Pulmonary Vascular Malformations
Jeffrey S. Pollak
Pulmonary vascular malformations may involve abnormalities of the arteries, veins, communications between these two, lymphatics, and associated lung abnormalities. This chapter will concentrate on pulmonary arteriovenous malformation as well as acquired fistula and aneurysm, which are often amenable to interventional radiologic management. Conditions having abnormal systemic arterial supply into abnormal or normal lung tissue such as bronchopleural sequestration and scimitar syndrome artery are typically managed surgically or expectantly, although embolization of arterial supply may occasionally be appropriate (1). Conditions with abnormal venous drainage are usually also managed conservatively.
Indications
1. Pulmonary arteriovenous malformations (PAVMs): consist of a congenital connection between a pulmonary artery and vein, without a normal capillary bed. These are the most common type of pulmonary arteriovenous connections. They are associated with hereditary hemorrhagic telangiectasia (HHT) (Osler-Weber-Rendu syndrome) in 56% to 97% of patients (2,3) and are more commonly multiple in that setting.
2. Acquired pulmonary arteriovenous fistula: are less commonly, clinically significant and can occur in a variety of conditions (4):
a. Cirrhosis (hepatopulmonary syndrome): These are rarely large enough to warrant embolization.
b. Glenn or Fontan shunts for congenital heart disease
c. Infections: schistosomiasis and actinomycosis
d. Metastatic thyroid carcinoma and gestational trophoblastic disease
e. Amyloidosis
f. Fanconi syndrome
g. Erosion of an aneurysm into a vein
h. Trauma
3. Pulmonary artery aneurysms: True and false aneurysms of the pulmonary arteries have numerous etiologies (5):
a. Poststenotic and hyperdynamic states (such as with left-to-right shunts), usually in the setting of congenital heart disease
b. Degenerative vascular disorders, including connective tissue diseases such as Marfan and Ehlers-Danlos
c. Inflammatory conditions
(1) Necrotizing infections with vascular erosion (e.g., Rasmussen aneurysm of tuberculosis, fungal, pyogenic)
(2) Mycotic aneurysms from septic emboli from right-sided endocarditis
(3) Syphilis
(4) Primary vasculitis (e.g., Behçet syndrome, Takayasu arteritis)
d. Neoplasms, usually with erosion into a pulmonary artery
e. Pulmonary artery hypertension
f. Trauma, especially iatrogenic trauma, as from pulmonary artery catheters
g. Hughes-Stovin syndrome. A rare idiopathic condition in which patients have pulmonary artery aneurysms and venous thromboses. Its relationship to Behçet syndrome is uncertain.
Contraindications
There are no absolute contraindications to pulmonary artery embolization; however, occlusion of a malformation or fistula in someone with severe pulmonary hypertension should be done cautiously given the risk of further elevation of pulmonary artery pressure and cor pulmonale.
Pulmonary Arteriovenous Malformations
1. This disorder results in scattered arteriovenous malformations (AVMs), manifested primarily as mucocutaneous telangiectases and less frequently as larger visceral AVMs. Its prevalence is estimated at 1 in 5,000 to 10,000.
2. Several different genes have been found to cause HHT, with the three identified ones coding for proteins involved with transforming growth factor-β signal transduction. The two most common are HHT1, which results from a defect in endoglin, and HHT2, resulting in a defect in activin receptor-like kinase 1. The third is a combined syndrome of HHT with juvenile polyposis.
3. A definite clinical diagnosis of the heterozygous, autosomal dominant disorder depends on the presence of at least three of the following four features. The diagnosis is possible if only two are present:
a. Multiple telangiectases of the skin and mucous membranes
b. Repeated episodes of spontaneous epistaxis, occurring in over 90% of patients
c. An autosomal dominant pattern of inheritance
d. Typical visceral malformations
(1) PAVM in approximately 20% to 70%, more common in HHT1 than HHT2
(2) Central nervous system in approximately 10%, more common in HHT1 than HHT2. Still, the most common neurologic events in patients with HHT are due to paradoxical embolization through PAVMs.
(3) Gastrointestinal tract telangiectases and less commonly larger AVMs occur in 55% to 70% and can produce bleeding in approximately 25%.
(4) Liver AVM occurs in 41% to 74% but are symptomatic in less than 10%, and these patients generally have HHT2.
4. Genetic testing can identify approximately 85% of patients with HHT.
Pathology of PAVM (4)
1. Types
a. Simple PAVMs are fed by an artery contained within one pulmonary segment and account for 80% to 90% of PAVMs. The artery may have more than one distal branch supplying the malformation.
b. Complex PAVMs are fed by arteries from more than one pulmonary segment and account for 10% to 20%.
c. Diffuse involvement of one or more segments or lobes, typically basilar, accounts for 5%.
d. The nidus connecting the artery(ies) and vein(s) may be a single aneurysmal sac or a plexiform, septated, multichanneled connection, with complex PAVMs more commonly having the latter type of nidus.
e. A systemic artery will rarely be found to supply a PAVM.
2. Location
a. Lower lobes in approximately 65%
b. Upper lobes, right middle lobe, and lingula in 35%
3. Multiplicity
a. Multiple PAVMs in over 50%
b. Bilateral PAVMs in over 40%
1. Right-to-left shunting can result in
a. Arterial hypoxemia. Clinical manifestations include dyspnea, fatigue, cyanosis, clubbing, and rarely polycythemia; however, patients are also often asymptomatic.
b. Paradoxical embolization. This most commonly manifests in the brain but can affect other organs. Thromboembolic embolization can result in stroke and transient ischemic attack (TIA) in 11% to 55% of patients, whereas bacterial embolization has been reported to result in brain abscess in 5% to 25%.
c. High-output heart failure. This is uncommon but has been reported in neonates.
2. Rupture of thin-walled PAVMs can result in hemoptysis and hemothorax in 3% to 18%.
3. Migraine headaches are more common in patients with PAVM.
4. Conditions in which the risk of PAVM complications appears greater are pregnancy and pulmonary hypertension, during which enlargement of PAVM may occur. Preadolescent children appear to be at lower risk for major complications, particularly with smaller lesions.
5. Symptoms can be related to associated disorders, such as other manifestations of HHT.
Embolotherapy for Pulmonary Arteriovenous Malformations
1. Goals
a. Detect PAVM with high sensitivity but also high specificity.
b. Characterize size, number, and location of PAVMs. This will determine whether the PAVM(s) need specific treatment. For any one PAVM, the presence of a feeding artery of 2 to 3 mm or greater is an indication to consider invasive treatment.
2. Who to evaluate?
a. Patients with symptoms or signs suggestive of PAVM by history, physical examination, or incidentally found on imaging
b. Screen all patients with HHT.
