ISCHEMIC STROKE / CLASSIFICATION AND PATHOGENESIS
Pulmonary A-V malformation
Created 24.01.2018 , last update 23.10.2021
- pulmonary arteriovenous malformations (PAVMs) comprise 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
- it is estimated that 70-80% of PVAMs are related to 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
- polycythemia with hyperviscous syndrome
- 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
- patent foramen ovale (PFO)
- 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
Neurological complications
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1. epistaxis, recurrent |
2. telangiectasia
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3. visceral lesions
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4.pozitive family history |
definitive diagnosis: ≥3
probable diagnosis: 2 criteria diagnosis unlikely: < 2 criteria |
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
- 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 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
- 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