Lung and Heart Transplantation

Determining Who Gets a Lung Transplant

In 2013, approximately 1900 lung transplantations were performed in the United States according to the Organ Procurement and Transplantation network. This represents a relatively small number compared to other organs including kidney (~17,000) and liver (~6500). Lung transplantation is performed in patients with advanced lung disease from a variety of causes ( Table 41.1 ). Trends over the past decade have shown increased utilization of lung transplantation in interstitial lung disease patients, primarily idiopathic pulmonary fibrosis, compared to those with chronic obstructive pulmonary disease.

Selection Process

Lung transplant recipients are chosen based on their lung allocation score. This system was developed in 2005 in an attempt to prioritize waiting list candidates based on their need and expected posttransplantation survival. Priority is given to patients who are likely to have a significantly greater 1-year survival with a transplant compared to a patient without a transplant. Some of the variables included in the lung allocation score include age, body mass index, diagnosis, lung function (i.e., forced vital capacity), need for oxygen, P co ₂ levels, pulmonary artery systolic pressure, and the presence of comorbidities such as diabetes and renal failure.

Some absolute contraindications to lung transplantation include a history of malignancy (nonskin) in the past 2 years, untreatable nonlung major organ dysfunction, noncurable infection, such as viral hepatitis B, and significant chest wall deformity.

Problem Solving With CT and PET

Radiology is valuable in screening for lung cancer prior to transplantation. Patients with advanced lung disease have a significantly higher incidence of bronchogenic carcinoma compared to the population as a whole. Volumetric CT of the chest is routinely performed in candidates when their lung allocation score predicts a reasonable likelihood of transplantation in the near future. It is important to note that bronchogenic carcinoma may have an atypical radiographic appearance in patients with advanced lung disease because of the significant architectural distortion of the lung ( Fig. 41.1 ). Any persistent focal lung opacity should be viewed as possible malignancy. ¹⁸ F-fluorodeoxyglucose (FDG) PET is useful in patients with indeterminate CT abnormalities and is particularly helpful in distinguishing malignancy from scar in patients with fibrotic lung disease.

How a Lung Transplantation Is Performed

A bilateral or single lung transplantation may be performed. A bilateral transplantation is required for patients with chronic infection, such as those with cystic fibrosis. Bilateral lung transplantation is also preferred at many institutions for all patients because there is evidence to suggest improved survival compared to a single lung transplant. Single lung transplantation is preferred for patients who are at a higher surgical risk, such as older patients. It also may be performed when complications, such as bleeding, necessitate early termination of the surgery.

The surgical procedure is performed one lung at a time. The pulmonary veins, pulmonary artery, and bronchus are divided. These are then reanastomosed to the allograft, typically in reverse order. Of note, the lymphatic, bronchial arterial, and neurogenic connections are not reestablished in the allograft. Cardiopulmonary bypass may be required in selected patients.

Common Surgical Complications

Major postoperative complications have become less common, given advances in technique over the past several decades. The most common complications include postoperative pleural hematomas, sternal dehiscence, and anastomotic issues.

Problem Solving With Chest X-Ray and CT

Postoperative pleural hematomas may be seen in the first few days after surgery and are more common in patients with significant pretransplantation pleural inflammation and adhesion formation, as in patients with cystic fibrosis. Pleural hematomas are usually discovered on chest radiographs and manifest as a significant pleural collection that develops immediately or within the first few days after surgery.

Sternal dehiscence is often the result of infection resulting in weakening of the bone. It usually occurs within the first few months after transplantation. Typical CT findings include separation of sternal fragments, areas of bone lysis, and significant fluid collections adjacent to the sternum. Sagittal and coronal reformats may be helpful in visualizing the distortion of the three-dimensional structure of the sternum.

Anastomotic breakdown usually involves the bronchial connection and is typically seen in the first month after transplantation. Pneumomediastinum and/or pneumothorax may indicate that the anastomosis is not intact. Postoperative air in the mediastinum is a normal finding in the first several weeks after surgery, but a predominance of air around the bronchial anastomosis should raise concern for an anastomotic dehiscence ( Fig. 41.2 ). Additionally, significant mediastinal air after the first few weeks is also suggestive. Extraluminal air should not be confused with the normal finding of a telescoped bronchial anastomosis.

Breakdown of the pulmonary arterial or venous anastomoses is rare, but has a high rate of mortality. This manifests as saccular extraluminal collections of contrast at anastomotic sites. Stenoses may also occur at the vascular anastomoses.

Typical Medical Therapy After Transplantation and Normal Surveillance Regimens

After receiving a lung transplant, recipients are treated with lifelong immunosuppression. The lung is unique because of its constant exposure to infectious agents in the environment; thus immunosuppression is a balance between the risk of infection and rejection. Typical regimens include a combination of a calcineurin inhibitor (e.g., tacrolimus), antimetabolite (e.g., mycophenolate mofetil), and corticosteroids. Asymptomatic patients undergo regular bronchoscopy, pulmonary function tests (PFTs), and CT imaging. This surveillance is most intensive in the first year posttransplantation and then subsequently falls off in regularity. Patients with any symptom will also undergo a similar diagnostic evaluation.

Most Common Complications of Lung Transplantation and the Role of Imaging in Monitoring These Complications

Complications in lung transplantation may be due to the surgery itself, the immunosuppression regimen, or an immune reaction against the allograft. Diagnosis of these complications is a multidisciplinary endeavor that incorporates clinical symptoms, laboratory findings, bronchoscopic findings, pathologic information, and radiology. Radiology is a key component in the detection and characterization of abnormalities. Complications tend to occur at predictable intervals after transplantation, and imaging findings must always be interpreted in this context ( Table 41.2 ). The role of imaging includes the following.

Primary Graft Dysfunction

Primary graft dysfunction (PGD) is a form of acute lung injury that occurs within 72 hours of transplantation. It is a result of multiple factors relating to the harvesting and reimplantation of the graft, including ischemic injury, the preservation process, and reperfusion on reimplantation. PGD replaces previously used terms such as reperfusion edema, reimplantation edema, and primary graft failure. PGD is seen in 10% to 50% of lung transplant recipients and is the most common cause of early mortality. It also predisposes patients to the development of late complications, namely chronic allograft dysfunction. It is graded (0–3) using two parameters, the oxygenation (ratio of Pa o ₂ /Fi o ₂ ) and the presence or absence of radiographic infiltrates consistent with pulmonary edema.

Problem Solving With Chest X-Ray and CT

Typical radiographic or CT features of PGD include diffuse or symmetric bilateral consolidation and/or ground-glass opacities appearing within 72 hours after transplantation ( Fig. 41.3 ). Interlobular septal thickening on CT, representing interstitial edema, is also commonly seen. To make a diagnosis of PGD, other causes of diffuse pulmonary opacities should be excluded, including hyperacute rejection, venous anastomotic obstruction, cardiogenic pulmonary edema, and pneumonia. Abnormalities are most severe within the first 2 weeks after lung transplantation, but typically show significant improvement by at least the 12th week.