Oesophagus - Pathology

()Map ALIMENTARY SYSTEM (Map)

Introduction

• The oesophagus is the part of alimentary tract that tends to go wrong least often.

Functional Anatomy

• The oesophagus is a fibromuscular tube, lined by stratified squamous epithelium and lubricated by mucus, salivary, nasal and bronchial secretions, which acts to transport ingesta from the pharynx to the stomach.
• Failure of oesophageal function results in obstruction and in failure of ingesta to pass to the stomach.
• In the bovine there may also be failure of eructation and tympany may develop.

Defence Mechanisms

• The oesophagus has no serosa and is covered by the fibrous tissue of the neck and mediastinum, from which it derives its blood supply.
• Consequently, infection spreads easily and healing is more difficult.
• Oesophageal disease is therefore difficult to treat and is consequently very serious.

Developmental Pathology

Congenital Achalasia - Megaoesophagus

Megaoesophagus (Courtesy of Alun Williams (RVC))

• This condition has been termed achalasia but this implies (in man) a cardiac sphincter defect, which is not found in the dog.
• A functional rather than a physical blockage

• Inherited disorder in several breeds:
  • Autosomal recessive in Fox Terrier.
  • Also in Miniature Schnauzer, Great Dane, German Shepherds and others.
  • Also in Siamese cats.

Clinical

• See at approx. 6-7 months of age when growing quickly.
• Eats food, vomits, eats again and vomits again because oesophagus has no tone to it.
• Oesophagus may become extremely dilated producing a megaoesophagus.
• Can affect the whole length of oesophagus.

Pathogenesis

• Appears to be due to due to delay in maturation of oesophageal innervation, either:
  • in upper motor neurones of central swallowing centre or
  • in the afferent sensory arm of the reflex involved with peristalsis.

• If dog eats from raised bowel may be satisfactory as food goes down by gravity.
• Once in stomach it is passed on normally.

Megoesophagus Secondary to Dextra-Aorta

Dextra-aorta (Courtesy of Alun Williams (RVC))

• Vascular rings are congenital abnormalities of the aortic arch system which interfere with oesophageal function. Normally, the aortic arch, pulmonary artery and ductus arteriosus (ligamentum arteriosum) all lie on the left side of the oesophagus.
• However, when there is anomalous development of the aortic arch, for example in the right-sided arch, the oesophagus becomes enclosed within a ring formed by the heart base, aorta, ductus arteriosus and pulmonary artery.
• The compression and stricture produced by the “ring” presents passage of solid food beyond the heart base and food accumulates rostral (cranial) to the obstruction, resulting in dilatation or megaoesophagus.
• In most cases food is eventually regurgitated undigested.
• The condition is seen in pups just after weaning and if these are presented for treatment before severe dilatation occurs, then surgical correction of the ring (if possible) offers a good prognosis.

Immune Mediated Pathology

Autoimmune

Myasthenia Gravis

• Animals develop antibodies to nicotinic acetylcholine receptors.
• Results in generalised muscle weakness and or megaoesophagus.

Key-Gaskell syndrome

• Autonomic polyganglioneuropathy in cats
• Abnormal function of the sympathetic and parasympathetic system.
• Whole autonomic system involved – affected animals usually die.
  • Similar to grass sickness in horses.

Clinical

• Cats show:
  • Mega-oesophagus
  • Dilated pupils
  • Whole gut is involved (very little peristalsis)
  • Constipation.

• Generalised autonomic effects:
  • Reduced salivation
  • Reduced lachrymation
  • Bradycardia
  • Constipation
  • Pupillary dilatation

Pathology

• Histologically there is marked reduction in the number of neurones in all autonomic ganglia in the ventral horn of all levels of spinal cord accompanied by proliferation of non-neuronal cells.
• Similar changes in brain stem nuclei of cranial nerves.

Pathogenesis

• Acquired disease - outbreaks occurred in the past, now only occasionally seen but seems to be getting more common again.
• Possibly toxic cause.
• Possibly in dry food or in vaccine?
• Agent not really known, but produces general damage to autonomic nervous system.

Proliferative Pathology

Papular

Bovine Papular Stomatitis

Oesophageal lesions of BPS (Courtesy of Alun Williams (RVC))

Lesions of Bovine Papular Stomatitis may also be found in the oesophagus.

Neoplastic

Upper Alimentary Tract Carcinoma Complex

Aetiology

• The most important oesophageal neoplasm is squamous cell carcinoma in the cow.
• This tumour is seen as part of a more general syndrome of upper alimentary tract neoplasia in adult cattle grazing rough pasture on which the bracken fern (Pteridium aquilinum) is present.
• The syndrome is seen in various part of the world including the Western Highlands of Scotland, Brazil and Kenya.
• In affected animals, squamous carcinomas may be present in the oropharynx, oesophagus and rumen and there may also be intestinal adenocarcinomas and bladder tumours, or the condition known as enzootic bovine haematuria.

Pathogenesis

• Experimentally, the feeding of bracken to laboratory animals will result in alimentary and bladder tumours.
• However, in many naturally-occurring cases of upper alimentary carcinoma in cattle there are coexisting viral papillomata, some of which show malignant change.
• The relationship between the ingestion of bracken and the presence of virus in the aetiology of the malignancies is currently the subject of intensive investigations.
• It may be that both are involved in the carcinogenesis.

Macroscopically

• These upper alimentary squamous carcinomas are most often seen as:
  • large
  • fungating
  • often superficially-necrotic
  • protruding into the lumen of the alimentary tract;
• There is often a marked scirrhous reaction.
• The tumours are locally aggressive and may permeate local lymphatics and metastasise to local lymph nodes.

Microscopically

The tumour consists of cords or groups of squamous cells, which may form keratin. Individual or multiple papillomata may be found in association with the carcinomata.

• The presence of the tumours interferes with normal alimentary function
  • there may be difficulty in chewing and swallowing or in cudding and eructation.

Squamous Cell Carcinoma of Other Species

• Squamous cell carcinomas of the oesophagus are occasionally seen in other species, notably in the cat, where the tumour tends to infiltrate around the oesophageal wall resulting in a “ring carcinoma”.
• The affected cat has progressive difficulty in eating and swallowing.

Degenerative Pathology

Acquired megaoesophagus

• Occurs spontaneously in adult in any disorder that disrupts normal reflex involved in swallowing either peripheral or central.
• These can include:
  • Viral encephalitides
  • Peripheral neuropathies
    • Degeneration or inactivity of local myenteric nerve plexuses (Auerbach’s plexuses),
    • or to lesions in the vagus nerve or the central nucleus in the medulla of the brain which supply the oesophagus.
  • Poisonings such as:
    • Lead
    • Tetanus
    • Botulism
  • Myopathies.

• The result is the presence of a hypotonic oesophagus in which food accumulates causing distension
• Usually the thoracic oesophagus from the thoracic inlet to the diaphragm is affected and grossly the oesophagus is dilated, thin-walled and hypotonic.

Traumatic Pathology

Impaction

Upper Block	Lower Block
Acute vomiting	Gradual intestinal distention
Dehydration	Mucosal destruction
Alkalosis	Toxaemia
Pre-renal azotaemia	Peritonitis

• Commonly in cattle, horses and dogs.
• The most common sites of obstruction are the thoracic inlet, the base of the heart, and the hiatus oesophagus of the diaphragm, i.e.: the narrowest points.

Horse

• With foods that expand in oesophagus such as haylage etc.
• Also seen with whole apples.

Cattle

Impaction of a bovine oesophagus (Courtesy of Alun Williams (RVC))

• May eat a spherical object that obstructs the oesophagus mostly in anterior 1/3rd of oesophagus and can often be palpated in live animal.
• Potatoes can be a cheap source of feed and if fed whole can become stuck in oesophagus.
• If obstruction occurs further down can be difficult to diagnose and remove.
• Cattle develop bloat when oesophagus obstructed.
• Apples fairly easily to dislodge.

Dog

• Usually with small bones
• Animals that feel protective of feed may gulp food down quickly, particularly if given small chops / knuckle bones.
• Knobbly shape may make bone lodge in oesophagus, particularly just anterior to heart.
• Very difficult to dislodge (because of shape).
• Pressure necrosis occurs very quickly around it and can erode through oesophagus within about 24 hours.
• Small bone may also lodge in duodenum if they pass through the stomach.

Rupture

• Perforation may occur with sharp foreign bodies. This may lead to cellulitis or pleurisy and other complications.
• Rupture of the oesophagus admits pathogenic organisms to the mediastinum and fascial planes of the neck. Both are composed of loose connective tissue and communicate with each other.
• Infection spreads rapidly as a cellulitis, aided possibly by peristalsis and pulsation of the carotid arteries, and soon leads to pleurisy.
• Rupture is almost always fatal.

Learning Tools

Oesophagus Flashcards