Pulmonary A-V malformation

Created 31/10/2021, last revision 07/11/2023

pulmonary arteriovenous malformation (PAVM) comprises abnormal connections between pulmonary arteries and veins
- synonyms: pulmonary AVM, pulmonary arteriovenous fistula, pulmonary arteriovenous aneurysm
PAVMs are rare in the general population
- it is estimated that 70-80% of PVAMs are related to HHT (hereditary hemorrhagic telangiectasia – Osler-Weber-Rendu), mainly HHT1 (10-fold more than HHT2) → more about HHT see here
- ≥ 15% of patients do not fulfill the criteria for a diagnosis of HHT and have no other systemic disease
neurological complications occur in ~ 50% of patients
- paradoxical embolism ⇒ TIA/stroke, ICH, or a cerebral abscess
- concurrent cerebral AVM (CAVM) ⇒ ICH or epilepsy

Pathophysiology

direct arterio-venous shunts without embedded capillaries
PAVM, together with PFO, patent ductus arteriosus, and other congenital heart defects, belongs to conditions at risk of paradoxical embolism
- contrary to PFO, where the shunt is frequently seen only post-Valsalva maneuver, the shunt in PAVM is continuous
- concurrent occurrence of PAVM and PFO is possible
additional pathogenetic mechanisms besides paradoxical embolism include:
- polycythemia with hyperviscosity syndrome
- hypoxia
- air embolism originating from a defect in the PAVM wall
PAVMs may be located in any lung segment (with a predilection for the lower lobes)

the clinical presentation depends on the infarct location; it is indistinguishable from other forms of embolism
caused by any right to left shunt (RLS)
- patent foramen ovale (PFO)
- pulmonary arteriovenous malformation
- patent ductus arteriosus
- iatrogenic communications
- atrial/ventricular septal defects
embolus type:
- thrombus
- fat
- air
- amniotic fluid
- tumor tissue

according to the feeding artery
- simple (2/3) – single feeding artery with a single draining pulmonary vein
- complex (1/3) – multiple feeding arteries or draining veins
- diffuse type (~5%) – dozens to hundreds of malformations
by other symptoms
- isolated PAVM
- PAVM in HHT (together with telangiectasias)

generally slow progression with potential acceleration during pregnancy and adolescence
the clinical course differs in isolated PAVM and PAVM associated with HHT
symptoms most commonly occur between the 3rd and 6th decades of life
asymptomatic course observed in up to 50% of patients (mostly in PAVM < 2cm)
mortality and morbidity are mostly associated with stroke and brain abscess, less commonly with hypoxemic respiratory failure, hemoptysis, or hemothorax

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1. epistaxis, recurrent

2. telangiectasia
(multiple)

3. visceral lesions

4.positive family history

definitive diagnosis: ≥3
probable diagnosis: 2 criteria
diagnosis unlikely: < 2 criteria

good screening method to detect right-sided shunt (usually a massive shunt is present)

recommended as the screening test of choice for PAVMs in HHT – sensitivity 94-100%, specificity 80%
after administration of agitated saline solution, it usually takes 3-8 cardiac cycles to visualize microbubbles in the atrium
- in septal shunts, contrast is visible almost immediately
grading (significant association between TTCE grade and presence of PAVMs on CT was found) [Zukotynski, 2007]
- grade 1 – minimal opacification of the left ventricle
- grade 2 – moderate opacification
- grade 3 – extensive opacification without outlining the endocardium
- grade 4 – extensive opacification with the endocardial definition

non-contrast +/- contrast-enhanced
CE-MRA is suitable for screening; it enables accurate detection and staging of pulmonary AVMs, appropriate differentiation of lesions requiring embolization
- there are limitations in detecting PAVMs <5 mm
CT
- high sensitivity (comparable to DSA)
- thin-slice (2-3 mm) non-contrast CT with 3-D reconstruction is recommended
- the benefit of performing a contrast-enhanced CT pulmonary angiogram must be weighed against the risk of introducing air with paradoxical embolism

the gold standard for diagnosis
- however, CTA seems to have a higher sensitivity (83%) compared to DSA (68%) but with slightly lower specificity
diagnostic DSA remains a critical component in the treatment of PAVMs (embolization)

an initial imaging modality for patients presenting with hypoxemia or hemoptysis
low sensitivity (70%) makes it not ideal for screening
non-specific soft tissue mass with uniform density can be detected in larger PAVMs

therapy targets:
- prevent neurological complications
- prevent pulmonary hemorrhage
- improve hypoxemia
indications for invasive management:
- progressive PAVM growth
- paradoxical embolization
- symptomatic hypoxemia
- feeding vessels ≥3 mm
no specific medical treatment

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lobectomy or pneumonectomy are rarely performed
thoracoscopic procedures are preferred, especially in short-feeding arteries with an increased risk of coil migration

no clear evidence, and therefore, no recommendations are available
high risk of complications with PAVM in HHT ⇒ prefer direct mechanical thrombectomy
in isolated PAVM, the risk is significantly lower ⇒ intravenous thrombolysis may be considered [Lin, 2019]

lifetime antibiotic prophylaxis is recommended for surgical and dental procedures
extreme caution is needed during intravenous administrations to prevent air embolism
in patients with known untreated PAVM, follow-up CT scan every 2-3 years + annual oximetry are advised
exclude cerebral AVM (CAVM) in patients with PAVM; hepatic AVM is not routinely evaluated
annual follow-ups are performed after endovascular treatment
screening in offspring of parents with HHT:
- pulse oximetry every 1-2 years
- O₂ saturation < 97% ⇒ perform TTE
- in the presence of TTE abnormalities, chest CT is indicated

in HHT patients, antithrombotic therapy is not absolutely contraindicated; however, careful monitoring is required [Gaetani, 2020] [Garg, 2014]
- higher risk is associated with anticoagulant therapy
after a stroke or myocardial infarction, the benefit of antiplatelet therapy is likely to outweigh the risk of bleeding