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Assessment of Pulmonary Vascular Disease

Bradley S. Messenger and Ronald J. Oudiz

Abstract

Pulmonary hypertension (PH) is deﬁ ned as an abnormal elevation of pulmonary arterial pressure (PAP), with a mean PAP ≥25 mmHg. A classiﬁ cation system organizes this heterogeneous patient population into ﬁ ve groups based on the underlying etiology, pathogenesis, and pathophysiology associated with the PH. A thorough diagnostic workup is necessary to determine the precise etiology, treatment strategy, and prognosis for patients with PH. Cardiac Computed Tomography is a useful tool in PH for detection of disease, workup, and characterization of the underlying etiologies as it describes the cardiac structures and functional abnormalities seen with PH.

Keywords

Pulmonary Arterial Hypertension • Pulmonary Artery • Right Ventricle • Pulmonary Embolism • Right Heart Catheterization • Cardiac Structure

Pulmonary hypertension (PH) is deﬁ ned as an abnormal elevation of the pulmonary arterial pressure with diverse etiologies and pathogenesis. It is hemodynamically deﬁ ned as a mean pulmonary artery pressure ≥25 mm Hg and pulmonary vascular resistance >3 Wood units. The presence of PH typically leads to the right ventricular failure syndrome [ 1 ] of dyspnea, ﬂ uid overload, and untimely death, and is responsible for millions of US hospital admissions annually.

Diseases of the pulmonary circulation span a variety of disease entities including pulmonary arterial hypertension (PAH), pulmonary venous hypertension, chronic thromboembolic pulmomary hypertension (CTEPH), pulmonary arteriovenous malformation, pulmonary arterial stenosis, pulmonary arterial aneurysm, pulmonary venoocclusive disease, and pulmonary

capillary hemangiomatosis. (See section “ Classiﬁ cation of

PH ”, below) In this chapter, we provide an overview of PH

characteristics seen on cardiac CT.

Classiﬁ cation of PH

The simplicity of deﬁ ning pulmonary hypertension with hemodynamic data belies the challenges of diagnosing and managing this disorder. The patient population is heterogeneous with multiple potential etiologies, prognoses, and treatment options. The modiﬁ ed classiﬁ cation from the 5th World Symposium on PH held in Nice, France in 2013 (revised from the previous revision in 2008) divides PH into ﬁ ve groups, shown in Table 19.1 . The largest groups in the Western world are Groups 2 and 3, respectively the left sided heart disease and hypoxic lung disease [ 2 ].

Group 1 PH: PAH

Group 1 pulmonary hypertension is referred to as pulmonary arterial hypertension (PAH), a disease of the precapillary

B. S. Messenger , MD (*) Division of Cardiology, Department of Medicine , Harbor-UCLA Medical Center , k1000 West Carson Street , Torrance , CA 90502 , USA e-mail: Bradley.messenger@gmail.com

R. J. Oudiz , MD Department of Medicine, Los Angeles Biomedical Research Institute , The David Geffen School of Medicine at UCLA, Harbor-UCLA Medical Center , Torrance , CA , USA

1 9

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pulmonary circulation due to a complex process intrinsic to the pulmonary vasculature. As many entities clinically mimic PAH, it is a diagnosis of exclusion, requiring a thorough workup and proper consideration of more common etiologies such as left-sided heart disease and hypoxic lung disease. PAH, like PH, is similarly deﬁ ned hemodynamically as a mean pulmonary artery pressure ≥25 mmHg at rest and PVR >3 Wood units, but the pulmonary capillary wedge pressure measures ≤15 mmHg [ 3 ].

The natural history of PAH is variable based upon etiology but it typically follows a progressive course with a poor prognosis if left untreated [ 4 ]. Most patients with PAH present with exertional dyspnea that worsens over months to years. Exertional angina, syncope, and peripheral edema appear later in the course when increasing pulmonary vascular resistance strains and ultimately impairs right ventricular function. The diagnosis of PAH is often delayed due to the nonspeciﬁ c symptoms and subtle ﬁ ndings on physical examination {5].

Idiopathic and Heritable PAH

Idiopathic PAH (IPAH) is a diagnosis of exclusion in which no etiology nor family history can account for the disease. The incidence of IPAH is rare, with an estimated incidence of 1–2 cases per million per year worldwide [ 6 ]. The disor- der is approximately 4 times more common in women [ 7 , 8 ], presenting in the third decade for women and in the fourth decade for men without racial or ethnic predisposition [ 6 ].

PAH has a familial component is some patients. Germline mutations in the bone morphogenetic protein receptor type 2 ( BMPR2 ) gene can be detected in approximately 70 % of cases [ 8 , 9 ]. Mutations in activin receptor-like kinase type 1 (ALK-1 or endoglin have been found in familial PH with a strong association for concomitant hereditary hemorrhagic

telangiectasia. BMPR2 mutations, however, have also been detected in 11 % to 40 % of apparently idiopathic cases without a family history [ 10 , 11 ], so the distinction between idio- pathic and familial BMPR2 mutations may be artiﬁ cial. Interestingly, in up to 30 % of families with PAH, no BMPR2 mutation has been identiﬁ ed. Thus, heritable forms of PAH include IPAH with germline mutations and familial cases with or without identiﬁ ed germline mutations [ 12 , 13 ]. Genetic testing is not mandatory in heritable PAH, genetic testing should only be performed after genetic counseling, with a discussion of the risks, beneﬁ ts, and limitations of such testing [ 14 ].

PAH Associated with Connective Tissue Diseases

The prevalence of PAH has been well established for patients with systemic sclerosis (SSc). Two recent prospective studies using echocardiography as a screening method and right heart catheterization for conﬁ rmation found a prevalence of PAH in SS of between 7 % and 12 % [ 15 , 16 ]. The prevalence of PAH in systemic lupus erythematosis and mixed connective tissue disease remains unknown; although its incidence is greater than IPAH, it occurs less frequently than in SSc [ 17 – 20 ]. In the absence of ﬁ brotic lung disease, PAH has also been reported infrequently in Sjögren syndrome [ 21 ], polymyositis [ 22 ], and rheumatoid arthritis [ 23 ]. Approximately one half of patients with PH and connective tissue diseases will die within 1 year if left untreated [ 24 ]. PH is also a frequent complication of idiopathic pulmonary ﬁ brosis (IPF). IPF patients with concomitant PH have a two to threefold increase in mortality compared to IPF patients with normal pulmonary arterial pressures [ 25 ]. However, the presence or severity of PH does not correlate with the level of IPF disease seen on high resolution CT [ 26 ]. It is increasingly being recognized that PH in patients with IPF is the sequelae of a “primary” occlusive pulmonary vasculopathy, rather than being purely secondary to ﬁ brotic destruction of the vascular bed [ 27 ].

PAH Associated with Congenital Heart Disease (CHD)

PAH related to CHD results from the effects of a longstanding abnormal increase in pulmonary blood ﬂ ow which leads to pathologic changes in the pulmonary vasculature, particularly in the smaller vessels. This results in increased pulmonary vascular resistance, which in turn has deleterious effects upon the heart and larger pulmonary vascular structures. Direct shunts can increase pulmonary blood ﬂ ow and pressure (patent ductus arteriosis) (Fig. 19.1 ).

Eisenmenger syndrome is deﬁ ned as CHD with an initially large systemic-to-pulmonary shunt that induces progressive pulmonary vascular disease and PAH, resulting in reversal of the shunt and central cyanosis [ 28 , 29 ]. Eisenmenger syndrome represents the most advanced form

Table 19.1 Summary of CT ﬁ ndings in pulmonary hypertension

Pulmonary arteries Enlarged proximal vessels Pruning of the distal vessels Calciﬁ cation of the proximal pulmonary arteries Thrombosis Aneurysms Heart RA, RV, and IVC dilation RV hypertrophy Decreased RV systolic function Flattened interventricular septum (“D-shaped” and undersized left

ventricle) Pericardial thickening and/or effusion Others Hypertrophy of bronchial arteries Segmental bronchial artery to bronchus ratio > 1:1 in 3 or 4 lobes Retrograde opaciﬁ cation of the inferior vena cava or hepatic vein

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of PAH associated with CHD (Fig. 19.2 ). A large proportion of patients with CHD develop some degree of PAH [ 30 – 32 ]. The prevalence of PAH associated with congenital

systemic- to- pulmonary shunts in Europe and North America ranges between 1.6 and 12.5 cases per million adults, with 25–50 % of this population affected by Eisenmenger syndrome [ 33 ].

PAH Associated with Schistosomiasis

Though not prominent in industrialized nations, schistosomiasis may be the most common cause of PAH in the world given the expected 200 million people infected with the parasite [ 34 ]. The mechanism of PH is probably multifactorial, and includes mechanical obstruction, local vascular inﬂ ammation related to eggs, and portal hypertension [ 35 , 36 ]. These cases can have a similar clinical presentation to IPAH [ 37 ], with similar histopathologic ﬁ ndings [ 38 ], and thus similar radiographic appearance. PAH occurs almost exclusively in the 10 % of infected patients who develop hepatosplenic schistosomiasis [ 39 ].

Pulmonary Veno-Occlusive Disease and Pulmonary Capillary Hemangiomatosis

Pulmonary veno-occlusive disease (PVOD) accounts for a small number of pulmonary hypertension cases, most commonly in children and young adults [ 40 ]. The estimated annual incidence rate is 0.1–0.2 cases of PVOD per million persons in the general population [ 41 , 42 ].

Patients with PH due to PVOD frequently present with congestive heart failure symptoms of dyspnea on exertion, peripheral edema, and radiographic signs of pulmonary edema with Kerley B lines that is expected with postcapillary PH. However, the hemodynamics at right heart catheterization similar to pre-capillary PH and may lead clinicians to diagnose idiopathic PH [ 40 ]. Vasodilator therapy, as used to treat a subset of idiopathic PH patients, can cause acute pulmonary edema, so distinguishing PVOD from IPAH has important clinical signiﬁ cance.

CT imaging may help raise a clinician’s suspicion for PVOD. The CT ﬁ ndings of the disease includes smooth septal thickening, diffuse or mosaic ground-glass opacities, multiple small nodules, and pleural effusion [ 43 – 47 ]. PVOD and pulmonary capillary hemangiomatosis (PCH) also show the presence of crackles and clubbing on physical examination, hemosiderin-laden macrophages on bronchoalveolar lavage [ 48 ], as well as lower carbon monoxide diffusing capacity and PaO 2 [ 47 ]. In a comparison study, PVOD patients had peripheral ground glass opacities (GGO) in 93 % of cases compared with 13 % incidence of GGO in patients with PAH [ 49 ]. Thickened interlobular septa and mediastinal adenopathy were also strongly correlated with PVOD compared with PAH patients [ 41 ].

The only effective treatment for PVOD is lung transplant with most diagnoses being made at time of transplant or autopsy.

Fig. 19.1 64 slice multi-detector CT in a 20 year-old woman with patent ductus arteriosis ( black arrow ), seen well in this sagittal view with resultant dilation of the main pulmonary artery

Fig. 19.2 CT scan in a 22 year-old woman with Eisenmenger syndrome due to atrial septal defect and pulmonary hypertension. Right cardiac chambers are enlarged with marked right ventricular hypertrophy ( black arrow )

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Group 2 PH: Pulmonary Hypertension due to Left Heart Disease

One of the most commonly seen forms of PH is pulmonary hypertension due to left heart disease. Since the etiology of their PH is distal to the pulmonary arterial system, Group 2 patients have “post-capillary” PH. Like other forms of PH, it manifests clinical signs and symptoms of the right heart failure syndrome. Group II PH includes patients with preserved or reduced ejection fraction, valvular heart disease and certain forms of congenital heart disease affecting left ventricular ﬂ ow and/or performance.

Group 3 PH: Pulmonary Hypertension due to Lung Diseases and/or Hypoxia

A subcategory of lung disease characterized by a mixed obstructive and restrictive pattern includes chronic bronchiectasis, cystic ﬁ brosis [ 50 ], and a newly identiﬁ ed syndrome characterized by the combination of pulmonary ﬁ brosis, mainly of the lower zones of the lung, and emphysema, mainly of the upper zones of the lung [ 51 ]. The prevalence of PH in all of these conditions remains largely unknown. However, in a recent retrospective study of 998 patients with chronic obstructive pulmonary disease who underwent right heart catheterization, only 1 % had severe pulmonary hypertension (mean PA pressure >40 mm Hg) [ 52 ]. In the syn- drome of combined pulmonary ﬁ brosis and emphysema, the prevalence of PH is almost 50 % [ 51 ].

Group 4 PH: Chronic Thromboembolic Pulmonary Hypertension (CTEPH)

Pulmonary embolism (PE) is an obstruction of a pulmonary artery caused by a blood clot, air, fat, or tumor tissue. The most common cause of the obstruction is a blood clot (thrombus) usually from a peripheral vein. The average annual incidence of venous thromboembolism (VTE) in the United States is 1 per 1000, with about 250,000 incident cases occurring annually [ 53 – 55 ]. The challenge in under- standing the real disease is that an additional equal number of patients are diagnosed with PE at autopsy [ 53 , 56 ]. It is estimated that between 650,000 and900,000 fatal and nonfatal VTE events occur in the US annually [ 57 ]. The classic triad of signs and symptoms of PE (hemoptysis, dyspnea, chest pain) are neither sensitive nor speciﬁ c, and many patients with PE are initially asymptomatic; most patients who have symptoms often have atypical and/or nonspeciﬁ c symptoms.

Diagnostic Workup of PE

Many diagnostic tests have been suggested for the evaluation of patients with suspected VTE. These include the history and physical examination to the electrocardiogram, chest radiography, echocardiography, ventilation-perfusion scintigraphy, pulmonary angiography, CT and MR angiography, lower-extremity venography, and sonography. Although the diagnostic accuracy of laboratory tests such as D-dimer has increased (a negative result in combination with a low-probability clinical assessment provides reasonable certainty for excluding PE), radiographic imaging plays an important role in the diagnosis of PE, especially with the development of multi-detector CT (MDCT) and increased use of CT pulmonary angiography.

Although normal chest x-ray ﬁ ndings are observed in 24 % of patients with PE, an elevated hemidiaphragm can be observed in 20 % of patients with acute PE [ 58 ]. An elevated hemidiaphragm, consolidation, pleural effusion, or atelectasis occurs in about 2/3 of patients with acute PE. Especially in a massive PE (Fig. 19.3 ), local hyperlucency is seen when a lobar or segmental artery is occluded (Westermark sign), and engorgement of a major hilar artery (Fleischner sign) can be detected [ 59 , 60 ]. Abrupt tapering or termination of a pulmonary vessel (knuckle sign), a pleural- based density or costophrenic density (Hampton’s hump), and alveolar or interstitial pulmonary edema may occur. Most of the above chest x-ray ﬁ ndings are nonspeciﬁ c. Nuclear scintigraphy (ventilation-perfusion or V/Q scanning) is useful if multidetector CT angiography (MDCTA) is not available. The V/Q scan in a patient with an acute PE will demonstrate an area

Fig. 19.3 64 slice multi-detector CT in a patient with pulmonary embolism. An axial section at the level of the main pulmonary artery shows the ﬁ lling defect ( white arrows ) of bilaterally enlarged pulmo- nary arteries with massive thromo-emboli. A small amount of right pleural effusion ( white arrowhead ) is observed

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distal to thrombus that is not properly per fused, increasing the V/Q mismatch.

Perfusion defects appear the same on a VQ scan whether the pulmonary embolus is acute or chronic. In contrast, CT ﬁ ndings of acute versus chronic emboli differ. In CTEPH, there may be intraluminal thrombi and dilated bronchial arteries. Furthermore, a mosaic pattern of hyperattenuation and hypoattenuation is frequently seen, representing the variation in perfusion between pulmonary segments [ 40 ]. Other evidence of CTEPH on CT includes abrubt narrowing of vessels, intimal irregularities, or total occlusions. Yet, there is greater concern that CT ﬁ ndings may be difﬁ cult to detect. A study from Tunariu, et al. found a sensitivity of 51 % for CTPA compared with 96 % sensitivity for VQ scans [ 61 ]. The speciﬁ city of CTPA can also be limited by the sub- tly distinct mosaic pattern of hyperattenuation and hypoattenuation found in Group 1 PAH. With improved ECG-gated CT imaging, recent studies have shown much improved sensitivity. He, et al found the sensitivity of VQ scan to be 100 % if high and intermediate risk results were interpreted as positive for a PE with sensitivity declining to 96 % but speciﬁ city rising to 95 % if only high risk results were counted as abnormal [ 62 ]. CT had a sensitivity of 92 % with speciﬁ city of 95 % in the same patient cohort [ 62 ]. While V/Q scan remains slightly more sensitive, CT imaging now serves as a viable alternative given improvements in sensitivity and speciﬁ city with newer scanners.

Pulmonary angiography, the gold standard for diagnosing PE, is being replaced in many institutions with MDCTA, which is less invasive, easier to perform, and has high sensitivity (83 %-100 %) and speciﬁ city (89 %-97 %) [ 63 – 65 ]. The PIOPED studies (large multicenter trials for CCTA in suspected PE) report negative predictive values as high as 99 %.

The newest noninvasive method for the evaluation and diagnosis of PE is MRI. Although not as extensively studied as other imaging techniques, it can be utilized for the patients with renal dysfunction or an iodine contrast allergy. CT angiographic ﬁ ndings are shown (Figs. 19.3 and 19.4 ).

Chronic thromboembolic pulmonary hypertension (CTEPH) represents a frequent cause of PH (Fig. 19.4 ). The incidence of CTEPH is uncertain; however, it is known to occur in up to 4 % of patients after an acute pulmonary embolism [ 66 , 67 ]. It is strongly recommended that patients with suspected or conﬁ rmed CTEPH be referred to a center with expertise in the management of this disease to consider the feasibility of performing pulmonary thromboendarterectomy, currently the only curative treatment. The decision depends on the location of the obstruction (central vs. more distal pulmonary arteries), the correlation between hemodynamic ﬁ ndings, and the degree of mechanical obstruction.

Methods of Detecting and Characterizing PH

The appropriate classiﬁ cation of patients with suspicion of PAH requires a rigorous diagnostic approach. PH symptoms are nonspeciﬁ c and progress slowly over months to years. Exertional dyspnea is the most common symptom with fatigue occurring in a minority of cases. Manifestations of syncope, peripheral edema, and angina may be more concerning and frequently appear in patients with evidence of impaired right ventricular function. Clinicians should have a higher index of suspicion for PAH in patients using amphetamines or diet pills, a history of autoimmune disease, or a known family history of PH.

Guidelines put forth from the AHA/ACCF recommend a rigorous workup for pulmonary hypertension which includes the diagnostic algorithm as shown in Table 19.2 [ 3 ]. Transthoracic echocardiography (TTE) is often used as a ﬁ rst-line screening test to exclude or identify patients with severe PH by estimating systolic PA pressure and looking for evidence of the cardiac hemodynamic perturbations seen with PAH, such as right-sided cardiac and great vessel

Fig. 19.4 64 slice multi-detector CT in a 58 year-old man with multiple bilateral pulmonary embolism. ( a ) “Saddle embolus” ( black arrow ) at the bifurcation of right pulmonary Artery (PA). ( b ) “Tram line” ( white arrow ) and “ring shape” ( black arrowhead ) features of emboli at both peripheral PAs

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chamber enlargement and dysfunction, ﬂ attening of the interventricular septum, and pericardial effusion. Echocardiography is also useful for evaluating congenital heart disease and left-sided heart disease.

Suggested radiographic imaging includes a chest x-ray and, depending on the need, CT radiography. The chest radiographic ﬁ ndings of PH are hilar fullness characteristic of dilated central pulmonary arteries, pruning of the

peripheral arteries, and right-sided cardiac chamber enlargement [ 3 , 5 ]. The chest radiograph may suggest an underlying cause for PH and is thus recommended in the workup of suspected PH.

Right-sided heart catheterization (RHC) is the most accurate test for determining cardiopulmonary hemodynamics and remains the gold standard by which the diagnosis of PH is made and hemodynamic severity is calculated. A RHC is required not only to conﬁ rm the presence and the severity of PH, but also to exclude left-sided heart disease, potentially correctable intracardiac left-to-right shunting, and to perform acute vasodilator testing.

Because the signs and symptoms of PH are non-speciﬁ c and there is no reliable non-invasive test for its detection, patients often undergo computed tomography (CT) as part of their diagnostic work-up. CT is able to evaluate the lung parenchyma (for interstitial or emphysematous changes), the pulmonary artery (calciﬁ cation, dilation, embolism, patent ductus), the pulmonary veins, the cardiac chambers (hypertrophy, dysplasia, enlargement, thrombus, septal defects), the coronary vessels, and the IVC simultaneously.

It is important to be aware of the CT ﬁ ndings that may suggest the diagnosis of PH, such as an enlarged main pulmonary artery (Figs. 19.5 ). Radiographically, PH is said to be more likely when the main pulmonary artery diameter (MPAD) is ≥29 mm (sensitivity 69 %, speciﬁ city 100 %) [ 6 , 7 ] and/or the ratio of the main pulmonary artery to ascending aorta diameter is >1 (sensitivity 70.8 % and speciﬁ city

76.5 %) [ 8 , 68 ]. Others have reported that the most speciﬁ c CT ﬁ ndings for the presence of PH were both a MPAD ≥29 mm and segmental artery-to-bronchus ratio of >1:1 in three or four lobes (speciﬁ city 100 %) [ 9 ]. In addition, the MPAD correlates with the severity of pulmonary hypertension; two studies have deﬁ ned the upper limit of normal for main pulmonary artery diameter as 32 mm [ 6 , 10 ]. An addi- tional feature of PH is rapid tapering or “pruning” of the distal pulmonary vessels (Fig. 19.5 ).

With improvements in ECG-gated CT technology, newer methods have been developed with similar accuracy in predicting the presence of PH. Revel et al. demonstrated that a reduction in distensibility of the right pulmonary artery has a high speciﬁ city for PH[ 69 ]. Distensibility is determined by evaluating the change in cross-sectional area of the right PA during systole compared with diastole. The difference in maximum area from the minimum area is divided by the maximum area and multiplied by 100 to get a percentage of distensibility. A value of less than 16.5 % had 86 % sensitivity and 96 % speciﬁ city for PH [ 69 ]. RV thickness is a known ﬁ nding in PH with RV free wall thickness >6 mm (81 % sensitivity and 91 % speciﬁ city), RV/LV lumen ratio >1.28 (sensitivity of 85 % and speciﬁ city of 86 %), and RV wall/LV wall ratio >0.32 as accurate predictors of PH [ 70 ]. With a high degree of speciﬁ city, CT imaging provides important

Table 19.2 Clinical classiﬁ cation of pulmonary hypertension

1. Pulmonary arterial hypertension (PAH)

1. Idiopathic PAH

2. Heritable BMPR2 mutation (familial or isolated) ALK1, endoglin (with or without hereditary hemorrhagic

telangiectasia)

Unknown

3. Drug- and toxin-induced

4. Associated with Connective tissue diseases HIV infection Portal hypertension Congenital heart diseases Schistosomiasis Chronic hemolytic anemia

5. Persistent pulmonary hypertension of the newborn

6. Pulmonary veno-occlusive disease (PVOD) and/or pulmonary capillary hemangiomatosis (PCH)

2. Pulmonary hypertension due to left heart disease

1. Systolic dysfunction

2. Diastolic dysfunction

3. Valvular disease

3. Pulmonary hypertension due to lung diseases and/or hypoxia

1. Chronic obstructive pulmonary disease

2. Interstitial lung disease

3. Other pulmonary diseases with mixed restrictive and obstructive pattern

4. Sleep-disordered breathing

5. Alveolar hypoventilation disorders

6. Chronic exposure to high altitude

7. Developmental abnormalities

4. Chronic thromboembolic pulmonary hypertension (CTEPH)

5. Pulmonary hypertension with unclear multifactorial mechanisms

1. Hematologic disorders: myeloproliferative disorders,

splenectomy

2. Systemic disorders: sarcoidosis, pulmonary Langerhans cell

histiocytosis, lymphangioleiomyomatosis, neuroﬁ bromatosis, vasculitis

3. Metabolic disorders: glycogen storage disease, Gaucher

disease, thyroid disorders

4. Others: tumoral obstruction, ﬁ brosing mediastinitis, chronic

renal failure on dialysis

ALK1 activin receptor-like kinase type1, BMPR2 bone morphogenetic protein receptor type2

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evidence for pulmonary hypertension that should prompt clinicians to pursue a workup for pulmonary hypertension.

The presence of calciﬁ cation in the pulmonary arteries suggests more severe disease [ 9 ], as does pericardial thicken- ing and/or effusion [ 12 ]. Some studies have reported that hypertrophy of the bronchial artery occurs frequently in patients with idiopathic PAH (IPAH) and Eisenmenger’s syndrome [ 13 , 14 ]. These studies also reported that pulmo- nary artery thromboses and aneurysms were common in patients with congenital heart disease (CHD) as compared to patients with IPAH, while dilation and mural calciﬁ cation was seen in similar frequency in both groups [ 13 ].

It is generally accepted that in patients with chronic, unrepaired systemic-to-pulmonary shunts the CT ﬁ ndings can appear very similar to those found in precapillary pulmonary hypertension such as IPAH and PAH associated with connective tissue disease, portal hypertension, and HIV infection. Commonly, right (or pulmonic) ventricular hypertrophy is seen, with right ventricular enlargement and associated right atrial enlargement (Fig. 19.6 ).

As the right ventricle enlarges, the interventricular septum becomes ﬂ attened (Fig. 19.7 ) and eventually convex to the left side [ 15 – 17 ], and thus septal ﬂ attening is a com- monly noted cardiac abnormality found in patients with PH [ 18 ]. If cine-CT is performed, reduced right ventricular sys- tolic function may also be present. The presence of retrograde opaciﬁ cation of the inferior vena cava or hepatic vein during contrast-enhanced CT may be a nonspeciﬁ c sign of

Fig. 19.5 Electron Beam CT scan in a 22 year-old woman ( a ) and 64 slice multi-detector CT in a 40 year-old man ( b ), both with pulmonary hypertension. Pulmonary arteries ( PA ) are enlarged and tapering dis- tally, with an increased main PA to aorta ratio

Fig. 19.6 64 slice multi-detector CT in a 44 year-old man with secondum atrial septal defect ( ASD ) and pulmonary hypertension demon- strating right atrial ( RA ) and right ventricular ( RV ) enlargement

Fig. 19.7 64 slice multi-detector CT in a 31 year-old man with sinus venosum atrial septal defect (ASD) and pulmonary hypertension demonstrating right atrial (RA) dilation and right ventricular (RV) hypertrophy, and ﬂ attening of the inter-ventricular septum ( black arrow ), indicating high right sided pressures

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signiﬁ cant pulmonary hypertension and/or right ventricular dysfunction [ 19 ] (Fig. 19.8 ).

Although hemodynamics cannot be directly measured with CT, the sequelae of chronic pulmonary hypertension can be seen with structural cardiac changes. The increased pulmonary vascular resistance that occurs with PH places greater strain on the right ventricle. Right ventricular hypertrophy (>6 mm thickness) is a common ﬁ nding, and as the RV begins failing in the setting of persistently elevated afterload, an increased in RV end diastolic volume will occur [ 71 ]. RV enlargement leads to increasing RV pressure and volume, which are reﬂ ected in the bowing of the interventricular septum. CT ﬁ ndings of RV/LV >1 and LV septal ﬂ attening are sensitive and speciﬁ c markers for PH. In small studies by Contractor et al and Lim et al, found these signs had a sensitivity of 78 %–92 % and a speciﬁ city of 100 % for echocardiographic ﬁ ndings of RV dysfunction. [ 71 – 73 ] Systolic eccentricity index (sEi) correlates well with pulmonary hypertension severity [ 74 ]. In normal conditions, the LV cavity is shaped like a circle. With increasing RV pressure and volume overload, the septal wall ﬂ attening leads to a deformed, D-shaped left ventricle. The length of the septum (D1) becomes longer than the width of the LV cavity (D2), with a ratio of D1/D2 >1 (normal score is 1) that is the eccentricity score [ 74 ]. Most studies have evaluated sEi with

echocardiographic data, but cine-CT provides the necessary axial images of the LV in systole and diastole to calculate the index.

Although CT imaging of the great vessels is a simple and straightforward noninvasive methodology, it has not gained widespread acceptance as a screening test for PH [ 1 ]. Table 19.1 summarizes the CT ﬁ ndings of PH. While CT cannot diagnose pulmonary hypertension, clinicians should be aware that a wealth of information regarding the end result of the chronic hemodynamic effect of PH upon cardiovascular anatomy. A diagnosis and its underlying etiology may be highly suggested by closely evaluating the pulmonary vasculature and cardiac anatomy on CT imaging.

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