• pulmonary arteriovenous malformations (PAVMs) consist of abnormal communications between the pulmonary arteries and veins
    • synonyms:  pulmonary AVM, pulmonary arteriovenous fistula, pulmonary arteriovenous aneurysm
  • occurrence of PAVM in the general population is rare
    • in about 70-80% are associated with HHT (hereditary hemorrhagic telangiectasia – Osler-Weber-Rendu), mainly HHT1 (10x more than HHT2) → more about HHT see here
    • ≥ 15% of patients do not meet the criteria for the diagnosis of HHT and have no other systemic disease
  • neurological complications are seen in ~ 50% of patients
    • paradoxical embolism ⇒ TIA/stroke, ICH, or a cerebral abscess
    • concurrent cerebral AVM (CAVM) can lead to ICH or epilepsy

Pathophysiology

  • direct arterio-venous shunts without embedded capillaries
  • together with PFO, patent ductus arteriosus, and other congenital heart defects, it belongs to diseases at risk of paradoxical embolism
    • unlike PFO, where the shunt is often seen only after the Valsalva maneuver, in PAVM, the shunt is continuous
    • coexistence of PAVM and PFO is possible
  • other pathogenetic mechanisms besides paradoxical embolism:
    • polycythemia with hyperviscous syndrome
    • hypoxia
    • air embolization from a defect in the PAVM wall
  • PAVM can be localized in any part of the lung; there is a predilection towards the lower lobes
  • underlying pathology = any right-to-left shunt (RLS)
    • patent foramen ovale (PFO)
    • pulmonary arteriovenous malformation
    • patent ductus arteriosus
    • iatrogenic communications
    • atrial/ventricular septal defects
  • source of embolism:
    • thrombus
    • fat
    • air
    • amniotic fluid
    • tumor tissue

Classification

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Clinical presentation

  • mostly slow progression, possible acceleration during pregnancy and adolescence
  • the course differs in isolated PAVM and PAVM within HHT
  • symptoms occur most frequently between the 3-6th decade
  • asymptomatic course in up to 50% of patients (mostly in PAVM < 2cm)
  • mortality / morbidity is associated with PAVMs are mostly associated with stroke and brain abscess, less commonly with hypoxemic respiratory failure, hemoptysis or hemothorax.

Systemic and pulmonary symptoms

  • epistaxis (almost 100% in HHT)
  • hemoptysis, dyspnoea, chest pain
  • GIT bleeding
  • skin and mucosal telenagiectasias (in HHT) Rendu-Osler-Weber (Hereditary Hemorrhagic Telangiectasia)
  • myocardial infarction
  • peripheral infarcts (splenic, renal, mesenteric)

Neurological complications

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1. epistaxis, recurrent

2. telangiectasia
(multiple)

  • lips
  • oral cavity
  • fingers
  • nose

3. visceral lesions

  • GIT telenagiectasias
  • PAVM
  • hepatal AVM
  • cerebral AVM (CAVM)
  • spinal AVM

4.pozitive family history

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

Diagnostic evaluation

Pulmonary AVM

TCCD → bubble test see here

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

Contrast transthoracic echocardiography (cTTE)

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

CT+CTA / MRI+MRA   Pulmonary arteriovenous malformation (PAVM) on CT angiography Pulmonary arteriovenous malformation (PAVM) on MR angiography (Schneider, 2008)

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

Digital subtraction angiography Pulmonary arteriovenous malformation (PAVM) on DSA

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

Chest X-ray

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

Management

  • therapy targets:
    • prevention of neurological complications
    • prevention of pulmonary hemorrhages
    • improvement of hypoxemia
  • indications for invasive management:
    • progressive PAVM growth
    • paradoxical embolization
    • symptomatic hypoxemia
    • feeding vessels ≥3 mm
  • no specific medical treatment

Endovascular treatment

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Surgical treatment

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

Thrombolysis in patients with PAVM

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Prevention

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Antithrombotic medication in stroke prevention

  • in HHT, antithrombotic therapy is not absolutely contraindicated; careful monitoring, however, is necessary  [Gaetani, 2020] [Garg , 2014]
    • higher risk is bound to anticoagulant therapy
  • after stroke or myocardial infarction, the benefit of antiplatelet therapy probably outweighs the risk of bleeding
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