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That part of the thorax contained between the two pleural cavities.

  1. Most common meditational tumor – thymus
  2. Second most common neurogenic tumor.
    Mediatinum classified into:
    1. Superior compartment - above the aortic arch
      Thyroid/ Aneurysms/ Oesophageal/ Neurogenic  
    2. Anterior - is bordered by the sternum anteriorly, the pericardium posteriorly and the mediastinal pleura laterally. (4 T's)
      1. Thymus/ Thyroid/ Teratoma (and other germ cell tumours)/ Terrible Lymphoma and other lymphoid diseases (sarcoid, Castlemann's NSCLC, SCLC)
      2. Also pericardial cyst and Morgagni hernia inferiorly
      3. Most common anterior meditational tumor – thymus
    3. Middle (visceral) compartment - from the anterior pericardium back to the pre-vertebral fascia and bounded by both pleura, includes the heart, trachea, main bronchi and oesophagus. (BLAB)
      1. Bronchogenic carcinoma/ Lymphoma/ Aneurysms (and other vascular, including cardiac tumours)/ Bronchogenic cyst  
    4. Posterior compartment - better referred to as the paravertebral sulci, includes those structures medial to the pleura but excluding the vertebral column. (NOBA)
      1. Neurogenic/ Oesophageal (duplication and para-oesophageal hernia)/ Bone/ Aneurysms
      2. Most common tumor of posterior mediastinum is neurogenic tumor
    5. Presentation
      1. Mediastinal tumours in children are usually symptomatic with respiratory symptoms such as cough, stridor and dyspnoes.
      2. Malignant lesions are often accompanied by lethargy, fever, malaise and chest pain.
      3. In adults many lesions are asymptomatic, found incidentally on routine chest radiographs. However, obstructive symptoms do occur when the tumour impresses on the superior vena cava, oesophagus or tracheo-bronchial tree and cardiac tamponade can be caused by large anterior compartment tumours.
      4. Invasion of phrenic, recurrent laryngeal or sympathetic chain nerves may cause breathlessness, hoarseness or Horner’s syndrome.  
    6. Diagnosis
      1. CT scan or MRI scan outline the exact site of the lesion and will give clues to the diagnosis, a variegated appearance suggesting teratoma. Scans will also give an indication of malignant invasion of adjacent structures and pleural metastases which in the case of thymoma produce a "droplet" pattern. Q
      2. Fine needle aspiration cytology is frequently inadequate to differentiate thymoma from lymphoma and almost never provides enough tissue to differentiate between types of lymphoma.
      3. Mediastinoscopy, mediastinotomy via anterior mini-thoracotomy or thoracoscopy may be required to provide enough issue for the pathologist to make a full diagnosis.
      4. In patients who are unstable due to compression or obstruction of a vital organ treatment with steroids, radiotherapy or chemotherapy may be commenced before a full diagnosis is obtained surgically.
      5. Thymic tumours are associated with a number of paraneoplastic or "parathymic" syndromes.
      6. The rare paraganglionic neurogenic tumours may be functional in that they produce biogenic amines resembling phaeochromocytoma.
      7. Vanillylmandelic acid or homovanillic acid may be detectable in the urine.
      8. Haematological markers of germ cell tumours (beta-HCG and alpha feto-protein) should be sought.  
    7. Neurogenic tumours of the mediastinum
      1. Neurogenic tumours account for 20-30% of all mediastinal tumours rising to 50-60% in children. Q
      2. Von Recklinhausen’s neurofibromatosis is associated with an increased incidence of neurogenic tumours of all histological types. Q
Most tumours are benign neurilemmomas (also known as schwannomas) or ganglioneuromas (classification) and are completely cured by excision.  
  1. Treatment
    1. Benign – resection
    2. Complete resection also leads to high cure rates in the intermediate malignancy ganglioneuroblastoma and even frankly malignant neuroblastoma and paraganglionoma.
    3. Malignant schwannoma can rarely be excised completely and leads to death within a year of diagnosis: incompletely excised paraganglionoma usually proves fatal regardless of adjuvant therapy though survival is substantially longer.
    4. Neuroblastoma is more sensitive to chemotherapy and when used in combination with radiotherapy even incompletely excised tumours can achieve reasonable long-term survival.
    5. Radiotherapy can also reduce local recurrence of incompletely excised neurilemmoma, neurofibroma and ganglioneuroblastoma  
  2. Tumours of the thymus
    1. The thymus is a bilobed lymphoid organ sited in the superior mediastinum in adults.
    2. It is relatively large at birth and enlarges to a maximal size during puberty.
    3. In adulthood, it regresses as its functional tissue is replaced by fatty connective tissue.
    4. The thymus is thought to have a central role in the development of immune function.
    5. There are three general categories of thymic tumours: thymoma, thymic carcinoma and tumours of other thymic elements. Q
    6. Thymomas are one of the most common mediastinal neoplasms - 90% are benign. Q 
  3. Thymoma
    1. Thymomas are of particular fascination because of their unusual para-neoplastic associations.
    2. The best known of these is myasthenia gravis but the number of syndromes associated with thymoma is extensive (Parathymic syndromes).
    3. The tumour contains both epithelial and lymphocytic elements which can also make differentiation from lymphoma difficult. 



Three main types are:

  • Benign - the most common, accounting for 80-90% of thymomas. Characterized by a diffuse proliferation of neoplastic thymic epithelial cells and an abundance of lymphocytes. There is no capsular invasion. Q
  • Malignant type I - cytologic features are identical to the benign thymoma but with additional invasion of the capsule. Occasionally, there may be metastases to the lungs and bone.
  • Malignant type II - known as thymic carcinoma. There is capsular invasion and cytologic pleomorphism. The tumour often resembles a squamous cell carcinoma.

Classification: Masoaka staging system categorises thymoma purely on encapsulation and invasion of local tissues, and the Muller-Hermelink morphological classification. Q

  1. Clinical features
    1. Mean age of patients with thymomas is 50 years; rare in children where they are associated with a poor prognosis
    2. Males : females = 1:1
    3. Radiographic mass - most common in anterosuperior mediastinum Q
    4. Variable clinical presentation dependent upon the aggressiveness of the lesion. Basic patterns include:
      1. asymptomatic
      2. features attributable to local pressure effects e.g. cough, dyspnoea, dysphagia and superior venal caval obstruction
      3. associated systemic disorders. 
Associated conditions
  1. Myasthenia gravis - the most common association but less often associated with more aggressive thymomas
  2. Haematologic cytopenias e.g. aplastic anaemia
  3. Hypogammaglobulinaemia
  4. Collagen vascular diseases e.g. systemic lupus erythematous
  5. Non-thymic malignancies 

Di George syndrome


The DiGeorge syndrome is an example of a selective T-cell deficiency caused by the failure of development of the third and fourth pharyngeal pouches.


These pouches give rise to the following structures:


Thymus/  parathyroids/ aortic arch / portions of the lips and ears


Consequently, DiGeorge syndrome may present with as immune deficiency state - usually T cells, but sometimes B cells, and also aberrant calcium metabolism, congential heart disease and abnormal facies.

Nezelof syndrome


Nezelof syndrome is congenital hypoplasia of the thymus with retention of normal parathyroid function.


It should be contrasted to DiGeorge syndrome in which there is absence of the parathyroids.

  1. Thymic Carcinoma
    1. Thymic carcinoma is exceedingly rare and are of squamous histology and most have metastases at the time of diagnosis and follow an aggressive course.
    2. Treatment consists of chemotherapy and radiotherapy appropriate to the corresponding histological type. 

Parathymic Conditions

  1. Myasthenia gravis
  2. Peripheral neuropathy
  3. Polymyositis
  4. Dermatomyositis
Haematologic disorders
  1. Red cell aplasia
  2. Pernicious anaemia
  3. Erythrocytosis
  4. Pancytopoenia
  5. Autoimmune haemolytic anaemia
  6. Leukaemia
  7. Multiple myeloma
Immune deficiency disorders
  1. Acquired hypogammaglobulinaemia
  2. T-cell deficiency syndrome
  3. Auto-immune disorders
  4. Systemiclupus erythematosus
  5. Rheumatoid arthritis
  6. Sjogren’s syndrome
  7. Scleroderma
Dermatologic disorders
  1. Pemphigus
  2. Lichen planus
  3. Chronicmucosal candidiasis
  4. Alopecia areata
Endocrine disorders
  1. Multipleendocrine neoplasia
  2. Cushing’s syndrome
  3. Thyrotoxicosis
  1. Giant cell myocarditis
  2. Nephrotic syndrome
  3. Ulcerative collitis
  4. Hypertrophic osteoarthropathy
  5. Lymphoidinterstitial pneumonitis

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