is inferiorly related. The brachial plexus is a superolateral relation of the thoracic inlet. The brachial plexus emerges between the anterior and middle scalene muscles, superior to the first rib, and passes obliquely and inferiorly, underneath the clavicle, into the shoulder and then the arm. Impingement of the plexus in the region of the scalenes, ribs, and clavicles is responsible for thoracic outlet syndrome.

Clavicle plain bone of short length that serves as a strut between the scapula and the sternum

The clavicle or collarbone is a long bone that serves as a strut between the shoulder blade and the sternum or breastbone. There are two clavicles, one on the left and one on the right. The clavicle is the only long bone in the body that lies horizontally. Together with the shoulder blade it makes up the shoulder girdle. It is a touchable bone and in people who have less fat in this region, the location of the bone is clearly visible, as it creates a bulge in the skin. It receives its name from the Latin: clavicula because the bone rotates along its axis like a key when the shoulder is abducted. The clavicle is the most commonly fractured bone. It can easily be fractured due to impacts to the shoulder from the force of falling on outstretched arms or by a direct hit.

Neck part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk

The neck is the part of the body on many vertebrates that connects the head with the torso and provides the mobility and movements of the head. The structures of the human neck are anatomically grouped into four compartments; vertebral, visceral and two vascular compartments. Within these compartments, the neck houses the cervical vertebrae and cervical part of the spinal cord, upper parts of the respiratory and digestive tracts, endocrine glands, nerves, arteries and veins. Muscles of the neck are described separately from the compartments. They bound the neck triangles.

Mediastinum central compartment of the thoracic cavity that separates the lungs

The mediastinum is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax. The mediastinum contains the heart and its vessels, the esophagus, the trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus and the lymph nodes of the central chest.

Function

Structures that pass through the thoracic inlet include:

Trachea cartilaginous tube that connects the pharynx and larynx to the lungs

The trachea, colloquially called the windpipe, is a cartilaginous tube that connects the pharynx and larynx to the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from the larynx and branches into the two primary bronchi. At the top of the trachea the cricoid cartilage attaches it to the larynx. This is the only complete tracheal ring, the others being incomplete rings of reinforcing cartilage. The trachealis muscle joins the ends of the rings and these are joined vertically by bands of fibrous connective tissue – the annular ligaments of trachea. The epiglottis closes the opening to the larynx during swallowing.

Esophagus organ in vertebrates

The esophagus or oesophagus, commonly known as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the stomach. The esophagus is a fibromuscular tube, about 25 centimeters long in adults, which travels behind the trachea and heart, passes through the diaphragm and empties into the uppermost region of the stomach. During swallowing, the epiglottis tilts backwards to prevent food from going down the larynx and lungs. The word oesophagus is the Greek word οἰσοφάγος oisophagos, meaning "gullet".

Thoracic duct

In human anatomy, the thoracic duct is the larger of the two lymph ducts of the lymphatic system. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal. The other duct is the right lymphatic duct. The thoracic duct carries chyle, a liquid containing both lymph and emulsified fats, rather than pure lymph. Thus when it ruptures, the resulting flood of liquid into the pleural cavity is known as chylothorax.

This is not an exhaustive list. There are several other minor, but important, vessels and nerves passing through, and an abnormally large thyroid gland may extend inferiorly through the thoracic inlet into the superior mediastinum.

The oesophagus lies against the body of the T1 vertebra, separated from it by the prevertebral fascia, and the trachea lies in front of the oesophagus, in the midline, and may touch the manubrium. The apices of the lungs lie to either side of the oesophagus and trachea, and is separated from them by the other vessels and nerves listed above. Furthermore, they extend slightly superior past the level of the inlet (e.g. the horizontal plane of the first rib).

Additional images

Related Research Articles

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Cervical vertebrae Vertebrae of the neck

In tetrapods, cervical vertebrae are the vertebrae of the neck, immediately below the skull. Truncal vertebrae lie caudal of cervical vertebrae. In sauropsid species, the cervical vertebrae bear cervical ribs. In lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes. Most mammals have 7 cervical vertebrae, with the only 3 known exceptions being the manatee with 6, the two-toed sloth with 5–6, and the three-toed sloth with 9.

Subclavian vein paired large vein

The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorption of fats and lipids, by allowing its products that have been carried by lymph to enter the bloodstream, where it can enter the hepatic portal vein. Their diameter is approximately 1–2 cm, depending on the individual.

Axillary artery Large blood vessel bringing oxygenated blood to the thorax

In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla (armpit) and the upper limb. Its origin is at the lateral margin of the first rib, before which it is called the subclavian artery.

Scalene muscles Muscles on the sides of the neck

The scalene muscles are a group of three pairs of muscles in the lateral neck, namely the anterior scalene, middle scalene, and posterior scalene. They are innervated by the fourth, fifth, and sixth cervical spinal nerves (C4-C6).

Subclavius muscle

The subclavius is a small triangular muscle, placed between the clavicle and the first rib. Along with the pectoralis major and pectoralis minor muscles, the subclavius muscle makes up the Anterior Axioappendicular Muscles also known as anterior wall of the axilla.

Posterior triangle of the neck

The posterior triangle is a region of the neck.

Subclavian triangle

The subclavian triangle, the smaller division of the posterior triangle, is bounded, above, by the inferior belly of the omohyoideus; below, by the clavicle; its base is formed by the posterior border of the sternocleidomastoideus.

Intercostal arteries Arteries supplying the space between the ribs

The intercostal arteries are a group of arteries that supply the area between the ribs ("costae"), called the intercostal space. The highest intercostal artery is an artery in the human body that usually gives rise to the first and second posterior intercostal arteries, which supply blood to their corresponding intercostal space. It usually arises from the costocervical trunk, which is a branch of the subclavian artery. Some anatomists may contend that there is no supreme intercostal artery, only a supreme intercostal vein.

Inferior cervical ganglion

The inferior cervical ganglion is situated between the base of the transverse process of the last cervical vertebra and the neck of the first rib, on the medial side of the costocervical artery.

Root of the lung

The root of the lung is located at the hilum of each lung, just above the middle of the mediastinal surface and behind the cardiac impression of the lung. It is nearer to the back than the front. The root of the lung is connected by the structures that form it to the heart and the trachea. The rib cage is separated from the lung by a two-layered membranous coating, the pleura. The hilum is the large triangular depression where the connection between the parietal pleura and the visceral pleura is made, and this marks the meeting point between the mediastinum and the pleural cavities.

Prevertebral fascia

The prevertebral fascia is a fascia in the neck.

Outline of human anatomy Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

References