Oesophagus

A 25cm muscular tube that connects the pharynx to the stomach

Embryology

• Cranial part of the gut tube, which starts forming around week four
• Respiratory diverticulum (lung bud) forms at its ventral wall, and gradually partitions itself off ventrally by the trache-oesophageal septum
• Rapidly lengthens with descent of the heart and lungs

Gross anatomy

Relations:

• • Pleura
    • On the right, full length of oesophagus is against pleura, except where azygos comes forward to join SVC
    • On the left, aortic arch separates oesophagus from pleura superiorly; lower down, oesophagus is in direct contact with pleura
    • Posterior to lower thoracic oesophagus, the two pleural cavities almost touch
  • Vagus nerves
    • Come into contact below carina
    • Note form plexus around mid-oesophagus, forming two discrete trunks below that
    • Beware left RLN above aortic arch
  • Phreno-oesophageal ligament
    • Attaches the oesophagus anteriorly to the peritoneum, and endo-abdominal fascia
    • Formed as a condensation of the endo-abdominal fascia from the under-surface of the diaphragm. The endo-abdominal fascia splits into two layers - filmy outer layer, continuing downwards to GOJ; and a stronger superior layer which passes upwards through the hiatus to blend with areolar tissue surrounding the oesophagus.
    • Seen macroscopically as the layer of tissue which binds the oesophagus to the edges of the oesophageal hiatus, seen as a white line similar in appearance to the white line of Toldt elsewhere.

Path:

• • Begins at the lower border of the cricoid cartilage (C6), at the base of the pharynx, in the midline
    • Posteriorly related to pre-vertebral fascia, then vertebral bodies and longus colli muscles
  • It curves slightly to the left as it passes down through the thoracic inlet and through the superior mediastinum
  • Back to midline at T5, then deviates to right, away from aortic arch
    • Note thoracic duct directly posterior to oesophagus at this level - high risk for injury
  • At T7 passes to left again, under the left main bronchus, and curves forward to pass in front of the thoracic aorta
    • Pericardium and left atrium in front
    • Anterolateral part of thoracic vertebrae to the right
  • Through the diaphragm at the oesophageal hiatus (T10)
    • Separated from aorta by left pillar of oesophageal hiatus
  • Into the cardia of the stomach at T11
  • 3cm of oesophagus in abdomen while supine

Segments:

• • Pharyngeal
  • Cervical - from cricopharyngeus to the thoracic inlet
  • Thoracic - from thoracic inlet to oesophageal hiatus in the diaphragm
  • Abdominal - from diaphragm to stomach

Description

• • 25cm long, extending C6 to T11
  • Normally 2.5cm in diameter
  • Anchored superiorly to cricoid cartilage
  • Tethered along length e.g. to left and right pleura
  • Upper oesophageal sphincter - 15-17cm from teeth
    • Formed from the inferior pharyngeal constrictor muscle, which acts as the bridge between the pharyngeal and oesophageal musculature
    • Inferior pharyngeal constrictor is formed by thyropharyngeus and cricopharyngeus muscles, which both insert into the median pharyngeal raphe
      • Thyropharyngeus (oblique fibres) originates from the thyroid cartilage, just adjacent to cricothyroid
      • Cricopharyngeus (transverse fibres) originates from the cricoid cartilage
    • Nerve supply from pharyngeal plexus
    • The high-pressure zone of cricopharyngeus forms a true anatomic sphincter (mean pressure 60mmHg) - thus the lower part of inferior pharyngeal constrictor forms the upper oesophageal sphincter
    • Killian triangle is a site of potential weakness, between the fibres of the two pharyngeal constrictor muscles. This is the site of Zenker diverticulae.
    • V-shaped area of Laimer forms at the apex of the longitudinal oesophageal muscles extending up towards the posterior surface of the thyroid cartilage
    • If incising the inferior pharyngeal constrictor, make the incision as posterior as possible to avoid damaging or constricting the arytenoids and other muscles of the laryngeal inlet

Lower oesophageal sphincter - 38-40cm from teeth

• • More of a physiological sphincter/zone of high pressure (mean pressure 24mm Hg)
  • See below under physiology of swallowing
  • Made up of four anatomic structures:
    • Intrinsic musculature of the distal oesophagus - muscle fibres relax as part of swallowing, then return to a state of tonic contraction
    • Sling fibres of the gastric cardia - oriented diagonally from the cardia-fundus junction to the lesser curve of the stomach, located at the same anatomic depth as the circular muscle fibres of the oesophagus
    • The crura of the diaphragm - contracts during inspiration to counter the intra-thoracic pressure differentiation
    • Increased intra-abdominal pressure, which is transmitted to the GOJ, increasing the pressure on the distal oesophagus and preventing spontaneous reflux of gastric contents
  • Can be identified by two endoscopic and two external features:
    • Z-line (squamocolumnar junction)
    • GOJ: transition from smooth oesophageal lining to rugal folds of stomach
    • Collar of Helvetius/loop of Willis - where circular muscular fibres of the oesophagus join the oblique fibres of the stomach (externally)
    • Gastro-oesophageal fat pad (externally)

Anatomical areas of narrowing:

• • UOS - 14mm diameter - 15cm from incisors
  • Bronchoaortic constriction (T4) - 15-17mm diameter - 25cm from incisors
  • Diaphragmatic constriction (T10) - 16-19mm diameter - 40cm from incisors

Arterial supply - branches are small and many

• Cervical - mostly from inferior thyroid arteries (from thyrocervical trunk on left and subclavian on the right)
• Thoracic
  • Supra-carinal: oesophageal branches off the right and left bronchial arteries
  • Infra-carinal: 4-6 oesophageal arteries off the aorta
• Abdominal - ascending left gastric artery and both inferior phrenic arteries (although these are infrequently involved)
• Capillary network within the length of the oesophagus within the submucosal layer
• Extensive collaterals means that the thoracic oesophagus can be fully mobilised and left in situ if an oesophagectomy is unable to be completed. The inferior thyroid artery can also be ligated without jeopardising a cervical stump, perhaps because of good anastomoses with the superior thyroid artery.

Venous drainage

• Submucosal venous plexus, which then drains into:
  • Cervical - inferior thyroid veins, which drain into left subclavian and right brachiocephalic veins
  • Thoracic - azygos and hemiazygos
  • Abdominal - left and right phrenic veins and left gastric and short gastric veins
• There is also a subepithelial plexus in the distal 5cm, which can enlarge and bleed as oesophageal varices

Lymphatics

• Upwards flow in proximal two-thirds, and downwards flow in distal third
  • Upwards to deep cervical nodes near inferior thyroid artery origin and tracheobronchial nodes
  • Downwards to coeliac nodes
• Two interconnected plexuses:
  • Submucosal - penetrates muscularis propria, then drains into deeper plexus
  • Deeper plexus - runs longitudinally in the oesophageal wall, draining into regional lymph node beds
• C.f. thoracic lymphatics under 'thoracic cavity'

Innervation

Sympathetic

• • Cervical sympathetic trunk arises from the superior ganglion in the neck, extends beside oesophagus into the thoracic cavity, and terminates in the cervicothoracic (stellate) ganglion. Gives off branches along the way to the cervical oesophagus.
  • Thoracic sympathetic trunk continues on from the stellate ganglion, giving off branches to the thoracic oesophagus.
  • Greater and lesser splanchnic nerves innervate the distal thoracic oesophagus.
  • Abdominal part receives sympathetic innervation from fibres along the left gastric artery.

Parasympathetic

• • Fibres from vagus nerve
    • Superior laryngeal nerve supplies inferior pharyngeal constrictor
    • Right and left RLN innervates cervical oesophagus, including cricopharyngeus.
      • Injury to superior laryngeal nerve RLN can lead to hoarseness and aspiration through laryngeal and upper oesophageal sphincter dysfunction.
    • Vagal fibres also innervate distal oesophagus, with these branches entering the oesophagus as high as 5cm above the GOJ, causing sphincteric relaxation associated with swallowing, belching, vomiting and some reflux
    • In the thorax, vagus sends fibres to the striated muscle, and parasympathetic preganglionic fibres to the smooth muscle of the oesophagus
• Auerbach plexus surrounds the thoracic oesophagus - both SNS and PNS
• Meissner plexus in submucosal layer of thoracic oesophagus

Tissue architecture

• Two main layers (no serosa, unlike the rest of the alimentary tract)
  • Mucosa - mostly stratified squamous non-keratinizing epithelium, up to the Z-line, where it transitions to cardiac mucosa/junctional columnar epithelium
    • Four distinct layers within the mucosa:
      • Epithelium
      • Basement membrane
      • Lamina propria
      • Muscularis mucosae - longitudinal fibres
  • Submucosa is found deep to muscularis mucosae - strongest layer for holding sutures
    • Lymphatic and vascular networks
    • Mucous glands
    • Meissner neural plexus
    • Fibrous tissue
  • Muscularis propria
    • Inner circular layer (continuation of cricopharyngeus)
      • Transitions from the circular muscles of the oesophagus to the oblique muscles of the stomach at the incisura, known as the collar of Helvetius
    • Thin septum of connective tissue, which also contains the Auerbach plexus (interconnected ganglia)
    • Outer longitudinal muscle layer
      • Begins at back of cricoid cartilage by a tendon which gives rise to two fasciculi which spread out to constitute the longitudinal muscle
      • Extends into abdomen, becoming the longitudinal muscle of the cardia of the stomach
    • Proximal third predominantly striated muscle; distal third entirely smooth muscle; middle third a mixture
• Final outside layer of fibroalveolar adventitia

Physiology

• Swallowing
  • Three phases:
    • Oral
      • Elevation of the tongue
      • Posterior movement of the tongue
      • Elevation of the soft palate
    • Pharyngeal
      • Elevation of the hyoid
      • Elevation of the larynx
      • Tilting of the epiglottis
    • Oesophageal
      • UOS relaxes, and peristaltic contractions of the posterior pharyngeal constrictors propel the bolus into the oesophagus
      • UOS closes, reaching 90mm Hg pressure, preventing reflux
  • Peristalsis
    • Primary - progressive - move down the oesophagus at 2-4cm/sec
    • Secondary - progressive - generated by distension or irritation of the oesophagus rather than voluntary swallowing
    • Tertiary - non-progressive, non-peristaltic, monophasic or multiphasic. Can occur after voluntary swallowing or spontaneously between swallows. Unco-ordinated contractions which are responsible for oesophageal spasm.
  • Lower oesophageal sphincter
    • Normally 2-5cm in length, with a minimum total length of 2cm and at least 1cm of intra-abdominal length being required for normal functioning
    • Requires vagal-mediated relaxation to open - occurs 1.5 to 2.5 seconds after pharyngeal swallowing, and lasts 4-6 seconds
    • Post-relaxation contraction occurs normally
• Reflux mechanism
  • Factors:
    • Adequate pressure and length
    • Radial symmetry
    • Motility of the oesophagus and stomach
    • Neurotransmitters, hormones and peptides all influence tone