eMedicine Specialties > Radiology > Chest

Lung, Arteriovenous Malformation: Follow-up

Author: Sat Sharma, MD, FRCP(C), FCCP, FACP, DABSM, Program Director, Associate Professor, Department of Internal Medicine, Divisions of Pulmonary and Critical Care Medicine, University of Manitoba; Site Director of Respiratory Medicine, St Boniface General Hospital
Coauthor(s): Krantikumar Rathod, MD, Lecturer, Section of Vascular and Interventional Radiology, Department of Radiology, KEM Hospital, Parel, Mumbai, India; Bruce Maycher, MD, Director of Pulmonary Radiology, St Boniface General Hospital; Associate Professor, Department of Radiology, University of Manitoba
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Updated: Oct 22, 2007

Intervention

Shunt fraction measurement

The shunt fraction is most accurately assessed by using the 100% oxygen method. This method involves the measurement of PaO₂ and SaO₂ after the patient breathes 100% oxygen for 15-20 minutes. The fraction of cardiac output that is shunted as a result of right-to-left circulation is elevated in patients with PAVM (normal, <5%). In determining the presence of a shunt fraction of more than 5%, the 100% oxygen method has a sensitivity of 87.5% and a specificity of 71.4%.

Right heart catheterization

Most patients with PAVM have normal or low pulmonary arterial pressure. Despite severe oxygen desaturation, the mean pulmonary arterial pressure is low in most patients. The cardiac output is generally normal to moderately elevated. Several patients have developed new pulmonary hypertension or increased baseline pulmonary hypertension after the embolization or resection of a large PAVM.

Therapeutic embolization

The procedure of choice for treating a PAVM is therapeutic embolization rather than lung resection. Lung surgery is performed only when the PAVM is larger than 1 cm or when the risk of systemic embolization is significant.

Embolization therapy, or embolotherapy, is a form of treatment based on occluding the feeding arteries to a PAVM.

The first successful case of embolotherapy for the treatment of PAVM was reported in 1977 and involved the use of handmade steel coils. Since then, embolization with coils and/or detachable balloons has been reported in numerous series of more than 250 patients. Other embolic materials include polyvinyl alcohol, cotton wool coils, and stainless steel coils.

Indications

The indications for embolotherapy include the following:

• Progressive enlargement of the lesions
• Paradoxical embolization
• Symptoms
• Hypoxemia
• The presence of feeding vessels of 3 mm or larger

Technique

Coil embolotherapy involves localization of the PAVM by means of angiography, followed by selective catheterization of the feeding artery. A steel coil is advanced through the catheter and is placed distal to any branch of the vessel. Sometimes, more than 1 coil is required to completely occlude the vessel. Multiple PAVMs may be embolized in a single session.

The second embolotherapy technique uses detachable balloons. After the PAVM is localized, a balloon catheter is exchanged over a guide wire and positioned at the neck of the PAVM.

Results

Results of follow-up CT scanning at 1 or more years after embolotherapy indicate that 96% of PAVMs are undetectable or reduced in size.

One series followed up 45 patients who underwent embolotherapy of large (>8 mm) PAVMs.⁸ Approximately 98% of the PAVMs were occluded on the initial attempt, 84% of patients remained successfully treated, and 16% of patients had persistent PAVMs. The persistence of PAVMs was caused by recanalization of initially successful occlusion in 4 patients and by the interval growth of new feeding vessels in 3 patients. All 8 of the persistent PAVMs were successfully occluded during a second procedure, although 1 PAVM required a third procedure for permanent occlusion.

A summary of 10 published series of therapeutic embolizations for PAVM documented an average success rate of 98.7%. Balloon embolotherapy is generally used in a PAVM that has a feeding vessel larger than 7-10 mm.

Embolotherapy appears to be the treatment of choice because it avoids major surgery, general anesthesia, and the loss of the pulmonary parenchyma. Embolotherapy is a clear choice in patients with multiple or bilateral PAVMs or in patients who are poor candidates for surgery.

Postcatheterization care and precautions

Postcatheterization precautions include hemorrhage, vascular disruption after balloon dilation, chest pain caused by minor lung infarctions, nausea and vomiting, and arterial or venous obstruction caused by thrombosis or vasospasm.

Complications

Possible complications that have been reported are blood vessel rupture, tachyarrhythmias, bradyarrhythmias, and vascular occlusion. Pleuritic chest pain is the most common complication and is observed in 12% of patients. This pain usually responds well to analgesics. Radiographic evidence of pulmonary infarction is observed in 3% of patients.

An air embolism may occur during embolotherapy in 4.8% of patients. In these patients, transient symptoms, such as angina, perioral paresthesias, and bradycardia, may develop. Migration of the embolotherapeutic device distal to the PAVM has been reported in 1.2% of embolization attempts.

Long-term follow-up evaluation has revealed potentially serious complications in 2% of patients treated with embolotherapy. Symptomatic recanalization was observed with 0.5% of procedures.

New or increased pulmonary hypertension after embolization has been reported in several patients. The incidence of complication appears to be higher when feeding vessels larger than 8 mm are occluded.

Medicolegal Pitfalls

• Because a PAVM may occur as a solitary pulmonary nodule on chest radiographs, a percutaneous needle biopsy may lead to catastrophic pulmonary hemorrhage. Therefore, PAVM should be considered in the differential diagnosis of a pulmonary nodule and excluded before a needle biopsy is performed.
• A chest radiograph should be obtained to rule out PAVM in patients presenting with a brain abscess.
• The family members of patients with HHT or PAVM should be screened with the methods described below in Special Concerns.
• Consider intrapulmonary shunts secondary to PAVM in the differential diagnosis of PAVM.

Special Concerns

• Screening of family members with PAVM or HHT
  • Family members of patients with HHT should be routinely screened for possible PAVM. The incidence of PAVM is approximately 15-20% in unselected patients with other clinical features of HHT. Whenever PAVM is diagnosed, screening of the patient's family members is particularly important. The incidence of PAVM is approximately 35% among relatives of persons with HHT and PAVM.
  • The evaluation of family members should be initiated with history taking, a focused physical examination, chest radiography, and a 100% oxygen shunt study.
  • Individuals with an increased shunt fraction on a 100% shunt study may be referred for contrast-enhanced CT scanning or pulmonary angiography. When patients with abnormal radiographic chest findings have a shunt fraction in the reference range, they should be referred for contrast-enhanced echocardiography or radionuclide perfusion scanning. If the subsequent exam results are abnormal, contrast-enhanced CT scanning or pulmonary angiography must be performed to confirm the diagnosis.
  • Routine screening of family members with CT scanning or contrast-enhanced echocardiography is expensive, and pulse oximetry is insensitive as a screening tool.
  • In cases of HHT, routine genetic screening of family members is likely to play an increasingly important role in the future. Once the genetic defect has been identified in a given family with HHT, genetic screening has 100% sensitivity and specificity for clinical HHT in individual family members. Therefore, in families with a known genetic mutation, genetic screening of all family members is recommended.
• Screening of pregnant patients
  • In pregnant women with HHT and PAVM, the risk of complications is significant. In one series, maternal complications occurred in almost 50% of pregnancies in patients with PAVM.
  • In pregnant women with PAVM, worsening of the right-to-left shunt, fatal pulmonary hemorrhage, and stroke may occur. Progression of the vascular malformations in the cerebral, pulmonary, and hepatic circulation during pregnancy also has been documented.
  • Because of the above factors, all women with HHT or a family history of HHT who are considering pregnancy should be screened for PAVMs.

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