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
PAVM can be localized in any part of the lung; there is a predilection towards the lower lobes

the clinical presentation depends on the area of resulting infarction; usually, it is indistinguishable from other forms of embolism
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

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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

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1. epistaxis, recurrent

2. telangiectasia
(multiple)

3. visceral lesions

4.pozitive 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 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

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

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

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

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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

*Hunt-Hess grading system*
Grade	Description	Probability of severe morbidity/ mortality
0	unruptured aneurysm – incidental finding	–
1	asymptomatic mild headache and/or mild nuchal rigidity	22 %
2	lucidity cranial nerve palsies moderate to severe headache, meningeal syndrome	22 %
3	somnolence, lethargy, or confusion mild focal neurological deficits	50 %
4	stupor moderate to severe hemiparesis early decerebrate rigidity (posturing)	87 %
5	deep coma decerebrate rigidity (posturing) moribund appearance	100 %