Show Summary Details
Page of

Mediastinal abnormalities 

Mediastinal abnormalities
Chapter:
Mediastinal abnormalities
Author(s):

Stephen Chapman

, Grace Robinson

, John Stradling

, Sophie West

, and John Wrightson

DOI:
10.1093/med/9780198703860.003.0033
Page of

PRINTED FROM OXFORD MEDICINE ONLINE (www.oxfordmedicine.com). © Oxford University Press, 2021. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy and Legal Notice).

date: 26 October 2021

Introduction to mediastinal abnormalities

The mediastinum is the area within the centre of the chest containing the heart, great vessels, nerves, lymph nodes, trachea, oesophagus, and thymus. Two-thirds of mediastinal masses are benign. Age 20–40; presence of symptoms and anterior location of a mass are all associated with an increased likelihood of malignancy. Common symptoms of mediastinal disease include cough, chest pain, and dyspnoea, as well as symptoms relating to any structure being compressed such as dysphagia, stridor, or SVCO. Mediastinal disorders can also be asymptomatic. They may be found incidentally following a CXR.

Anatomy

Anterior mediastinum

The area behind the body of the sternum and in front of the fibrous pericardium. Contains the thymus, which also extends superiorly.

Posterior mediastinum

The area in front of the vertebral bodies and behind the fibrous pericardium. Contains the spinal nerve roots, the descending aorta and oesophagus, the azygos and hemiazygos veins, the thoracic duct, and vagus and splanchnic nerves.

Superior mediastinum

The area located between the thoracic inlet superiorly, the manubrium of the sternum anteriorly, by the superior four thoracic vertebrae posteriorly, and inferiorly where a horizontal plane would cross through the sternal angle. It contains the aortic arch and its large branches and the upper half of SVC. It also contains the trachea, the oesophagus, the thoracic duct, and the phrenic, vagus, cardiac, and left recurrent laryngeal nerves.

Middle mediastinum

The area containing the heart and pericardium, the ascending aorta, the lower half of the SVC, part of the azygos vein, the pulmonary arteries and veins, the tracheal bifurcation, phrenic nerves, and the IVC.

These areas are easily seen on a lateral CXR (represented in Fig. 33.1).

Fig. 33.1 Anterior, posterior, superior, and middle mediastinum.

Fig. 33.1 Anterior, posterior, superior, and middle mediastinum.

Likely nature of mediastinal mass according to anatomical site

Anterior mediastinal mass

  • Thymoma (superior)

  • Thyroid (superior)

  • Germ cell tumour

  • Lymphoma

  • Ascending aortic aneurysm

  • Pleuropericardial cyst

  • Pericardial fat pad

  • Morgagni anterior diaphragmatic hernia (see Mediastinal abnormalities p. [link]).

Superior mediastinal mass

  • Bronchogenic cyst.

Posterior mediastinal mass

  • Neural tumour

  • Foregut duplication or cyst

  • Lipoma

  • Descending aortic aneurysm

  • Bochdalek posterior diaphragmatic hernia (see Mediastinal abnormalities p. [link]).

Approach to the patient with a mediastinal mass

  • Full history

  • Examination, including skin, lymphadenopathy (neck, axillae, groins), and testes

  • Look for fatigability: ptosis, ophthalmoplegia, inability to maintain upward gaze

  • Look for signs of SVCO or stridor

  • Blood tests, including AFP, β‎HCG, anti-acetylcholine receptor (AChR) antibody

  • CXR and lateral CXR (if not already done)

  • Arrange CT scan of chest

  • Try and locate old CXRs.

Mediastinal abnormalities 1

Neural tumours

Mostly occur in the posterior mediastinum. 75% are benign in adults. MRI often helpful in assessment.

  • Schwannomas and neurofibromas are benign peripheral nerve sheath tumours. They may be multiple. Usually asymptomatic, although can cause segmental pain. Slowly enlarge and rarely can cause cord compression, with dumb-bell-shaped tumours straddling the intervertebral foramen. Can be surgically excised

  • Malignant peripheral nerve sheath tumours or neurosarcomas include new malignant growths and benign neurofibromas that have undergone malignant change. They may cause systemic features of malignancy and can invade locally and metastasize

  • Autonomic nervous system tumours, including neuroblastomas and ganglioneuromas, range from benign to malignant. Surgical removal is the treatment of choice, with radiotherapy and chemotherapy if the tumour is malignant.

Thymoma

Tumour of epithelial origin arising in the thymus. May contain functioning thymic tissue. ♂=♀. Rare below age 20. Myasthenia gravis is present in 30–40% of patients with a thymoma; this is often unimproved after thymectomy and may even develop after the thymoma is removed. 20% of patients presenting with myasthenia gravis are found to have a thymoma, particularly if patients are over 50 and ♂. This group is likely to have positive AChR autoantibodies, which bind to AChRs at the post-synaptic motor endplate, decreasing available acetylcholine binding sites, causing nerve fatigability.

Patients with thymomas are usually symptomatic with pain, dyspnoea, dysphagia, or myasthenia gravis symptoms. Thymomas contained within the thymic capsule tend to be benign, although they do have malignant potential; those that have extended outside the capsule are malignant and may involve local structures or metastasize. Diagnose with CT, and treat with surgical excision of the thymus, avoiding prior FNA or biopsy, as this may cause tumour seeding outside the capsule. Consider post-operative radiotherapy and chemotherapy for invasive tumours, especially those not completely excised. Thymectomy is indicated in patients with myasthenia gravis, even without thymoma, as it may lead to symptomatic improvement. This gives best results in those with detectable AChR antibody levels and younger patients early in the disease course, particularly those with severe disease.

Thymic cyst

may be congenital or acquired 2° to inflammation. Asymptomatic unless large and causing symptoms of compression. Benign but usually treated with surgical excision, as diagnostic certainty may be difficult.

Thymic carcinoid

Not associated with myasthenia gravis and behaves aggressively, with local recurrence and metastasis. May be associated with Cushing’s syndrome. Treatment with surgery, chemotherapy, or octreotide.

Also:

thymic carcinoma, thymic lipoma, and thymic hyperplasia.

Germ cell tumours

Arise from immature germ cells, which fail to migrate during development. Tend to be in an anterior and midline location.

  • Mature cystic teratomas represent 80% of germ cell tumours. These are benign and occur in young adults. ♂=♀. Often asymptomatic but can erode surrounding structures and cause symptoms. CXR shows well-defined mass, which may contain flecks of calcification. Treatment is by surgical excision

  • Seminoma occurs in men age 20–40y. Mediastinal seminomas are malignant and almost always arise within the thymus and are histologically indistinguishable from those occurring in the testes. Can be 1° mediastinal tumour or metastasis from testicular tumour; therefore, always examine testes and perform USS. Patients frequently present with chest pain. CXR shows non-calcified lobulated anterior mediastinal mass, confirmed with CT. Serum AFP is normal, and this aids diagnosis. Diagnose with surgical biopsy. Surgical excision is not recommended as is usually incomplete. Treatment is with cisplatin-based chemotherapy initially, which can cause infertility, and, therefore, patients may wish to consider sperm banking before treatment. Tumours are radiosensitive, so radiotherapy used if they are bulky. Long-term survival expected in 80%. Better prognosis than non-seminomatous germ cell tumours

  • Non-seminomatous germ cell tumours (including choriocarcinoma, teratocarcinoma, and yolk sac tumours) are all malignant and occur in men in their 30s. They are symptomatic due to local invasion, and they metastasize. CXR shows mediastinal mass, and diagnosis is with surgical biopsy. β‎HCG and AFP are raised. Treatment is with cisplatin-based chemotherapy. β‎HCG and AFP are markers of disease and fall with tumour response.

Thyroid

Retrosternal goitre occurs, especially in older women. Usually asymptomatic unless large and compressing the trachea, causing dyspnoea and stridor. May be seen on plain CXR. CT and radioactive iodine isotope scans are helpful in diagnosis. Flow–volume loops are abnormal if there is tracheal compression. Surgery is recommended if there is airway compromise but can lead to tracheomalacia afterwards.

Also:

parathyroid adenoma.

Mediastinal abnormalities 2

Lymphoma

The mediastinum is frequently involved in patients with Hodgkin’s lymphoma. CT scan is necessary to assess the extent of this and to assess response to treatment. To establish the histological diagnosis of lymphoma, an adequate tissue sample is required; this should be from a biopsy, rather than a fine-needle aspirate. This may be best achieved surgically via mediastinoscopy. Examine patient for peripheral lymph nodes, as these may be easier to biopsy. Treatment is with chemotherapy initially.

Enlarged lymph nodes

  • Metastases from breast, lung, and oesophageal cancer

  • Castleman’s disease Giant lymph node hyperplasia. Rare. Two forms:

    • Angio-follicular hyperplasia causing mediastinal or hilar lymph node mass. Often asymptomatic or may cause cough or wheeze due to localized compression. Non-progressive. May have fever and raised ESR. Nodal biopsy shows follicles of pericapillary lymphocytes and proliferation of the plump and eosinophilic capillary endothelial cells. Removal of node(s) may improve symptoms and be curative. Can also occur on pleura

    • Multicentric Castleman’s disease is a more aggressive disease that usually occurs in association with HIV infection. Lymphoproliferative disorder with prominent systemic symptoms (night sweats, fatigue, weight loss) as well as generalized lymph node enlargement, hepatosplenomegaly, paraproteinaemia, and skin rash. Biopsy shows prominent plasma cell infiltration. Related to IL6 overproduction and human herpesvirus-8 infection. Treatment is with rituximab first line, which induces remission in a high percentage of patients. For patients with aggressive disease or poor performance status, rituximab ± steroids ± chemotherapy (etoposide and vincristine) may be preferred first line, but prognosis is poor. Can progress to non-Hodgkin’s lymphoma. Rapidly fatal without treatment

    • Also: lymphangioma.

Cysts

  • Foregut duplications or bronchogenic cysts can be related to the oesophagus or the airways, especially near the carina. Lined by respiratory epithelium. Often diagnosed in childhood, as they cause dyspnoea, stridor, or cough due to limited space to expand. Seen on CXR and CT and treated with surgical excision

  • Pleuropericardial cysts mostly occur at the cardiophrenic angles and can measure up to 25cm diameter. ♂=♀. Usually asymptomatic but may cause chest pain. CXR shows smooth, round shadow abutting the heart. Excision can be carried out at thoracoscopy, but conservative management is favoured. Also known as springwater cysts.

Inflammation

  • Mediastinitis occurs after oesophageal perforation or rupture, due to malignancy, instrumentation, or vomiting (Boerhaave’s syndrome). Patients are ill, with pain and fever. CXR may show widened mediastinum or air in the mediastinum. Pneumothorax or pleural effusion may also be seen. Treatment includes repairing the defect, parenteral feeding, and antibiotics. High morbidity and mortality

  • Mediastinal fibrosis Rare idiopathic condition that occurs in middle age. Symptoms depend on which aspects of the mediastinum are involved but may include dyspnoea, wheeze, haemoptysis, hoarse voice, dysphagia, PHT, SVCO. CXR shows a widened mediastinum. Diagnosis made on biopsy, particularly to exclude malignancy. Treatment is supportive; steroids and surgical debulking ineffective. Prognosis variable, depending on sites involved. May be associated with retroperitoneal fibrosis, radiotherapy, methysergide, autoimmune disease, or infection with TB, histoplasmosis, Aspergillus, or Nocardia.

Mediastinal emphysema

or pneumomediastinum. Can be caused by sneezing, straining, Valsalva manoeuvres, vomiting, substance abuse, parturition, positive pressure ventilation, instrumentation, or TBB. Usually symptomless but occasional pain. Hamman’s sign may be present (click with each heartbeat on auscultation over lung). Treat with high-flow O2. Resolves spontaneously.

Vascular

Aortic aneurysms are usually asymptomatic, but symptoms relate to compression of adjacent structures. May diagnose on CXR as a widened mediastinum. This is best imaged via CT or MRI. Surgery should be considered to prevent death from rupture.

Further information

Duwe BV et al. Tumors of the mediastinum. Chest 2005;128:2893–909.Find this resource: