(Cл) The mediastinum

(Сл)The mediastinum is a non-delineated group of structures in the thorax,

surrounded by loose connective tissue. It is the central compartment of the thoracic cavity.

It contains the heart, the great vessels of the heart, esophagus, trachea, phrenic nerve, cardiac nerve, thoracic duct, thymus, and lymph nodes of the central chest.(Сл)

AnatomyThe mediastinum lies between the right and left pleura in and near the median

sagittal plane of the chest.It is surrounded by the chest wall anteriorly, the lungs laterally and the spine

posteriorly. It is continuous with the loose connective tissue of the neck, and extends inferiorly onto the diaphragm.(Сл)

It extends from the sternum in front to the vertebral column behind, and contains all the thoracic viscera excepting the lungs. It may be divided for purposes of description into two parts: an upper portion, above the upper level of the pericardium, which is named

the superior mediastinum; and a lower portion, below the upper level of the pericardium.

This lower portion is again subdivided into three parts, viz., that in front of the pericardium,

the anterior mediastinum; that containing the pericardium and its contents,

the middle mediastinum; and that behind the pericardium, the posterior mediastinum.

The Superior Mediastinum is that portion of the interpleural space which lies between the manubrium sterni in front, and the upper thoracic vertebræ behind. It is bounded below by a slightly oblique plane passing backward from the junction of the manubrium and body of the sternum to the lower part of the body of the fourth thoracic vertebra, and laterally by the pleuræ. It contains the origins of the Sternohyoidei and Sternothyreoidei and the lower ends of

the Longi colli; the aortic arch; the innominate artery and the thoracic portions of the left

common carotid and the left subclavian arteries; the innominate veins and the upper half of the superior vena cava; the left highest intercostal vein;

the vagus, cardiac, phrenic, and left recurrent nerves; the trachea, esophagus, and thoracic duct; the remains of the thymus, and some lymph glands. The Anterior Mediastinum exists only on the left side where the left pleura diverges from the mid-sternal line. It is bounded in front by the sternum, laterally

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by the pleuræ, and behind by the pericardium. It is narrow, above, but widens out a little below. Its anterior wall is formed by the left Transversus thoracis and the fifth, sixth, and seventh left costal cartilages.

It contains a quantity of loose areolar tissue, some lymphatic vessels which ascend from the convex surface of the liver,

two or three anterior mediastinal lymph glands, and the small mediastinal branches of the internal mammary artery.

The Middle Mediastinum is the broadest part of the interpleural space. It contains

the heart enclosed in the pericardium, the ascending aorta, the lower half of the superior vena cava with the azygos vein opening into it, the bifurcation of the trachea and the two bronchi, the pulmonary artery

dividing into its two branches, the right and left pulmonary veins, the phrenic nerves, and some bronchial lymph glands.

The Posterior Mediastinum is an irregular triangular space running parallel with the vertebral column; it is bounded in front by the pericardium above, and by the posterior surface of the diaphragm below, behind by the vertebral column from the lower border of the fourth to the twelfth thoracic vertebra, and on either side by the mediastinal pleura. It contains the thoracic part of the descending aorta, the azygos and the two hemiazygos veins, the vagus and splanchnic nerves, the esophagus, the thoracic duct, and some lymph glands.

(Сл) Cervical mediastinoscopyMediastinoscopy is a procedure in which a lighted instrument (mediastinoscope) is inserted through a neck incision to visually examine the structures in the top of the chest cavity and take tissue samples. This procedure can be used to biopsy lymph nodes surrounding the airway to help diagnose or see how far a particular disease has

Anterior mediastinotomyThis parasternal approach to the mediastinum has been used most commonly in situations in which standard cervical mediastinoscopy was believed, or found to be, inadequate. The classic approach is to perform it in the upper left parasternal area in order to gain access to the aortopulmonary window and areas of the anterior mediastinum inferior to the aortic arch. In many centers, anterior mediastinotomy

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is being replaced by either extended cervical mediastinoscopy or video-assisted thoracoscopy (VATS) techniques.As with cervical mediastinoscopy, this procedure has no real role in the evaluation or treatment of mediastinal cysts in children or adults.Posterior mediastinotomyThis is a rarely used procedure for biopsy of some of the posteriorly situated lymph nodes or a mass in the paravertebral sulcus. Posterior mediastinotomy is most commonly performed on the right side in a paravertebral location immediately lateral to the paravertebral muscles. As with the anterior mediastinotomy, small segments of several ribs in the area may be excised for extrapleural access to the ipsilateral paravertebral sulcus.The mediastinoscope also may be used for lymph node biopsy with this approach. It is rarely used for mediastinal tumors and cysts because these are more appropriately managed by either standard thoracotomy or VATS techniques.13 Video-assisted thoracoscopyVATS techniques have been used successfully for biopsy of various mediastinal masses and are commonly used for the sampling of perihilar lymph nodes.VATS findings can be used to confirm the diagnosis, and the technique has been used for resection of a number of mediastinal cysts.14,15 Sternotomy and thoracotomyIn spite of the numerous minimally invasive options available for histologic diagnosis of mediastinal tumors and cysts, open surgical access is needed at times.In some cases, standard sternotomy or thoracotomy may be the safest method available to obtain an adequate tissue diagnosis and to perform appropriate resection.

(Сл) All mediastinum diseases may categorized by

Injury of mediastinal organs Inflammation of mediastinal organs and tissue Mediastinal tumors

(Сл) Injury of mediastinal organs

Seventy five (75%) percent of chest traumas due to blunt or penetrating injuries are accompanied by injuries of other organ systems. Twenty five percent of deaths due to blunt trauma are constituted by chest injuries where chest trauma is an aggravating factor in 50%

Cardiac injuries take place as high as 64% in cases of thoracic organ injuries.There is a pathological condition seen after blunt cardiac injury which is called

myocardial concussion.Blunt cardiac injuries occur due to motor vehicular accidents, sport games,

animals, fall from heights and blow during fightsMost common mechanism of blunt cardiac injury is crushing.

Blunt cardiac injuries are seen in 9 to 38% of cases with severe thoracic trauma(Сл)

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Clinical and autopsy studies pointed out that myocardial injury was defined in 15 to 75% of cases with blunt thoracic trauma. This situation may appear as a wide variety of disorders such as

life-threatening arrhythmias, anomalies of conduction system, congestive heart failure, cardiogenic shock, hemopericardium, pericardial tamponade, cardiac rupture, valvular rupture, intraventricular thrombus, thromboemboli, air emboli, coronary artery occlusion, ventricular aneurysm and constrictive pericarditis. Signs and diagnosis

(Сл) Jugular venous distension, peripheral coldness and chills are accompanied by

hypotension and faint heart sounds in auscultation. In this picture of shock; triad of severe jugular venous distension, hypotension

and faint heart sounds is called Beck's triad. The presence of this triad should suggest cardiac tamponade and urgent

pericardial puncture should be carried out to drain blood under sterile conditions. Relatively small amounts of blood (approx. 100 ml) required to restrict cardiac

activity and interfere with cardiac filling. Removal of small amounts of blood or fluid (often as little as 15-20 ml) by pericardiocentesis may have enormous beneficial effectsdiagnosis is often difficult:

(Сл)If the patient was taken to the operating room and the pericardium was opened

to remove blood, the bleeding sites of myocardium should be localized and repaired. Urgent surgeryindications for early (or emergency) surgery:Absolute indications: cardiac arrest due to tamponade or exsanguinations continued haemorrhage: immediate blood loss from chest drain > 1500 ml of

total blood volume. Loss > 500 ml in first hr. or 200 ml/hr thereafter is also an indication for thoracotomy. Decision to operate should be made early before occurrence of a dilutional coagulopathy

dangerous predicted track/mediastinal traversing massive air leakRelative indications:

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thoracoabdominal injury bullet embolism high-velocity gunshot wound missile retrieval. Relative contraindications: cardiac contusion pulmonary parenchymal contusion pneumomediastinum (without other injury). (Сл)

If a patient is in shock or preshock condition and his central venous pressure (CVP) is more than 12 mm Hg, pericardiocentesis should be carried out. If the pericardiocentesis fluid is hemorrhagic, the patient should either be taken into operating room or blood/fluid replacement should be done. If rapid venous distension develops and CVP rises up, surgery is again the treatment of choice. If CVP only changes slightly with volume replacement and hemodynamic stability is maintained, either supportive treatment or surgical intervention for hemostasis could be chosen.(Сл)Among the investigations reflecting the blunt cardiac injuries are: CK-MB isoenzymes, Cardiac troponin Cardiac troponin (CTI) is the gold

standard diagnostic marker for myocardial injury. Increase in CTI starts within the first hour and continues about 4 to 7 days.

radioisotope scanning, continuous ECG monitoring, echocardiography and cardiac catheterization.(Сл)

. ECG changes are not specific ECG may reveal ST segment elevations and branch blocks. ST segment elevations are thought to be due to transient myocardial ischemia or

coronary arterial spasm. Any type of arrhythmia and ST segment changes may be seen. Sinus tachycardia, atrial flutter or atrial fibrillation are the most common ones. (Сл)These cases usually have normal echocardiographic findingsEchocardiography is getting to be used more commonly in diagnosis of blunt cardiac injuries. In blunt cardiac injuries, it is important to be able to perform echocardiography at the emergency service in detecting hemopericardiumUnderlying injury may be ruptured heart, aortic disruption, or myocardial contusion without rupture.

(Сл) Esophageal Injury

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Esophageal tears are estimated to occur in 1% of patients with blunt trauma, but they are far more common with penetrating or iatrogenic trauma. Esophageal rupture carries a high mortality rate secondary to rapidly developing mediastinitis. Survival improves dramatically if the esophageal injury is recognized and treated within 24 hours of its occurrence

(Сл) Clinical presentation of esophageal tears/rupture includes hematemesis, chest pain, dysphagia, odynophagia and rapid onset of sepsis, fever, tachycardia, hypotension and shock. Patients often complain of sudden, sharp epigastric pain radiating to the interscapular area. Dyspnea, cyanosis, and shock are late symptoms

(Сл) Diagnostic Modality– CT findings of esophageal rupture include focal extraluminal air collections

at the site of tear and a hematoma of the mediastinal or esophageal wall

– CT findings in esophageal tear/perforation can be summarized as follows: Extraluminal air in the mediastinum/surrounding the esophagus is the most reliable sign and when taken in conjunction with the clinical presentation has 92% accuracy

(Сл) Esophageal perforations that are treated surgically within 24 hours have good results. The outcome obviously depends on comorbidity and to whether postoperative pulmonary complications occur. Even with prompt therapy, the mortality rate is high, varying from 30-50%.

(Сл) With delay in diagnosis, the mortality rate exceeds 90%. Mortality rates from perforation caused by instrumentation are lower than other causes (15-20%), although clearly still notable. Vertebral osteomyelitis has been reported in association with penetrating and after blunt traumatic esophageal rupture

Inflammation of mediastinal organs and tissue(Сл)Mediastinitis is inflammation of the tissues in the mid-chest, or mediastinum. It can be either acute or chronic.

Acute mediastinitis is usually bacterial and due to rupture of organs in the mediastinum. As the infection can progress rapidly, this is considered a serious condition.

Chronic sclerosing (or fibrosing) mediastinitis, while potentially serious, is caused by a long-standing inflammation of the mediastinum, leading to growth of

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acellular collagen and fibrous tissue within the chest and around the central vessels and airways.

It has a different cause, treatment, and prognosis than acute infectious mediastinitis.

(Сл)Acute

Before the development of modern cardiovascular surgery, cases of acute mediastinitis usually arose from either perforation of the esophagus or from contiguous spread of odontogenic or retropharyngeal infections.

However, in modern practice, most cases of acute mediastinitis result from complications of cardiovascular or endoscopic surgical procedures.Patients may have a tear in their esophagus that causes mediastinitis.

Causes of the tear include: A procedure such as endoscopy Forceful or constant vomiting Trauma

Other causes of mediastinitis include: Cancer Histoplasmosis Radiation Sarcoidosis Tuberculosis

Risk factors include: Problems in the upper gastrointestinal tract Recent chest surgery or endoscopy Weak immune system

(Сл)Symptoms:

Chest pain Chills Coughing up blood Fever Malaise Shortness of breath

(Сл)Treatment usually involves aggressive intravenous antibiotic therapy and

hydration. If discrete fluid collections (such as abscesses) have formed, they may have to be surgically drained.

ChronicChronic mediastinitis is usually a radiologic diagnosis manifested by diffuse

fibrosis of the soft tissues of the mediastinum. This is sometimes the consequence of prior granulomatous disease, most commonly histoplasmosis. Other identifiable

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causes include tuberculosis and radiation therapy. Fibrosing mediastinitis most frequently causes problems by constricting blood vessels or airways in the mediastinum. This may result in such complications as superior vena cava syndrome or pulmonary edema from compression of pulmonary veins.

Treatment for chronic fibrosing mediastinitis is somewhat controversial, and may include steroids or surgical decompression of affected vessels.

(Сл)Mediastinal tumors

The mediastinum is a site for the development of epithelial, mesenchymal, lymphoproliferative, neurogenic, & germ cell neoplasms.

Because of the broad spectrum of tissue types in this region, and the variety of cell morphology even within the same neoplasm, adequate sampling cannot be overemphasized; close communication with the interventional radiologist or endoscopist is mandatory.

Utilization of fine needle aspiration biopsy (FNAB) for the diagnosis of mediastinal tumours is much less than for other body sites.

A study comparing the efficacy of mediastinal FNAB & core needle biopsy showed both methods performed with an overall diagnostic accuracy of 100%.

FNA is increasingly being used to sample mediastinal masses by combining it with endoscopy and ultrasound.

Classification of mediastinal tumors I. EPITHELIAL TUMORSII. LYMPHOPROLIFERATIVE DISORDERSIII. GERM CELL TUMORSIV. NEURAL TUMORS

(Сл)I. EPITHELIAL TUMORSA. ThymomaThymoma arises in the antero-superior mediastinum, is a neoplasm of older adults, and occurs in up to 40% with a paraneoplastic syndrome. The cytologic diagnosis is demanding. Smears vary depending on the area sampled, what cell type (epithelial or lymphoid) is most common, whether spindle cell foci are present, and whether fluid has been aspirated. B. Thymic CarcinomaPrimary carcinomas of the thymus are rare lesions. The vast majority are actually derived from the lung. Histologic variants of thymic carcinoma include keratinizing squamous cell carcinoma, sarcomatoid carcinoma, neuroendocrine carcinoma, mucoepidermoid carcinoma, and undifferentiated (lymphoepithelioma-like) carcinoma. No substantial series exists. The cytopathology is similar to that seen in lung aspirates.

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By the year 1990, the nomenclature of thymic epithelial neoplasms was sufficiently confusing that the World Health Organization (WHO) to select a panel of experts for devising a new, uniform histologic classification for these tumors. After several years of deliberation, this panel produced a compromise formula that designated thymic epithelial neoplasms according to letters and numbers into 6 categories. This WHO schema was published in 1999, [14] and soon achieved wide acceptance and recognition.

The WHO classification of thymic epithelial neoplasms divided these tumors based on the cytologic appearance of the tumor cells into three classes designated as types A, B and C. Type A thymoma was defined as a tumor primarily composed of a proliferation

of oval or spindle epithelial cells, usually with scant lymphocytes. Type B was defined as a tumor composed of round, dendritic or epithelioid

cells with variable numbers of lymphocytes. These tumors were further subdivided according to the proportional increase (in relation to the lymphocytes) and emergence of atypia of the neoplastic epithelial cells into types B1, B2 and B3.

Tumors showing a combination of the above were designated as type AB. Tumors showing overt cytologic features of malignancy were designated as thymoma type C.

The problem with applying this schema is that the "normal" thymus can vary in its morphologic appearance depending on the age of the patient and the functional status of the gland. Thus, the "normal" thymus of infancy and childhood is quite different from the "normal" thymus in the adult. With loss of the functional activity of the thymus (i.e., recruitment and programming of T-memory cells), the thymus undergoes a process of involution, whereby the lymphocytes decrease in number and are replaced by fat, and the epithelial cells undergo atrophy and diminish in size, adopting a small, spindled appearance.

(Сл)Thymoma sometimes accompanied by MyastheniaMyasthenia gravis is a chronic autoimmune neuromuscular disease (see

autoimmune disease) characterized by varying degrees of weakness of the skeletal (voluntary) muscles of the body. The name myasthenia gravis, which is Latin and Greek in origin, literally means "serious muscle weakness." With current therapies, however, most cases of myasthenia gravis are not as serious as the name implies.

(Сл)Patients with non-metastatic thymoma or thymic carcinoma or with

myasthenia gravis (with or without thymoma) are candidates for thymectomy. Treatment for myasthenia gravis is initiated by a neurologist, who recommends surgical treatment when indicated. Some of the common indications are: failure of medical treatment; young patients with short duration of symptoms; and patients who experience significant disability from their medical treatment.

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In thymic surgery for myasthenia gravis, the presence or absence of a thymoma dictates the extent of the surgical procedure required. While total thymectomy for myasthenia without thymoma can be performed through a partial sternotomy, the presence of thymoma requires a full sternotomy. During any kind of thymic procedure, the most important step is understanding the anatomy of the phrenic nerves and their close relationship to the thymus

Surgical staging of a thymoma is crucial in determining the survival of the patients. Shamji and coauthors reported a five year survival rate in patients with stage I disease of 91%, stage II disease of 80%, and in stage III disease of 42% (8). Thymic carcinoma and thymic carcinoid have poor prognosis regardless of the stage of the lesion. Postoperative adjuvant therapy may be beneficial for malignant thymoma in selected cases.

(Сл)LYMPHOPROLIFERATIVE DISORDERS -Malignant diseases of the lymphoid cells and cells from the

reticuloendothelial system. Lymphoproliferative disorders are those in which lymphocytes, white blood cells produced in the lymphatic tissue (the lymph nodes, spleen, thymus, for example), are over-produced or act abnormally.A. Hodgkin LymphomaHodgkin lymphoma (HL) is the most common mediastinal lymphoma. There is a predilection for women with a peak in the 2nd - 4th decade. In Caucasians, HL comprises up to 35% of all lymphomas in contrast to only 5-10% in Orientals.B. Large Cell LymphomaLarge cell non-Hodgkin lymphoma (NHL) of the mediastinum can be a primary tumor arising in the thymus, or a lymphoma secondarily involving lymph nodes in this region. C. Lymphoblastic Lymphoma (LL)One of the three most common NHL of children. Experience has shown that FNAB is an excellent method for the diagnosis of LL. This aggressive neoplasm comprises 1/3rd to ½ of pediatric lymphomas. The peak incidence is in adolescent and young adult males.

(Сл)An anterior mediastinal mass occurs in up to 80% of patients is often massive, and may induce a superior vena cava syndrome.

(Сл)GERM CELL TUMORSA. Germinoma/SeminomaMature teratoma is the most common form of mediastinal germ cell tumor (GCT). Germinoma/seminoma is the 2nd most frequent type. Men in the 2nd - 4th decade are affected. These may be discovered as incidental lesions on chest X-ray, but

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large masses are symptomatic. The possibility of a metastasis always needs to be excluded. B. Non-Seminomatous Germ Cell TumorsThe major subtypes in this category include yolk-sac tumor, embryonal carcinoma, and choriocarcinoma. Clinical features are similar to those for seminomatous GCT.

(Сл)Germ cell tumors occur most frequently in the gonad, but in rare cases, they occur in extragonadal locations, usually in or near the midline. A variety of extragonadal germ cell tumors are known. The mediastinum is the most common extragonadal location. In adults, approximately 10-15% of mediastinal tumors are germ cell tumors; in children, 25% of mediastinal tumors are germ cell tumors. Germ cell tumors derive from germ cell rest remnants in the mediastinum.

Germ cell tumors may be benign or malignant. Benign varieties include benign teratoma and teratodermoids. Malignant tumors include seminomas and nonseminomatous tumors (malignant teratomas). Nonseminomatous tumors are further classified as teratocarcinomas, choriocarcinomas, embryonal carcinomas, and endodermal sinus or yolk-sac tumors. About 80% of mediastinal germ cell tumors are benign; these occur with equal frequency in males and females. Malignant tumors are predominant in men; the male-to-female ratio is 9:1. Benign germ cell tumors are termed teratomas or dermoids if they are primarily solid. Some tumors are predominantly cystic; these are referred to as epidermoid or dermoid cysts. Most patients are men 20-40 years of age.

About one third of patients are asymptomatic. Symptoms, when present, are related to the size of the lesion. Human chorionic gonadotropin (HCG) levels are elevated in 7-18% of patients, but alpha-fetoprotein (AFP) levels are usually normal. Metastatic spread involves the regional lymph nodes, lungs, and bone. The neoplasm is highly chemosensitive and radiosensitive, and 5-year survival rates greater than 75% are not uncommon.

Malignant germ cell tumors are subdivided into seminomas and malignant teratomas (nonseminomatous tumors). Seminoma is the second most common mediastinal GCT.(Сл)NEURAL TUMORSThe vast majority of posterior mediastinal neoplasms are neurogenic. A. SchwannomaNeurogenic tumors account for ≈ 20-30% of mediastinal neoplasms. Schwannoma is the most common mediastinal neural tumor. Patients are usually 20-40 yrs. B. GanglioneuromaOlder female children and young adults are affected. Most are paraspinalC. Neuroblastoma/GanglioneuroblastomaThe most common childhood tumor in that site.

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(Сл)Symptoms: Almost half of mediastinal tumors cause no symptoms and are found on a chest x-ray performed for another reason. Symptoms that do occur are due to pressure on (compression of) local structures and may include:

Chest pain Chills Cough Coughing up blood (hemoptysis) Fever Hoarseness Night sweats Shortness of breath

Approximately one third of adults with a mediastinal tumor or cyst have symptoms; two thirds of children present with symptoms, which are usually related to the respiratory tract. In adults, asymptomatic masses are most likely to be benign.

In general, symptoms associated with the respiratory tract are predominant in children because, in children, the airway is malleable and the small thorax makes the effects of compression more obvious than is the case with adults. Respiratory symptoms include persistent cough, dyspnea, and stridor. If the location and size of the mass result in partial or complete obstruction, obstructive pneumonia can also occur.

Mediastinal tumors that produce bioactive substances may be associated with gynecomastia and precocious puberty.

Systemic symptoms of malignant tumors, such as weight loss, fever, malaise, and vague chest discomfort, are more common in children than in adults, but they do occur in some adults.

Superior vena cava obstruction may cause more severe symptoms than those commonly associated with malignancy (eg, cough, dyspnea, stridor, dysphagia).

Invasion of the chest wall and/or pleura by a malignant tumor may produce persistent pain and pleural effusions.

Invasion of mediastinal and/or thoracic nerves may produce local and referred pain, as well as various other findings, such as hoarseness from recurrent nerve involvement, diaphragmatic paralysis from phrenic-nerve involvement, Horner syndrome from autonomic-nerve invasion, and even motor paralysis from direct spinal-cord involvement. Pain in the shoulder or upper extremity may occur as a result of invasion of the ipsilateral brachial plexus.

(Сл)Signs and tests: A medical history and physical examination may show:

Fever High-pitched breathing sound (stridor )

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Swollen or tender lymph nodes (lymphadenopathy) Unintentional weight loss Wheezing

Further testing may include: Chest x-ray CT-guided needle biopsy CT scan of the chest MRI of the chest Mediastinoscopy with biopsy

(Сл)Treatment: Treatment for mediastinal tumors depends on the type of tumor.For thymic cancers, surgery is the treatment of choice. It may be followed by radiation or chemotherapy, depending on the stage of the tumor and the success of the surgery.For lymphomas, chemotherapy followed by radiation is the treatment of choice.For neurogenic tumors of the posterior mediastinum, surgery is the treatment of choice.

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