Bronchial artery embolization
Bronchial artery embolization is a treatment for hemoptysis, abbreviated as BAE. It is a kind of catheter intervention to control hemoptysis by embolizing the bronchial artery, which is a bleeding source. Embolic agents are particulate embolic material such as gelatin sponge or polyvinyl alcohol, and liquid embolic material such as NBCA, or metallic coils.
Basic principle
It is said that hemoptysis is caused by the formation of anomalous anastomosis between the bronchial artery and the pulmonary artery, and if the bronchial artery is embolized, hemorrhage will cease. This is a fundamental concept of BAE. Traditionally, BAE was mostly performed as an emergency hemostatic procedure. Recently, it is often performed as an elective catheter treatment to prevent recurrence after massive hemoptysis, or control chronic repetitive hemoptysis. Although it is termed bronchial artery embolization, various systemic arteries other than the bronchial artery also form a shunt with the pulmonary artery and cause hemoptysis. Therefore, it is common to embolize such non-bronchial arteries, but the expression of bronchial artery embolization, BAE, rather than the universal expression “arterial embolization” is more common. The therapeutic outcomes are improving due to the combined approach such as spreading the treatment target to non-bronchial arteries, development of 3D-CT angiography following the development of MDCT, the advancement of devices such as coils and micro-catheters, and the evolution of therapeutic strategies. BAE has become the gold standard for hemoptysis for its dramatic improvement. Although the hemostatic effect is greatly affected by the underlying disease, some high-volume centers report hemostatic rate of about 90.4% within one year of treatment, and 85.9% even in two years after treatment. The occlusion of the blood vessels in the brain, heart, and kidneys, which are supplied by the so-called end arteries, can cause cerebral, myocardial, and renal infarctions. In BAE, both bronchial mucosal necrosis and pulmonary infarction seldom occur. It is presumed that this is because the pulmonary circulation is dually controlled by the bronchial artery and the pulmonary artery; and even if the blood flow in the bronchial artery is lost, blood flow from the pulmonary artery is slightly maintained. In the case of non-bronchial arteries, it is empirically known that some collateral circulations also develop. In addition, direct hemorrhage from the pulmonary artery is rare, which requires embolization of the pulmonary artery.Treatment indications
BAE is effective for hemoptysis in most underlying diseases such as bronchiectasis, nontuberculous mycobacterial disease, cryptogenic hemoptysis, pulmonary aspergillosis, and pulmonary tuberculosis sequelae. According to Ishikawa who reported long-term treatment results of BAE for 489 hemoptysis patients, each underlying disease's ratio is 34.0%, 23.5%, 18.4%, 13.3%, 6.8%, respectively. Other diseases for which BAE is effective include lung abscess and pulmonary actinomycosis.As for lung cancer, hemoptysis is caused mostly by bleeding from the tumor itself, and not by the bronchial-pulmonary artery shunt mechanism; embolism of the feeding vessels for the tumor causes necrosis of the cancer which may evoke massive hemoptysis. In addition, subsequent chemotherapy and endovascular treatment cannot be performed if the route of anticancer drugs is permanently obstructed. Lung cancer needs a different strategy. Seki et al. reported the usefulness of endovascular treatment for lung cancer hemoptysis. Kichang et al. reported BAE for hemoptysis in 84 lung cancer patients, and demonstrated that massive hemoptysis and cavity formation were significantly poor prognosis factors; re-hemoptysis rate was 23.8% in their follow-up period.
Treatment technique details
A catheter with a diameter of less than 2 mm is inserted at the base of the foot or the artery in the wrist. The tip of the catheter is inserted into the orifice of the bronchial artery or other non-bronchial hemoptysis-related arteries. Contrast agent is injected through the catheter, and when abnormal findings are observed, such as systemic–pulmonary shunts, proliferations of the capillary vessels, or extravasation of the contrast medium to the lung tissues, they were super selectively embolized using the 3 Fr microcatheter system. A thinner microcatheter is passed through the catheter into the blood vessel, and then, embolic material is injected into the appropriate site. Thus, hemostasis is performed by ceasing or reducing the pressure applied to a bronchial -pulmonary shunt. BAE is performed under local anesthesia, and the required time is about 1 hour to 3 hours.Effectiveness
In the past, BAE was mostly considered a palliative or a bridge therapy to surgical operation owing to the high rate of re-hemoptysis with BAE. But with the improvement in treatment strategy and devices, it is regarded as a permanent therapy for hemoptysis nowadays.There are few facilities in which sophisticated BAE is feasible, and there are significant disparities between hospitals in the treatment quality and their experience. In most of the facilities, BAE is operated by interventional vascular radiology doctors, but in recent years, specialized high volume centers where a trained pulmonologist performs BAE are emerging. It is particularly effective for cryptogenic hemoptysis. Ando, Masuda et al. reported in their article that the hemostatic rate is 97% at 20 months, which is equivalent to the results of the article by Ishikawa. Ando, Masuda et al. state that micro bronchial aneurysms are involved in 22.9% of cryptogenic hemoptysis
For pulmonary aspergillosis, BAE was relatively less effective and was once thought to be contraindicated, but hemostatic rates have improved in recent years. Ando, Masuda et al. demonstrated that the re-hemoptysis rate was significantly higher in cases of disease progression.
The hemostatic rate in each underlying disease by Ishikawa is shown below. In this paper, both re-hemoptysis and death are defined as composite endpoints, and among these, only re-hemoptysis free rate is shown in the following table. It is originally a long-term performance data for 3 years; In the third year, the 95% confidence interval was too wide except for cryptogenic hemoptysis; hence, they are regarded as statistically unreliable figures. Therefore, the third year result is not posted here except for idiopathic hemoptysis. The poorest hemostatic rate after 2 years was observed in nontuberculous mycobacterial disease. The result shown by Okuda, Masuda et al. was similar. It is considered to reflect the progressive nature of the disease.
| Underground diseases | 1 year | 2 year |
| Total | 90.4% | 85.9% |
| Bronchiectasis | 87.6% | 85.1% |
| NTM | 89.0% | 75.9% |
| Cryptogenic Hemoptysis | 97.8% | 97.8% |
| Pulmonary aspergillosis | 86.4% | 82.1% |
| Tb sequelae | 91.3% | 85.3% |
Below are the treatment results summarized according to underlying diseases based on peer-reviewed papers published by Eishinkai Kishiwada Rehabilitation Hospital Hemoptysis and Pulmonary Circulation Center, and The National Hospital Organization Tokyo Hospital Pulmonary Circulation and Hemoptysis Center ; the top two representatives of high-volume centers in Japan.
| 1year | ２year | ３year | Cases | Follow-up period | |
| Tokyo Hp | 97.0% | 35 | 3 years | ||
| EHPC | 97.8% | 97.8% | 97.8% | 90 | 5.7 years |
| 1 year | 2 year | 3 year | Cases | Follow-up period | |
| Tokyo Hp | 79.1% | 73.8% | 63.3% | 43 | 5 years |
| EHPC | 89.0% | 75.9% | N.A. | 115 | 5.7 years |
| 1 year | 2 year | 3 year | Cases | Follow-up period | |
| Tokyo Hp | 65.8% | 50.0% | 47.9% | 41 | 5 years |
| EHPC | 86.4% | 82.1% | N.A. | 65 | 5.7 years |
In cases of recurrence, re-BAE is possible to perform several times.
As a secondary effect, Ishikawa et al. argue that BAE will decrease purulent sputum in 70% of patients, though it has not been proven.
Embolic material
These include polyvinyl alcohol, n-butyl-2-cyanoacrylate, gelatin sponge, metallic coil, etc.PVA
Woo et al. reported 406 cases of BAE long-term results, including 293 cases of PVA and 113 cases of NBCA.NBCA
This is a kind of medical instant adhesive. Generally, there are many complications such as non-target blood vessel embolization and adhesion of catheter and vessel wall. However, in the article by Woo et al., major complication rate was 0%.This kind has many advantages, such as low cost, instantaneous embolization, and very low recanalization rate since it does not depend on the patient's thrombus formation. It appears to be the best indication for traumatic bleeding control, particularly, in the peripheral bronchial aneurysms that the micro-catheter cannot access in BAE procedures, is a very good indication, and Mine, Hasebe et al. reported a technique called B-glue; NBCA combined with a balloon.
Gelatin sponge
is a transient embolic material, and in most cases, it dissolves within one to two weeks, and blood flow resumes. For this reason, it is important for emergency hemostatic purposes such as palliative treatment until surgery, which was the former positioning of BAE. GS is not suitable for the prevention of recurrence after massive hemoptysis or elective BAE for chronic repetitive hemoptysis. Wada et al. demonstrated that hemostatic rate was 24% in their retrospective analysis of BAE for 33 patients using GS.Metallic coil
There are three kinds of platinum vascular embolic coil. One is a detachable coil, which is expensive, but can be deployed repetitively until electric detach. This enables safest and fully controlled embolization. The second one is pushable coil, which is affordable, and allows for only one deployment. The third one is mechanical detachable coil; it has a moderate price range, and repetitive deployment is feasible. Ishikawa termed BAE with metallic coil as ssBACE, and published the world's largest number of cases of ssBACE long-term results in 2017. As described below, there are no reports on spinal cord ischemia in ssBACE, which is considered the most serious complication of BAE. This is one of the strongest merit of ssBACE.Despite a rumor that it cannot be re-treated if ssBACE is performed once, Ryuge demonstrated in their article on “the mechanism of re-hemoptysis” that the technical success rate in re-BAE was at least 97.7%.
Re-hemoptysis mechanism
Ryuge classified the re-hemoptysis mechanism after ssBACE into four as shown below. They also demonstrated that for the improvement of the long-term results in ssBACE in the future, suppressing recanalization is necessary.Some readers misunderstand that 45.2% of the embolized coils recanalized. This, in fact, is the ratio of re-hemoptysis mechanism occurring in 9.6% cases in 1 year, and in 14.1% of those in 2 years.
Recanalization was the main cause of re-hemoptysis, and the suppression of new hemoptysis-related vessels, which is the second cause, cannot be controlled by the BAE procedure itself. It was shown that suppression of the recanalization was the key to improvement in ssBACE result in future.
| Mechanism | Ratio | Explanation |
| Recanalization | 45.2% | Blood flow recurrence in the embolized area |
| New HRA | 38.5% | Totally new hemoptysis-related artery |
| Bridging collateral | 14.7% | Collateral from the proximal of the same artery |
| Conventional collateral | 1.7% | Collateral from the different artery |
Complications
In the past, paraplegia caused by spinal cord ischemia due to erroneous embolization of the anterior spinal artery was well known as a rare, but serious complication. Super selective BAE using microcatheter reduced the incidence of the spinal ischemia.Major complications reported by Ishikawa et al. are presented below.
Mediastinal hematoma occurs by injury of hemoptysis-related vessel, mainly by wire, and can easily bail out by proximal coil embolization.
| Complications | Cases | Incidence |
| Mediastinal hematoma | 5 | 1.0% |
| Symptomatic cerebellar infarction | 2 | 0.4% |
| Aortic dissection | 1 | 0.2% |
| Symptomatic Cerebral infarction | 0 | 0% |
| Spinal ischemia | 0 | 0% |
| Death | 0 | 0% |