Imaging Pearls ❯ Chest ❯ Vascular Malformations and AVMs
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- PAVM Lung
Pulmonary Arteriovenous Malformation (PAVM)also referred to as a pulmonary arteriovenous fistula (PAVF)is an abnormal direct communication between a pulmonary artery and a pulmonary vein, bypassing the normal intervening capillary bed.
This creates a high-flow, low-resistance right-to-left shunt, which has significant implications for systemic oxygenation and embolic risks. - PAVM and Syndromes
Hereditary Hemorrhagic Telangiectasia (HHT / Osler-Weber-Rendu Disease): * This is the single most important clinical association. Approximately 80%90% of PAVMs occur in patients with HHT. Conversely, about 30%50% of patients with HHT will develop a PAVM.
PAVMs in patients with HHT are much more likely to be multiple and bilateral compared to sporadic cases, which are typically solitary. - PAVM and Complications
The Triad of Complications: Because the capillary filter is bypassed, patients are at high risk for:
Paradoxical Embolism: Thrombi or bacteria cross directly into the systemic circulation, leading to stroke or brain abscesses.
Hypoxemia: Cyanosis, clubbing, and dyspnea due to the right-to-left shunt of deoxygenated blood.
Hemorrhage: Massive hemoptysis or hemothorax if the thin-walled malformation ruptures. - The Triad Component Appearance
A Feeding Artery: A dilated, tortuous pulmonary artery branches off the main arterial tree and heads directly toward the lesion.
An Aneurysmal Nidus / Sac: A well-circumscribed, intensely enhancing vascular nodule or sac where the vessels meet.
A Draining Vein: A dilated, early-enhancing pulmonary vein exiting the sac and traveling back toward the left atrium.
- A pulmonary arteriovenous malformation (PAVM) is a fistulous connection between a pulmonary artery and a pulmonary vein that bypasses the normal pulmonary capillary bed resulting in a right-to-left shunt. Because of the potential for paradoxical emboli, PAVMs are treated when their feeding arteries exceed 3 mm or patients are symptomatic. PAVMs are often encountered in patients with suspected hereditary hemorrhagic telangiectasia (HHT). Sporadic cases are uncommon. The radiologist may be called on to diagnose a PAVM after positive transthoracic contrast-enhanced echocardiography in a patient with suspected HHT to direct patient management and avoid potential complications. The radiologist may also be required to evaluate a potential PAVM detected at CT performed for other reasons.
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - Understanding the CT appearance of PAVMs limits misdiagnosis, directs appropriate treatment, and allows subsequent family screening for HHT (and avoidance of unnecessary screening when a PAVM mimic is encountered). Both vascular and nonvascular pulmonary lesions can mimic PAVMs. Vascular mimics include fibrosing mediastinitis, venovenous collaterals, arterial collaterals, pulmonary artery pseudoaneurysms, hepatopulmonary vessels, Sheehan vessels, meandering pulmonary veins, and pulmonary vein varices. Nonvascular mimics include granulomas, nodules, mucoceles, bronchoceles, ground-glass opacities, and atelectasis. The authors review the CT technique for evaluating PAVMs and the appearance of PAVMs and their mimics
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - Pulmonary arteriovenous malformations (PAVMs) are fistulous connections between a pulmonary artery and a pulmonary vein that bypass the normal pulmonary capillary bed resulting in a right-toleft shunt. PAVMs are predominantly congenital and result from abnormal development of pulmonary arteries and veins from a common plexus. Hereditary hemorrhagic telangiectasia (HHT) is the most common association, accounting for approximately 80%90% of all cases of PAVMs . Moreover, PAVMs occur in 20%50% of patients with HHT. Patients with HHT often have multiple PAVMs. Sporadic congenital PAVMs are uncommon. Although rare, acquired causes of PAVM include prior surgery, trauma, infection, hepatopulmonary syndrome, congenital heart disease (single-ventricle cardiac repair), and metastatic disease .
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - Granulomas are the most commonly encountered pulmonary nodules and are often associated with small pulmonary arteries. While granulomas may have a feeding artery, no draining vein should be present. It is essential to understand that all PAVMs will have a feeding artery and draining vein. Moreover, the noncontrast portion of the chest CT examination can be used to distinguish calcification within a hyperattenuating center of a nodule from an enhancing nidus seen in a PAVM. In our experience, PAVMs do not tend to calcify. The presence of multiple tiny adjacent satellite nodules is also strongly suggestive of a granulomatous process..
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - Careful attention to the vascular anatomy of a lesion will improve diagnostic accuracy. Identifying the vascular connections will allow distinguishing of PAVMs from their mimics. All PAVMs should have a feeding artery and draining vein with an intervening vascular nidus. The draining vein is typically the larger of the two vessels. Occasionally, telangiectatic PAVMs are predominantly ground-glass opacities. However, these lesions usually exist in concert with other more classic PAVMs. Moreover, identifying ancillary findings suggestive of an alternative diagnosis, such as air trapping in the setting of bronchial atresia or calcification, can confirm an alternative diagnosis and prevent a false-positive MDCT PAVM diagnosis.
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - Fibrosing mediastinitis is an inflammatory condition characterized by mediastinal fibrosis. Fibrosing mediastinitis is strongly associated with prior Histoplasma exposure in endemic regions. Mediastinal fibrosis may result in vascular obstruction with a preference for venous structures, a characteristic behavior different from that of lung cancer. Chronic vascular obstruction may lead to collateralization and formation of pulmonary venovenous collaterals (left-to-left shunts) mimicking the appearance of PAVMs. These lesions do not require embolization, although occasionally endovascular stent placement may be performed to relieve venous stenoses. The diagnosis of venovenous collaterals rests on the absence of a feeding artery and obstruction of one of the central pulmonary veins.
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - There are three phases of response to pulmonary embolism: vascular occlusion, pulmonary infarction, and collateral circulation development (9). Collateral circulation from enlarged bronchial arteries often occurs following pulmonary embolism. Collateralization from adjacent pulmonary arteries or from systemic pleural or diaphragmatic vessels may also occur in areas of chronically thrombosed vasculature or infarction. These nonbronchial collaterals can also occur in areas of prior trauma or surgery and result in hemoptysis. This rare form of systemic-to-pulmonary or pulmonary-topulmonary circulation may manifest as a dilated tortuous pulmonary artery mimicking a PAVM . Additionally, these arterial collaterals may extend to the pleural surface. Differing from PAVMs, there will be no associated nidus or draining vein.
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - Pulmonary vein varices are localized aneurysms of a pulmonary vein that are either congenital or acquired and can be mistaken for a PAVM. Congenital varices occur when a collateral intrapulmonary vein bypasses an atretic segment of normal pulmonary vein. Congenital varices are typically of no clinical significance. Acquired pulmonary vein varices arise most frequently in the setting of mitral disease causing pulmonary venous hypertension. Rarely pulmonary vein varices can be acquired as a result of an inflammatory or infectious process. Acquired varices typically occur within the right lung and have been shown to rupture or develop thrombosis. The lack of an arterial connection is a key distinguishing feature from PAVMs. The presence of concurrent mitral disease or adjacent parenchymal scarring can further support the diagnosis of an acquired pulmonary vein varix.
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668 - PAVMs are frequently encountered in patients with suspected HHT and are rarely incidentally detected at routine MDCT. Avoiding a falsepositive diagnosis of a PAVM prevents unnecessary angiographic workup. A multitude of vascular and nonvascular pulmonary lesions can mimic the appearance of PAVMs. Accurate diagnosis of these lesions is essential as many of these lesions require no treatment or different treatment from that of PAVMs. We use a dedicated PAVM protocol with an imaging evaluation approach focused on identifying the key vasculature features of a PAVM, most importantly identifying a feeding artery and draining vein. Recognizing and understanding key imaging features of PAVM mimics prevents misdiagnosis and unnecessary more invasive workup.
CT Appearance of Pulmonary Arteriovenous Malformations and Mimics
Demetrios A. Raptis, Ryan Short, Caroline Robb, et al.
RadioGraphics 2022; 42:5668
- Interruption of the inferior vena cava: facts
- Interruption of the inferior vena cava (IVC) with azygos continuation is a rare congenital anomaly, in which the IVC is interrupted below the hepatic vein and venous return beyond this point is restored by the dilated azygos and hemiazygos veins draining into the superior vena cava.
- this congenital anomaly could be isolated, but often it is part of more complex syndrome including for example cardiac malformations, asplenia, and polysplenia syndrome. Interruption of the IVC with azygos continuation is the second most common abnormality associated with polysplenia syndrome - “The polysplenic syndrome is defined by the presence of multiple spleens, usually numbering between two and six. In contrast to accessory spleens, the spleens are of uniform size. Accessory spleens usually measure between 1 and 2 cm and are not considered as a form of the polysplenic syndrome. Splenosis, an acquired rather than congenital condition that arises in the context of traumatic splenic rupture, can be ruled out by patient history.”
Polysplenia syndrome
B. De La Villeon et al.
Journal of Visceral Surgery,Volume 148, Issue 5,2011, Pages e395-e396, - "Splenosis typically consists of multiple small implants of splenic tissue; it can mimic peritoneal carcinomatosis or endometriosis depending on the clinical context.”
Polysplenia syndrome
B. De La Villeon et al.
Journal of Visceral Surgery,Volume 148, Issue 5,2011, Pages e395-e396, - "The syndrome of polysplenia is often accompanied by a variable spectrum of visceral and vascular developmental anomalies. It is rarely diagnosed in adults. While it is estimated that 2.5/100,000 infants are born with this anomally, fewer than 5% are still alive at five years of age due to the associated severe cardiac anomalies.The syndrome is associated with multiple congenital malformations that may involve the solid organs and digestive tube of the abdominal cavity, the heart, or the great vessels. The diagnosis is often made during surgical exploration for an associated cardiac or digestive anomaly. Among the most common vascular anomalies are agenesis of the suprarenal inferior vena cava with persistent continuity of the azygos vein, and pre-duodenal position of the portal vein. Biliary atresia is found in nearly 50% of cases, common mesentery in more than 75% of cases, and an abbreviated or annular pancreas in 85–90% of cases.”
Polysplenia syndrome
B. De La Villeon et al.
Journal of Visceral Surgery,Volume 148, Issue 5,2011, Pages e395-e396 - “Anomalies include asplenia, the congenital absence of the spleen. This can be isolated or part of a clinical sequela of a broader syndrome such as Ivermark syndrome, a heterotaxy syndrome occurring in 1 in 10,000 to 40,000 cases. CT will show lack of spleen and Tc-99 red blood cell scan will show lack of uptake.”
MDCT Findings of Splenic Pathology
Sangster GP et al.
Current Problems in Diagnostic Radiology 2021 (in press)
- “Hereditary hemorrhagic telangiectasia(HHT),also known as Osler- Weber-Rendu disease, is an auto- somal dominant genetic disorder affecting 1 in 8000 people. HHT is known to be caused by at least three mutations: ENG (type I HHT) encoding endoglin; ACVRL1 (type II HHT) encoding activin receptorlike kinase 1 (ALK-1); and SMAD4, associated with juvenile polyposis. Clinically, HHT is diagnosed according to the Curaçao criteria, which include multiple mucocutaneous telangiectases, epistaxis, visceral arteriovenous malformations (AVMs), and a family history of HHT in a first-degree relative .”
CT Angiography Findings of Pulmonary Arteriovenous Malformations in Children and Young Adults With Hereditary Hemorrhagic Telangiectasia
Shin SM et al.
AJR 2020; 214:1369–1376 - "Pulmonary AVMs (PAVMs) are seen in as many as 49% of patients with HHT. Although serious complications are rare, PAVMs can lead to life-threatening events including massive hemorrhage from PAVM rupture and complications of right-to-left cardiac shunt, including pulmonary hypertension, paradoxic embolism with stroke, and cerebral abscess. PAVMs tend to be progressive with age. To prevent progression in size and the serious complications associated with PAVMs, early detection and intervention are critical.”
CT Angiography Findings of Pulmonary Arteriovenous Malformations in Children and Young Adults With Hereditary Hemorrhagic Telangiectasia
Shin SM et al.
AJR 2020; 214:1369–1376 - "The imaging findings of PAVM have been well described in adult chest CT studies and include presence of a feeding artery, a draining vein or veins, and an aneurysmal sac or nidus. A feeding artery larger than 3 mm is currently accepted as an indication for prophylactic embolization in an effort to reduce the risk of cerebral complications, although smaller lesions can be embolized if symptomatic.”
CT Angiography Findings of Pulmonary Arteriovenous Malformations in Children and Young Adults With Hereditary Hemorrhagic Telangiectasia
Shin SM et al.
AJR 2020; 214:1369–1376 - "The most common PAVMs in children and young adults with HHT were less ma- ture than those seen in adult populations. Use of MIP enabled more precise detec- tion of the afferent and efferent vessels. The highest grade in each patient had the strongest correlation with the severity of pulmonary right-to-left shunt. Unlike the situation in older adults, age was not an important factor in determining the severity of PAVMs in children and young adults. Even in patients without symptoms, PAVMs are noted in most patients with abnormal CE- TTE findings."
CT Angiography Findings of Pulmonary Arteriovenous Malformations in Children and Young Adults With Hereditary Hemorrhagic Telangiectasia
Shin SM et al.
AJR 2020; 214:1369–1376 - "Routine screening of all patients with HHT for PAVM is recom- mended, and contrast-enhanced transthoracic echocardiography (CE-TTE) and chest CT have been the primary imaging tools.”
CT Angiography Findings of Pulmonary Arteriovenous Malformations in Children and Young Adults With Hereditary Hemorrhagic Telangiectasia
Shin SM et al.
AJR 2020; 214:1369–1376
- Vascular Malformations and Hemangiomatosis Syndromes
- Blue rubber bleb nevus syndrome
- Proteus syndrome
- Klippel-Trenauney Sydrome
- Kasabach-Merritt syndrome - Proteus Syndrome: facts
- Hemihypertrophy, partial gigantism
- Vascular tumors and AVMs
- Lipomas and fatty tumor proliferation
- splenomegaly - Klippel-Trenaunay Syndrome: Facts
- Three key findings
– Port wine stain
– Abnormal vascular structures
– Osseous and soft tissue hypertrophy - Kasabach-Merritt Syndrome: facts
- Consumptive thrombocytopenia and coagulopathy
- Can lead to DIC
- May have large hepatic or splenic hemangioma
- Association with angiosarcoma and AVMs - Pulmonary Arteriovenous Malformations: Facts
- Congenital in origin
- 60-90% of patients have hereditary hemorrhagic telangiectasia (aka Rendu- Osler-Weber syndrome)