Type:
Educational Exhibit
Keywords:
Lung, CT, CT-High Resolution, Complications, Transplantation
Authors:
M. Chan, D. Patsios; Toronto, On/CA
DOI:
10.26044/ranzcr2021/R-0332
Imaging findings OR Procedure details
Surgical Techniques
- Early surgical techniques utilised an end-to-end anastomosis, wrapped with intercostal muscle or omentum to improve healing. Omental wrap predisposed to complications such as diaphragmatic hernias.
- Current surgical techniques use a 'telescopic' technique which involves bronchial overlap (smaller bronchus is telescoped into the larger bronchus). Performed without omental wrap with good success.
- Lobar implantation may occur when the donor lung is large for the recipient body - only parts of the donor lung are implanted (e.g. pulmonary fibrosis recipients).
Airway Complications
- The donor bronchus depends on collateral perfusion from the pulmonary circulation in the initial postoperative period. Bronchial arteries are not reanastomosed.
- Anastomotic healing is limited by ischemia, possibly causing ulceration, dehiscence or stricture.
- Reduced complication rates with improved surgical and donor preservation techniques, better immunosuppression, and post-transplant surveillance.
Bronchial Dehiscence
- Most common airway complication in the early postoperative period.
- Best assessed by bronchoscopy.
- CT demonstrates extraluminal gas +/- focal bronchial wall defects.
- Indirect signs: persistent air leak, pneumothorax, and pneumomediastinum.
- CXR: unreliable for early bronchial dehiscence.
Bronchial Stricture
- Occur in the later postoperative period (~10%).
- Usually diagnosed by bronchoscopy
- CT with multiplanar reformats can demonstrate the degree of stenoses and length of webs.
- CXR: do not demonstrate strictures well.
Bronchomalacia
- Distal affected lung can be hyperlucent
- Can be treated with stent insertion.
Pleural complications
- Seen in up to 22% of patients after lung transplantation.
- Double lung and heart-lung transplants frequently result in a single communicating pleural space and may cause bilateral complications.
Pneumothorax
- Most common pleural complication
- Usually resolves with thoracostomy and drains.
- New, persisting, or enlarging pneumothorax should prompt further investigation for the source.
- Can occur following surveillance intervention (e.g transbronchial biopsy).
Pleural effusions
- Simple effusions frequently occur in almost all patients after lung transplantation.
- Increased capillary permeability, impaired lymphatic clearance of the transplanted lung.
- Most resolve within 2 weeks.
- Persistent or delayed effusions can suggest complications (e.g. empyema, rejection or post-transplant lymphoproliferative disorder).
- Empyema occurs in 4% of patients
- Can be bilateral and patients can rapidly deteriorate.
- Associated with increased mortality.
Vascular complications
- Rarely occur. Arterial stenosis arise more common than venous stenosis.
- Pulmonary infarction risk is greatest in the immediate postoperative period due to no alternative for bronchial circulation.
- Generally associated with poor outcomes, sometimes mitigated with dilation or stent placement.
Parenchymal complications
- Many lung parenchymal findings have non-specific radiological findings.
- Correlation with the time interval from transplantation, clinical findings, and transbronchial biopsy are often required.
Reimplantation Response (Reperfusion Oedema)
- Non-cardiogenic pulmonary oedema occurs in 95% of patients
- Begins on Day 1, always present by Day 3, peaks by Day 4-5, and resolves by Day 10.
- Persistence beyond Day 7 suggests infection or acute rejection.
- Most patients are minimally symptomatic; a minority are severely dyspnoeic and hypoxaemic.
- Pathogenesis is probably multifactorial:
- Increased vascular permeability from ischemia/reperfusion
- Lymphatic interruption
- Lung denervation
- Decreased surfactant production
- Surgical trauma.
- It is usually diagnosed after exclusion of left ventricular failure, fluid overload, transplant rejection, and infection.
Acute Rejection
- Usually occurs within the first 3 weeks, typically between Day 5-10.
- Transplant recipients can experience 2-3 significant rejection episodes in the first 3 months.
- Repeated episodes increase the risk of chronic rejection.
- The most useful feature is the dramatic clinical and radiographic response to corticosteroids and increased immunosuppression.
- Radiographic features may be similar to those of reimplantation response and infection.
- CT findings:
- new, persisting, or progressive perihilar and basal opacities, pleural effusions with septal lines, 5-10 days after transplantation, without other signs of left ventricular failure, are suggestive of acute rejection.
- ground-glass opacities that are patchy and localized in mild rejection, but widespread in severe rejection.
- interlobular septal thickening, nodules, consolidation and volume loss.
- CT has limited accuracy in the diagnosis or grading of severity of acute rejection.
- Transbronchial biopsy to confirm the diagnosis and exclude infection.
Infection
- Most common complication post-transplantation, a major cause of morbidity and mortality.
- Increased susceptibility to infection due to immunosuppression, lung denervation with loss of the cough reflex, impaired mucociliary function, and lymphatic drainage
- Pneumocystis pneumonia is now uncommon due to the routine trimethoprim-sulfamethoxazole prophylaxis.
Bacterial Infection
- Accounts for >50% of all infections after transplant.
- Usually occurs within the first-month post-transplant, but may recur.
- Fatality is unusual in the immediate post-operative period due to broad-spectrum antibiotics.
- The most common causative organisms include gram-negative bacilli (e.g. Klebsiella, Pseudomonas) and gram-positive organisms (e.g. Staphylococcus aureus and Hemophilus pneumoniae).
- Radiologic features include lobar or multifocal consolidation, cavitation and nodules.
- In cystic fibrosis patients, Burkholderia cepacia is associated with severe post-operative infections and inferior survival rates.
Fungal Infection
- Less common than viral infections, but have higher mortality.
- Usually occur between 10-60 days post-transplantation.
- Lung transplant recipients have a higher prevalence of aspergillosis than other immunocompromised patients.
- Candida and Aspergillus are the most common.
- Candida frequently colonises the airways; invasive pulmonary infection is uncommon.
- Aspergillus can cause indolent pneumonia or fulminant angioinvasive infection with systemic dissemination. Aspergillus can cause ulcerative tracheobronchitis (radiographically occult) and can lead to anastomotic dehiscence, subsequent bronchial stenosis or bronchomalacia.
- CT findings: Combination of ill-defined nodules, cavitary opacities, consolidation, and ground-glass opacification.
Viral Infection
- Cytomegalovirus (CMV) is the second most common cause of pneumonia in lung transplant patients.
- Most occur 1-12 months after transplantation, peak incidence at 1-4 months.
- Increased risk of superimposed bacterial and fungal infections.
- Patients may be asymptomatic or develop fulminant pneumonia which may be fatal.
- Primary infection: CMV seronegative recipients and graft seropositive donors. Infection develops in >90%, potentially serious in 50-60% of cases. Thus CMV matching is performed whenever possible.
- Secondary infection: reactivation of latent virus following immunosuppression or infection with a different CMV strain. Usually less serious than primary infection.
- Diagnosis confirmed via endobronchial sampling.
- Risk factor for bronchiolitis obliterans syndrome (BOS).
- Other viral infections include herpes simplex virus, adenovirus and respiratory syncytial virus.
- CXR findings: normal or demonstrate diffuse parenchymal haziness or reticulonodular interstitial opacities and small effusions.
- CT findings: ground-glass attenuation, reticulation, micronodules, consolidation and small effusions.
Post-Transplant Lymphoproliferative Disorder (PTLD)
- Pathologically varies from a histologically benign polyclonal lymphoid proliferation to aggressive high-grade lymphoma. Most cases are of B-cell origin.
- Incidence is approximately 5% (range 1.8-20%), more common than other solid organ transplant patients.
- Most occur within a year, peaking at 3-4 months, range 1 month to several years.
- Incidence variability may reflect differences in immunosuppression, age, rates of Epstein Barr virus (EBV) and cytomegalovirus (CMV) prophylaxis. (I.e. higher risk for an EBV-seronegative recipient with EBV-seropositive donor or aggressive immunosuppression).
- CT findings: solitary or multiple pulmonary nodules or masses.
- Extrapulmonary involvement is uncommon.
- Clinical manifestations: low-grade fever, lethargy, and weight loss or asymptomatic.
- Most cases respond to antiviral agents or reduced immunosuppression.
Chronic Lung Allograft Disorder (CLAD)
- Umbrella term defining a persistent, unexplained decline in pulmonary function (FEV1, with/without FVC) >20% from post-operative baseline. Two types:
- Bronchiolitis Obliterans Syndrome (BOS)
- Restrictive Allograft Syndrome (RAS)
Bronchiolitis Obliterans
- Usually presents 6-18 months post-transplant, but seen as early as 2 months.
- Affects up to 50% of patients, now the major limitation for long-term survival.
- Probably a manifestation of chronic immunological rejection.
- Risk factors: multiple acute rejection/infection episodes, gastric reflux, and HLA-mismatching.
- Affects small airways and is not demonstrated by transbronchial sampling in the early stages. Often clinically diagnosed.
- Radiographic appearance: normal-decreased vascular markings, peribronchial cuffing, and subsegmental atelectasis. Lung volumes can be mildly increased.
- CT findings: Bronchial dilation/wall thickening, mosaic attenuation, air trapping.
Restrictive Allograft Syndrome (RAS)
- 25-35% of patients with CLAD, demonstrating >10% decline in lung capacity.
- Worse prognosis compared to BOS.
- Imaging patterns include pleuroparenchymal fibroelastosis, organising diffuse alveolar damage and non-specific interstitial pneumonitis.
Other complications
- Recurrent disease in the transplanted lung is uncommon (1%). Reported conditions include sarcoidosis, lymphangioleiomyomatosis, and diffuse mucinous pulmonary adenocarcinoma.
- Iatrogenic complications include post-transbronchial biopsy nodules and drug toxicity.
- Single lung transplants are at higher risk for neoplasm (7-9%).
- Recently with COVID-19, some transplanted lungs may have had pre-existing COVID that was unknown at transplantation.