Introduction:
Aortobronchial fistula is a rare yet fatal condition which if left untreated, has a high mortality rate. Some studies reveal that the incidence is underestimated because more than 30% of cases are diagnosed only while performing an autopsy. The mortality rate is high because of low suspicion and the nature of the disease wherein there is sudden massive hemoptysis that could be life-threatening.
What Is Aortobronchial Fistula (ABF)?
Fistulas are abnormal communication between any organ or blood vessel or any other structures. When it happens between an aorta and tracheobronchial tree, it is called aortobronchial fistula. Most of the time, the communication is between the aneurysm and the bronchus wall. The left bronchial tree is most commonly involved as the distance between the descending aorta, and the left bronchial tree is less than the distance between the ascending and right.
What Are the Causes?
Earlier in the 1960s, mycotic aneurysms which are caused by tuberculosis, syphilis were the leading cause of ABF. It was also due to degenerative aneurysms, and postoperative pseudoaneurysms. Now, it is due to previous surgical graft treatment for aortic coarctation, or a chronic aortic aneurysm. Primary aortobronchial fistula occurs very rarely in a patient who has not undergone cardiac surgery. In recent times, atherosclerosis and iatrogenic conditions have become the most common cause of an ABF. It may also be due to pseudoaneurysms, traumatic thoracic aorta injuries, and penetrating aortic ulcers.
What Are the Symptoms of Aortobronchial Fistula?
Hemoptysis is the most typical symptom of aortobronchial fistula. But it is common in many other medical conditions also. A hemoptysis episode in a patient who has had a thoracic aortic aneurysm or undergone an aortic surgery should be intensely suspicious of aortobronchial fistula. Sometimes, even the first episode can end up fatal for the patient. Patients who develop ABFs often present with mild and intermittent hemoptysis, for which the etiology is diverse. It is further complicated to arrive at a proper diagnosis because of the lack of a diagnostic test that can clearly demonstrate an aortobronchial fistula. Other symptoms include back pain, chest pain, a mass near the aorta, or shock.
How to Diagnose Aortobronchial Fistula?
Diagnosis could be challenging even with radiography, CT (computed tomography) scan, bronchoscopy, and echocardiography. Diagnostic tests should be undertaken as soon as the airway is stabilized and hemodynamic status is assessed after an episode of hemoptysis. The chest radiographs demonstrated aneurysm in 46.5 % of the cases, but the most reliable test is a thoracic aortogram. A fistulous tract was rarely identified preoperatively by angiography and bronchoscopy, and it is potentially hazardous as it can dislodge a sealing clot. Findings on CT include pseudoaneurysm, aortic anatomy abnormalities, lung parenchyma consolidation, and compression of the bronchial tree. CT is more efficient in determining the cause for hemoptysis than a bronchoscopy. Mostly, the diagnosis is based on the clinical signs rather than the imaging findings. After the diagnosis, a multidisciplinary involvement with considerations for patient risk factors and clinical stability should be made.
What Are the Treatment Options?
When a patient has massive hemoptysis, the initial management will aim at protecting the airways and ensuring a stable hemodynamic volume. If the bleeding site is known, the patient is placed in a lateral decubitus position, with the bleeding side down. This prevents aspiration into the unaffected lung. The patient is then shifted to an intensive care unit, where careful monitoring and effective management are provided. Suppose the respiratory or hemodynamic status of the patient is compromised in that case, an emergency rigid bronchoscopy is attempted to clear the airways and safely isolate the non-affected lung, thus preserving ventilation. Once the hemodynamic and respiratory conditions are stabilized, then surgical management should be considered.
Traditionally, the surgery involved closure of the aortic side of the fistula by patch closure or prosthetic graft placement and repair of the bronchial side of the fistula by either resection or simple closure by direct suturing. The currently available treatment options include conservative therapy, open-heart surgery, and THEVAR (thoracic endovascular aortic repair). Thoracic endovascular stenting is a simpler and less invasive approach than traditional open-heart surgeries. However, they also have a risk of endoleak, migration, left arm ischemia, and infection due to direct communication with the contaminated airway. The treatment method to be used in each patient will depend upon the individual anatomy of the infected area, but careful steps must be taken to maintain distal perfusion. All the infected material or the prosthetic material must be removed, and a viable autologous biological barrier must be placed to avoid future recurrence of fistulas. It can be taken from the pleura, diaphragm, a vascularized intercostal or internal artery pedicle, or non-infected residual aneurysm sac.
What Are the Complications?
Studies show that complications occur many years after the intervention. As a consequence of infection or inflammation, there is always a chance for graft infection and erosion leading to recurrence of fistula. Other complications include stroke, paralysis, respiratory failure, acute renal insufficiency, ischemic cardiac events, acute hemorrhage, and secondary graft infection.
Conclusion:
Aortobronchial fistula is often a rare complication of thoracic aortic operations. If diagnosed, the survival rate is greater than 80%. If not, the condition is fatal. Hence an early diagnosis and prompt treatment are essential for the survival of the patient. Thoracic endovascular aortic repair of aortobronchial fistulas is an emerging treatment modality for this rare but highly lethal condition. In addition, the ABF may recur after an initially successful THEVAR procedure. The feasibility and long-term durability of this intervention are mainly unknown. Hence, continued clinical and radiographic surveillance is necessary.
