Version May 2024
INTRODUCTION — Pulmonary arteriovenous malformations (PAVMs) are abnormal communications between pulmonary arteries and veins [1]. Alternative names include pulmonary arteriovenous fistulae, pulmonary arteriovenous aneurysms, cavernous angiomas of the lung, and pulmonary telangiectases [2].
PAVMS are associated with significant morbidity and mortality (eg, stroke, cerebral abscess, massive hemoptysis). However, not all patients with PAVMs require definitive therapy.
The approach to treating patients with PAVMS is discussed in this topic. The epidemiology, etiology, and pathology, as well as clinical features, and diagnostic evaluation of patients with suspected PAVMs are reviewed separately. (See "Pulmonary arteriovenous malformations: Epidemiology, etiology, and pathology in adults" and "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults".)
NATURAL HISTORY — True estimates of morbidity and mortality as well as natural history data are unknown because these data are mostly reported in retrospective case series.
Morbidity and mortality associated with PAVMs are mostly associated with the development of serious complications including stroke and brain abscess, and less commonly with hypoxemic respiratory failure and life-threatening hemoptysis or hemothorax.
Most PAVMs remain stable in size. However, up to 25 percent will enlarge slowly, usually at a rate of 0.3 to 2 mm/year in sac size. Macroscopic PAVMs (ie, those seen on chest computed tomography [CT]) do not spontaneously resolve. Studies performed in patients with hereditary hemorrhagic telangiectasia (HHT) also support slow growth of PAVMs over five years, with an increase in shunt by no more than one grade [3]. However, a more recent study looked at 21 adult patients with HHT who had 88 small PAVMs and found no significant change in feeding artery diameter (mean 1.4 mm, range 0.8 to 3.7 mm) or sac size (mean 4.3 mm, range 2.1 to 11.1 mm) over a mean of 8.4 years.
Detailed discussion of the rate of PAVM-associated complications is provided separately. (See "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Features attributable to PAVM complications'.)
PATIENTS SUITABLE FOR EMBOLOTHERAPY — Not all PAVMs require intervention. When indicated, embolotherapy is the mainstay of treatment as most PAVMs (>99 percent) can be successfully treated with this therapy (algorithm 1). Although many interventional radiologists at local hospitals have treated one or more PAVM, we believe that most PAVMs are best managed by referral to a center that has expertise in PAVM treatment, usually hereditary hemorrhagic telangiectasia (HHT) centers (www.cureHHT.org) [4]. This affords the best opportunity to treat all appropriate PAVMs in the least number of sessions and minimize the chance of PAVM persistence, especially for patients with PAVMs that are large, complex, and multiple.
Patient selection — Selecting patients to treat is dependent upon factors including the feeding artery diameter (FAD), the clinical suspicion for the presence of a symptomatic PAVM, and the patient’s ability to tolerate the procedure (algorithm 1). Most of these factors are typically identified during the diagnostic evaluation but additional unsuspected PAVMs identified during pulmonary angiography may also be targeted for embolization. (See "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Diagnostic approach'.)
A decision to intervene must also take into consideration the risk of complications of the procedure. However, compared with other alternative therapies (surgical excision and lung transplant), the procedural risk of embolotherapy is considerably lower. Assessing the preoperative pulmonary risk is discussed separately. (See "Evaluation of perioperative pulmonary risk".)
While the indications for the treatment of PAVMs have not been clearly defined due to a lack of high quality studies evaluating the efficacy in different populations, we and others generally agree with the approach outlined in the sections below [4].
Feeding artery ≥2 to 3 mm — For patients who have one or more PAVM with a FAD ≥3 mm on chest CT, regardless of the presence or absence of symptoms, we and others suggest pulmonary angiography be performed [4-7]. At the time of pulmonary angiography, PAVMs with FAD ≥3 mm are targeted for embolization and smaller PAVMs are embolized, if technically feasible (image 1 and image 2). There is a move in the HHT community towards embolizing all PAVMs with FAD ≥2 mm [8-11]. Our own practice is to favor embolotherapy in PAVM with FAD 2 to 3 mm and discuss the risks and benefits of this approach with patients.
Support for this approach comes from two lines of evidence:
●First, it is generally accepted that PAVMs with large feeding arteries (typically associated with a high-grade shunt) are associated with an increased risk of complications, particularly stroke [12-14]. As examples:
•When compared with grade 0 or grade 1 shunts (ie, low-grade shunt) seen on contrast echocardiography, grade 2 and 3 shunts (ie, large shunts) are associated with a four- and ten-fold increased risk for development of cerebral complications, respectively [15]. (See "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Transthoracic contrast echocardiography'.)
•Several observational studies and most experts agree that the risk of neurologic complications, particularly stroke, is greatest in those with a FAD ≥2 to 3 mm [5-7,14,16]. (See "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Features attributable to PAVM complications'.)
●Second, studies report a reduction in neurologic complications (stroke, transient ischemic attack [TIA], abscess, migraines, seizures, diplopia, dizziness) when PAVMs, particularly those with a FAD ≥2 to 3 mm, are treated with embolization, when compared with the expected rates of neurologic complications reported in separate cohort series (0 to 5 percent versus 13 to 36 percent) [6,14,17,18].
However, retrospective data suggest that neurovascular complications can occur with PAVMs of any size [19]. Data from 1665 patients with HHT reported no association between feeding artery size and the rate of neurovascular complications. However, feeding artery diameter was missing in almost half of the patients included in the study. Further data are needed to define feeding vessel size as a risk factor for neurovascular complications.
Symptomatic lesions — Patients with symptomatic PAVMs are also considered for embolotherapy regardless of imaging features. As examples, for patients whose PAVM has a FAD <2 mm on CT or who have atypical lesions on CT (or rarely a seemingly normal CT), who also have symptoms suggestive of an underlying treatable PAVM, we typically perform diagnostic pulmonary angiography with a view to identifying a potential PAVM(s) suitable for embolotherapy. This is especially true for patients who have a grade 3 shunt on transthoracic contrast echocardiography and multiple PAVMs with FAD <2 mm. Symptoms suggestive of a treatable PAVM include severe hypoxemia, paradoxical embolization (eg, stroke or brain abscess), and hemoptysis.
Support for this approach is derived from our clinical experience and rare case reports that suggest possible benefit from embolization of PAVM with feeding arteries <2 mm, as well as from data extrapolated from the larger studies described above that report benefit to the more aggressive approach of embolizing smaller angiographically visible vessels, when feasible [6,14,17].
PATIENTS NOT SUITABLE FOR EMBOLOTHERAPY
Asymptomatic lesion and feeding artery <2 mm — For most patients who are asymptomatic and the feeding artery is <2 mm, we suggest that they be followed with intermittent clinical observation and a non-contrast CT every 5 to 10 years (algorithm 1). During observation, pulmonary angiography targeted at embolization of suitable PAVMs should be performed in patients who develop symptoms suggestive of a treatable PAVM or for PAVMs that definitely enlarge over time.
Poorly accessible lesions — Although rare, some patients present with lesions that require treatment (ie, feeding artery diameter [FAD] ≥2 to 3 mm) but are not technically amenable to catheter-directed embolotherapy. As an example, distal lesions with hyperacute branching of the feeding pulmonary artery may make it technically difficult to access the PAVM. In our opinion, an interventional radiologist with experience in embolotherapy in a center with expertise in PAVMs (usually a hereditary hemorrhagic telangiectasia [HHT] treatment center) should be consulted before resorting to surgery for lesions that cannot be embolized due to technical difficulties. In the event that this approach fails, then surgical excision may be performed. However, in our experience and that of other HHT treatment centers, it is very rare to encounter an untreated PAVM with a FAD >2 mm that cannot be treated with embolotherapy. (See 'Embolotherapy' below and 'Surgical excision' below.)
Others — Additional patient populations may be considered at high risk for PAVM closure with embolization including those with severe pulmonary hypertension (PH) or comorbidities that affect procedural safety.
Special consideration should be given to those with severe PH, where PAVM closure may be associated with a rise of pulmonary artery pressures, although this finding is inconsistent [20]. In addition, patients with severe PH may be at increased risk of sedation-related hypotension and cardiac collapse. All patients with PAVM and PH should be referred to a center with experts in both PH and PAVM management. While most experts agree that patients with severe PH are considered at increased risk when undergoing embolization, each case should be considered on an individual basis and take into account factors including the mean pulmonary artery pressure, pulmonary vascular resistance (PVR), PAVM size, and prior evidence of a PAVM-related complication (eg, stroke) [10]. For example, embolization may be less risky in those with PH when the PAVM is small and the PVR is low while patients with larger PAVMs and higher PVRs are likely to be at higher risk. (See "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Pulmonary hypertension' and "Treatment and prognosis of pulmonary arterial hypertension in adults (group 1)", section on 'Surgical or periprocedural care'.)
PATIENTS WHO FAIL EMBOLOTHERAPY
Persistent lesion — For most patients who undergo embolotherapy, symptoms improve and complications are avoided (up to 94 percent) [21-24]. However, in 8 to 25 percent of cases, the PAVM shows persistent perfusion following coil embolization, usually defined by <70 percent decrease in sac size or CT contrast-enhancement of the sac [21,22]. Persistence may be less common after embolization with Amplatzer Vascular Plugs and Microvascular Plugs [22,25] (see 'Embolization material' below). The four main causes of PAVM persistence include [21-23]:
●Recanalization through the original embolic material (most common)
●Reperfusion through new feeding pulmonary arteries or capillary beds
●Continued perfusion through missed feeding arteries
●Reperfusion through systemic arteries
In one study of 23 patients with 53 persistent PAVMs, recanalization was the most common pattern, seen in 91 percent, followed by pulmonary reperfusion in 25 percent and missed feeders in 15 percent [21]. Systemic reperfusion is the least common cause of persistence; analysis of seven studies showed systemic reperfusion in only 3 percent of patients with persistence [21]. Common causes for recanalization include using too few coils, embolizing too proximally in the feeding artery, and use of oversized coils. Failed embolization may be apparent immediately or develop over years.
In almost all cases, repeat embolotherapy is indicated (algorithm 1). Although the true outcomes with repeat embolotherapy are unknown, in one study 84 percent of recanalized PAVM were successfully treated with repeat embolotherapy, in contrast to only 44 percent with pulmonary reperfusion [21]. During repeat treatment of recanalized PAVMs, higher persistent occlusion rates can be achieved if embolization is performed distally rather than proximally [26]. (See 'Embolotherapy' below.)
Although most experts will treat persistent PAVM, their natural history is unknown. In one study of 30 patients with persistent PAVM, 12 were asymptomatic and 18 were symptomatic [23]; of the latter patients, only 11 percent had symptoms attributable to the persistent PAVM and these were minor symptoms (dyspnea and headache). In another study, persistence in 373 treated PAVMs at five years was seen in 12 percent of nonsmokers, 22 percent of 1 to 20 pack-year smokers, and 38 percent of >20 pack-year smokers [27].
Transthoracic contrast echocardiography (TTCE) may predict the need for embolotherapy. In one study, grade 3 shunt on TTCE in patients who failed embolotherapy predicted those who needed repeat therapy [24].
Failed repeated embolization — In patients who fail one or two trials of repeated embolization, surgical excision of individual PAVMs may be performed. However, surgical excision is rarely needed as most patients respond to embolotherapy. Surgical techniques and outcomes associated with surgery are discussed below. (See 'Surgical excision' below.)
Refractory lesions — The vast majority of patients with PAVMs respond to embolization and/or surgery. For the few patients that are refractory to such treatment or whose PAVM cannot be resected, lung transplantation is an option, especially for those with diffuse bilateral disease [28,29]. However, lung transplantation should be considered only for patients who are at considerable risk of dying from their underlying PAVM because severe postoperative hemorrhage and fatal multiorgan failure can occur following transplantation [30], especially since the long-term outcome of patients with hypoxemia due to refractory PAVM is excellent without transplantation [31]. (See "Lung transplantation: General guidelines for recipient selection".)
SPECIAL POPULATIONS
Untreatable contrast allergy — Although an untreatable allergy to contrast material is sometimes cited as an indication for surgery, in our experience, almost all patients with a contrast allergy can be pretreated for their allergy (eg, multiple doses of glucocorticoids, combined with use of a different contrast agent from the one that caused the previous reaction) so that embolization can be safely performed. The management of contrast allergy is presented separately. (See "Patient evaluation prior to oral or iodinated intravenous contrast for computed tomography" and "Diagnosis and treatment of an acute reaction to a radiologic contrast agent" and 'Embolotherapy' below.)
Pregnancy — There is a high incidence of PAVM rupture during the second and third trimesters of pregnancy resulting in hemothorax and hemoptysis [32]. One prospective evaluation of embolotherapy of 13 PAVMs in seven pregnant patients reported no ill effects in mother or baby [33]. A detailed estimation of fetal radiation exposure suggested that pregnant women with significant PAVMs can safely undergo embolotherapy during the second and third trimesters [10]. Safety is optimized by minimizing the field of view and fluoroscopy time and waiting until the second trimester to perform the procedure. The indications for embolotherapy are the same as for the general population. For those who do not require embolotherapy, CT may rarely need to be repeated during pregnancy for the evaluation of highly symptomatic lesions. (See "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Hemothorax and hemoptysis' and 'Patients suitable for embolotherapy' above and "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Computed tomography'.)
EMBOLOTHERAPY
Procedure — Embolotherapy is an interventional radiology procedure usually performed under conscious sedation. It refers to the angiographic occlusion of the feeding arteries to a PAVM under fluoroscopic guidance. Principles of conscious sedation and indications for pulmonary angiography in patients with PAVMs are discussed separately. (See "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications" and 'Patient selection' above.)
The first component of the procedure is diagnostic contrast-enhanced pulmonary angiography, the purpose of which is to do the following:
●Confirm and characterize PAVMs identified on CT (suspected)
●Characterize PAVMs missed on CT (unsuspected)
●Identify PAVMs that are potentially suitable for embolization
Typically, diagnostic right and left pulmonary angiography is performed by injection of contrast through a percutaneous catheter (often inserted through a sheath in the femoral vein) positioned in the right and left main pulmonary arteries. This approach maximizes visualization of lesions suitable for embolization in both lungs.
The second component of the procedure is embolization [8]. Once angiographically identified as suitable for embolization, lesions are then localized through selective contrast injections and treated by catheter-directed placement of embolic material (usually coils or vascular plugs) into the PAVM until blood flow ceases (image 3) [34]. If coils are used, we prefer tight packing of multiple coils to effectively eliminate flow into the PAVM; this also reduces the risk of post-procedural recanalization and the necessity for repeat embolization. (See 'Embolization material' below.)
Multiple and even bilateral PAVMs may be embolized during a single session [8], and additional sessions may be performed after a hiatus of one to two weeks if additional PAVMs remain perfused, which is usually identified by the end of the procedure.
Diffuse multiple small PAVMs in the same segmental or lobar territory are a unique management challenge (image 4 and image 5). Diffuse PAVMs are often too small and too expansive such that embolization is often not feasible. Although attempts can be made to embolize discrete PAVMs with a feeding artery diameter (FAD) ≥2 to 3 mm within a diffuse region in order to reduce the risk of stroke and cerebral abscess, it often has only a modest effect on the associated severe hypoxemia because shunting through the remaining unembolized PAVMs persists [30]. Some experts address this issue by placing embolization material starting distally within the area of diffuse PAVM and packing coils into the entire pulmonary arterial supply of the affected segment; this technique, sometimes termed "catheter segmentectomy," has been shown to reduce symptoms in some patients and should be performed in a center with expertise in the treatment of PAVMs [35].
Although the exact mechanism of PAVM regression following embolotherapy is unknown, it is generally thought that PAVMs undergo thrombosis and sac retraction due to reduced flow and the presence of thrombogenic material within the PAVM feeding artery. Whether sacs undergo fibrosis is also unknown.
Embolization material — The type of material used is often institution-dependent. We prefer the use of nonferrous coils or vascular plugs due to our extensive experience with these materials.
●Coils – Metallic coils (usually platinum) are used in many institutions. Optimal results are obtained when at least two coils are placed as close as possible to the AVM sac, ideally within 1 to 2 mm [36]. For every 1 mm increase in the distance between coils and sac, the risk of persistence increases by 28 percent [36]. Steel coils, while used in the past are now generally avoided in favor of platinum coils, which are generally softer and have less interference with MRI. An advantage of using detachable coils is that they can be deployed and repositioned if necessary.
One retrospective study of 90 patients who underwent coil embolization of 219 PAVMs (most had FAD 2 to 3 mm) showed that embolization of the distal feeding artery plus the nidus produced higher persistent occlusion rates compared with embolization of the feeding artery alone [11]. Another retrospective study of 42 PAVMs reiterated these findings [37].
●Vascular Plugs – Detachable nitinol vascular plugs have been used to occlude PAVMs since 2005. The later generation Amplatzer Vascular Plugs (AVP) and newer Microvascular Plugs (MVP) are highly effective and can occlude a PAVM with a single device. A review of seven case series reported 16 cases of persistence following embolization of 237 PAVMs with various generations of AVPs (mean 6.8 percent, range 0 to 16 percent) [10]. The main benefits of AVPs are that they can be precisely deployed close to the PAVM sac, they can rapidly occlude PAVMs with large feeding arteries, and they have a low risk of device migration. Migration can be additionally avoided by sizing AVPs 30 to 100 percent larger than the FAD. The main drawbacks of AVPs are that they are generally more expensive than coils and may take longer to occlude flow than coils. Recanalization through the mesh of the AVP can also occur. In one series, the latter drawbacks were circumvented by deploying one or two platinum coils immediately proximal to the AVP [8].
MVPs are smaller plugs consisting of a polytetrafluoroethylene membrane over a nitinol skeleton [38]. They have the potential advantages of immediate vascular occlusion and lower persistence rates, and the smaller sizes are deliverable through a microcatheter. Four series have reported on the use of MVPs to treat a combined 227 PAVMs in 104 patients; during follow-up, only four patients (1.8 percent) had persistence of PAVM at various durations of follow-up [38-41].
●Balloons – Detachable balloons have been used in the past but are no longer available. One historical problem with balloons was their propensity to deflate over time.
●Other alternatives – Alternative embolic materials such as glue and polyvinyl alcohol have little role in the treatment of PAVM. In one study of highly selected cases of PAVM recurrence, embolization within the pre-existing coil pack using an ethylene vinyl alcohol copolymer liquid embolic agent was safe and effective [42].
Several studies have directly compared the results of various embolic materials [25,39,43,44]. In a retrospective study of 157 PAVMs in 25 patients, PAVM persistence at various follow-up times was 2 percent for MVP, 15 percent for AVP, and 47 percent for coils [39]. The persistence rates were significantly lower for MVP or AVP versus coils only [39]. A larger study of 112 patients with 393 PAVMs also compared these three embolic devices and showed PAVM persistence rates to be 0 percent for MVP, 8 percent for AVP, and 16 percent for coils; these differences were significant both with and without propensity score weighting [44]. In a third study of 322 PAVMs in 136 patients, PAVM persistence at various follow-up times was 4.5 percent for AVP, 14 percent for AVP plus coils, and 12 percent for coils [25]. Another study randomized 46 PAVMs in 25 patients to closure with either Interlock fibered coils or Nester coils and found no significant difference in persistence or complications [43].
Clinical and radiographic outcomes — In most patients, embolotherapy results in an immediate improvement in the radiographic appearance of PAVMs (ie, cessation of flow), symptoms (eg, dyspnea), and oxygenation. Over the long-term it also reduces the rate of serious complications especially neurologic events including stroke and cerebral abscess.
The procedural success rate in the first one to two years is as high as 98 percent according to small observational case series [5,45-50]. As an example, in one cohort of 39 patients with bilateral PAVMs who were followed for a mean of 43 months, embolization was completely or partially successful radiographically in 97 percent of patients and was associated with improvement in dyspnea (in 80 percent of patients), New York Heart Association (NYHA) functional class, and arterial oxygen tension (PaO2) [46].
Most studies examining outcomes beyond two years report successful prevention of PAVM-associated neurologic complications [6,14,18]. As examples:
●One retrospective longitudinal cohort study reported five-year outcomes in 112 patients with 349 PAVMs (FAD 1.8 to 12.4 mm) who had at least one PAVM with a FAD ≥3 mm [6]. The overall success rate was 83 percent and treatment was most successful (96 percent) for patients in whom all angiographically visible vessels were embolized. Overall, only three patients had a transient ischemic attack (TIA) and two had a cerebral abscess over the study period. In addition, the more aggressive approach of targeting all angiographically visible vessels during the procedure was associated with fewer patients requiring repeat embolization (4 versus 42 percent). (See 'Natural history' above and "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Features attributable to PAVM complications'.)
●In another case series of 221 patients with large PAVMs (average FAD >8 mm) treated with embolotherapy, stroke and/or cerebral abscess occurred in only 2 percent of patients over a five-year follow-up period [18].
●In another cohort study of 201 individuals with HHT-associated PAVMs, most of whom were asymptomatic, embolization reduced the risk of stroke with no strokes or abscesses occurring in patients following obliteration of all angiographically visible PAVMs [14].
These complication rates in treated patients contrast favorably with those in patients who were not treated (historical controls). The impact of embolotherapy on less frequent complications of PAVMs (eg, hemoptysis, polycythemia) is unknown but presumed to be similar.
Procedural complications — While death due to the effects of sedation (eg, respiratory arrest), bleeding (eg, a venipuncture site), or cardiac arrest (eg, from ruptured PAVM) is possible, we are unaware of any reports of procedural mortality from embolization.
Post-procedural (ie, short term) complications include the following [5,45,46]:
●Pleuritic chest pain (5 to 13 percent)
●Stroke (<0.5 percent)
●Transient ischemic attacks (1 percent)
●Transient air embolization (5 percent)
●Radiographic pulmonary infarction (3 percent)
●Deep venous thrombosis (DVT) due to catheter placement (1.5 percent)
●Distal migration of embolic material (especially detachable balloons) (<1 percent)
●Proximal migration of the embolization coil (<1 percent)
●Arterial wall damage with potential perforation (<1 percent)
Pleuritic chest pain, the most common procedural complication, is usually self-limiting and typically responds to a short course of non-steroidal inflammatory agents, but occasionally a short tapering course of prednisone (eg, 5 to 10 days) is necessary for more protracted pain. Infrequently, one or two additional courses of steroids may be necessary for recurrent pleurisy. Neurologic complications and DVT are treated in a similar fashion to patients without PAVMs. In case of migration of the embolization material, various interventional techniques can be used to retrieve the material if necessary. However, this complication is very rare at centers with expertise in PAVM management. Severe hemorrhage from a perforated PAVM can be treated with more proximal embolization or more rarely with surgical excision.
Long-term complications can be observed a few weeks to months following the procedure [18,21,51]. These include:
●Recanalization of previously occluded PAVMs (5 to 20 percent)
●Growth of new feeding arteries (pulmonary or systemic collaterals) to the occluded PAVM (2 to 6 percent)
●The development of pleurisy four to six weeks after embolization (1 to 2 percent)
●The development of new or worsening pulmonary hypertension (<1 percent)
PAVM persistence (eg, recanalization, pulmonary reperfusion, new feeding vessels) can be treated with repeat embolization.
The development of pulmonary hypertension infrequently occurs in patients with large PAVM, multiple PAVM, or clinical evidence of either baseline pulmonary hypertension or an elevated cardiac output. The risk is likely greatest in patients with more than 20 percent right to left shunt at baseline. It can be theoretically minimized by estimating the post-treatment pulmonary hemodynamics prior to embolization. (See "Clinical features and diagnosis of pulmonary hypertension of unclear etiology in adults".)
Follow-up — Following embolization, patients should be monitored closely for clinical improvement (eg, symptoms, oxygenation) and for complications of the procedure, as discussed above. (See 'Clinical and radiographic outcomes' above.)
The optimal frequency and modality for follow-up is unknown. Our approach is similar to that of other experts and includes the following as a general guideline [4]:
●In the immediate postoperative period, patients should be monitored clinically and with pulse oximetry to document symptomatic and physiologic improvements.
●Multi-detector contrast-enhanced chest CT with 1 to 2 mm thin slice formatting and transthoracic contrast echocardiography (TTCE) should be performed three to six months after embolization. CT is required to confirm continued closure of the PAVM, which is usually indicated by 70 percent or greater reduction of PAVM sac size and decrease in the draining vein diameter. During the past five years, we have used transthoracic contrast echocardiography to determine additional follow-up.
•If the initial post-embolization CT shows continued successful treatment (eg, no persistent PAVM) and the TTCE shows a grade 0 or 1 shunt, we usually recommend future follow-up with TTCE only every three to five years in order to avoid radiation from CT scans. If the TTCE worsens to grade 2 or 3 during future follow-ups, we repeat the CT at that time. The basis for this approach is that patients with a grade 1 shunt are at very low risk for complications from untreated PAVM [15]. Using this approach, we have not seen any complications as long as the patient observes antibiotic prophylaxis before dental procedures. (See "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Transthoracic contrast echocardiography'.)
•If the initial post-embolization CT shows persistence of PAVM or the TTCE shows a grade 2 or 3 shunt, we recommend future follow-up with CT only. Addition of TTCE to the initial follow-up may also be useful in evaluating the CT findings. For example, if the CT shows several areas of possible persistence but the TTCE shows a marked reduction in shunt grade from 3 to 1, the persistence is less likely to be clinically important. Conversely, if the TTCE shows no change in shunt grade, the persistence may warrant additional evaluation.
Worsening symptoms, failure to improve radiographically, or the development of new PAVMs on CT warrant further evaluation with pulmonary angiography and retreatment for either continued perfusion of the PAVM or the development of new lesions amenable to embolotherapy. (See 'Patients suitable for embolotherapy' above.)
ALTERNATIVE THERAPIES
Surgical excision — Surgical excision of individual PAVMs is rarely needed but may be performed in patients who fail repeated embolization (especially if complicated by recurrent hemoptysis) as well as in patients with life-threatening acute hemorrhage from a ruptured PAVM in a facility without access to embolotherapy. The number of patients that require surgery has not been accurately reported. However, in the era of embolotherapy, rates have declined from approximately 20 percent to <1 percent at experienced centers.
Patients with small, well-demarcated individual lesions (eg, <5 cm) that are few in number and suitable for wedge resection or lobectomy, are likely better surgical candidates than those with multiple large lesions in different lobes or lungs, which might require a pneumonectomy or bilateral thoracotomy for complete resection.
Surgical techniques used to treat PAVMs include vascular ligation, local excision, lobectomy, and pneumonectomy. The choice among these depends upon the location and extent of PAVMs as well as the expertise of the operating surgeon. While most PAVMs are amenable to video-assisted thoracoscopic surgery, some may require an open thoracotomy. (See "Overview of minimally invasive thoracic surgery".)
Surgery to treat PAVMs is associated with a morbidity and mortality that is similar to that of other thoracic surgeries. Only one death out of 124 patients has been reported from complications of PAVM surgery [5,52]. Acute right heart failure has been rarely reported, likely due to removal of the PAVM with a subsequent acute increase in the pulmonary vascular resistance [53].
Surgical therapy is not always curative. Recurrence or enlargement of other existing PAVMs has been reported in up to 12 percent of patients [54-59]. In addition, enlargement of previously unrecognized PAVM and stroke have been reported.
Lung transplantation — Lung transplantation is an option for the few patients that are refractory to repeated embolization, especially for those with diffuse bilateral disease or those considered at high risk of dying from their disease. Details regarding lung transplantation are discussed separately. (See "Lung transplantation: General guidelines for recipient selection".)
ADJUNCTIVE THERAPIES
Avoiding air embolism during intravenous injections — Patients with PAVMs are at risk for air embolism. Meticulous care should be taken to avoid the introduction of air bubbles when fluids or medications are given intravenously. This includes inserting intravenous catheters with the insertion site positioned below the heart and using in-line filters for nearly all intravenous infusions, when possible. Since the goal is to filter out macroscopic air bubbles, any type of blood (usually 170 to 260 microns) or in-line intravenous (0.22 to 0.45 micron) filter should be adequate. Importantly, filters cannot be used for intravenous contrast injection. Filters should be fine for iron infusions based on particle size data and cumulative experience of experts at HHT centers. While filters are the preferred method to avoid air embolism at many hereditary hemorrhagic telangiectasia (HHT) centers, the inability to use a filter should not preclude important or urgent medical care. In this case careful attention to preparation of the intravenous fluid and monitoring of the infusion to avoid air bubbles is warranted. (See "Air embolism".)
Scuba diving and air travel — Patients with PAVMs should avoid scuba diving due to the theoretically increased risk of venous air embolism. (See "Air embolism".)
Despite the occurrence of hypoxemia in association with PAVMs, symptomatic in-flight hypoxemia is uncommon [60]. For patients with known hypoxemia due to PAVMs, clinicians should use the usual travel recommendations given to those with hypoxic lung disease. (See "Assessment of adult patients for air travel" and "Evaluation of patients for supplemental oxygen during air travel".)
Antibiotic prophylaxis — Patients with CT-identified PAVMs should be given antibiotic prophylaxis prior to dental and other potentially non-sterile procedures to avoid bacteremia and the subsequent development of cerebral abscess [30]. Such treatment may be lifelong, even after PAVM embolization, because many patients continue to have a positive contrast echocardiography following embolization therapy and are felt to be at continued risk for cerebral abscess [61]. For those with negative or low-grade (grade 1) contrast echocardiography after embolization, antibiotic prophylaxis is not necessary [10].
Whether or not antibiotic prophylaxis should be given to those with presumed microscopic PAVM (ie, a positive contrast echocardiogram but negative CT chest) has not been fully defined. Our practice is to give antibiotic prophylaxis to all patients with grade 2 or 3 shunt on contrast echocardiography using the American Heart Association guidelines for bacterial endocarditis. (See "Prevention of endocarditis: Antibiotic prophylaxis and other measures".)
Pharmacological therapy — Several investigational agents have been proposed as pharmacological therapies for the treatment of nasal, gastrointestinal, and liver lesions in patients with hereditary hemorrhagic telangiectasia (HHT). These include estrogens, antifibrinolytic agents, and antiangiogenesis agents. However, whether or not these agents have any potential for treating HHT patients with PAVMs is unknown. Pharmacological therapy for HHT is discussed separately. (See "Hereditary hemorrhagic telangiectasia (HHT): Evaluation and therapy for specific vascular lesions", section on 'Gastrointestinal lesions'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Hemoptysis" and "Society guideline links: Hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome)".)
SUMMARY AND RECOMMENDATIONS
●Definition – Pulmonary arteriovenous malformations (PAVMs) are abnormal communications between pulmonary arteries and veins. PAVMS are associated with significant morbidity and mortality (eg, stroke, cerebral abscess, massive hemoptysis). However, not all patients with PAVMs require definitive therapy. (See 'Introduction' above.)
●Natural history – True estimates of morbidity and mortality as well as natural history data are unknown because these data are mostly reported in retrospective case series. Morbidity and mortality associated with PAVMs are mostly associated with the development of serious complications including stroke and brain abscess, as well as life-threatening hemoptysis or hemothorax. Most PAVMs remain stable in size. However, approximately 25 percent will enlarge slowly, usually at a rate of 0.3 to 2 mm/year. Macroscopic PAVMs (ie, those seen on CT scan) do not spontaneously resolve. (See 'Natural history' above and "Pulmonary arteriovenous malformations: Clinical features and diagnostic evaluation in adults", section on 'Features attributable to PAVM complications'.)
●Patients suitable for embolotherapy – Not all PAVMs require intervention. When indicated, most patients are treated with embolotherapy, angiographic occlusion of the feeding arteries to a PAVM under fluoroscopic guidance. Selecting who to treat is dependent upon factors including the feeding artery diameter (FAD), PAVM-related symptoms, and the patient’s ability to tolerate the procedure (algorithm 1). (See 'Patients suitable for embolotherapy' above.)
•Feeding artery ≥2 to 3 mm – For patients who have one or more PAVM with a FAD ≥2 to 3 mm, we suggest treating the PAVM with embolotherapy rather than observation (Grade 2C). A similar approach is suggested in patients with atypical lesions or PAVMs with FAD <2 mm that are accompanied by symptomatic hypoxemia, paradoxical embolism, or hemoptysis. Embolotherapy results in an immediate improvement in the radiographic appearance of PAVMs, symptoms, and in oxygenation. Over the long-term, it also reduces the rate of serious complications especially neurologic events including stroke and cerebral abscess. (See 'Feeding artery ≥2 to 3 mm' above and 'Symptomatic lesions' above and 'Embolotherapy' above.)
●Patients not suitable for embolotherapy – This includes the following:
•Asymptomatic patients with feeding artery <2 mm – For patients with asymptomatic PAVMs in whom the feeding artery is <2 mm, we suggest that they be followed with yearly clinical observation, and a non-contrast CT every five years. PAVMs that progressively enlarge or become symptomatic during follow-up should undergo evaluation for embolotherapy with pulmonary angiography. (See 'Patients not suitable for embolotherapy' above.)
•Poorly accessible lesions – For patients who present with PAVMs that require treatment but are not amenable to catheter-directed embolotherapy (eg, hyperacute branching of the pulmonary artery), we suggest that an interventional radiologist with experience in embolotherapy in a center with expertise in PAVMs be consulted before resorting to surgery. (See 'Poorly accessible lesions' above.)
●Patients who fail embolotherapy – For patients who fail embolization or in whom new PAVMs develop following embolotherapy, we suggest repeated embolization. Surgery is an option for patients who fail repeated embolization as well as for patients whose lesions are suitable for intervention but are deemed not amenable for embolotherapy by an experienced radiologist, as well as for those who present with life-threatening acute hemorrhage from ruptured PAVM in a facility without access to embolotherapy. (See 'Patients who fail embolotherapy' above and 'Embolotherapy' above and 'Alternative therapies' above.)
●Adjunctive therapy – Patients with PAVMs should receive antibiotic prophylaxis prior to dental and other potentially nonsterile procedures. In addition, when receiving intravenous fluids or medications, meticulous care should be taken to avoid the introduction of air bubbles (eg, use of intravenous in-line filters). (See 'Adjunctive therapies' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges James R Gossage, MD, who contributed to earlier versions of this topic review.
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