Mediastinal Cysts

Practice Essentials

The mediastinum is an area of the body in which a wide range of tissue variability exists. Therefore, tumors and cysts that occur in this area can represent many different clinical entities and pathologic processes. An understanding of the embryology of this area and an awareness of the anatomic relations of the normal structures within the mediastinum are essential in the proper determination of the exact nature of a mass or tumor located in this area.

Any discussion of neoplasms or other masses found within the mediastinum requires delineation of the boundaries of that area. In defining the location of specific mediastinal masses, the portion of the thorax defined as the mediastinum extends from the posterior aspect of the sternum to the anterior surface of the vertebral bodies and includes the paravertebral sulci. The mediastinum is limited bilaterally by the mediastinal parietal pleura and extends from the diaphragm inferiorly to the level of the thoracic inlet superiorly.

Because a number of mediastinal tumors and other masses are most commonly found in particular mediastinal locations, many authors have artificially subdivided the area for better descriptive localization of specific lesions. Most commonly, the mediastinum is subdivided into three spaces or compartments in discussing the location or origin of specific masses or neoplasms, as follows^[1] :

• The anterior compartment extends from the posterior surface of the sternum to the anterior surface of the pericardium and great vessels
• The middle compartment is located between the posterior limit of the anterior compartment and the anterior longitudinal spinal ligament
• The posterior compartment is the area posterior to the heart and trachea and includes the paravertebral sulci

The most common tumors and masses in the anterior compartment are of thymic, lymphatic, or germ cell origin.^{[2, 3]}  More rarely, the masses found are associated with the aberrant parathyroid or thyroid tissue. Neoplasms and other masses originating from vascular or mesenchymal tissues also may be found. Rarely, bronchogenic cysts may be found in the anterior mediastinum, and some have been reported within the thymus.^[4]

Whereas neoplasms of the middle mediastinum are most commonly of lymphatic origin, neurogenic tumors also may occasionally occur in this area.^[5]  Another significant group of masses identified in this compartment consists of cystic structures associated with a developmental abnormality of the primitive foregut or the precursors of the pericardium or pleura.^[6]  These include bronchogenic, esophageal, gastric, and pleuropericardial cysts. In addition, more complex cysts related to embryologic abnormalities (eg, neurenteric or gastroenteric cysts) can be found.

Isolated cystic abnormalities of lymphatic origin, such as hygromas or lymphangiomas,^[7]  can develop within the middle mediastinal compartment, but more commonly, they are extensions of these abnormalities from the cervical lymphatics.

Neurogenic tumors are by far the most common neoplasms of the posterior mediastinum. Tumors originating from lymphatic, vascular, or mesenchymal tissues can also be found in this compartment. Bronchogenic cysts can also be found in this area and have been found in the paravertebral sulcus.

Surgical resection is indicated for most mediastinal cysts. All large and symptomatic bronchogenic cysts are included in the group, as are all enteric gastroenteric and neurenteric cysts. Some authors do not recommend resection of small asymptomatic bronchogenic cysts, whereas others advise aspiration of such cysts and resection only for those with symptoms or recurrence.

Excision of pleuropericardial cysts and simple mesothelial cysts is indicated for diagnostic purposes only. Thymic cysts require excision or enucleation. Thoracic duct cysts require excision and accompanying ligation of the thoracic duct.

Surgical removal is not indicated as primary treatment for (1) pleuropericardial cysts, lymphogenous cysts, and simple mediastinal cysts, provided an accurate nonsurgical diagnosis has been performed and (2) some cases of bronchogenic cysts found in adult patients in which the cyst is small and the patient has no symptoms. (This opinion varies among authors.)

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Anatomy

With respect to the location of specific mediastinal masses, the portion of the thorax defined as the mediastinum extends from the posterior aspect of the sternum to the anterior surface of the vertebral bodies and includes the paravertebral sulci. The mediastinum is limited bilaterally by the mediastinal parietal pleura and extends from the diaphragm inferiorly to the level of the thoracic inlet superiorly.

Traditionally, the mediastinum is artificially subdivided into three compartments for better descriptive localization of specific lesions. In most cases, when specific masses or neoplasms are discussed, the location or origin is defined as being in the anterior, middle, or posterior compartments or spaces.

The anterior compartment, or anterior mediastinum, extends from the posterior surface of the sternum to the anterior surface of the pericardium and great vessels. It normally contains the thymus gland, adipose tissue, and lymph nodes.

The middle compartment, or middle mediastinum, is located between the posterior limit of the anterior compartment and the anterior longitudinal spinal ligament. This area contains the heart, the pericardium, the ascending and transverse portions of the aorta, the brachiocephalic vessels, the main pulmonary arteries and veins, the superior vena cava (SVC) and the inferior vena cava (IVC), the trachea and mainstem bronchi, and numerous lymph nodes.

The posterior compartment, or posterior mediastinum, comprises the area posterior to the heart and trachea and includes the paravertebral sulci. It contains the descending thoracic aorta and ligamentum arteriosum, the esophagus, the thoracic duct, the azygos vein, and numerous neural structures (including the autonomic ganglion and nerves, lymph nodes, and adipose tissue).

Foregut cysts of the mediastinum are found most commonly in the middle and posterior compartments but have been reported in the anterior compartment.^{[8, 6]} These cysts are usually found in close association with the tracheobronchial tree or the esophagus. Foregut cysts have also been found in the lung and pericardium and (rarely) have been reported in areas outside the chest (eg, the subcutaneous tissues of the anterior and posterior chest wall and the abdominal cavity).

Cysts of other types may be found in any of the three compartments.

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Pathophysiology

Tumors and cysts of the mediastinum can produce abnormal effects at both systemic and local levels.

Local

Because of the malleable nature and small size of the pediatric airway and other normal mediastinal structures, benign tumors and cysts can produce abnormal local effects. These effects are more evident in children than in adults.

Compression or obstruction of portions of the airway, the esophagus, or the right heart and great veins by a large or enlarging tumor or cyst can occur, resulting in a number of symptoms. Rarely, bronchogenic cysts have been described as causing SVC syndrome (SVCS) or pulmonary artery compression. Infection can occur primarily within some of these mediastinal lesions (particularly those of a cystic nature) or can result secondarily in nearby structures (eg, lungs) as a result of local compression and subsequent obstruction.

Malignant mediastinal tumors can cause all of the same local effects as those associated with benign lesions but can also produce abnormalities by invasion of local structures. Local structures most commonly subject to invasion by malignant tumors include the following:

• Tracheobronchial tree and lungs
• Esophagus
• SVC
• Pleura and chest wall
• Any adjacent intrathoracic nerves

Pathophysiologic changes that can be produced by invasion of specific structures are as follows:

• Obstructive pneumonia and hemoptysis
• Dysphagia
• SVCS
• Pleural effusion
• Various neurologic abnormalities, such as vocal cord paralysis, Horner syndrome, paraplegia, diaphragmatic paralysis, and pain in the distribution of specific sensory nerves

Systemic

A number of mediastinal tumors can produce systemic abnormalities. Many of these manifestations are related to bioactive substances produced by specific neoplasms.

Foregut and other cysts of the mediastinum generate no bioactive substances that produce systemic effects. They can be responsible for secondary systemic symptoms related to infection, or even sepsis, if they are secondarily infected or if their location imposes on airway structures, causing obstructive pneumonia.

Additional complications that can arise from the cysts themselves are rupture or perforation into the airway. Complications (eg, SVCS and unilateral pulmonary artery hypoplasia or stenosis) have been ascribed to the effects of long-standing compression by a cyst. Finally, some authors have attributed the onset of atrial, and even ventricular, arrhythmias to the presence of a bronchogenic cyst.

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Etiology

The tumors and cysts found in the mediastinum have various causes.

Various cysts can originate in the mediastinum. Although they are not actually neoplasms, they represent space-occupying lesions that usually result from abnormal embryologic development. These include the following:

• Foregut cysts
• Gastroenteric (enterogenic) cysts
• Neurenteric cysts
• Mesothelial cysts
• Thoracic duct cysts

Cysts can also be associated with teratomas within the mediastinum. Thymic cysts are discussed in Thymic Tumors.

Foregut cysts are believed to develop from abnormal primitive foregut development.^[8]

Bronchogenic cysts likely arise from an abnormality of the normal budding of the ventral foregut, the precursor of the trachea and major bronchial structures. The walls of these cysts are lined by ciliated pseudostratified columnar epithelium and may contain bronchial glands, smooth muscle bundles, and other tissues found in the tracheobronchial tree.

Enterogenous cysts arise from abnormal development of that portion of the dorsal foregut that becomes the gastrointestinal (GI) tract. Most commonly, these cysts are lined with some form of GI epithelium. Esophageal duplication cysts are believed to arise in early development, when vacuolization of the solid early esophagus occurs to form the esophageal lumen. If an isolated vacuole fails to merge with the central esophageal lumen, a duplication cyst may occur.

Neurenteric cysts develop at a location where the dorsal foregut and the primitive notochord are in close relation. Many theories about their development have been proposed; however, the common feature noted in many of these theories is that some adhesive process appears to cause a vacuole of the foregut to become incorporated into the notochord tissue. Classic cysts of this type are lined with enteric and neural tissue. They are often associated with other defects and anomalies of the vertebral column, and many cases described in the literature are those in which the cyst communicates with, or extends into, the spinal canal.

Mesothelial cysts are generally made up of a capsule of fibrous tissue with an inner single-cell layer of mesothelial cells. The most common type of mesothelial cyst found in the mediastinum is the pleuropericardial cyst, which is generally located at the anterior cardiophrenic angle. Other mesothelial cysts occurring in the mediastinum are simple mesothelial cysts and lymphogenous cysts.

Other primary cysts of the mediastinum include thymic cysts and thoracic duct cysts, the latter being very rare. Thymic cysts usually have an inner lining that is a single layer of cuboidal cells and islands of normal thymic tissue in the wall. Thoracic duct cysts may or may not communicate with the duct itself. They are composed of the same tissue as the normal lymphatic channels.

Although these abnormalities are considered benign lesions, a few cases have been reported in which malignant tissue has been found within the wall of a resected bronchogenic cyst. Malignant cell types found include squamous cell carcinoma and adenocarcinoma.

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Epidemiology

A review of collected series reveals that many mediastinal neoplasms and masses vary in incidence and presentation, depending on patient age. Also, numerous mediastinal tumors characteristically occur in specific areas within the mediastinum.

In adults, historically, the most common type of mediastinal tumor or cyst found has been the neurogenic tumor, followed in frequency by thymic tumors, lymphomas, and germ cell tumors. After these four types, foregut and pericardial cysts have been the next most common types. However, subsequent data suggest that thymic tumors have become the most common type of mediastinal tumor.^[1]

In children and infants, neurogenic tumors are the most commonly occurring tumors or cysts, followed by foregut cysts, germ cell tumors, lymphomas, lymphangiomas and angiomas, tumors of the thymus, and pericardial cysts.^[6]

Bronchogenic and other types of foregut cysts account for 10-18% of all mediastinal masses identified in infants and children and 20-32% of all mediastinal masses when all age groups are included.^[5]

Approximately two thirds of mediastinal tumors and cysts are symptomatic in the pediatric population, whereas only approximately one third produce symptoms in adults. The higher incidence of symptoms in the pediatric population is most likely related to the fact that a mediastinal mass, even a small one, is more likely to have a compressive effect on the small, flexible airway structures of a child.

Roughly 50-66% of cystic lesions found in persons of all age groups are bronchogenic cysts.

Males have a slightly greater incidence of bronchogenic cysts compared to females.

Foregut and other mediastinal cysts do not display a greater incidence in any specific racial, ethnic, or geographic population.

Neurenteric and gastroenteric cysts are considered rare lesions. Enteric cysts, also known as esophageal duplications, are relatively rare.

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Prognosis

The prognosis after resection of a mediastinal tumor varies widely, depending on the type of lesion resected. After resection of mediastinal cysts and benign tumors, the prognosis is generally excellent.^[9]

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History and Physical Examination

A large percentage of mediastinal tumors and cysts produce no symptoms and are found incidentally during a chest radiograph or other imaging study of the thorax performed for some other reason (see the image below).^[2]  Symptoms are present in approximately one third of adult patients with a mediastinal tumor or cyst but are more commonly observed in the pediatric population, in which nearly two thirds of individuals present with some symptoms. In adults, asymptomatic masses are more likely to be benign.^[10]

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An asymptomatic mass is found incidentally after chest radiography in an adult patient.

Symptoms associated with the respiratory tract predominate in pediatric patients because airway compression is more likely. This occurs because of the significant malleability of the airway structures and the small size of the chest cavity in infants and children. Symptoms most commonly observed include persistent cough, dyspnea, and stridor. If the location and size of the mass produces partial or complete obstruction, obstructive pneumonia can also occur. Infectious symptomatology, and even signs of sepsis, can occur if a mediastinal cyst becomes infected.

Constitutional symptoms, such as weight loss, fever, malaise, and vague chest pain, commonly occur in association with malignant tumors in pediatric patients but also may be signs associated with secondary infection of a congenital cyst, such as a bronchogenic cyst.

Symptoms associated with compression of some portion of the respiratory tract can be produced by benign lesions in adults. This is much less likely to occur in adults compared to children. Infectious symptoms or sepsis from infection of a mediastinal cyst can also occur in adults, although, again, this is very unlikely in persons in this age group.

Bronchogenic cysts are asymptomatic in as many as 20-30% of children. When they are symptomatic, children most commonly present with vague respiratory problems or dysphagia. They may have a history of recurrent respiratory problems or pneumonia. Symptoms in infants can range from none to significant upper airway distress (see the image below) manifested as severe stridor and wheezing. Likewise, physical examination findings can range from normal to significantly decreased breath sounds on the affected side.

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Chest radiograph of an infant in respiratory distress with a large air-filled bronchogenic cyst in the right chest. Arrow indicates inferior border of....

A large percentage of adults with bronchogenic cysts are asymptomatic, though several authors report that more than 50% of those followed nonsurgically become symptomatic and usually manifest symptoms of airway or esophageal compression or infection. In those adults who present with symptoms, respiratory complaints or dysphagia predominate.

Neurenteric cysts can manifest in persons of any age group. When they are identified in symptomatic infants or children, clinical findings are usually those of airway compression. A triad consisting of the presence of a mediastinal mass, symptoms referable to the airway, and the presence of a vertebral anomaly has been observed in approximately 70% of pediatric patients with neurenteric cysts.

Communication of a neurenteric cyst with the spinal canal has been reported. Patients with this added abnormality may develop neurologic symptoms, including gait abnormalities, back pain, and motor or sensory deficits.

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Chest Radiography

The usual way in which an asymptomatic mediastinal mass is identified is through a posteroanterior (PA; see the image below) or lateral radiograph of the chest for an unrelated cause. Chest radiography is obviously the first study that would be performed in an individual with symptoms referable to the thorax.

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Posteroanterior chest radiograph showing a large bronchogenic cyst causing compression of the right mainstem bronchus and right lung in a child.

The lateral chest radiograph findings(see the image below) are very helpful in determining the involved compartment of the mediastinum. This information, combined with the age, sex, and associated clinical findings, aids the physician in the proper choice of subsequent diagnostic studies.

View Image

Lateral chest radiograph (same patient as in Image above) of a large right-sided bronchogenic cyst in a child.

Foregut cysts are usually completely filled with fluid and have the appearance of a mediastinal mass. In the case of some cysts that may communicate with the tracheobronchial tree, the cyst may be completely or partially filled with air. This has the radiographic appearance of a radiolucent mass or a well-defined round lesion with an air-fluid level. (See the images below.)

View Image

Chest radiograph of a child with a large right-sided bronchogenic cyst. This cyst is partially filled with fluid and is also causing some compression ....

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Esophagography

In the past, the findings from barium esophagography have been used to help delineate masses or cysts found in the mediastinum. Computed tomography (CT) has generally replaced this study for the evaluation of most foregut cysts, especially bronchogenic cysts.

Barium esophagography has been used in patients who primarily present with symptoms of dysphagia. The displacement of the esophagus by neurenteric cysts and enterogenous or duplication cysts of the esophagus is usually seen clearly.

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Computed Tomography of Chest and Mediastinum

CT is a routine part of the diagnostic evaluation of mediastinal tumors, cysts, and other masses. (See the image below.) CT scans can greatly assist in determining the exact location of the mediastinal tumor and in determining its relation to adjacent structures.^[11] CT findings are also useful for differentiating masses that originate in the mediastinum from those that encroach on the mediastinum from the lung or other structures.

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CT scan image of a child (same patient as in Image above) with a large right-sided bronchogenic cyst with an air-fluid level.

Though not infallible, CT scans are very useful in differentiating tissue densities. Such differentiation greatly assists in distinguishing structures that are cystic or vascular from those that are solid.

As noted, CT with contrast has, in most cases, virtually replaced barium esophagography as an evaluation tool for these abnormalities in infants and children.

CT myelography has been performed in individuals with neurenteric cysts and neurologic symptoms to help determine the presence and level of spinal cord compression.^[12]

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Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is useful both in the initial diagnosis of a mediastinal mass and in follow-up evaluations after treatment.^[13]  It provides superior vascular imaging and can help better delineate the relation of an identified mediastinal mass to nearby intrathoracic vascular structures.^[11] It can be used to help differentiate between a possible mediastinal mass and a vascular abnormality (eg, an aortic aneurysm).

MRI offers direct multiplanar imaging. It can be used when iodinated contrast is contraindicated. Images provide increased detail in the subcarinal and aortopulmonary window areas and in the inferior aspects of the mediastinum at the level of the diaphragm.

MRI is superior to CT for the evaluation of masses located at the thoracic inlet or at the thoracoabdominal level.

In infants and children, MRI is excellent for helping delineate the relation of a neurenteric cyst with the spinal canal and the associated vertebral abnormalities.

Because the patient is not exposed to radiation, MRI may be preferred to CT by some physicians for the evaluation of a mediastinal cyst in a child or infant. However, children and infants require sedation when undergoing MRI. This factor may increase the risk for those pediatric patients with signs of airway obstruction who require such an examination. The physician may have to decide which risk is greater.^[14]

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Radionuclide Scanning

Technetium (Tc)-99 pertechnetate scans have been used to help identify neuroenteric cysts in the mediastinum, producing positive isotope uptake in gastric mucosa lining the cyst.

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Ultrasonography and Echocardiography

Ultrasonography (US) has been used to differentiate solid from cystic mediastinal masses^[15]  and to assist in determining connections between a mass and adjacent structures.^[16]  US studies have been more useful in the evaluation of masses associated with the heart and in vascular abnormalities. In view of the accuracy and detail provided by CT, MRI, and selected radionuclide studies, US techniques, though potentially useful for differentiating mediastinal lesions,^{[17, 18]} have not generally been used as primary tools in the evaluation of mediastinal tumors and cysts.

Antenatal US has been helpful in the discovery of a number of abnormalities in the fetal thorax, including bronchogenic cysts. These findings can greatly enhance care of the newborn.^[19]

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Arteriography

Very few indications exist for arteriography in the evaluation of a mediastinal cyst.

It may be helpful in differentiating between a bronchogenic cyst and an extralobar sequestration of the lung. It also may assist in determining whether the lesion in question originates from a mediastinal vascular structure, such as the heart or a great vessel.

Magnetic resonance angiography (MRA) will likely replace conventional angiographic methods when such studies are required in the workup of patients with mediastinal cysts.

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Procedures

Transthoracic needle biopsy

In the past, percutaneous biopsy methods were believed too dangerous to use in the evaluation of mediastinal masses, and open surgical biopsy was the diagnostic procedure of choice.

Fine-needle aspiration (FNA) has been occasionally used for the diagnosis of primary bronchogenic cysts. However, most authorities do not recommend aspiration of a cyst, because a sample of the cyst wall, required for diagnosis, is not obtained by this method. In addition, most cysts recur after simple aspiration. This technique is not recommended for esophageal cysts.^[20]

Cervical mediastinoscopy

Cervical mediastinoscopy is a commonly used surgical diagnostic procedure for evaluating the retrovascular pretracheal area of the mediastinum. It is used most commonly for staging of bronchogenic carcinoma and for evaluation of hilar and paratracheal lymphadenopathy.

Mediastinoscopy is not usually indicated for the evaluation of foregut or other mediastinal cysts in adults or children.

Anterior mediastinotomy

This 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 is being replaced by either extended cervical mediastinoscopy or video-assisted thoracoscopic surgery (VATS) techniques.

Like cervical mediastinoscopy, this procedure has no real role in the evaluation or treatment of mediastinal cysts in children or adults.

Posterior mediastinotomy

This 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 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 means of either standard thoracotomy or VATS.^[21]

Video-assisted thoracoscopic surgery

VATS 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.^{[22, 23]}

Sternotomy and thoracotomy

In 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.^[24]

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Histologic Findings

Foregut cysts

The cell type lining the inner aspect of the cyst helps identify these lesions histologically. Bronchogenic cysts are lined with ciliated, columnar epithelium. Hyaline cartilage, bronchial glands, and smooth muscle may also be seen in the wall of the cyst.

Esophageal cysts

Esophageal cysts are characterized by a double layer of smooth muscle in their walls. The cellular lining of these cysts ranges from squamous to ciliated columnar epithelium to gastric epithelium alone or in combination.

Neurenteric cysts often have two components. The intraspinal component is often thin-walled, having only a single layer of columnar epithelium within a thin layer of connective tissue. The extraspinal portion has a thicker wall with several layers of smooth muscle and contains gastric mucosa within.

Gastroenteric cysts in the mediastinum are thought to be identical to neurenteric cysts but without a communication or association with the spinal canal or vertebral column. Most of these cysts are lined with gastric mucosa, and many also have several of the normally seen gastric layers, including submucosa and muscularis.

Esophageal duplication cysts have been reported as lined with various cell types ranging from squamous to gastric to respiratory epithelium.

Mesothelial cysts, such as pleuropericardial cysts, are thin-walled and are lined with mesothelial cells.

Thoracic duct cysts

Thoracic duct cysts and other cysts of the lymphatic system are lined with occasional endothelial cells.

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Approach Considerations

Treatment selection for a given mediastinal tumor or cyst depends on the diagnosis of the lesion being investigated. Surgical resection is indicated in a large percentage of cases.

Surgical resection is indicated for most mediastinal cysts. All large and symptomatic bronchogenic cysts are included in the group, as are all enteric gastroenteric and neurenteric cysts. Some authors do not recommend resection of small asymptomatic bronchogenic cysts, whereas others advise aspiration of such cysts and resection only for those with symptoms or recurrence.

Excision of pleuropericardial cysts and simple mesothelial cysts is indicated for diagnostic purposes only. Thymic cysts require excision or enucleation. Thoracic duct cysts require excision and accompanying ligation of the thoracic duct.

Surgical removal is not indicated as primary treatment for (1) pleuropericardial cysts, lymphogenous cysts, and simple mediastinal cysts, provided that an accurate nonsurgical diagnosis has been performed, and (2) some cases of bronchogenic cysts found in adult patients in which the cyst is small and the patient has no symptoms. (This opinion varies among authors.)

Video-assisted thoracoscopic surgery (VATS) is employed by thoracic surgeons in the treatment of a number of mediastinal diseases. It has been commonly used for biopsy of masses and lymph nodes. Although VATS has been successful used to resect a variety of mediastinal cysts in both adult and pediatric patients,^{[25, 26]} maintaining careful patient selection in these cases is important. The most important goal of these surgical procedures is complete resection of the cyst. If this cannot be accomplished by means of VATS technology, standard thoracotomy should be used. Single-port as well as multiple-port VATS approaches have been found to be feasible for mediastinal cystectomy.^[27]

Robotic-assisted approaches to resection of mediastinal cysts have also been described.^[28]

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Surgical Therapy

Surgical resection is the treatment of choice for most cysts that occur in the mediastinum. In particular, it is the treatment of choice for foregut, gastroenteric, and neurenteric cysts of the mediastinum.

The entire cyst wall should be resected to prevent recurrence. In many cases, a portion of the cyst wall may be densely adherent to adjacent structures, usually the tracheobronchial tree or the esophagus. Nevertheless, complete resection can be accomplished in most cases. In cases in which complete removal is not possible, the mucosal lining should be removed from the portion of cyst wall left within the mediastinum. This is performed in an attempt to prevent recurrence.

Pleuropericardial cysts may require resection for diagnosis, though the diagnosis is often made by nonsurgical means. Lymphangiomatous or thoracic duct cysts should be resected, and the communication with the thoracic duct should be ligated.

Preparation for surgery

The standard preoperative management applicable to all chest surgical cases also applies to the preoperative management of individuals undergoing resection of mediastinal tumors.

Airway management is of paramount importance in dealing with tumors that can produce a mass effect on these structures. For safe management of the airway distorted or narrowed by a mediastinal mass, consider a detailed preoperative assessment of the airway, and ensure adequate visualization and readily available supplementary equipment (eg, flexible bronchoscope). Placement of a double-lumen endotracheal tube to provide single-lung ventilation is usually preferred for any procedure in which a thoracotomy approach is used.

Appropriate preoperative, intraoperative, and postoperative antibiotic coverage is warranted. In cases where infected cysts are resected, modify antibiotic coverage when culture results identify the organism(s) involved.

Operative details

As in all thoracic surgical cases, position the patient properly for the indicated procedure. Tumors or cysts located in the anterior mediastinum are generally approached through a median sternotomy. Those located in the posterior or middle mediastinum and paravertebral sulci, such as most neurogenic tumors and foregut cysts, are approached through a posterolateral thoracotomy.

Use of a double-lumen endotracheal tube for single-lung ventilation is preferable for those procedures performed through a thoracotomy and for all VATS procedures.

Occasionally, emergency resection of a bronchogenic cyst is required in an infant with severe airway obstruction. Although most of these cases can be managed by using standard anesthesia techniques with positive-pressure ventilation and nitrous oxide, a few require special care. Several authors have described the intraoperative use of an ultrathin fiberoptic bronchoscope to assist in the management of the airway and the assessment of oxygen and anesthetic delivery during these difficult cases.

VATS techniques have been used to resect of bronchogenic and neurenteric cysts in adults and children. Because of cyst size, location, and adherence to adjacent structures, VATS is not appropriate for every case, and careful case selection is important.

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Postoperative Care

Care of patients after resection of mediastinal cysts is similar to that after any noncardiac surgery of the chest.

Extubation can be performed at the completion of the case or shortly thereafter in the postanesthesia recovery area. Patients who require ventilatory support for a longer time should be treated accordingly.

Pulmonary toilet is an essential part of postoperative management after any kind of chest surgery to prevent atelectasis and to mobilize and clear any bronchial secretions. Various methods to assist with pulmonary toilet are available.

Pain control is a critical factor in postoperative management after thoracic surgery. Adequate cough effort and ventilatory excursion cannot be maintained without satisfactory pain control. Administration of analgesic agents via thoracic epidural catheter is an excellent and highly effective method of pain management. Lumbar epidural catheters can also be used, and, with proper choice of analgesic agents, they provide good pain relief.

Patient-controlled analgesia (PCA) is another widely used method and is preferred to traditional intramuscular or intravenous administration of narcotics and other agents. It is not as efficient for pain control as epidural analgesia.

At some point after oral intake has begun, pain medication can be converted to oral analgesic agents.

Wound management is straightforward. Operative dressings are removed after 24 hours in most cases. Thoracic surgical incisions heal well and have an extremely low rate of dehiscence and infection.

Chest tubes are managed in the same way as in other forms of thoracic surgery. Most cases of mediastinal tumor or cyst resection or biopsy do not involve pulmonary or esophageal resection. Chest tubes are maintained on –20 cm of water-seal suction, and drainage from the tubes is measured daily. Patients are followed with daily chest radiographs, and films are evaluated for findings of residual undrained collections, complete pulmonary expansion, lobar atelectasis and infiltrates, and other abnormalities.

When drainage from the chest tubes is less than 50-100 mL in 24 hours, no air leak is present, and the chest radiograph shows full pulmonary expansion with no collections on the operated side, the chest tubes may be removed.

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Complications

Complications that occur after resection of mediastinal cysts are similar to those that can occur after any thoracic surgical procedure.

As with any thoracic surgical procedure, postoperative pulmonary complications are most common. Atelectasis is a common postoperative complication and can develop into pneumonia if not treated aggressively. Aggressive pulmonary toilet and pain management are key factors in the prevention of these complications.

Wound infections after sternotomy or thoracotomy are rare. The chest wall has an excellent blood supply, and, with few exceptions, healing occurs readily. Also, existing intrathoracic infection is generally not a factor during resection of any of the noted mediastinal tumors, and these operations are considered clean procedures. The exception to this may be in cases of resection of some foregut cysts that may have secondary infection present.

Injury to the phrenic nerve can occur, resulting in temporary or permanent diaphragmatic paresis. This can cause the patient to have symptomatic dyspnea and atelectasis on the affected side. Children of individuals with marginal pulmonary status from underlying pulmonary disease or those with neuromuscular abnormalities causing weakness of the muscles of respiration may experience significant respiratory difficulties from this complication.

Injury to a vagus nerve can also occur during surgery of the mediastinum. Usually, only one vagus nerve is injured and the remaining intact nerve maintains parasympathetic input to the gut without symptoms. If both vagus nerves are injured, difficulties with gastric emptying may occur because the innervation to the pylorus is disrupted.

Recurrence of the cyst is a potential long-term complication. This can occur if the entire mucosal lining of the cyst is not removed. Cases in which this is most likely are those in which a portion of the cyst is adherent to a vital mediastinal structure and is left behind. Attempted resection of infected cysts is associated with a higher likelihood of this complication. In addition, incomplete resection is more likely when VATS technology is used because visibility and mobility of the operative field are more limited than they would be with a standard thoracotomy.

In general, mortality and morbidity related to the resection of foregut and other mediastinal cysts are extremely low.

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Long-Term Monitoring

Patients who undergo resection of mediastinal cysts can be followed for a short time (ie, 3-6 months) postoperatively while wound healing and progression of patient activity are being monitored.

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