Makindo Medical Notes

Related Subjects: |Pulmonary Stenosis |Pulmonary Regurgitation |Pulmonary Hypertension |Pulmonary Embolism

Introduction

Pulmonary arteriovenous malformations (PAVMs) are abnormal connections between pulmonary arteries and veins, bypassing the capillary bed and leading to a right-to-left shunt within the pulmonary circulation. This shunting allows deoxygenated blood to enter the systemic circulation without gas exchange, resulting in hypoxemia and various clinical manifestations. PAVMs are significant because they can cause serious complications, including paradoxical embolization leading to stroke or brain abscess, hypoxemia, and hemoptysis.

Epidemiology

• PAVMs are rare, with an estimated prevalence of 2-3 per 100,000 population.
• Approximately 50-70% of patients with PAVMs have hereditary hemorrhagic telangiectasia (HHT), also known as Osler-Weber-Rendu syndrome.
• PAVMs are slightly more common in women than men.

Etiology and Pathophysiology

PAVMs result from an abnormal development of the pulmonary vasculature, leading to direct communications between pulmonary arteries and veins. The etiologies include:

• Hereditary Hemorrhagic Telangiectasia (HHT):
  • An autosomal dominant genetic disorder characterized by telangiectasias and AVMs in various organs.
  • Mutations in genes involved in angiogenesis, such as ENG (endoglin) and ACVRL1 (ALK-1), are implicated.
  • PAVMs occur in up to 50-70% of patients with HHT.
• Idiopathic: In patients without HHT, the cause is often unknown.
• Acquired Causes:
  • Hepatic cirrhosis: Due to increased pulmonary blood flow and angiogenic factors.
  • Trauma or surgery: Rarely, may lead to the development of PAVMs.
  • Chronic infections: Such as schistosomiasis, although this is uncommon.

Clinical Features can vary widely, from asymptomatic to severe symptoms

• Dyspnea and Hypoxemia: Due to right-to-left shunt and decreased arterial oxygenation.
• Cyanosis: May be present in cases with significant shunting.
• Clubbing: Digital clubbing can develop over time due to chronic hypoxemia.
• Epistaxis: Common in patients with HHT due to mucocutaneous telangiectasias.
• Neurological Complications:
  • Stroke: Paradoxical emboli can bypass the pulmonary filter, leading to cerebral infarction.
  • Brain Abscess: Bacteria can bypass filtration, causing cerebral infections.
  • Risk of neurological events is approximately 1-2% per year in untreated PAVMs.
• Hemoptysis and Hemothorax: Rupture of PAVMs can cause bleeding into airways or pleural space.
• Heart Failure: Large or multiple PAVMs can lead to increased cardiac output and heart failure.
• Murmur or Bruit: Occasionally, a pulmonary bruit may be heard over the malformation.

Diagnosis

• Chest Radiography (CXR):
  • May show a well-defined round or oval lesion, often in the lower lobes.
  • CXR can be normal, especially in small PAVMs.
• Contrast Echocardiography (Bubble Study):
  • Injection of agitated saline into a peripheral vein; appearance of bubbles in the left atrium after several cardiac cycles suggests intrapulmonary shunt.
  • Helps differentiate intracardiac from intrapulmonary shunts.
• Transesophageal Echocardiography (TEE): May be used to rule out intracardiac shunts.
• Computed Tomography Pulmonary Angiography (CTPA):
  • The gold standard for diagnosis.
  • Provides detailed images of PAVMs, their size, number, and feeding vessels.
• Magnetic Resonance Imaging (MRI): Less commonly used but can provide additional information.
• Pulmonary Angiography:
  • Invasive but can be both diagnostic and therapeutic.
  • Allows for embolization of PAVMs during the procedure.
• Oxygen Saturation and Arterial Blood Gases: May show hypoxemia and increased alveolar-arterial gradient.
• Genetic Testing: For HHT if clinical suspicion is high.

Differential Diagnosis

• Intracardiac shunts (e.g., atrial septal defect, patent foramen ovale)
• Pulmonary embolism
• Bronchiectasis
• Lung neoplasms
• Pulmonary sequestration
• Other causes of hypoxemia and cyanosis

Management

• The primary goal is to prevent complications such as stroke, brain abscess, and hemorrhage. Management strategies include:
• Transcatheter Embolization:
  • The treatment of choice for accessible PAVMs.
  • Embolization materials include coils or plugs to occlude feeding arteries.
  • Minimally invasive with high success rates and low complication rates.
• Surgical Resection:
  • Reserved for cases not amenable to embolization or with complications.
  • Lobectomy or segmentectomy may be performed.
• Management of HHT:
  • Regular screening for AVMs in other organs (e.g., brain, liver).
  • Genetic counseling and family screening.
  • Management of epistaxis and other bleeding manifestations.
• Preventive Measures:
  • Antibiotic prophylaxis before dental or surgical procedures to prevent brain abscess (although this is controversial and not universally recommended).
  • Avoidance of air bubbles in intravenous lines; use of air filters during infusions.
• Follow-Up:
  • Regular monitoring with imaging to detect new or recurrent PAVMs.
  • Repeat embolization may be necessary if PAVMs recanalize or new ones develop.

Prognosis

With appropriate treatment, the prognosis for patients with PAVMs is generally good. Embolization effectively reduces the risk of neurological complications and improves oxygenation. However, patients require lifelong monitoring due to the potential for new PAVMs to develop, especially in the context of HHT.

References

• Guttmacher AE, Marchuk DA, White RI Jr. Hereditary hemorrhagic telangiectasia. N Engl J Med. 1995;333(14):918-924.
• Shovlin CL, Condliffe R, Donaldson JW, et al. British Thoracic Society Clinical Statement on Pulmonary Arteriovenous Malformations. Thorax. 2017;72(12):1154-1163.
• Faughnan ME, Palda VA, Garcia-Tsao G, et al. International guidelines for the diagnosis and management of hereditary hemorrhagic telangiectasia. J Med Genet. 2011;48(2):73-87.
• Meier NM, Foster RM, Ahmed A. Diagnosis and Management of Pulmonary Arteriovenous Malformations. Curr Treat Options Cardiovasc Med. 2018;20(9):74.