Canis ISSN: 2398-2942

Mediastinal disease

Contributor(s): Serena Brownlie, Richard B Ford

Introduction

  • Cause: trauma (most common), infection/inflammation, neoplasia, foreign body.
  • Signs: clinical features of mediastinal disease usually associated with pressure on structures within cranial or caudal mediastinum:
  • Diagnosis: radiography, ultrasonography, diagnosis may be made from aspirated fluid and tissue samples, or during surgical inspection.
  • Treatment: often symptomatic or surgical.
  • Prognosis: good to poor depending on etiology therefore accurate diagnosis essential.

Pneumomediastinum

  • Air enters mediastinal space → enhanced visibility mediastinal structures on radiography. Identification of outer edges of tracheal wall, azygous vein and major vessels of mediastinum can be made Thorax pneumomediastinum - radiograph lateral.
  • Most common form idiopathic.
  • Cause: air escape from trachea, bronchi, lungs or esophagus, as a consequence of:
    • Trauma (most common)
    • Neoplastic erosion.
    • Iatrogenic, eg investigations of thoracic structures or complications of surgery.
  • Air enters mediastinum through thoracic inlet from head and neck wounds, or from the abdomen. Air can also track subcutaneously and between forelimb muscle groups from mediastinum unless underlying cause can be identified.
  • Treatment: most cases of pneumomediastinum should be left to resolve spontaneously.
  • Prognosis: complete resolution can take up to 3 weeks.
    Attempts to aspirate air trapped in mediastinum can be dangerous → high risk of puncturing mediastinal structures.
  • Surgery: only considered if breathing seriously impaired and a lesion can be identified and accessed.

Mediastinitis

  • See Mediastinitis Trachea: foreign body.
  • An inflammatory process in the mediasinum.
  • Cause:
    • Esophageal perforation, eg foreign body penetration Pharynx: stick injury , iatrogenic during bougienage , ballooning or neoplasia Esophagus: neoplasia.
      • Tracheal damage, eg bronchoscopic injury, trauma.
      • Thoracic trauma or migrating foreign body.
      • Extension of infection from adjacent tissue, eg pneumonia Lung: bacterial pneumonia.
      • Complication of thoracic surgery.
      • Following bacteremia.
  • Signs: pain and fever in association with signs referrable to mediastinal disease.

Mediastinal narrowing

  • Cause: scar tissue formation following chronic inflammation.

Mediastinal widening

  • Cranial mediastinal widening:
    • Mediastinitis, associated with foreign body penetration of esophagus.
    • Edema.
    • Hemorrhage.
    • Abscessation.
    • Granuloma.
    • Lymphadenopathy
    • Neoplasia.
    • Fat.
  • Chemodectomas (heart-based, aortic body tumors) typically result in pericardial effusions, although discrete masses may be seen at the heart base.
    In young animals the mediastinum may appear wide, but this may be due to the normal size and shape of the juvenile thymus.
  • Caudal widening beyond level of heart base:

Pathogenesis

Etiology

  • Herniation of abdominal contents around heart.
  • Lymphadenopathy.
  • Edema.
  • Hemorrhage.
  • Abscessation.
  • Granuloma.
  • Bougienage of esophagus → perforation.
  • Foreign body perforation of thoracic, or cervical, trachea Trachea: foreign body or esophagus Esophagus: foreign body.
  • Neoplasia:
    • Malignant lymphoma Lymphoma.
    • Chemodectomas Chemodectoma 8 year female (heart-based, aortic body tumors).
    • Thymoma Thymoma.
    • Extension of pulmonary pleural neoplasm.

Pathophysiology

  • Increased pressure on, or damage to, structures within cranial and caudal mediastinum → variable symptoms, eg tachypnea, dyspnea, cough, respiratory noise, dysphagia, regurgitation, retching, Horner's syndrome, edema, laryngeal paralysis, heart failure.
  • Mediastinal disease → space occupying lesions → pressure on, or damage to structures, within cranial or caudal mediastinum:
  • Trachea:
    • Dyspnea.
    • Coughing.
    • Respiratory noise.
  • Esophagus:
    • Dysphagia.
    • Regurgitation.
    • Retching.
  • Sympathetic trunk:
    • Horner's syndrome.
  • Recurrent laryngeal nerve:
    • Laryngeal paralysis.
  • Distension of mediastinum (may) → reduced lung capacity → tachypnea.
  • Masses in mediastinum compromises venous and lymphatic drainage → head and forelimb edema (vena cava syndrome).
  • Herniation of abdominal contents around the heart → right-sided cardiac failure (pericardiodiaphragmatic hernia).
  • Lymphadenopathy may → mediastinal widening. Lymph node enlargement close to hilar and sternal regions readily recognized.
  • Mediastinal lymphadenopathy usually recognised with malignant lymphoma.
  • Chemodectomas (heart-based, aortic body tumors) → pericardial effusions Pleural: effusion.
  • Subcutaneous emphysema (a consequence of mediastinal disease and airway penetration).

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Tidwell A S (1998) Ultrasonography of the thorax (excluding the heart). Vet Clin North Am 28 (4), 993-1015 PubMed.
  • Day M J (1997) Review of thymic pathology in 30 cats and 36 dogs. JSAP 38 (9), 393-403 PubMed.
  • Rogers K S & Walker M A (1997) Disorders of the mediastinum. Comp Cont Ed Prac Vet 19 (1), 69-83 VetMedResource.
  • Roush J K, Bjorling D E & Lord P C (1990) Disease of the retroperitoneal space in the dog and cat. JAAHA 26 (1), 47-54 VetMedResource.
  • Parker N R, Walter P A & Gay J (1989) Diagnosis and surgical management of esophageal perforation. JAAHA 25 (5), 587-594 VetMedResource.

Other sources of information

  • Bauer T & Woodfield J A (1995) Mediastinal, pleural, and extrapleural disease. In: Textbook of Veterinary Internal Medicine 4th edn. Eds S J Ettinger & E C Feldman. Philadelphia: W B Saunders & Co. pp 812-842.


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