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SURGICAL DISEASES OF MEDIASTINUM 2 hours

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C 3

- Surgical Diseases Of Mediastinum


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The mediastinum is the central portion of the chest and extends from: the thoracic inlet above

the diaphragm below.

It is bounded

anteriorly by the sternum,

laterally by the mediastinal pleura,

posteriorly by the vertebral bodies.

To assist in the localization of mediastinal abnormalities, the

mediastinum is traditionally divided into :

superior,

anterior,

middle, and

posterior compartments.

SURGICAL DISEASES OF MEDIASTINUM

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If on a lateral chest radiograph, a line is drawnfrom the lower end of the manubriumto the lower edge of the body of the fourth thoracic vertebral body,the superiormediastinum is the area above that line.

The pericardial sacand its contents divide the inferior mediastinum into its anterior,middle, and posterior compartments. 4

T4


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The contents of the mediastinum and its compartments are :

Superior Mediastinum Thymus gland Aortic arch and great vessels Upper trachea Upper esophagus

Anterior Mediastinum

Thymus gland Lymph nodes

Middle Mediastinum

Pericardium Heart Tracheal bifurcation

Main-stem bronchi Subcarinal and peribronchial lymph nodes Ascending aorta

Posterior Mediastinum

Esophagus Descending aorta Nerves (sympathetic, parasympathetic, and intercostal)


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CT has permitted visualization of mediastinal structures that in the past wereobscured on the standard posteroanterior chest radiograph by the sternum, spine,and cardiac silhouette


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(A) Scan at level of the aortic arch and mid trachea.

(B) Scan at level of carina.

(C) Scan at the level of the left atrium.


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ACUTE MEDIASTINITIS Acute infection of the mediastinum,

regardless of the cause, is associated withgreat morbidity and mortality.

Although acute mediastinitis can follow:

penetrating wounds of the chestcomplicated with

esophageal perforation- the mostcommon cause of acute suppurativemediastinitis.

tracheobronchial tree,wounds cardiac operationsin which the

mediastinum has been opened


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INFECTIONS

CAUSES OF ESOPHAGEAL PERFORATION

INSTRUMENTAL

Endoscopy

Dilation

Intubation

Sclerotherapy

Laser therapy

NONINSTRUMENTAL

Barogenic trauma

Postemetic (Boerhaave syndrome)

Blunt chest or abdominal trauma

Other (eg, labor, convulsions, defecation)

Penetrating neck, chest, or abdominal trauma

Operative trauma

Esophageal reconstruction (anastomotic disruption)

Vagotomy, pulmonary resection, hiatal hernia repair,

esophagomyotomy

Corrosive injuries (acid or alkali ingestion)

Erosion by adjacent infection

Swallowed foreign body

ESOPHAGEAL PERFORATION


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Pathophysiology Regardless of the specific cause, the resulting mediastinitis and his severe consequences

demand prompt recognition and treatment of the esophageal disruption. Esophageal and gastric contents are sucked into the mediastinumby respiratory movements

and negative intrathoracic pressure. Salivary enzymes, gastric acid, bile, and food enter the mediastinum, the presence of oral

bacteria in these fluids initiates a fulminant infection and an inflammatory response

progresses. This mediastinal burn produces massive fluid accumulation, which can displace the trachea,heart, or lungs

The entire process is aggravated if there is preexisting esophageal diseaseClinical Features

Patients with esophageal perforation characteristically present with: cervical or thoracic pain, difficulty swallowing,

respiratory distress, fever. Pain features depends w i th esophageal per forat ion locat ion

Cervical or upper thoracic esophagusgenerally cause cervical or high retrosternal pain Middle or distal esophagusproduce anterior thoracic, posterior thoracic, interscapular, or

epigastric pain. Upper thoracic esophagealperforations may produce signs of right pleural effusion Distal esophagealperforation is associated with left pleural effusion.


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ESOPHAGEAL PERFORATIONACUTE MEDIASTINITIS


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Diagnosis

Pain or fever after esophageal instrumentation or operation is indicative of an esophagealperforation and is an indication for an immediate contrast esophagogram with hidro solublecontrast substance.

A chest roentgenogrammay help to confirm the diagnosis by demonstrating air in the softtissues of the neck or mediastinum(pneumomediastinum) or a hydrotho rax orpneumothorax.

A contrast-enhanced CT scanmay lead to the diagnosis

The morbidity and mortality rates associated with esophageal perforation are directly

related to the time interval between diagnosis of the injury and its repair or drainage


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Barium esophagogram demonstrates a perforation (arrow) in the

middle third of the thoracic esophagus.



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Management(Principles of Surgical Treatment) The init ial treatmentof an acute esophageal perforation focuses on:

decreasing bacterial and chemical contamination of the mediastinum

restoring intravascular volume losses.

Oral intake is withheld, the patient is instructed not to swallow saliva. A disposable

oral dental suctionis often helpful for evacuating oral secretions.

Broad-spectrum intravenous antibiotics with activity against oral flora are

administered using a combination of a cephalosporin (cefazolin or cefamandole), 1 g/4

h, and an aminoglycoside (gentamicin or tobramycin), 1 to 1.5 mg/kg/8 h.

Nasogastric tube decompression of the stomach is instituted to minimize possible

gastroesophageal reflux and further soiling of the mediastinum.

Therapy of esophageal perforation is influenced by:

The location of the tear The size of the tear

The cause of the tear,

The length of delay in diagnosis,

The extent of mediastinal and pleural contamination

The presence of intrinsic esophageal disease.

The treatment of an acute esophageal perforation must be individualized.


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ESOPHAGEALPERFORATIONACUTE MEDIASTINITIS


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Nonoperative Therapy

Although most esophageal perforations require operative intervention, BUTselected patientsmay be managed nonoperativelywith: Cessation of oral intake, Administration of antibiotics, Intravenous hydration until the disruption heals or the small contained cavity begins

to decrease in size.

Criteria for nonoperative therapy of an esophageal perforation include the following: A local, contained disruptionwithout evidence of pleural contamination

(hydrothorax or pneumothorax), A walled-off extravasation in which contrast material drains back into the

esophagus, Minimal or no symptoms, Minimal or no evidence of systemic infection(fever or leukocytosis).

The usual clinical settings in which such perforations are encountered are: cervical esophageal tears caused by esophagoscopy; intramural dissectionsthat have occurred during dilation of a stricture or pneumatic

dilation for achalasia; asymptomatic esophageal anastomotic disruptiondiscovered on a routine

postoperative contrast study.


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When treating such perforations conservatively,

oral hygiene should be optimizedto minimize further contamination by oral bacteria A nasogastric tubeis seldom helpful. Nutrition may be maintained by a nasogastric feeding tube, gastrostomy, or jejunostomy or

by intravenous hyperalimentationuntil oral intake can be resumed, usually 1 to 3 weeks afterthe injury.

Nonop erative therapyis best suited for patientspresenting more than 24 hours after the injurywith no systemic evidence of sepsis and clearly demonstrable, contained, internally drained leakson barium esophagogram.

Infants with iatrogenic perforation can often be successfully managed without operation.

Perforations complicatingpneumatic dilationfor achalasia occur in 4% to 6% of patients, andmost are small and well-managed medically with antibiotics and intravenous hyperalimentation.

For the remainder o f pat ients with perforat ions, operat ive therapy is general ly indicated.

Operative Therapy Of Esophageal Perforations

Cervical and Upp er Thoracic Esoph ageal Perforat ions lead to:

Progressive contamination of the mediastinumas infection descends dependently along thefascial planes from the neck.

Unless adequate drainageis accomplished, death from mediastinitis follows.

Most cervical and upper thoracic perforations may be adequately drained through a cervicalapproach, placing drains in the retroesophageal space.

An incision is made parallel to the anterior border of the sternocleidomastoid muscle, which is retracted laterally along with the carotid sheath and itscontents. The trachea, thyroid gland, and strap muscles are retracted medially. It may be necessary to divide the omohyoid muscle, middle thyroid vein, andoccasionally the inferior thyroid artery to reach the prevertebral fascia. Once this is identified, blunt finger dissection into the prevertebral space gives accessto the abscess cavity, and appropriate drains are placed and brought out through the skin incision.

When a cervical esophageal perforation extends into either pleural cavity or the lower mediastinum, the cervical approach is inadequate, and transthoracicdrainage is required.


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Operative Therapy Of Esophageal Perforations(suite)


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Approach for drainage of a cervical

esophageal perforation.



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Operative Therapy Of Esophageal Perforations(suite)Thoracoesophageal Perforations

Normal esophagus

The earlier an esophageal perforation is recognized and treated, the better is the chancefor successful primary repair.

Most agree that such perforations that are not associated with intrinsic esophagealdisease are best treated with primary repair of the tear combined with wide mediastinal

drainage. A change in philosophy has occurred regarding the application of primary repair to

perforations occurring in an normal esophagusregardless of the duration of the injury. Perforations of the lower thirdof the esophagus are approached through a left

thoracotomyin the sixth or seventh interspace, while more proximal thoracic esophagealtears are approached through a right thoracotomy.

Mediastinal drainageis achieved by opening the mediastinal pleura from the level of the

tear to the thoracic inlet superiorly and the diaphragm inferiorly, irrigating themediastinum, and placing a large-bore chest tube that allows transpleural drainage. Perforations of the intraabdominal esophagusunassociated with pleural contamination

are approached through the abdomen.Esophagu s With Intr ins ic Disease

Perforations associated with distal obstruction from intrinsic esophageal diseaseconstitute a problem because breakdown of an attempted repair is common in thepresence of distal obstruction.

The associated obstruction must be relieved at the same time of repair and drainage.


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Operative Therapy Of Esoph ageal Perforat ions (suite) In situations in which immediate esophageal reconstruction is not possible, the stomach

is divided from the esophagus, the cardia is oversewn, The intrathoracic esophagus is

then mobilized through the diaphragmatic hiatus and a cervical incision, delivering the

entire thoracic esophagus through the neck wound and placing it on the anterior chest

wall.

The mediastinum can be copiously irrigated through the cervical incision and the

diaphragmatic hiatus at the time of esophagectomy A feeding jejunostomy is used for enteral alimentation until reconstruction is performed

several weeks later.


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Irrigation of the posterior mediastinum

after transhiatal esophagectomy for

irreparable esophageal disruption.



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Late Esophageal Perforation

The longer the time interval between the occurrence of the perforation and operative

treatment, the more inflamed are the tissues adjacent to the tear and, at least

theoretically, the greater is the risk of failure of primary suture repair.

Patients with late-recognized esophageal perforationshave been treated in a variety of

ways,with wide drainage alone, drainage and closure, drainage over a T-tube,

esophageal resection, exclusion and diversion, and even nonoperative management.


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Infection after cardiac surgery Infection after a median sternotomy for cardiac surgery is a serious complication,

especially if the patient has prosthetic aortic graft material at the base of the wound.

Mediastinitis in this setting is typically heralded by sternal instability, drainage from thewound, and fever.

Various approaches have been used to treat postoperative sternal wound infections: simple dbridement and sternal reapproximation to

staged reconstruction and the use of muscle flap rotation into the sternal woundedges.

We favor thorough sternal and mediastinal dbridement and one-stage reconstructionwith a rotated muscle flap or omentum to fill the retrosternal space.

Regardless of the technique used, it is important to obliterate the retrosternal space toprevent reaccumulation of infection.

Adequate dbridement of all exposed cartilage from the sternum and ribs is critical

because cartilage is avascular, does not heal, and promotes formation of a chronicdraining wound sinus.

If the sternum is clearly devascularized, it is necessary to remove completely all necroticbone and cartilage and to then fill the anterior mediastinal space with a muscle flap, whichalso aids with chest wall stability.


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INFECTION AFTER CARDIAC SURGERYACUTE MEDIASTINITIS


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Descending necrotizing mediastinitis(DNM) is a lethal form of AMin which infectionarisingfrom the oropharynx spreads to the mediastinum. DNMtypically develops as a complication of oropharyngeal infection(eg, odontogenic,

peritonsillar, or retropharyngeal abscesses, Ludwig angina, or infection after a pharyngeal perforation).

Although transcervical drainage is generally adequate treatmentfor AM resultingfrom a cervical esophageal perforation, this approach does not provide adequate drainagein the patient with descending necrotizing mediastinitis, and the resulting mortality rate

for this condition approaches 40%.

Althoughthe standard chest radiographmay demonstrate typical findings ofmediastinitis, the CT scan is the most valuable tool in this conditionfor evaluatingthe presence of a gas-forming infectionwithin the mediastinum and for following theadequacy of surgical drainage.

These patients are ill with: fever, pleuritic chest pain,

dysphagia, and varying degrees of airway obstruction resulting from dissection of large amountsof air and acute inflammation within the mediastinal fascial planes.

They require a tracheostomyto ensure an adequate airway during treatment of theacute mediastinitis:

If only the superior mediastinum is involvedand the infection remains above thelevel of the fourth thoracic vertebra, standard transcervical mediastinal drainagemay be adequate but this is rarely the case.


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Descending Necrotizing Mediastinitis


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Most of these patients have extensive mediastinitis, which requires acombination of : Transcervical and subxiphoid or transthoracic drainage.

Broad-spectrum aerobic and anaerobic antibiotic coverage should beinstituted immediately when the diagnosis is considered, and culture-specific antibiotics should be used as the culture reports return.

The highly lethal nature of this fulminant infection cannot be overemphasized,and patients may experience exsanguination from erosion of the great vesselsof the neck and mediastinum, aspiration, cranial nerve paralysis, brainabscesses, and necrotizing fasciitis.

Recognition of the fact that one is dealing with more than localized uppermediastinal infection of the type commonly associated with acute esophagealperforations is critical. Aggressive drainage of the mediastinum using thecervical, subxiphoid, or transthoracic route is virtually the only means ofsalvaging these patients.


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Descending Necrotizing Mediastinitis


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Chronic Granulomatous Mediastinitis (CGM) CGM frequently involve paratracheal (right more than left) and subcarinal

mediastinal lymph nodes. Tuberculosis was in the past, the most common cause of mediastinal

granulomatous infection; Histoplasmosis is now the leading etiologic agent.

The granulomatous reaction within the mediastinal lymph node may incite an

intense surrounding inflammatory response that produces mediastinal fibrosis,which can cause compression of the superior vena cava (SVC), esophagus,trachea, or airways.

Resection of large, acutely inflamed mediastinal lymph nodes involved withhistoplasmosishas been recommended to minimize the late sequelae of thisdisease.

In cases of vena cava obstruction due to mediastinal fibrosis, vascular

reconstruction using either a spiral vein graft or a Gore-Tex graft may be required ifsymptoms are severe.

The necrosis of the adjacent esophageal and tracheobronchial wallswith thedevelopment of a bronchoesophageal fistulais another potential complication ofmediastinal granulomatous disease.This complication requires a transthoracic approach, identification and division ofthe fistulous opening, closure of both the tracheal and esophageal openings, andinterposition of a flap of viable adjacent pleura or mediastinal fat to preventreformation of the fistula.


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Chronic Granulomatous Mediastinitis


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MEDIASTINAL TUMORS AND CYSTS

Mediastinal tumors can arise: primarily, secondary metastases to mediastinal lymph nodes and direct invasion of the

mediastinum by tracheobronchial, esophageal, or other malignancies.

The differential diagnosisof a mediastinal mass includes:

Neoplasms, Congenital cysts, which are not neoplastic.

The most reported series of mediastinal tumors include both congenital and neoplasticprocesses:

Neurogenic tumors are most common and account for 21% of mediastinalmasses

Thymomas (20%), Cysts (20%), and Lymphomas (12%).


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The locations of tumors in the mediastinal compartments are as follows:


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Superior Mediastinum

Thymoma Lymphoma

Thyroid adenoma

Parathyroid adenoma

Anterior MediastinumThymoma

Teratoma

Carcinoma

Lymphangioma

Hemangioma

Lipoma

Posterior Mediastinum

Neurogenic tumor Enteric cyst

Middle Mediastinum

Pericardial cyst Bronchogenic cyst

Lymphoma


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MASAOKA STAGING SYSTEM FOR THYMOMA


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Stage Definition

I Macroscopically, completely encapsulated;microscopically, no capsular invasion

IIA Macroscopic invasion in surrounding fatty tissues ormediastinal pleura

IIB Microscopic invasion into the capsule

III Macroscopic invasion into a neighboring organ,

such as pericardium, great vessels, or lungIVA Pleural or pericardial dissemination

IV B Hematogenous or lymphogenous metastases


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GENERALITIES

In nearly two thirdsof adult patients, mediastinal masses cause the following symptoms:

chest pain,

cough,

Dyspnea

Half of symptom at ic m ediast inal tumors are mal ignant,

95% of asymp tomat ic m ediast inal massesdiscovered fortunately are benig n.

Chi ldren have a higher incidence of mal ignancy of m ediast inal tumo rs than adul ts . Patients with mediast inal masses and evidence of involvement of adjacent

structures are mo re l ikely to have mal ignant disease.For example:

Hoarsenessis indicative of recurrent laryngeal nerve invasion,

Horner syndrom esignifies invasion of the ste l late gangl ion,

SVC syndrom eor t racheal comp ressionsuggests mediastinal infiltration by tumor,

Back painmay be indicative of chest wall invasion with intercostal nerve involvement

IMAGING STUDIES

A variety of radiographic studies are used in assessing a mediastinal mass:

The standard posteroanterior and lateral chest radiographassists in localization

of the mass.

Fluoroscopy, barium esophagogram, and laminographyhave also been of value.

These latter studies have all been replaced by

CT


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IMAGING STUDIES (suite)

magnetic resonance imaging, (MRI)

These modern imaging studies provide the most information about:

the exact location of the mediastinal mass,

its vascularity,

relation to adjacent mediastinal structures, and

consistency (ie, cystic, solid, or fat).

Aortographyis needed to differentiate a mediastinal tumor from an aneurysm.

BIOPSIES

Fine-needle aspirationor core-needle biopsyof mediastinal masses under CT scan or fluoroscopic

guidance may provide enough tissue for cytologic or pathologic diagnosis,

A transbronchial needle aspirationof subcarinal or paratracheal lymphadenopathy using the flexible

fiberoptic bronchoscope and fluoroscopic guidance,

Mediastinoscopy,This procedure provides access to paratracheal and subcarinal lymph nodes for

the purpose of biopsy but is inappropriate for the assessment of an anterior mediastinal mass.

requires general anesthesia, involves passage of a rigid endoscope through a low cervical incision along the anterior trachea into

the mid-mediastinum. Because the mediastinoscope follows the course of the trachea into the mid-mediastinum, i t cannot

be angled forward suff ic iently to reach the anter ior mediastinum.In patients thought to have an unresectable anterior

mediastinal or anterior hilar tumor (eg, lymphoma or metastatic carcinoma), a limited anterior second or third interspace

parasternal (Chamberlain) approach can be used. Diagnosis of the paratracheal, superior mediastinal and hilar regions can also

be obtained through a transaxillary third interspace minithoracotomy, displacing the apex of the lung downward.


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Thoracoscope-directed biopsyis appropriate in most patients who require diagnosisbefore complete excisionm, when the other modalities fail, For most newly diagnosedmediastinal masses, unless there is strong evidence to suggest unresectability, excisionalbiopsy is the standard approach.


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PULMONARY ANGIOGRAM

Acute shortness of breath. The right pulmonaryartery is cut off by an extrinsic mediastinal

mass.

POSTEROANTERIOR (A) AND LATERAL (B) CHEST ROENTGENOGRAMS

a mediastinal neurofibroma that appears as a typically rounded posterior

mediastinal paravertebral mass.


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NEUROGENIC TUMORS

Neurogenic tumors, are the most common mediastinal tumors, typically occur in a

paravertebral location in the posterior mediastinum, where they arise from the

intercostal nerves or sympathetic nerve trunks.

Their classic appearance on a standard posteroanterior and lateral chest radiograph is that of a

rounded paravertebral mass.

The spectrum of neurogenic tumors includes:

neurilenoma,

neurofibroma,

neurosarcoma,

ganglioneuroma,

neuroblastoma,

paraganglioma, and

pheochromocytoma.

In adults, most neurogenic tumors are benign; in chi ldren, they tend to be malignant.

Because of their neural crestorigin some neurogenic tumors have hormo nal act iv i ty.

Elevated vasoactive intestinal polypeptide levels have been reported with ganglioneuromas

and neurofibromas, whereas elevated urinary vanillylmandelic acid levels occur with

ganglioneuromas.

Neurogenic mediastinal tumors may produce hypertension, flushing, diaphoresis, diarrhea,

and abdominal distention, just as is the case with pheochromocytomas.

Mediastinal neurofibromas arise from the nerve sheaths and fibers and occur in patients with

von Recklinghausen disease.


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Ganglioneuromasarise from the sympathetic chain, contain ganglion cells,and are themost common neurogenic tumor in children.

The biologic behaviorof these tumors varies considerably.

The ganglioneuroblastoma, the most aggressive, is associated with an 85% 5-year

survival rate if it is completely excised.

Neuroblastomaswhich are highly aggressive malignant tumors that require

multimodality therapy combining resection, radiation, and chemotherapy.Neuroblastomas in childrenmay be associated with a neurologic syndrom ethat includes cerebellar ataxia, opsoclonus,

and polymyoclonia; these neurologic changes often regress when the tumor is resected.

The cellular DNA content of the tumor has been used as a predictor of response

to chemotherapy and as a prognostic indicator in children with neuroblastomas.

A major preoperative concern in the patient with a neurogenic tumor is whether there

is an intraspinous extension of the tumor through the intervertebral foramen.

A tumor with both an intraspinous and intrathoracic component is termed a dum bbel l

neurogenic tumor(10%) and has the potential for intraoperative disaster if it is notrecognized and planned for preoperatively.

This should be suspected in any patient with a posterior mediastinal tumor who

presents with either radicular pain, vertebral body pedicle erosion, or enlargement of

an intervertebral foramenon spinal radiographs or CT scan.

In such situations, either a myelogram or magnetic resonance imaging scan of the

spine is indicated to determine if there is an intraspinous component of the tumor.


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MR imagedemonstrating intraspinous and intrathoracic

components of a dumbbell neurogenic tumor.

CT tomography shows the mass to be cystic

(cursor), and the right pulmonary artery draped

over it.


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Patients with an asymptomatic posterior mediastinal tumor that is suspected on thebasis of chest radiograph and CT scan to be a neurogenic tumor require only a routine

preoperative assessment before thoracotomy.

Those in whom an intraspinous component of the tumor has been demonstrated require

a combined neurosurgicalthoracosurgical approach.

If such a dumbbell tumor is inadvertently amputated during resection of the

intrathoracic component of the tumor, allowing the remainder of the tumor to retract

into the spinal canal, subsequent intraspinous bleeding may result in paraplegia ordeath.

Therefore, when dealing with a dumbbell neurogenic tumor, the intraspinous

component should be resected first and then the intrathoracic component.This is

achieved in one operation by extending the posterior laminectomy neurosurgical incisioninto a posterior thoracotomy in the appropriate interspace.


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Pheochromocytoma Pheochromocytomasare hormonally active tumors of the sympathetic nervous system.

They are termed chromaffin tumors because of their affinity for chromic salts on staining.

Chromaffin tissue is of neural crest origin and occurs inthe adrenal medulla, in the

sympathetic ganglia, in the paraganglia along the sympathetic chain and the organ of

Zuckerkandl, in small nests scattered along the aorta, in walls of blood vessels, and in the

heart, prostate, and ovary.

Any of these aberrant collections of chromaffin tissue can give rise to pheochromocytomas. 90 % of pheochromocytomas occur in the adrenal gland, where they produce excessive

catecholamines, predominantly norepinephrine. Ten percent of pheochromocytomas occur

in an extraadrenal location, and fewer than 2% of all pheochromocytomas occur in the chest.

using the relatively newly developed radiopharmaceutical 131I-metaiodobenzylguanidine

(131-MIBG), which has permitted scintigraphic localization of pheochromocytomas.

Using the 131-MIBG scan in combination with contrast-enhanced CT, a growing number of

cardiac pheochromocytomas are reported.

Intrathoracic pheochromocytomas present both diagnostic and therapeutic challenges.

Unlike pheochromocytomas of the abdomen or posterior chest, these tumors do not shell out

from adjacent tissue. They frequently require resection of involved myocardium or coronary

vessels with pericardial patching or coronary artery bypass grafting, and therefore

cardiopulmonary bypass must be available for their removal.


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Paragangliomas Paragangliomas (chemodectomas) of the parasympathetic nervous system do not

contain chromaffin and, unlike pheochromocytomas, usually do not produce hormones.

These tumors typically occur in carotid body, glomus jugulare, aorticopulmonary glomus,

vagal body, and ciliary glomus chemoreceptor tissues.

These relatively rare tumors most often are localized to the posterior mediastinum, as is the

case with most thoracic neurogenic tumors. In this latter location, where they arise from the

paravertebral sympathetic ganglia, they are readily resectable, as are most posteriormediastinal neurogenic tumors.

Teratoma

Teratomasare composed of cells that arise from more than one embryonic germ cell layer.

Totipotential cells of the ovary, testis, and embryonic rests that can differentiate into any of

the three primary germ cells layers give rise to teratomas. Mediastinal teratomas typically occur as dermoid cystsin the anterior mediastinum,

frequently growing to large size and containing hair and teeth.

Most teratomas are benign, and the 10% to 20% that are malignant are frequently

associated with elevated -fetoprotein and carcinoembryonic antigens.

When a malignant teratoma is suspected preoperatively, serum tumor marker levels should

be obtained and a needle biopsy performed to establish a tissue diagnosis.


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Multidrug chemotherapy, based primarily on cisplatin, is then instituted, and when thetumor markers fall to a normal range, wide resection of the tumor is carried out.

Although most teratomas are benign and can be resected through a median sternotomy,

their large size and the surrounding inflammatory response that they induce may

complicate the resection.

Thymoma

Thymic tumors occur more frequently in adults than in children. Rarely, infants with marked thymic enlargement due to hyperplasia require emergent

thymectomy to relieve their cardiorespiratory embarrassment.This approach is now

thought to be preferable to radiotherapy, which was used in the past, but which is

associated with a definite increased risk of malignancy in the field of radiation.

The relation between the thymus gland and myasthenia gravis has been appreciated for

many years. Myasthenia gravis is generally regarded as an immunologic disorder in which

serum antibodies form against acetylcholine receptors in the muscle. The thymus glandhas been postulated to be the source of the acetylcholine receptorlike antigen.

Some 10% to 20% of patients with myasthenia gravis have thymomas, and

60% have thymic hyperplasia. Nearly

75% of patients with thymomas develop myasthenia gravis within 10 years.Thymoma has been associated with other conditions besides myasthenia gravis, specifically, red blood cell

aplasia, Cushing syndrome, hypogammaglobulinemia, and collagen vascular disease.


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Thymectomy is generally most beneficial in young women with myasthenia gravis whohave no thymomas and a short duration of their disease. Most neurologists still use

anticholinesterase drugs (pyridostigmine and neostigmine), immunosuppressants

(azathioprine, antilymphocyte serum, antithymocyte serum), and occasionally steroids as

the primary treatment for myasthenia gravis. Any patient who has a thymoma should

undergo a thymectomy both to establish the diagnosis of the mediastinal mass and to

prevent potential spread of the tumor. One quarter of thymomas are malignant.

Traditional teaching has held that the diagnosis of malignant thymoma is extremelydifficult on the basis of histologic criteria, the most important determinant of malignancy

being the surgeons assessment of invasion by the tumor of adjacent tissues such as

pleura, blood vessels, pericardium, or lung. The Masaoka staging system for thymoma

combines both operative findings and histologic evaluation to guide therapy

A 10-year survival rate of 87% has been reported for encapsulated thymoma,

62% for locally invasive, and 40% if there is pleural seeding.

With the addition of chemotherapy and radiotherapy for patients with stage II or greater

disease, survival was markedly improved by the addition of neoadjuvant radiation and

chemotherapy.


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Miscellaneous Tumors

Mediastinal lymph node involvement by lymphoma may present as an anterior mediastinalmass on chest radiograph. Because the accurate diagnosis of lymphoma by cytology of tissueobtained from fine-needle aspiration is notoriously difficult unless there is associatedadenopathy at other sites that are more amenable to biopsy, biopsy of mediastinal lymph nodesmay be required to obtain adequate diagnostic specimens. Either mediastinoscopy (forparatracheal or subcarinal adenopathy), or an anterior mediastinotomy through a parasternalsecond or third interspace incision (Chamberlain) approach is used. Radical resection ordebulking of mediastinal lymphoma is inappropriate therapy because these tumors are more

responsive to combined radiation and chemotherapy. Large goiters of the thyroid gland may grow retrosternally into the superior mediastinum.

Although these substernal goiters present as an anterior superior mediastinal mass on chestradiograph, their resection rarely requires a sternal split, and they can virtually all be resectedthrough a standard transcervical approach. Because tracheomalacia may result from prolongedpressure on the trachea by the enlarged thyroid, prolonged ventilatory assistance may berequired postoperatively. Ectopic mediastinal thyroid tissue may present as a thyroid adenoma.These tumors characteristically present as asymptomatic mediastinal masses. Ten percent of

parathyroid adenomas are located within the anterosuperior mediastinum and may require avariety of studies for diagnosis and localization (eg, venous angiography with sequentialparathyroid hormone assays and CT, thallium, and technetium scanning).

Less common mesenchymal tumors of the mediastinum include fibrosarcomas andliposarcomas, fibrous histiocytomas, leiomyosarcomas, and mesotheliomas. Mediastinaltumors of the vascular and lymphatic systems (hemangiomas, hemangiopericytomas,and lymphangiomas) are extremely rare and usually occur in the anterior mediastinum.


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Mediastinal Cysts Mediastinal cysts are classified as:

bronchogenic,

enteric (duplication),

pericardial.

Bronchogenic cysts originate from the primordial respiratory tissues of the ventral foregutand are generally found in proximity to the trachea, main-stem bronchi, or posterior carina.

They have a ciliated respiratory epithelial lining. Although usually asymptomatic in adults and

presenting as a smooth mediastinal mass near the carina, these cysts can attain large size

and cause compression of adjacent structures.

Enteric (duplication or enterogenous) cysts arise from the dorsal foregut from which the

alimentary tract evolves and are therefore located in proximity to the esophagus in theposterior mediastinum, occasionally being found intramurally within the wall of the esophagus

Functioning gastric epithelium that lines some of these cysts may result in ulceration and

bleeding. Technetium scanning has been used to localize gastric mucosa within the

mediastinum. Enterogenous cysts are often associated with vertebral body abnormalities and

spinal cord attachments.


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Mediastinal Cysts (suite) Pericardial cysts Almost 75% of them occur in the right cardiophrenic angle, either in

continuity with the pericardial space or separately as a pericardial developmental abnormality.

They rarely cause symptoms and are most often detected on a chest radiograph obtained for

other reasons. In the past, resection of these masses was recommended to establish a tissue

diagnosis; the CT scan now usually can identify the cystic nature of the lesion, making the

need for resection less compelling. Percutaneous CT-guided needle aspiration of pericardialcysts has been recommended, and the fluid obtained is evaluated cytologically.


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Barium esophagogram, posteroanterior (A) and lateral

(B) views, showing an intramural esophageal

duplication cyst.


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Mediastinal emphysema (pneumomediastinum) Entry of air into the mediastinum may occur from the tracheobronchial tree, the neck, or

the abdomen. Both penetrating wounds of the mediastinum as well as blunt chest trauma

may be responsible for mediastinal emphysema.

Compression injuries of the thorax may cause a marked rise in intrathoracic pressure,

rupture of peripheral alveoli, and the initiation of dissection of air in the interstitial planes

of the lung toward the hilum and then into the mediastinum.

A forceful sneeze or bout of asthma can produce mediastinal emphysema in the same

way (spontaneous mediastinal emphysema).

Clinical presentation mediastinal emphysema may have a dramatic clinical presentation

but is usually not life-threatening.

Patients often complain of :

retrosternal discomfort

subcutaneous crepitus at the base of the neck air continues to dissect upward from the mediastinum into the subcutaneous tissue

planes, cervical, fascial, thoracic, truncal, scrotal, and extremity swelling and crepitus

can develop.

air within the periorbital tissues may cause sufficient swelling to prevent the patient

from opening the eyelids.

a precordial crunch is heard typically during systole (Hamman sign) on auscultation

over the anterior chest.


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Mediastinal emphysema (pneumomediastinum)


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Mediastinal emphysema (pneumomediastinum)(suite) Air is seen in the mediastinal tissue planes, along the pericardium, and in the soft

tissues of the neck, chest, and upper abdomen on chest radiographs.

Rarely in adults, tension pneumomediastinum may interfere with venous return to the

heart and result in cardiovascular collapse.

Most often, spontaneous mediastinal emphysema is self-limiting and requires little

treatment other than sedation and supplemental oxygen.

If an associated pneumothorax is identified, a tube thoracostomy should be performed. If

the patient is distressed by the inability to open the eyes, 5-mm decompressing incisions

made in the skin folds of the eyelids or neck using local anesthesia permit the

subcutaneous air to be milked out by gentle pressure, allowing the patient to open the

eyes.


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Mediastinal emphysema (pneumomediastinum)


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Superior vena cava syndrome is due to obstruction of the SVCand presents clinically : facial and upper extremity edema,

distention of the veins of the head, neck, arms, and upper thorax,

dusky rubor of these areas suggesting cyanosis.

Patients complain of :

periorbital swelling,

a full feeling in their head, and

a roaring in the ears aggravated by lying supine or bending.

Differential diagnosis

congestive heart failure,

cirrhosis,

constrictive pericarditis may be included in, these conditions are excluded by the

absence of swelling in the lower half of the body.

75% of patients with SVC syndrome have malignant disease within the mediastinumcompressing the SVC, most often bronchogenic carcinoma involving the right upper lobe.

SVC obstruction can also result from lymphoma and metastatic carcinoma within the

mediastinum.

25% of patients with SVC syndrome have a benign cause, such as mediastinal

granulomatous disease, idiopathic mediastinal fibrosis, goiter, or bronchogenic cysts.

Despite the rather characteristic clinical presentation that leaves little doubt as to the

diagnosis, many physicians still feel compelled to obtain a venogram.


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Superior vena cava syndrome


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Not only does this study add little information to that provided by the physical examination, but it may also be associated withconsiderable morbidity if injected contrast material extravasates into the subcutaneous tissues of the arm when an injection is

performed in the presence of marked venous hypertension. The venogram for evaluation of SVC obstruction has been replaced

with the use of MR imaging and angiography, which delineate mediastinal structures as well as vascular impingement from

extrinsic compression. In most patients with SVC syndrome due to malignant disease, cure is not possible because of the extent of

mediastinal invasion by the tumor. Nevertheless, a tissue diagnosis is important because it may alter therapy. Therefore, sputa

should be collected for cytologic evaluation. A central lung mass identified on CT scan may be diagnosed with bronchoscopy and

biopsy or transthoracic fine-needle aspiration biopsy. Mediastinoscopy has also been used in patients with SVC syndrome,

although there are two concerns with the use of this procedure in this setting. First, mediastinal venous hypertension may beresponsible for bleeding complications. Second, SVC obstruction may produce submucosal edema of the tracheobronchial tree

that can precipitate acute airway obstruction when aggravated by endotracheal intubation that is required for general anesthesia in

these patients. Both radiotherapy and chemotherapy are often effective in providing rapid and acute relief of SVC obstruction due

to malignant disease. Because of the poor prognosis of patients with SVC obstruction due to malignant disease, surgical therapy is

seldom indicated. Most patients with SVC obstruction due to benign disease gradually develop chest wall and mediastinal venous

collaterals, so that their symptoms improve with time. In rare cases, autogenous or prosthetic vein graft replacement or bypass is

used to relieve the SVC obstruction.


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Superior vena cava syndrome

c 3 Mediastinum

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