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Seminars in Anesthesia, Perioperative Medicine and Pain (2007) 26, 133-140

nterior mediastinal masses in children

errold Lerman, BASc, MD, FRCPC, FANZCA

rom the Department of Anesthesia, Women and Children’s Hospital of Buffalo, Buffalo, New York.

Anterior mediastinal masses may present life-threatening challenges for the anesthesiologist, particu-larly in children. Children with symptoms referable to the respiratory involvement may present withdyspnea, orthopnea, or pleuritic chest pain. Those with symptoms referable to cardiovascular involve-ment may present with syncope, shortness of breath with exertion and in certain positions, and swellingin the face. Chest x-rays, CAT scans, and echocardiography are commonly used to investigate thesemasses. The more common tumors in the anterior mediastinum are known by the four “T”s: thymoma,teratoma, thyroid, and terrible lymphoma. T-cell lymphomas represent the most rapid growing tumorswith a doubling time of 12 hours. These tumors may invaginate or compress adjacent structures, suchas the trachea, causing tracheomalacia and tracheal narrowing and/or may compress the pulmonaryartery and right atrium, infiltrate the pericardium, and restrict the superior vena cava, thereby compro-mising cardiac output. The key strategy when planning these cases is to consider the type of anesthetic,spontaneous ventilation, and the position of the child. Local anesthesia, sedation, or general anesthesiais suitable. Local anesthesia with sedation may be used in cooperative older children. Generalanesthesia should be accompanied by spontaneous ventilation. Muscle relaxants are proscribed. Chil-dren may not tolerate the supine position, especially after induction of anesthesia; turning the child tothe left decubitus or prone position restores ventilation and cardiac output. The key strategy to restorecardiorespiratory homeostasis when the anesthetized child with an anterior mediastinal tumor begins todeteriorate is to turn them to the lateral decubitus or prone position.© 2007 Elsevier Inc. All rights reserved.

KEYWORDS:Anesthesia;Cardiac arrest;Children;Anterior mediastinalmass

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natomy

he mediastinum is that space within the thoracic cavityhat is bounded anteriorly by the sternum, posteriorly by thearavertebral gutters and ribs, superiorly by the thoracicnlet, and inferiorly by the diaphragm.1 This space is di-ided into four regions relative to the pericardial sac: supe-ior, anterior, middle, and posterior (Figure 1). The superiorediastinum is that region superior to a line adjoining the

ternal angle and the lower border of the fourth thoracicertebra. The remainder of the mediastinum, below theuperior mediastinum, is divided into three regions: thenterior mediastinum lies between the sternum anteriorly

Address reprint requests and correspondence: Jerrold Lerman, Womennd Children’s Hospital of Buffalo, 219 Bryant Street, Buffalo, NY 14209.

cE-mail: [email protected].

277-0326/$ -see front matter © 2007 Elsevier Inc. All rights reserved.oi:10.1053/j.sane.2007.06.003

nd the pericardial sac posteriorly; the middle mediastinumncludes the pericardial sac and its contents; and the poste-ior mediastinum lies posterior to the pericardial sac. Al-hough tumors may arise in all regions of the mediastinum,t is those that are found in the anterior mediastinum thatresent the greatest challenges during anesthesia and thatill be addressed in this review.

ncidence andistribution of mediastinal masses

issue typing of mediastinal masses includes primary neo-lasm, metastases, infection, or cystic. The prevalence ofrimary neoplasms of the mediastinum is unknown, but is
onsidered extremely small. In contrast, the incidence of

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134 Seminars in Anesthesia, Perioperative Medicine and Pain, Vol 26, No 3, September 2007

econdary neoplasms (metastases) of the mediastinum inhildren, 40% to 50%, is approximately twice that in adults,5%. Mediastinal masses arise from one of the followingour tissue types: thymus, neurogenic, lymphomas, or germell neoplasms.2,3 Malignant lymphomas account for 23%f all mediastinal masses in children, the two major typeseing non-Hodgkins (NHL) and Hodgkins (HL). Lympho-as increase in incidence throughout childhood reaching a

enith in adolescence, hence the large number of adoles-ents who present with anterior mediastinal masses. Germell neoplasms account for less than 7% of these masses, theast majority being benign.

Of all mediastinal masses, 35% to 55% present in thenterior mediastinum. Eighty-five percent of these massesrise from thymic, lymphomatous, and germ cell tissues.he tumors found in the anterior mediastinum of childrenre referred to by the four Ts: thymoma, teratoma, thyroid/ther, and terrible lymphoma. The prevalence of these tu-ors in children (and adults) is shown in Table 1.Lymphomas are the most common tumor of the anterior

ediastinum. Two-thirds or more of these are NHL andne-third are HL. NHL may be grouped into three tissueategories: undifferentiated, which comprise 40% to 50%,re usually B cell type in origin and most commonly occurn the abdomen; lymphoblastic, which comprise 30% to0%, are T cell in origin and occur in the mediastinum; andarge cell, which comprise 20%, are B or T cell in origin andccur anywhere in the body. NHL is more common in

igure 1 The mediastinum is divided into four regions. Theuperior region is that region superior to a line joining the sternalngle with the lower border of the fourth thoracic vertebra. Theediastinum below this line is divided into three regions: anterior,iddle, and posterior. The anterior mediastinum is that space

etween the sternum and the anterior pericardial sac. The middleediastinum is that region enclosed by the pericardial sac. The

osterior mediastinum is that region posterior to the pericardialac. Used with permission from Dartmouth University (http://ww.dartmouth.edu/�anatomy).

ounger children, presents with more signs and symptoms

han HL, and in the case of lymphoblastic T cell tumors,ave a doubling time of as little as 12 hours. It is theymphoblastic T cell tumors that may present precipitouslyn a previously healthy child who suddenly becomes unableo breathe, walk, or talk. The remaining one-third of lym-homas are HL cell type in origin. HL and large cell NHLave a much slower doubling time than T cell (NHL)ymphoblastic tumors; hence, they are less likely to presentmergently.

Early diagnosis and intervention is crucial as in the casef T cell lymphomas, although the tissue type is essential forll of these malignant tumors if we are to design an effectivereatment plan. The prognosis for the lymphomas in chil-ren is: Hodgkins disease, 85% 5-year survival; lympho-lastic NHL, 80% 5-year survival; and large cell NHL, 60%o 70% 5-year survival. The treatment varies according tohe general tissue typing: Hodgkins should receive localadiation but can receive widespread chemotherapy andossible radiation, whereas NHL should only receive che-otherapy. In terms of NHL, radiation only adds to the

oxicity.Approximately 15% of all mediastinal masses occur in

he middle mediastinum. Lymph node masses account forost of the primary tumors as well as secondary metastases.nomalous development of great vessels, lymphangiomas,ericardial cysts, and foregut duplication cysts may alsoresent here.

Thirty to forty percent of all mediastinal masses in chil-ren arise from the posterior mediastinum. More than 90%f these masses are neurogenic in origin. The majority ofeurogenic tumors derive from the sympathetic ganglionichain. Neuroblastoma is one of the most common solidalignant tumors of childhood and the most prevalent in

hildren less than 4 years of age.

linical presentation

he clinical manifestations of anterior mediastinal massesary according to the size of the mass and the adjacenttructures. Approximately 50% of all mediastinal massesre incidental findings on CXR. The incidence of malig-ancy in those who present with symptoms is twice that inhose who are diagnosed incidentally. The presenting symp-oms depend on the local (from impact on adjacent struc-ures) and/or systemic effects (usually neurohumeral).

Table 1 Incidence of tumors in the anterior mediastinum3

Adult Child

Thymoma 47% 17%Teratoma 15% 24%Terrible lymphoma 23% 45%Thyroid/other Endocrine 16% Mesenchymal 15%

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135Lerman Anterior Mediastinal Masses in Children

Tumors that arise in the anterior mediastinum usuallyresent with signs and symptoms that are clinically moreignificant than those that arise in the other medastinalegions. The clinical manifestations relate to their effects onhe respiratory and cardiac organ systems, and these areisted in Table 2.

In contrast, neuroblastoma, a posterior mediastinal tu-or, commonly presents with nontumor-related symptoms

n 49% of cases, neurological symptoms in 16%, and acuteespiratory distress in only 14%.1 Primary presentation inhe mediastinum occurs in only 11% to 26% of cases. Ahoracic presentation is most common, with 9% presentingith spinal cord compression. In view of the only occa-

ional symptoms referable to the airways or vascular com-ression from posterior mediastinal masses, these massesill not be discussed further.

espiratory

The most common effect of an anterior mediastinal mass onhe respiratory system is extrinsic compression of the trachear carina. Chronic compression leads to tracheomalacia, nar-owing of the tracheal lumen, or deformation of the tra-hea.1,4,5 The severity of narrowing depends on the weight ofhe tumor, the duration of the compression, and the position ofhe subject. While the tumor is small, its effect on the tracheaemains minor. However, as the tumor grows and compresseshe trachea or carina continually, the trachea weakens (tracheo-alacia), narrows (tracheal compression), or bends (scabbard

rachea). In some positions, such as sitting, the tracheal lumenay be normal despite the close proximity of the tumor to the

rachea. In contrast, in the supine position, the combination ofhe effects of gravity on the mass and an increasing intrapleuralressure at end-expiration (approaching zero pressure) mayead to the most severe narrowing of the trachea. This remains

dynamic process that may be intermittent and may eludeiagnostic tests that are static in nature. Common presentingymptoms associated with tracheomalacia include cough, dys-nea, chest pain, dysphagia, and recurrent or unresolved pul-

Table 2 Signs and symptoms of anterior mediastinaltumors8

History Physical examination

Respiratorycough decreased breath soundscyanosis wheezingdyspnea stridororthopnea cyanosis

Cardiovascularfatigue neck or facial edemafaintness jugular vein distentionheadache papilloedemashortness of breath blood pressure instabilityorthopnea postural pressure changecough pulsus paradoxus

onary infection. m

Orthopnea is a common finding when an anterior medi-stinal mass compresses the trachea or bronchus. Theseymptoms may be alleviated by elevating the head/chestith one or more pillows.Pleural involvement may also complicate the presenta-

ion with the presence of pleural effusions, pleusrisy, andhest wall pain. Effusions may results from the direct spreadf tumor to the pleural space or obstruction of lymphaticrainage.

The nature of the tracheal involvement will determinehe signs and symptoms. A fixed tracheal narrowing limitsirflow during both inspiration and expiration, and thesehildren often have difficulty even at rest. In contrast, vari-ble tracheal obstruction presents with different symptomsepending on the location of the narrowing. Intrathoracicariable obstruction presents with symptoms primarily dur-ng expiration as a result of the positive intrathoracic pres-ure during expiration that compresses the trachea. Ex-rathoracic variable obstruction presents with symptomsuring inspiration as a result of the large negative intratho-acic pressure that causes tracheal collapse. These childrenay present first with exertional dyspnea.

ardiovascular

Cardiovascular dysfunction occurs less commonly inhildren with anterior mediastinal masses than respiratoryysfunction. Cardiovascular involvement may involve infil-ration of the pericardium and myocardium or compressionf the pulmonary artery or superior vena cava.1,6-8 The aortas usually spared from involvement because of its location,hick muscular walls, and large intraluminal pressure.

Pericardial involvement of the heart may include a peri-ardial effusion that progresses to cardiac tamponade oronstrictive pericarditis. Frank encasement of the pericar-ium by tumor may result in constrictive pericarditis. In-reased jugular venous pressure, hepatomegaly, and ortho-tatic pressure changes all suggest compromise of righteart function and/or pulmonary artery due to mass effects.dentification of pericardial involvement should be deter-ined before induction of anesthesia.In the awake child, the pulmonary artery is infrequently

ompressed by an anterior mediastinal mass because of thehielding effect of the aorta. However, once anesthesia isnduced, the pulmonary artery may become compressed. Aistory of isolated syncope or syncope during a forcedalsalva maneuver suggests compression of a major in-rathoracic vascular structure and limited cardiac output.wo physiological changes that occur with induction ofnesthesia, loss of negative interpleural pressure and theeight of the anterior mediastinal mass in the supine posi-

ion, together may compress one or both pulmonary arteries,hich may suddenly precipitate hypoxemia, hypotension,

bsence or diminished capnogram, or cardiac arrest.7 Toestore cardiac output, strategies to offset the gravitationalffects of the tumor on the pulmonary artery must be im-
ediately applied, including repositioning the child in the

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ecubitus or prone position or lifting the sternum by insert-ng one finger behind the sternal notch and one behind theiphoid process.1 In severe cases, extracorporeal membranexygenation (ECMO) with femoro-femoral bypass has beenecommended. However, unless a major vein and arteryave been cannulated before induction of anesthesia, whenhe cardiac output suddenly deteriorates, the probability thatCMO can be instituted and will be salutary is small.

Superior vena caval syndrome (SVCS) is a rare entity inhildren, even those with anterior mediastinal masses, andccurs in approximately 1.5% of children. Most cases ofVCS are iatrogenic, secondary to either congenital hearturgery or total parenteral nutrition. Mediastinal tumors,owever, represent the primary natural cause of SVCS inhildhood and adolescence. Fifty percent of these are pri-ary tumors of the mediastinum, 35% being lymphosarco-as.SVCS presents with signs and symptoms directly refer-

ble to impaired venous drainage of blood from the headnd neck (Table 2). The signs and symptoms of SVCSncrease in the supine position and when sitting but leaningorward. When SVCS develops slowly, compensatoryechanisms attenuate the symptoms. However, whenVCS develops rapidly, it is often poorly tolerated and mayequire emergency intervention.

Tumor-associated SVCS is one of the few emergenciesor which radiation therapy is the treatment of choice.9

hen SVCS is associated with lymphoma, chemotherapy,teroids, or radiation may be effective in alleviating theffects of SVCS. Failure to effectively alleviate SVCS hasesulted in difficulties in three children.10 When SVCS haseen treated with steroids, however, the biopsies yieldedecrotic tissue and may have delayed diagnosis and treat-ent.

iagnostic evaluation

iscovering a mediastinal mass is often an incidental find-ng on a plain CXR that was taken for another reason. In ainority of instances, children present with symptoms re-

erable to the anterior mediastinal mass that requires inves-

igure 2 PA and lateral chest x-rays of a teen with an anterior
tediastinal mass.
igation. Evaluation of the postero-anterior and lateral chest-ray films is important in order to differentiate normal

rom abnormal mediastinal contours (Figure 2). This canresent some difficulty, especially in the pediatric age rangehere normal structures such as the thymus may obscureediastinal structures. The most valuable initial investiga-

ion to localize the mass is a good-quality chest x-ray. This-ray should delineate the borders of the mass as well asrovide evidence of tracheal compression or deviation.

Computerized axis tomography (CAT) locates massesithin multiple compartments within the mediastinum, toelineate the characteristics of the mass (for example, cal-ification, fluid, and fat) to provide guidance for the bestpproach for biopsy, to provide detailed information totaging tumors, and to provide evidence of compression ofital mediastinal structures (Figure 3). Modern CAT scan-ers are extremely rapid and yield detailed images of struc-ures. Contrast-enhanced CAT scans facilitate differentia-ion of lung tissue, soft tissues, and highly perfusedtructures. Coupling the contrast-enhanced scans with theindows resolution of CAT scans facilitates detailed iden-

ification of organs, such as the lungs, with detailed imagingf its perfusion or intracardiac anatomy. Although CATcans only provide static assessments of the mass and itsffects on adjacent structures, the resolution of the scansrovides extremely high-quality imaging. In a retrospectivetudy of the incidence of tracheal compression as detectedy CAT scan, the presence or severity of symptoms did notorrelate with the extent of tracheal narrowing on CATcan. The presence of orthopnea (in two children) did ap-ear to correlate with the CAT scan results.11 Whether moreodern CAT scan images would improve the yield in this

egard is unknown. Kirks et al. reported that 50% of chil-ren with subclinical tracheal compression could be identi-ed by CAT scan.12 Despite the limitations of the CATcan, it remains a very valuable tool.

Magnetic reasonance imaging (MRI) is consideredquivalent to CAT scans for identification of mediastinalumors. However, because of its greater cost and limitedvailability, slower processing time, and limited capability

igure 3 CAT scan of a teen with an anterior mediastinalass.

o provide detailed resolution of the mediastinal structures,

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RI is often reserved for specific situations such as clari-ying equivocal CAT findings. The MRI may be superior toAT scans for differentiating between masses and cardio-ascular structures.13 At the present time, MRI has onlystablished itself as a secondary investigational tool forediastinal masses.A number of other diagnostic tools may be used to

nvestigate tumor involvement of adjacent structures. Bar-um swallow may differentiate between intrinsic and extrin-ic compression of the esophagus. Angiography and my-lography may also be useful to determine the source oflood supply and spinal or paraspinal involvement, respec-ively. Echocardiography is a very useful tool to investigateericardial involvement, myocardial contractility, and car-iac chamber and major vessel compression.

The investigative tools discussed thus far provide two-imensional static images that cannot account for the fullange of dynamic changes. Significant compression of aajor structure may be missed with static imaging because

he compression is dynamic. In the more mature child, testshat reflect dynamic changes, such as flow-volume loopshat evaluate dynamic airway obstruction and fiberopticronchoscopy, can be used.14,15 The shape of the flowolume loop may indicate the site of obstruction, eg, in-rathoracic or extrathoracic, and whether it is a fixed orariable obstruction. Measurements are best taken in bothupine and upright positions to assess fixed or variablebstruction. As an alternative to flow volume loops or toupplement their findings in determining the dynamicourse of tracheal compression in mature and cooperativehildren, fiberoptic bronchoscopy may be performed underocal anesthesia, awake, or with sedation and spontaneousentilation.16

To determine the extent of cardiac involvement, a 2D-chocardiograph of the heart and the mediastinal structuress essential. Echocardiography will not only provide evi-ence of depressed myocardial function, but can also iden-ify pericardial effusions, pericardial extension of tumor,nd great vessel compression. It should be emphasized that,ven in the presence of a normal pre-anesthetic cardiaccho, myocardial dysfunction and great vessel compressionay occur upon assuming the supine position, after induc-

ion of anesthesia, or with positive pressure ventilation.ompression of the pulmonary artery should be suspectednd the child turned to the prone position.

nesthesia considerations

reoperative evaluation

The preoperative assessment of the child with an anteriorediastinal mass is critical for the safe conduct of anesthe-

ia. Many of these children, however, do not present with aiagnosis of an anterior mediastinal mass. Rather, they may
resent with an isolated cervical lymph node for biopsy, for c
mediastinal node biopsy (via a Chamberlain procedure), oror a chronic central line placement for chemotherapy for aumor. Suspecting that a mediastinal mass is present andeviewing the chest x-ray with a radiologist may prevent atrategic error in decision-making that results in a catastro-he. Less commonly, these children present for tumor re-ection as the management is primarily nonsurgical. Rareumors of the mediastinum, such as sarcomas, may requireurgical resection, but these are the exceptional cases.

In the presence of tracheal compression/narrowing, chil-ren may complain of tachypnea, orthopnea, and limitedositions for sound sleep (ie, decubitus or prone positions).elected maneuvers may also provide evidence suggestivef tracheal narrowing. Positioning the child supine whilewake or raising his or her arms above the head mayrecipitate airway compression. With lesser degrees of re-piratory embarrassment, however, these maneuvers mayot be helpful. CAT scan and flow-volume loops are moreensitive means for identifying tracheal compression. Air-ay obstruction during general anesthesia is likely if the

ross-sectional diameter of the trachea is less than 50%uring awake studies.8,11 Fiberoptic bronchoscopy with lo-al anesthesia and/or sedation is the most useful techniqueo identify dynamic airway obstruction, but may not beeasible except in older children.

Involvement of the cardiovascular system is evidencedy a history of orthopnea or syncope, or by the presence ofulsus paradoxus, cyanosis, or SVCS. Rarely, right heartailure from pulmonary artery compression may yield aalpable liver. If any of these signs are present, then aardiac echocardiogram and CT scan of the thorax arendicated.

nesthetic management

The choice of anesthetic technique depends on the indi-ation for and urgency of the procedure (Figure 4). In mostnstances, these children require general anesthesia to com-lete their radiological investigations in order to establishhe diagnosis. The anesthetic choices for children with po-entially compromised cardiorespiratory systems include lo-al anesthesia, intravenous sedation, and general anesthesiainhalational or intravenous anesthetics). If peripheral sites,uch as cervical lymph nodes, pleural effusions, or bonearrow, are readily accessible, local anesthesia and/or se-

ation may be suitable in the more mature child. For botheripheral and central sites, general anesthesia is usuallyequired for younger children. The choice of anestheticechnique must be tailored to the child’s requirements andhe surgical considerations.

In the absence of alternatives to general anesthesia, sev-ral basic principles must be followed in order to safelynesthetize these children.4,8,14 First, the anesthesiologisthould be aware of all known and possible limitations inespiratory and cardiovascular function. Second, contin-ency plans to manage an unexpected cardiorespiratory
ollapse during anesthesia should be discussed and ratified

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ith the operating room team. It is important to rememberhat the absence of evidence of cardiorespiratory dysfunc-ion before induction of anesthesia does not preclude car-iorespiratory collapse and cardiac arrest after induction ofnesthesia.

Understanding the balance of the pressures that act onumors of the anterior mediastinum enables clinicians toredict the effects of anesthesia and changes in body posi-ion on cardiorespiratory homeostasis as well as to developtrategies to prevent and reverse cardiorespiratory collapse.umors of the anterior mediastinum occupy a retrosternalpace that is anterior to the heart and tracheobronchialree. In the supine position, two opposing forces maintainhe position of the tumor: the negative intrathoracic pressurenegative recoil of the lungs and rib cage) and gravity. Theegative intrathoracic pressure, which is the sum of bothnatomical (including intercostal and other muscle tone)nd physiological (respiration) forces, effectively pulls theumor in an upward direction. Opposing this negative pres-ure is gravity, which pulls the tumor downward in a pos-erior direction. In the supine position, if the intrathoracicressure becomes less negative, gravity becomes dominantnd pulls the tumor onto vulnerable structures, such as theracheobronchial tree and the right side of the heart (right

igure 4 Algorithm for the management of children with ante-ior mediastinal masses. Reproduced with permission.1

trium and pulmonary artery). Any maneuvers that make the n

ntrathoracic pressure less negative shift the balance ofressures in favor of gravity. Such maneuvers include in-uction of anesthesia, cessation of spontaneous ventilation,nd institution of positive pressure ventilation. Althoughnduction of anesthesia is a necessary element in facilitatinghe surgical procedure in children, stopping spontaneousentilation and instituting positive pressure ventilation areot. Spontaneous ventilation must continue after inductionf anesthesia in these children, and we must avoid positiveressure ventilation at all costs.

Understanding the net effect of pressures on these tumorshen the child assumes different positions is the second key

lement to ensuring a successful outcome. In the sittingpright position during spontaneous ventilation, the nega-ive intrathoracic pressure pulls tumors of the anterior me-iastinum upward. In this position, gravity pulls the tumorn a rostral direction, toward the abdomen, bypassing theajor structures in the mediastinum. If the child reclines to

he supine position, gravity pulls the tumor posteriorly ontotructures that lie behind it. If the child is turned to the leftateral decubitus position while breathing spontaneously,ravity pulls the tumor toward the left chest, not directlynto the vital mediastinal structures. Finally, if the child isurned prone, gravity pulls the tumor onto the back of theternum, away from all of the vital structures. In each of thebove cases, if the negative intrathoracic pressure dimin-shes, the net effect of gravity on the tumor increases, andhis increases the pull of the tumor onto adjacent structures.n the worst case scenario, with induction of anesthesia andositive pressure ventilation, the optimal position (to mini-ize the compression of mediastinal structures by the grav-

tational pull on the tumor) is the left lateral decubitus androne positions.

How can we use this understanding of the balance ofressures of tumors of the anterior mediastinum to facilitateracheal intubation? Because it is easier to perform laryn-oscopy and tracheal intubation in the left lateral decubitusosition than the right lateral or sitting position, I positionhese children in the left decubitus position before inductionf anesthesia and maintain that position, providing it isolerated (and it almost always is) during induction of an-sthesia, laryngoscopy, and tracheal intubation. In this po-ition, gravity pulls the tumor toward the left lung, awayrom the pulmonary artery and the tracheobronchial tree. Inare instances where the tumor is so large that it compressestructures even in the lateral decubitus position, then it maye necessary to either lift the sternum by (having the sur-eon) placing one finger in each of the sternal notch and theiphoid and lift, or once the trachea is intubated, turn thehild prone.

Children who are at high risk for cardiorespiratory col-apse are those who present with symptoms. These childrenre candidates for preoperative treatment of the tumor tohrink it and restore cardiorespiratory homeostasis.1 Preop-rative radiation therapy reliably shrinks anterior mediasti-
al masses, but does so at the risk of destroying so much

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umor tissue that the diagnosis becomes difficult. SVCS isne accepted indication for mediastinal radiation beforenduction anesthesia because of the known risks associatedith the syndrome.17 A brief pulse of steroid therapy (for-24 hours) may also shrink a massive tumor that places thehild at high risk for cardiorespiratory arrest at induction ofnesthesia with limited impact on the viability of tumorissue.18 Unfortunately, some tumors, such as T-cell lym-homas, undergo widespread apoptosis after even a briefteroid exposure. This has resulted in difficulty harvestingiable tissue for histopathology, which has prompted manyncologists to proscribe steroids before a tissue diagnosisas been established. A counter argument to this proscrip-ion is that many centers today depend more on subcellularests than on histopathology to diagnose the tumor type andts susceptibility to an intervention. This conflict betweentrategies to ensure the safe conduct of anesthesia and theeed to harvest viable tissue may require an open dialogueo reach a sensible and safe compromise. If the child is in orpproaching extremis and cannot or will not undergo theiopsy under local anesthesia, then pretreatment will beequired to shrink the tumor. First, if the child can benesthetized in the left decubitus position, then this mayesolve the conflict. Second, if the child cannot be anesthe-ized without an intervention and if there are multiple siteso biopsy, then localized radiation to shrink the offendingumor may be undertaken, leaving the other sites for biopsyntouched. Third, if there is only one site for biopsy, then aulse dose of steroids may be administered for a brief periodr until signs of the respiratory or cardiac compromise haveiminished. The tissue sample should then be harvested asoon as possible.

Steroids are well known to oncologists as effective strat-gies for inducing apoptosis in lymphomas, but not nearlys well known for this purpose in anesthesiology. The no-ion that glucocorticoids rapidly induce apoptosis in lym-homas, as well as leukemias and other hematological tu-ors, has been well described and researched in the

ncology literature.19,20 When steroid intervention was pro-osed for airway difficulties in children with lymphomas,he initial presumed mechanism of action was to decreasenflammation and swelling. However, steroids have a muchore complex role in cancer cell viability. Although the

teroid mechanism for inducing apoptosis has not been fullylucidated, this naturally occurring hormone may inducepoptosis in these hematologic tumors by either activating aro-apoptotic protein or by inhibiting transcription enzymesnd therefore preventing replication.19,20 The preponder-nce of evidence today suggests that the latter mechanism isominant, although the former cannot be completely dis-ounted. The mechanism of action of glucocorticoids hasroven to be quite complex, involving three distinctteps19,20: first, glucocorticoid receptor activation that thenctivates glucocorticoid receptor genes in the cytoplasm;econd, nuclear and mitochondrial proapototic activation;
nd third, execution by activation caspases and suppressing c
rosurvival factors. Further studies are needed to fully elu-idate the mechanism of action of glucocorticoids in induc-ng apoptosis in children with lymphomas.

The impact of general anesthesia on the patency of thearge airways in children with mediastinal masses dependsn the balance between negative intrathoracic pressure andravity. Spontaneous ventilation usually maintains sufficientegative intrathoracic pressure to offset the effects of gravity,ven when the child is in the supine position. Paralysis andositive pressure ventilation augments the effects of gravitynd may lead to compression of intrathoracic structures. Iniew of these changes, it is preferable to maintain spontaneousespiration throughout the anesthetic.21

Premedication is best avoided in the child with compro-ised cardiorespiratory systems. An intravenous (IV)

hould be inserted before induction of anesthesia using localnfiltration, EMLA, or nitrous oxide. It is prudent to site anV in both the upper and lower extremities in case bloodow is interrupted unexpectedly. In the case of SVCS or aight-sided mediastinal tumour, the IV should be sited in theower extremity. Capnography may alert the anesthesiolo-ist to a sudden reduction in cardiac output, thus enabling aorrective intervention to prevent cardiac arrest.

Position is the most important factor in preparing thehild for anesthesia and to manipulate should cardiorespi-atory collapse occur. Children who are minimally affectedy the tumor may be positioned supine for induction ofnesthesia. Those who have clinical manifestations of theumor, should be positioned in the left lateral decubitusefore induction of general anesthesia. I do not recommendnducing anesthesia and attempting to tracheally intubatehe child in the sitting position because it is difficult totabilize the head and neck and climb above the head toerform laryngoscopy and intubation. If the child deterio-ates after anesthesia is induced, while in the decubitusosition, then the origin of the deterioration should be iden-ified. If the deterioration is the result of airway obstruction,hen the child should be repositioned to the lateral decubitusr prone position after tracheal intubation, the sternum liftedas mentioned above), or a rigid bronchoscope passed be-ond the level of obstruction to relieve it. If the deteriorations the result of pulmonary artery compression or some otherardiac problem, then efforts to restore cardiac output, in-luding turning the child to the lateral decubitus or proneosition and lifting the sternum, should be considered. Inare instances, extracorporeal membrane oxygenation haseen used to re-establish gas exchange and cardiac output,lthough this author does not believe this is a practicallternative.

General anesthesia may be induced using an intravenous,nhalational, or combined technique, while maintaining spon-aneous respiration throughout. Intravenous agents commonlysed include propofol, ketamine, or fentanyl and midazo-am. Inhalational techniques include sevoflurane or halo-hane. The trachea may be intubated using direct laryngos-
opy or via fiberoptic bronchoscopy and local anesthesia. It

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s essential to avoid muscle relaxants and positive pressureentilation. Should the child’s lungs become difficult toentilate, the child may have to be repositioned and theirway bronchoscoped.19 If the mediastinal mass is large, asoon as the mass has been biopsied and the pathologistonfirms that tissue was sufficient, parenteral steroidshould be administered.

Unilateral re-expansion pulmonary edema (RPE) is aare complication of the treatment of lung collapse second-ry to pneumothorax, pleural effusion, or atelectasis. Aore acute form of RPE has been reported in associationith lung re-expansion after mediastinal tumor removal. It

s important to be aware that this complication may manifesttself immediately after tumor removal or possibly delayednto the recovery period.

Extubation is best performed when the child is awake,ence ensuring adequate return of airway reflex responsesnd the avoidance of laryngospasm. Children with signifi-ant tracheomalacia may manifest tracheal obstruction andespiratory difficulties in the recovery room.5 Airway ob-truction may be corrected by repositioning the child in theecubitus or prone positions, but if the airway does notmprove, the trachea may require reintubation. Post-extuba-ion stridor should be treated with racemic epinephrine andumidified oxygen.

A clear understanding of the pathophysiology of anteriorediastinal masses will enable successful management of

uch cases. Knowledge of the potential difficulties is essen-ial in order to anticipate cardiorespiratory complications.hree principles including a thorough preoperative assess-ent (history, physical examination, and laboratory exam-

nations), maintenance of spontaneous ventilation, androper positioning cannot be overemphasized. Before em-arking on such a surgery, the anesthesia, surgical, andursing teams must understand the risks of anesthetizing ahild with an anterior mediastinal tumor and the types ofnterventions (ie, positioning) that they may be required tossist with in an emergency. A cooperative team approacho managing children with these tumors is the most impor-ant factor to ensuring a successful outcome.

eferences

1. Cheung S, Lerman J: Mediastinal masses and anesthesia in children, inRiazi J (ed): The Difficult Pediatric Airway. Anesthesiol Clinics North
Am 16:893-910, 1998
2. Filler RM, Simpson JS, Ein SH: Mediastinal masses in infants andchildren. Pediatr Clin North Am 26:677-691, 1979

3. Mullen B, Richardson JD: Primary anterior mediastinal tumours inchildren and adults. Ann Thorac Surg 42:338-345, 1986

4. Ferrari LR, Bedford RF: General anesthesia prior to treatment ofanterior mediastinal masses in pediatric cancer patients. Anesthesiol-ogy 72:991-995, 1990

5. Mackie AM, Watson CB: Anaesthesia and mediastinal masses. An-aesthesia 39:899-903, 1984

6. Janin Y, Becker J, Wise K, et al: Superior vena cava syndrome inchildhood and adolescence: a review of the literature and report ofthree cases. J Pediatr Surg 17:290-295, 1982

7. Levin H, Bursztein S, Heifetz M: Cardiac arrest in a child with ananterior mediastinal mass. Anesth Analg 64:1129-1130, 1985

8. Pullerits J, Holzman R: Anaesthesia for patients with mediastinalmasses. Can J Anaesth 36:681-688, 1989

9. Davenport D, Ferree C, Blake D, et al: Response of the superior venacava syndrome to radiation therapy. Cancer 38:1577-1580, 1976

0. Halpern S, Chatten J, Meadows AT, et al: Anterior mediastinalmasses: anesthesia hazards and other problems. J Pediatr 102:407-410,1983

1. Schamberger RC, Holzman RS, Griscom NT, et al: CT quantificationof tracheal cross-sectional areas as a guide to the surgical and anes-thetic management of children with anterior mediastinal masses. J Pe-diatr Surg 26:138-142, 1991

2. Kirks DR, Fram EK, Volk P, et al: Tracheal compression by medias-tinal masses in children: CT evaluation. Am J Radiol 141:647-651,1983

3. Simpson I, Campbell PE: Mediastinal masses in childhood: a reviewfrom a paediatric pathologist‘s point of view. Prog Pediatr Surg 27:92-126, 1991

4. Neuman GG, Weingarten AE, Abramowitz RM, et al: The anestheticmanagement of the patient with an anterior mediastinal mass. Anes-thesiology 60:144-147, 1984

5. Azizkhan RG, Dudgeon DL, Buck JR, et al: Life threatening airwayobstruction as a complication to the management of mediastinalmasses in children. J Pediatr Surg 20:816-822, 1985

6. Monrigal JP, Granry JC, Rezzadori G, et al: Preanesthetic managementin children with tracheal compression due to mediastinal tumors.Anesthesiology 77:A1202, 1992

7. Lokich JJ, Goodman R: Superior vena cava syndrome. Clinical man-agement. JAMA 231:58-61, 1975

8. Borenstein SH, Gerstle T, Malkin D, et al: The effects of prebiopsycorticosteroid treatment on the diagnosis of mediastinal lymphoma.J Pediatr Surg 35:973-976, 2000

9. Greenstein S, Ghias K, Krett NL, et al: Mechanisms of glucocorticoid-induced apoptosis in hematological malignancies. Clin Cancer Res8:1681-1694, 2002

0. Frankfurt O, Rosen ST: Mechanisms of glucocorticoid induced apo-ptosis in hematological malignancies: updates. Curr Opin Oncol 16:553-563, 2004

1. Sibert KS, Biondi JW, Hirsch NP: Spontaneous respiration duringthoracotomy in a patient with a mediastinal mass. Anesth Analg
66:904-907, 1987

anterior mediastinal masses in children

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