Extracardiac complications of cardiac surgery

Extracardiac Complications of Cardiac Surgery By M. Kristin Thorsen and Lawrence R. G o o d m a n

HE NUMBER of coronary artery bypass operations nearly doubled between 1979 and 1984 and it is now the most commonly performed intrathoracie operation. During the same time period, other cardiac operations increased by 10%, and lung and bronchial surgery increased by 20%. Intrathoracic operations now account for 3% of all surgery, up from 2% 5 years ago. ~ The majority of cardiac operations are currently performed through a median sternotomy. This offers adequate access for most procedures and has a relatively low complication rate. Although minor wound problems are not infrequent, major problems such as dehiscence, sternal osteomyelitis, or mediastinitis ale infrequent. = This report concentrates on the radiographic appearance of the heart and lungs in the period immediately after cardiac surgery and the radiographic appearance of immediate and delayed postoperative complications, in separate sections, we will deal with the radiographic evaluation of cardiac transplantation and thoracic aortic surgery. We will not address the problems associated with each specific type of cardiac surgery (eg, ventricular septal defect [VSD], mitral valve, etc).

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Normal Postoperative Appearance Under ideal circumstances, the initial postoperative radiograph will show clear lungs and costophrenic angles, normal pulmonary vessels, and minimal widening of the mediastinum. A drainage tube is usually visible in the anterior mediastinum, as well as beneath the heart. These mediastinal drains are usually pulled two to four From the Department of Radiology, Medical College of Wisconsin, Milwaukee. M. Kristin Thorsen: Associate Professor of Radiology; Lawrence R. Goodman: Professor of Radiology. Address reprint requests to J~L Kristin Thorsen, MD, Medical College of Wisconsin. Department of Radiology, Milwaukee County Medical Complex. 8700 Iu Wisconsin Ave. Milwaukee, W153226. 9 1988 by Grune & Stratton. Inc. 0037-198X/88/2301--000455.00/0 32

days following surgery. Temporary transthoracic epicardial pacing wires and left atrial catheters are frequently present as well. A Swan-Ganz catheter and intra-aortic counterpulsation device may also be used for unstable patients. ~5

hnmediate Postoperative Complications Atelectasis. The pristine radiograph just described seldom exists because of the presence of atelectasis, edema, or pleural effusion. In a study of 99 patientsby Carter e;t al, 4 atelectasis was noted in 84 radiographs (left-sided in 40, right-sided in one, bilateral in 43). The atelectasis may range from mild elevation of the diaphragm and slightly increased density at the lung base to consolidation and partial collapse of an entire lobe. Although the atelectasis is usually present immediately, it may first appear or increase following extubation (Fig 1). Resolution is often slow. In many, residual scarring is a permanent sequela. Postoperative pneumonia complicating.atelectasis is uncommon. The frequency and severity of the atelectasis is greatest in the left lower lobe (LLL). Several factors contribute to this phenomenon. The LLL is retracted at surgery, frequently compressed by a large heart, lies in a gravity-dependent position, and is difficult "to suction with routine endobronchial catheters. In addition, topical cardiac hypothermia (used during surgery to decrease the metabolic needs of the heart) may freeze the phrenic nerve. This leads to paresis or paralysis of the left hemidiaphragm, which predisposes to LLL atelectasis. Decreased diaphragmatic motion may be apparent fluoroscopically for days or weeks after surgery. Recent attempts at protecting the phrenie nerve from the ice slurry appears to have decreased the frequency and severity ot" postoperative LLL atelectasis. 6 Pulmonary edema. A capillary-leak edema is extremely common in the immediate postoperative period. Vasoactive polypeptides are released during cardiopulmonary bypass and cause increased capillary permeability, leading to pulmonary edema. In the majority of patients, this is only detectable by decreased lung compliance or widening of the alveolar arterial gradient. In approximately 20% of cases, the postopSeminars in Roentgenology, Vol XXlU, No 1 (January), 1988: pp 32-48

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Fig 1. Postoperative edema and hemorrhage after coronary artery bypass procedure. The patient had recently undergone a repeat thoracotomy for postoperative hemorrhage. There is diffuse interstitial edema bilaterally. In addition, t h e r e is marked widening of the right paratracheal stripe and an apical cap on the right. Although the widening of the mediastinum is only moderate, persistent drainage of blood necessitated a third operation.

erative radiograph shows mild to moderate edema during the first 48 hours after surgery (Fig 1). The edema is usually reversible with respiratory support and diuresisY Another type of pulmonary edema may develop several days following surgery. Many patients develop generalized edema after cardiopulmonary bypass and accumulate fluid in the extravaseular space. After several days, this fluid is resorbed into the vascular space, and hypervolemia, hypoalbuminemia, hemodilution, and insidious pulmonary edema appear. In this group, left atrial pressure is usually elevated. Again, supportive therapy and diuresis usually reverses the process. Considerably less common but more serious is the patient whose cardiac output is inadequate upon coming off the cardiopulmonary bypass. These patients are frequently experiencing severe heart failure and require an aortic counter pulsation balloon device to assist the circulation (Fig 2). This device is usually seen with its radiopaque tip at or just beyond the distal aortic arch. By inflating the balloon during diastole, the proximal aortic pressure is increased, improving coronary artery perfusion. The balloon also propels blood distally, thereby decreasing afterload on the left ventricle. The distended balloon may be seen as a long lucency in the descending aorta.

Full blown adult respiratory distress syndrome following cardiac bypass is uncommon. Iannuzzi et al 8 found an incidence of <2% in patients without concomitant infection. Pleural disease. A small pleural effusion, especially on the left, is extremely frequent in the immediate postoperative period. Most are probably due to the irritation of the surgical procedure or to minor hemorrhage. There is a close correlation between the severity of atelectasis and the size of effusions as well. Most effusions regress within several days, often leaving minimal permanent blunting of the costophrenic angle. Mediastinal bleeding. The most significant complication of radiographic interest in the immediate postoperative period is postsurgical hemorrhage that requires reoperation. This occurs in only a small percentage of cases. Unfortunately, both mortality and postoperative complications following reoperation are considerably higher than from the initial operation. Therefore, every attempt is made to stabilize the patient rather than reoperate. Kirklin and BarrattBoyes2 have laid out the following criteria for reoperation: (1) excessive bleeding expected to exceed 1,500 mL, (2) sudden increase in tube drainage that has been minimal previously, (3) evidence of acute tamponade, and (4) marked widening of the cardiac silhouette on portable radiographs.

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Fig 2. Postoperative heart failure after aortic valve surgery. A butterfly edema pattern is present. An aortic countarpulsation device is present w i t h its tip in the aortic knob. There is a right apical cap (arrows) and mediastinal widening, both due to bleeding. Both regressed w i t h o u t surgical interv e n t i o n . (Reprinted w i t h permission. 3 )

Since every patient has some postoperative mediastinal widening, how wide is too wide? Katzberg et al 5 compared preoperative mediastinai width on the PA radiograph with postoperative mediastinal width on the AP radiograph, as it correlated with blood loss. Some severely hemorrhaging patients showed a relatively normal mediastinum and some patients with 60% widening did not require surgery. All patients with over 70% widening required surgery. Carter et al 4 reported seven patients (of 100 in their series) who required reoperation for mediastinal hemorrhage, four of whom had no radiographic evidence of widening of the mediastinum, one who had a widened mediastinum, and two who had an apical pleural cap. Thus, in a majority of patients, the chest tube drainage and clinical situation will dictate the need for reoperation (Figs 1 and 3). In a small percentage of patients, if the chest tube malfunctions progressive radiographic evidence of widening will indicate the need for reoperation. Extrapulmonary air collections. Pneumothorax, pneumomediastinum, pneumopericardium, and subcutaneous emphysema are frequently present following median sternotomy. These collections are usually self-limited and resolve over the next several days. It is not uncommon to find a small collection of air or an air-fluid level in the anterior mediastinum on the

initial lateral radiograph taken after the mediastinal drains have been removed. The majority are benign and not associated with mediastinitis. The air usually disappears over the next few days. Free air under the diaphragm, another wellknown complication of median sternotomy, is caused by the surgeon entering the peritoneal cavity while opening the lower sternum. This is a benign condition and without symptoms. Unless the patient has clinical findings of gastrointestinal perforation, free air under the diaphragm after sternotomy does not require further evaluation. 9 Thoracic cage lesions. In the immediate postoperative period, a lucent stripe down the middle of the sternum is visible on a postoperative radiograph in 30% to 50% of patients. The stripe is usually transient and seldom measures more than 3 mm in width. It represents a narrow gap in the sternum or presternal soft tissues. There is no correlation between this thin luceney and sternal dehiscence. Wider lucencies or progressive widening a(e of greater concern. Likewise, a single broken wire is often of no clinical significance, whereas reorientation of the sutures is often a sign, albeit a late one, of sternal dehiscence (see later). 5'1~ Rib fractures. Most reviews indicate that fracture of the first or second rib is present in 2% to 4% of postoperative radiographs and seldom of

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t

j

Fig 3. Postoperative hemorrhage after coronary artery bypass procedure. This patient recently underwent a repeat operation for mediastinal bleeding. There is n o w marked widening of the mediastinum w i t h "pseudoenlargement" of the cardiac silhouette. Despite the dramatic radiographic appearance, the patient's vital signs were stable and the tube drainage only moderate. Follow-up x-rays showed no further widening. Therefore, a repeat thoracotomy was not performed.

clinical importance. Greenwald et a112performed bone scans on 24 consecutive patients operated via a median sternotomy and demonstrated a total 0f44 fractures, 30 on the left andl4 on the right; the upper three ribs were most often involved. Even in retrospect only four of these fractures were visible on the radiographs. Although routine postoperative bone scanning is not recommended, it may be helpful in patients with unexplained chest pain, chest wall pain, or brachial plexus symptoms. Cardiac enlargement. An increase in the cardiac silhouette in the immediate postoperative period may be due to one of several conditions. Postoperative myocardial infarction and/or heart failure may cause cardiac enlargement. More frequently, the enlargement is due to fluid (serous, hemorrhage,- or infectious) in' the pericardial or mediastinal space (Fig 3). Pericardial disease. Pericardial hemorrhage with cardiac tamponade, postpericardiotomy syndrome, constrictive pericarditis, infection of the pericardium, and herniation of the heart through a pericardial defect are infrequent complications of cardiac surgery. Cardiac tamponade (Fig 4) has been reported in approximately, 3.5% of cardiac operations. ~3 The majority of these cases occur in the immediate postoperative period and result from postsur-

gical bleeding at graft suture lines or from arterial bleeders behind the sternum. Coagulopathy may also contribute to early bleeding. Removal of temporary pacing wires or left atrial lines may lead to cardiac tamponade one to two days following surgery. Patients with early cardiac tamponade usually have excessive tube drainage or direct blood loss from wound sites. Occasionally, a clot may obstruct the drainage of blood by

Fig 4. Pericardial tamponade following thoracic surgery. CT shows a moderate amount of pericardial fluid (arrowheads), which caused decreased cardiac output. Approximately 1,000 mL of bloody fluid was drained f r o m the pericardium.

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the tube. 14 In these cases, equalization of elevated right atrial, pulmonary artery diastolic, and pulmonary capillary wedge pressures combined with an enlarging cardiac silhouette on the chest roentgenogram are pathognomonic of impaired cardiac filling and pericardial tamponade) s However, in only half the patients with pericardial tamponade does the portable chest radiograph reveal cardiopericardial enlargement. A small amount of fluid may cause acute tamponade without an apparent increase in heart size. 16 Single chamber cardiac tamponade has also been reported as a complication of cardiac surgery, and in these cases the chest radiograph may not be helpfulJ 5"~7Early in the postoperative period, echocardiography may be technically difficult due to mediastinal drains and/or air in the thorax. CT can reveal the pericardial fluid in this situation and can also detect focal intrapericardial hematoma that causes single chamber compression. ~7In addition, CT will identify mediastinal hematoma that mimics enlargement of the cardiac silhouette. Late pericardial tamponade may occur from bleeding due to anticoagulation therapy or postpericardiotomy syndrome) 8 Chylopericardium following cardiac surgery may also occur secondary to intraoperative injury to the tributaries of the thoracic duct. 19 In later cases, two-dimensional echocardiography can easily detect pericardial fluid. CT may sometimes be helpful in further clarifying the extent and nature of the pericardial process. The postpericardiotomy syndrome is characterized by chestpain that develops usually after an interval of 2 to 4 weeks, but sometimes appears several months after cardiac surgery. 16 Other features of the syndrome include fever, pneumonitis, leukocytosis, pleural or pericardial effusion, arthralgias and ECG changes consistent with pericarditis. Although the syndrome is benign and usually self-limited, pericardial tamponade may occur, s~ An increased cardiac silhouette, basilar'infiltrates, and pleural effusion may be present on tile chest radiograph, or the chest film may be entirely normal. 16 CT or two-dimensional echocardiography can be used to detect pericardial effusions. Pericardial thickening may also occur secondary to the postpericardiotomy syndrome and is readily detected with CT. 21

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Constrictive pericarditis following surgery is rare. It usually presents 2 to 3 months following surgery with signs and symptoms of right-sided cardiac decompensation. The pathogenesis of constriction is unknown, but it has been associated with various pericardial irrigating solutions, local hypothermia, and air-drying of'the pericardium and hemopericardium. 22":4 Chest radiographs are not helpful in its diagnosis, unless pericardial calcification can be identified. Echocardiography is relatively insensitive for the detection of pericardial thickening. CT will often help distinguish constrictive pericarditis from restrictive cardiomyopathy. In the appropriate clinical setting, pericardial thickening of 5 to 20 mm on CT is suggestive of constrictive pericarditis. CT may also demonstrate dilatation of the inferior vena cava (Fig 5), ascites, and pleural effusions. Following contrast enhancement, angulation of the intraventricular system and compression of the right heart may be detected. The thickened pericardium will often enhance following the administration of intravenous (IV) contrast medium, thereby excluding pericardial effusion. A normal pericardium on CT virtually excludes the diagnosis of constrictive pericarditis.21,25 Pericardial infection is uncommon, occurring in <1% of patients following cardiac surgery. 16 Drainage from the mediastinal wound, a widened

Fig 5. Constrictive pericarditis. CT demonstrates a thickened pericardium (arrows) and dilatation of the inferior vena cava (IVC).

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mediastinum, or an increased cardiac silhouette on the chest radiograph may suggest pericardial infection. CT will usually demonstrate pericardial fluid. Marked thickening of the visceral and parietal pericardium may be present secondary to the inflammatory changes. Air may be present in the pericardial sac. Cardiac herniation with volvulus through a pericardial defect is a rare, often catastrophic event. It usually occurs in the first hours following pericardial surgery, t6 The clinical signs are

hypotension, distended neck veins, cyanosis, chest pain, and ischemic changes on ECG. Mortality is approximately 4 0 % . 26 The chest radiograph shows shift of the heart. Left-sided herniation results in a spherical-shaped left heart border, with an incisura between the great vessels and the more lateral heart marginY In right-sided herniation, the cardiac apex is shifted into the right hemithorax. Obstruction of the superior vena cava may occur with volvulus. 2s Recently, radiographic signs of impending her-

A

Fig 6. Cardiac herniation through a pericardial defect following right pneumonectomy. (A) Immediately after surgery, the right heart border appears globular with a "snow-cone" appearance, indicating partial cardiac herniation; (B) 90 minutes later complete cardiac herniation with volvulus has occurred. (Reprinted with permission. =9)

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niation have been described..The appearance of a globular or "snow-cone" configuration of the right heart border in the immediate postoperative period should raise the question of partial cardiac herniation (Fig 6). 29

Delayed Postoperative Complications Sternal dehiscence, osteomyelitis, mediastihal infection. These serious postoperative complications are uncommon, and occur in only 2% to 5% of patients. They are more frequent after re0peration, after previous sternal radiation, and with postoperative respiratory failure requiring

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assisted ventilation. They are associated with a high mortality and morbidity. A death rate of 70% has been reported with mediastinitis and osteomyelitis. With improved diagnostic and therapeutic approaches, the mortality has been markedly diminished. 3~ They are frequently interrelated: sternal dehiscence is ~ frequently associated with osteomyelitis of the sternum, and sternal infection is frequently associated with deeper mediastinal infection. An imaging workup for one should include all three. The earlier the correct diagnosis of infection is established and appropriate treatment instituted,

Fig 7. Normal sternal anatomy. (A) CT through the manubrium shows the subcutaneous tissue, pectoralis muscle, and anterior madiastinal structures to be sharply outlined with fat. Note that the posterior wall of the manubrium is irregular and spiculated, simulating disease (arrows). The cut through the angle of Louis often shows dense, irregular hone due to the inclusion of both the manubrium and body of the sternum and the intervening cartilage (arrowheads}. (B) Cuts through the body of the sternum show sharp cortical margins in a rectangular or oval configuration. Irregularities are often noted at the costal cartilage insertions (arrow).

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the better the prognosis. Unfortunately, the clinical and laboratory diagnoses are often diMcult and may take days or weeks to establish. Likewise plain films and tomography of the sternum and mediastinum are nonspecific. It has been our observation that the early and sometimes repeated use of contrast-enhanced CT may prove extremely helpful in determining the presence and extent of infection. Mediastinitis, the most serious of all the complications, occurs in 2% to 4% of sternotomy patients. The infection usually occurs four to 30 days after surgery. Some cases are associated with the classical clinical signs: fever, tenderness, and a draining sinus. More often than not, some of these signs are absent and the patient has systemic or nonlocalized symptoms. It is sometimes uncertain whether the draining sinus represents a superficial chest wall infection or is being fed by an infection of the sternum or mediastinum. In a recent study, Carrol et a135 found that in 77% of patients with proven mediastinitis, a confident diagnosis could not be made from the chest radiograph. In their series, 63% had a widened mediastinum, 54% had pleural disease, and only 22% had gas within the mediastinum. However, widened mediastinum and pleural fluid are often present in patients without infection. Contrast-enhanced CT is the procedure of choice in defining focal fluid collections and determining whether the presternal tissues, mediastinal tissues, or sternum are involved in the process. The normal sternum has a predictable CT appearance. The skin and muscles of the chest wall are sharply etched against the subcutaneous fat. The anterior and middle mediastinal vessels are likewise sharply delineated by fat. The sternum is a rectangular envelope of cortex, sometimes irregular at the rib insertions. The manubrium sterni is a larger rectangle of bone. Its cortical surface, which faces the anterior mediastinum, is frequently thinned and irregular a n d should not be confused with osteomyelitis. Likewise, the sternomanubrial junction (angle of Louis) may be an irregular rhomboid with varying degrees of calcification (Fig 7). An infrequent normal variant is the sternal foramen, a failure of fusion of calcification centers along the midline. The anterior and posterior margins of the sterum slope gradually toward the foramen.

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This should not be confused with a destructive lesion of the sternum) 6 CT performed 1 week after sternotomy in a patient with no clinical complications may show the following normal postoperative changes: (1) imperfect closure of the sternum. The two tables are at different levels or small gaps in closure exist. These small imperfections are frequent and appear to be of no clinical significance. (2) The presternal muscles and subcutaneous tissues appear normal or near normal. On occasion, mild edema or isolated scattered air bubbles may be seen. (3) The anterior mediastinum is always abnormal. Most patients show mild edema or hemorrhage with partial but not total obliteration of the mediastinal fat planes (Fig 8), or one or more focal, sharply marginated, high-density fluid collections (residual hemorrhage) (Fig 9). Occasionally a low-density, sharply marginated fluid collection is also seen (presumably serous). 36 Scattered small bubbles of air are not infrequent. In contrast, mediastinitis appears as total obliteration of the anterior fat planes with or without discrete fluid collections, seldom containing air. Beyond the first week focal mediastinal or pericardial fluid collections should be viewed with suspicion (Fig 10). 4"35"37'3g Likewise, a large collection of air or air and fluid beyond the first week is of concern. However, in the first week or two, these findings may be benign residuals of surgery. They must be carefully correlated clinically. The more time that has elapsed since

Fig 8. Normal postoperative change in an asymptomatic patient. Six days after surgery, the anterior mediastinal fat remains somewhat fuzzy. The great vessels are visible. No focal collection is seen beneath the sternum. Differentiation from early mediastinitis is not possible So soon a f t e r surgery. The same appearance 2 w e e k s later would strongly favor infection.

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frequently diagnosed clinically. The sternum is unstable with respiration or coughing. As mentioned earlier, a thin vertical lucency down the middle of the sternum does not indicate dehiscence. Progressive widening of that lucency or rearrangement of the sutures does. In most instances of dehiscence, the sutures do not break but rather cut through the sternum. Several wires will travel with the right half of the sternum while others travel with the 'left. Migrating or rearranged appearance of the sutures is probably the most specific radiologic sign of dehiscence, but a late one. 1~ Sternal osteomyelitis may be an isolated problem or associated with dehiscence or deeper infection. Conventional radiographs or tomograms have been extremely disappointing in evaluating this problem. Marked demineralization and frank bone destruction are the only

Fig 9. Postoperative change in an asymptomatic patient. A C T scan through the angle of Louis eight days after surgery shows a focal, anterior mediastinal fluid collection sharply outlined by anterior mediastinal fat. It is approximately the same density as the nonopacifled aorta and most likely represents a residual hematoma. Minimal edema remains in the subcutaneous tissues anteriorly.

surgery, the more weight one puts on these CT findings. When the radiologic and clinical findings are at odds or indeterminant, CT can be used as a baseline for a follow-up scan in several days or as a guide for percutaneous aspiration to confirm or disprove infection. A superficial infectionmay cause a draining sinus and fever, suggesting a deeper infection. CT has been helpful in localizing the superficial infection and exi:luding an anterior mediastinitis beneath it (Fig I 1). In our experience, patients returned to surgery with a diagnosis of mediastinitis without a definite fluid collection have not had a surgically treatable infection (Fig 9). Sternal dehiscence, often associated with osteomyelitis or anterior mediastinitis, is most

Fig 10. Focal mediastinal abscess and pericardial effusion 29 days after surgery for postoperative bleeding. The patient had developed fever and staphylococcus sepsis. CT through the midsternum shows a large anterior fluid collection probably involving both the mediastinum and pericardium (--3 to + 7 HU) (arrows). Some of the fatplanes are preserved. While the patient was being stabilized for repeat sternotomy, pus drained spontaneously through the surgical incision and the patient defervesced. A follow-up scan 13 days later showed a small residual collection. (Reprinted with permission, zT)

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Fig 11, Suspected postoperative infection. The patient had mild f e v e r and a persistent small air collection behind t h e s t e r n u m on a lateral radiograph. CT through the area shows a normal pericardium, normal anterior mediastinal fat, a single large air bubble w i t h o u t an air-fluid level, and minimal edema of t h e subcutaneous tissues. The irregular xyphoid at this level is normal. The CT w a s interpreted as " n o evidence of infection.'" He was t r e a t e d conservatively and defervesced over t h e n e x t 2 weeks.

reliable indicators of osteomyelitis on lateral tomograms of the sternum. Signs of dehiscence, soft tissue swelling, enlarging holes around the sutures, and "periosteal thickening" correlate poorly with the presence or absence of osteomye-

litis.39Just as with conventional radiography, CT may be negative at the time of initial clinical suspicion. It is our impression, based on only a few cases, that CT shows the bone demineralization and destruction long before conventional

Fig 12. Postoperative osteomyelitis. Over the previous several months the patient had numerous surgical procedures f o r debridement of osteomyelitis following median sternotomy. The manubrium w a s intact and t h e adjacent pre- and poststernal soft tissue planes w e r e normal. (A} This is t h e junction b e t w e e n intact bone and t h e previous surgical procedures. The sternum is markedly irregular and demineralized. The adjacent soft tissues are normal except for minimal anterior mediastinal thickening in t h e fat. The CT indicated no adjacent soft tissue infection. It w a s uncertain w h e t h e r t h e irregularity of the bone was f r o m the previous surgical procedures or from osteomyelitis of t h e inferior part of the manubrium. An open biopsy of these areas showed a m i x e d infection limited to t h e sternum b u t e x t e n d i n g superiorly to involve normal appearing bone as well.

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tomograms. It also affords a look at the adjacent soft tissues (Fig 12). Salit et al 4~used gallium 67 scanning to evaluate postoperative sternal osteomyelitis:~ The normal postoperative sternum shows a uniform mild uptake of gallium. Focal areas of intense gallium uptake strongly suggest osteomyelitis. In their study, gallium correctly identified five of the six patients with osteomyelitis. There was one false-positive among 27 normals. We have not had personal experience with this method. Pseudoaneurysm; aortic dissection. Any incision into the aortic wall sets the stage for aortic dissection or pseudoaneurysm formation. This incision may be for aortotomy for aortic valve replacement, for can'nulation for cardiopuimon: ary bypass, or for coronary artery bypass grafting.4~ The incidence of aortic dissection secondary to cardiac surgery has been reported to be < 1%. Pseudoaneurysm following cardiac surgery is even less common.42 Iatrogenic pseudoaneurysm or aortic dissection should be considered in the differential diagnosis of the postcardiac surgery patient who presents with a widened mediastinum or anterior mediastinal mass on a chest radiograph. Its appearance may be delayed weeks to years after surgery. Mediastinal infection may predispose to the breakdown of suture lines, causing these complications:3,44 Contrast-enhanced CT, using a dynamic scanning technique, may separat~ ascending aorta pathology from other causes of mediastinal widening, such as hematoma, abscess, tumor, or mediastinal fat. Pseudoaneurysm is manifest as a focal, contrast-filled outpouching from the ascending aorta. Thrombus may be present. The

neck of the pseudoaneurysm usually can be visualized using routine 10 mm thick sections. Occasionally, thinner sections (5 mm or 3 mm) may be required. CT may also identify the position of the pseudoaneurysm relative to the sternum (Fig 13): s Its recognition may avoid inadvertent rupture on midline sternotomy at reoperation. The CT findings of iatrogenie aortic dissection include two contrast-filled channels separated by an intimal flap. Other less specific findings of aortic dissection include displaced intimal calcification, a widened aorta, and an extra-aortic fluid collection:6 A pseudoaneurysm and aortic dissection may rarely coexist. The false channel may rupture and be contained by adherent fibrous tissue or pericardium, forming a pseudoaneurysm.

Cardiac Transplantation In 1967, Barnard performed the first orthotopic cardiac transplant in which the donor heart came from a patient who had irreversible brain injury. The recipient lived for 18 days: 7 Following Barnard's announcement, 101 cardiac transplants were performed in the first year. The initial enthusiasm for these procedures soon waned because the initial survival rates were low. With the advent of newer immunosuppressive agents, especially cyclosporine, cardiac transplantation is now frequently performed.4g In 1986 alone, 1,050 heart transplants were performed in the United States at approximately 74 medical centers. The 1-year survival rate has improved from 22% in 1968, to 88% in 1984.49 In orthotopic cardiac transplantation, the recipient heart is removed, leaving behind a cuff

Fig 13. Pseudoaneurysm of ascending aorta at prior cannulation site. The pseudoaneurysm (AN} is interposed between the ascending aorta (AO) and t h e superior vena cava (arrow), PA, pulmonary artery. (Reprinted with permission.e6)

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of the native atria and the severed ends of the great vessels. The donor heart, proximal aorta and pulmonary artery are joined to the recipient's native atria and great vessels. The normal postoperative radiograph often shows a double right atrial contour due to the overlap of the donor and ri~cipient right atria (Fig 14). 4s Early postoperative complications are similar to those observed in other open-heart procedures. Mediastinal bleeding requiring re-exploration has been reported in approximately 9% of cardiac transplant patients: ~ The chest radiograph may show progressive widening of the mediastinum or the presence of a new or enlarging pleural effusion. CT may reveal blood in the mediastinum, pericardial sac, or pleural space. Graft rejection is the most common fatal complication. Prior to the use of cyclosporine, frecluent ECGs to evaluate cardiac voltage, and chest radiographs were used to monitor for graft rejection. An increase in the cardiothoracic ratio was associated with cardiac graft rejection. In a review of the postoperative radiographs of 38 cardiac transplants, 14 of 17 patients who experienced cardiac rejection demonstrated an increase in cardiac size concurrent with the episode, s~ In the patients treated with cyclosporine, myocar-

Fig 14. CT of heart transplant. T w o days following transplantation, left pleural effusion and LLL atelectasis are seen behind the heart. A mediastinal drain and nasogastric tube (curved arrows) are present. The native left atrium (LA), right a t r i u m (RA), and superior vena cava (C} are shown. The region of the anastomosis is labeled with a dotted line. The donor atria (J), aorta (Ao), left ventricle (LV), and right ventricle (RV) are noted. The native descending aorta is also labeled Ao.

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dial edema, which is one of the most striking histologic features of rejection in patients treated conventionally, is almost comialetely absent, so that the clinical, ECG, and radiographic signs are no longer helpful. Serial endomyocardial biopsies are required to diagnose rejection. This is based on the degree of lymphocyte infiltration of the myocardium plus the presence of myocyte necrosis: 2 Transplant recipients begin immunosuppression therapy before surgery and continue for the rest of their lives. During the first 3 months postoperatively, when immunosuppressive levels are highest, the transplant recipient is at increased risk for opportunistic infections. Based on the Stanford experience, the infections are bacterial in 61% of cases, viral in 17%, fungal in 12%, protozoan in 5%, and nocardial in 5%. Involvement of the lungs was present in 65% of the infectious complications: ~ Radiographic findings in pulmonary infections are nonspecific. Areas of nondescript increased markings and of patchy airspace consolidation may appear. Fungus (especially aspergiilus) and gram-negative infections may cavitate. Empyema and lung abscess may supervene. Transplant patients have an increased risk of

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developing a malignant neoplasm. In one report of 124 cardiac recipients 3 months or longer after transplantation, eight developed carcinoma, ten lymphoma, and one leukemia. Six of the lymphomas occurred after the initial transplant; four occurred following retransplantation. The primary site of the lymphoma was the brain or spinal cord in four patients, the lung parenchyma in two, the soft tissue of the thigh at the antihuman thymocyte globulin (ATG) injection site in two, and the disease was systemic in two. The risk of developing lymphoma was greatest in patients under age 20, in those with idiopathic cardiomyopathy, and in those patients who had undergone retransplantation. 53'~4 Transplant patients may also develop coronary artery disease. This may lead to sudden death, arrhythmia, infarction, and left ventricular dysfunction. Accelerated graft arteriosclerosis is higher for patients with HLA-A2 and A3 incompatibilities, when donor age is :>35 years and

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elevated triglyceride serum levels are present in the recipient. The patient may require reimplantation if graft atherosclerosis is diffuse.55 Heterotopic heart transplantation offers an alternative to patients with end-stage heart disease and high pulmonary vascular resistance. With this technique, the donor heart is placed in the right pleural cavity and connected to the patient's circulation in such a way that both the right and left ventricles of the recipient are bypassed without interfering with their existing function (Fig 15). 56Complications of heterotopic transplantation include all of those associated with orthotopic transplantation plus the risk of emboli from thrombi in the poorly contracting native heart and significant RLL atelectasis from the position of the heterotopic h e a r t y Routine chest radiography and CT often reveal atelectatic changes, areas of consolidation, pleural effusion, and increasing cardiomegaly. Angiography may aid in the diagnosis of anastomotic

Fig 15. Heterotopic heart t r a n s plant. (A) Preoperative chest radiograph shows cardiomagaly and blunting of the left costophrenic angle. (B) Posttransplantation, the donor heart (DHi is located in the right hemithorax adjacent to the patient's native heart (NH}. Support lines and bilateral pleural effusions are noted,

~lz*-~ Fig 16. Acute aortic dissection. (A} CT shows the intimal flap (arrowheads) in the ascending and descending aorta. (B) Intraoperative photograph shows intimal flap (arrowheads} corresponding to CT findings. A, false lumen; B, true lumen; A V , aortiC- valve. The ostium of a coronary artery (arrow) is also shown. (C) The intimal tear has been repaired an d the aorta wrapped w i t h Teflon felt to prevent pseudoaneurysm formation. (D) Postoperative CT scan shows the Teflon felt w r a p and suturs line (arrow). The false lumen, A, and the true lumen, B, persist despite primary repair of the intimal tear. (Reprinted w i t h permission. ~ }

46

THORSEN AND GOODMAN

integrity and embolie disease. ~7 Radionuclide lung scanning m a y also be helpful in diagnosing pulmonary embolism. THORACIC AORTIC SURGERY

Postoperative Aortic Dissection

Aortic dissection is the most c o m m o n acute catastrophe involving the aorta, occurring two to three times more frequently than ruptured abdominal aortic aneurysm. 58 T h e primary surgical objective in the repair of aortic dissection is to prevent proximal dissection, which m a y lead to such life-threatening complications as pericardial tamponade, acute aortic insufficiency, or myocardial infarction. ~96~ T h e surgical approach to these patients i s v i a median sternotomy and consists of either (1) p r i m a r y repair of the intimal tear with oversewing of the triae and false channels, plus wrapping the aorta with Teflon felt to prevent pseudoaneurysm formation, or (2) resection of a segment of ascending aorta with obliteration of the false channel at the suture line and interposition of a tubular woven Dacron

graft. In the majority of cases, the natural aortic valve can be preserved. In some cases, aortic valve replacement a n d / o r coronary artery bypass grafting m a y be necessary. 62 Aortic dissection limited to the descending aorta is usually treated medically unless there is persistent pain, impending rupture, or coexisting M a r f a n ' s syndrome. These cases are approached via a left thoracotomy and the segment of aorta that contains the intimal tear is resected and replaced with a graft. 63 Despite surgical repair of the intimal tear and obliteration of the proximal portion o f the false channel, the dissection m a y remain patent from retrograde flow of blood via a re-entry tear in the distal aorta. C T with contrast-enhanced dynamic scanning techniques has been useful in delineating the details of the dissection (Fig 16). ~4'65 In addition to the persistence of the false channel, C T m a y demonstrate a postoperative pseudoaneurysm or extra-aortic fluid collection. A baseline postoperative C T scan should be obtained in case there is a later complication. 65

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