Congenital Absence of the Pericardium

    Congenital Absence of the Pericardium David Lopez, Craig R Asher PII: DOI: Reference:

S0033-0620(16)30139-6 doi: 10.1016/j.pcad.2016.12.002 YPCAD 771

To appear in:

Progress in Cardiovascular Diseases

Please cite this article as: Lopez David, Asher Craig R, Congenital Absence of the Pericardium, Progress in Cardiovascular Diseases (2016), doi: 10.1016/j.pcad.2016.12.002

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Congenital Absence of the Pericardium

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David Lopez, MD* [email protected]

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Craig R Asher, MD* [email protected]

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*From the Heart and Vascular Institute Cleveland Clinic, Weston, Florida

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Disclosures: None.

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Corresponding author: Craig R. Asher, MD 2950 Cleveland Clinic Blvd Weston, FL 33331 Tel. 954-659-5290 Fax. 954-659-5292 [email protected]

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Key words: congenital absence of the pericardium, partial pericardial defect, cardiac herniation; echocardiography, cardiac CT, cardiac MRI

ACCEPTED MANUSCRIPT Abstract Congenital absence of the pericardium (CAP) is one of the most rare cardiac congenital

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anomalies. It can occur as a complete absence of the entire pericardium, absence of the right or

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left portion of the pericardium or a partial, foramen-like defect of the right or left pericardium.

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While the majority of cases are clinically silent, multiple reports associate CAP with symptomatic presentation. The most feared complication of CAP is sudden death due to cardiac

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strangulation across a partial defect of the left pericardium. Given its rare occurrence, most clinicians and imaging specialists will have little experience with this condition and may fail to

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recognize it on thoracic or cardiac studies. Thus, the purpose of this review is to highlight the common clinical and multimodality imaging features associated with this anomaly and suggest a

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Abbreviations:

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management algorithm.

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CAP = Congenital absence of the pericardium

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CCT = Cardiac computed tomography CMR = Cardiac magnetic resonance imaging LAA = Left atrial appendage LP =Left pericardium LV =Left ventricle or ventricular RV =Right ventricle or ventricular

ACCEPTED MANUSCRIPT Introduction Congenital absence of the pericardium (CAP) is one of the most rare cardiac congenital

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anomalies. It can occur as a complete absence of the entire pericardium, absence of the right or

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left portion of the pericardium or a partial, foramen-like defect of the right or left pericardium

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(LP)1,2. While the majority of cases are clinically silent, multiple reports associate CAP with symptomatic presentation. The most feared complication of CAP is sudden cardiac death (SCD)

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due to cardiac strangulation across a partial defect of the LP1,3. Given its rare occurrence, most clinicians and imaging specialists will have little experience with this condition and may fail to

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recognize it on thoracic or cardiac studies2,4. Thus, the purpose of this review is to highlight the common clinical and multimodality imaging features associated with this anomaly and suggest a

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management algorithm.

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CAP was first described in 1559 by the Italian anatomist Realdus Columbus. Over the next 400

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plus years, CAP has been identified at autopsy or incidentally during surgery. The prevalence of CAP ranges from 0.007-0.015% in autopsy reports1 to 0.044% in a surgical case series2. One of

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the earliest descriptions of CAP came from Versé in 1909, finding 2 cases in a series of 13,000 autopsies. Similarly, in 1938 Southworth and Stevenson reported a single case of absent LP , in a series of 14,000 autopsies at Johns Hopkins Hospital1. A slightly higher prevalence of CAP has been found in more contemporary surgical reports with 15 cases described out of 34,000 cardiothoracic surgeries at the Mayo Clinic2. Based on case reports, it is generally thought that this lesion occurs more commonly in males than females with a 3:1 ratio1,5. However conflicting data shows no clear gender predominance. In the surgical series from the Mayo Clinic, 7 of the 15 patients were males and in a report of symptomatic patients with CAP, 3 out of 10 were

ACCEPTED MANUSCRIPT males2,6. CAP is typically an isolated lesion, but has been incidentally found in the setting of other congenital cardiac abnormalities2.

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The vast majority of cases of CAP involve partial or complete absence of the LP. Right-sided defects are exceedingly rare. In the 1938 autopsy series from Johns Hopkins Hospital, 52

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definitive cases were identified and reviewed. Among those classified as definitive, 76% had complete absence of the LP and 24% had partial absence or a foramen type defect of the LP.

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Right-sided or bilateral defects were only observed in 7 cases and associated with multiple birth

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defects. Concordantly, in the surgical series from the Mayo Clinic, 12 of the 15 cases had complete or partial defects of the LP. Among the 3 other cases, one had a partial defect of the

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right pericardium, one a partial defect of the anterior pericardium and one had absence of the entire pericardium.

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The majority of CAP cases reported in the literature were incidentally found in asymptomatic

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individuals. Some have been identified in the course of evaluating cardiac symptoms. The most common associated complaint is atypical, sharp or stabbing, and often left-sided positional chest

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pain6. Exertional symptoms are not usually reported. Except for one case of cardiac herniation between the pulmonary ligament and the diaphragm7, the mechanism of pain in those with complete absence of the LP left pericardium is not well understood. In the setting of partial defects herniation of the left atrial appendage and left ventricular apex leading to regional ischemia have been documented8–10. The most dramatic and feared presentation is sudden death due to cardiac strangulation across a left-sided partial defect, although to date, only about 3 cases have been reported in the literature3,5. Surgical treatment is usually recommended for those with significant symptoms or obvious herniation6. Two reports in the literature implicate CAP with severe tricuspid regurgitation due to leftward and posterior displacement of the heart, which

ACCEPTED MANUSCRIPT stretches the anterior right ventricular wall11,12. However, in one of these cases a large defect in the anterior leaflet of the tricuspid valve was found during the operation12. Thus congenital

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absence of the pericardium could have contributed, but was not the sole etiology of the

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regurgitation.

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Clinical and Radiological Diagnosis

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In 1915 the Canadian physician Maude Abbott proposed that the diagnosis of complete absence of the LP could be made clinically based on: (1) increased cardiac mobility, (2) unexplained

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cardiac enlargement and (3) leftward shift of the heart1,13. She predicted that cases of partial defects were impossible to diagnose clinically. Clinical signs have not proven sufficient to make

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the diagnosis. At a minimum a combination of physical exam, electrocardiography (ECG) and

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chest radiograph are needed to diagnose CAP14. In 1959 Ellis et al, were the first to describe the diagnosis of congenital absence of the LP based on the findings of plain chest x-ray, and

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subsequent confirmation by diagnostic pneumothorax13.. By injection of air into the left pleural

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space and demonstration of a right-sided pneumopericardium, an iatrogenic pneumothorax could be used to diagnose complete absence of the LP. Over the next decade diagnostic pneumothorax was increasingly used to demonstrate CAP in suspected cases. However, this invasive approach was not without risk and often was utilized in asymptomatic individuals in whom the findings of the diagnostic pneumothorax had little therapeutic value. In 1971 Morgan et al14 reported a series of 6 cases to demonstrate that complete absence of the LP can be clinically diagnosed by a combination of physical examination, ECG and plain chest x-ray without the need for diagnostic pneumothorax.

ACCEPTED MANUSCRIPT Common findings of CAP on physical exam include a displaced apical impulse palpated in the left axilla and a systolic ejection murmur at the base14. In an extreme case, Glancy et al15,

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reported the case of an asymptomatic 77-year-old man in whom the cardiac apex was so

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displaced that the apical impulse was palpated medial to the left scapula. The ECG typically demonstrates right axis deviation, r’ or right bundle branch block morphology in V1 and poor R-

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wave progression14. On plain chest x-ray, levoposition of the heart in the posteroanterior

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projection with an elongated heart border (sometimes referred to as Snoopy’s sign), a prominent pulmonary artery and radiolucency between the heart and the diaphragm has been described. In

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their case series, Gatzoulis et al6 most commonly observed a “tongue” of tissue between the aortic arch and the pulmonary artery, which appears as a prominent or sharp aortopulmonary

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window (Figure 1A). A herniated left atrial appendage (LAA) may be observed in the case of a

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foramen type defect in this region of the LP (Figure 1B).

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Although the clinico-radiological signs described by Morgan et al, are supported by other investigators, these are nonspecific and other cardiac conditions need to be excluded depending

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on the clinical scenario. Furthermore, despite these criteria, CAP may still go unrecognized because of lack of sensitivity of criteria, but more likely due to lack of suspicion for such a rare condition. In the Mayo Clinic surgical case series, none of the 8 cases with complete absence of the LP, which is more likely to be clinically recognized, were pre-operatively diagnosed even though all went to surgery after evaluation by presumably experienced cardiovascular clinicians at a tertiary referral institution.

ACCEPTED MANUSCRIPT Modern non-invasive pericardial imaging Appearance of the pericardium on non-invasive imaging

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With the advent of echocardiography, cardiac computed tomography (CCT) and cardiac

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magnetic resonance imaging (CMR) there are now non-invasive diagnostic tools to identify and

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better characterize CAP. However, visualization of the pericardium on non-invasive imaging is not an insignificant task. The pericardium consists of two adjacent layers, which are separated

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by a normally invisible trace amount of fluid. The thickness of the combined visceral and parietal pericardium is usually < 2 mm. Therefore to accurately resolve the pericardium, an in-plane

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spatial resolution of at least 1 mm is necessary. Furthermore, visualization of the pericardium on CCT or CMR relies on the contrast created by differences in tissue characteristics between the

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pericardium and the epicardial and pericardial fat layers which flank the visceral and parietal

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pericardium respectively (Figure 2). The amount of fat varies with body habitus and anatomic location. Specifically, epicardial fat between the myocardium and the visceral pericardium is

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often negligible or absent along the left ventricular (LV) lateral and posterior walls. Therefore

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the pericardium is difficult to see in this region since it has similar tissue characteristics as the myocardium (Figure 2). On echocardiography, the pericardium is even more difficult to visualize. Hence, it is important to integrate the direct visualization with other indirect features of absent pericardium in order to make the diagnosis. Echocardiography Echocardiographic features of CAP are described in Table 1. These features are generally associated with absence of the LP. This condition is suspected when there is (1) unusual imaging windows, (2) the appearance of an enlarged right ventricle (RV), (3) excessive cardiac motion, and (4) abnormal interventricular septal motion16. Among these findings, an enlarged

ACCEPTED MANUSCRIPT RV is the finding that most often leads to additional testing because of suspicion of left to right shunts or cardiomyopathy. The RV may be enlarged because of altered compliance with an

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absent LP or because of levoposition of the heart, resulting in an oblique image through the

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chamber

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In the parasternal long-axis view, the apex is pointed posteriorly, leading to a suboptimal traditional imaging plane (Figure 3). In addition, there is excessive motion of the heart and

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septal and posterior wall motion17,18. The normal epicardial-pericaridal space cannot be well

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visualized on two-dimensional or M-mode imaging.

Similar to the parasternal views, the apical views may appear off-axis and most often are

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laterally displaced. The classical appearance of a “teardrop” cardiac shape with widening of the ventricles and elongation of the atrium, along with a sharp angulation of the atrio-ventricular

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grove may be seen (Figure 3). In the apical 2-chamber view an outward bulging motion of the

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inferior wall in diastole has been recognized19.

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Other findings reported with CAP related to physiology and valve regurgitation have been described. A reduction in the systolic superior vena cava flow and the systolic/diastolic flow ratio in the pulmonary veins has been reported20,21. Significant degrees of tricuspid regurgitation may occur in some patients and is related to the abnormal geometry of the tricuspid annulus or chordal rupture11,12. Partial defects may be recognized as a hinge point in the lateral LV wall (Figure 4) or herniation of the LAA.

ACCEPTED MANUSCRIPT CCT and CMR General principles and imaging technique

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CCT and CMR have emerged as important modalities for advanced imaging of the pericardium.

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Accuracy for the diagnosis of CAP is probably comparable between the two modalities. Selection of one versus the other will depend on institutional availability, expertise and clinical

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scenario. CMR provides a more comprehensive evaluation, which includes direct pericardial

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visualization and assessment of cardiac function without exposure to ionizing radiation. On the other hand, CCT is a much faster examination and provides submillimeter in-plane spatial

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resolution for the visualization of the pericardium. Furthermore, radiation exposure with modern CT scanners has become increasingly lower, in the order of 1 millisievert for a prospective ECG-

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triggered protocol.

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CAP may be incidentally identified on standard non-gated chest CT and depending on the image

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quality further testing may not be necessary. When CCT is obtained specifically for suspected CAP a prospective ECG-triggered protocol should be utilized. A contrast-enhanced

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retrospective protocol would allow assessment of cardiac function; however the diagnostic accuracy may not improve significantly to justify the increased radiation exposure. The basic CMR examination must include T1-weighted (T1W) and cine sequences for direct pericardial imaging and functional assessment respectively22. Tissue tagging sequences may be useful to visualize the pericardium in selected cases. T2-weighted imaging is not necessary for this indication. Images should be obtained in multiple planes to maximize diagnostic accuracy. A complete exam would include whole heart coverage in the axial and sagittal or coronal planes plus selected vertical long-axis and short-axis views. Image acquisition parameters should be modified to optimize spatial resolution. Slices should be thin, around 5 mm, with an in-plane

ACCEPTED MANUSCRIPT resolution approaching 1 mm. Real-time images should be obtained in the 4-chamber and shortaxis orientation to assess for paradoxical septal motion. Suggested CCT and CMR imaging

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protocols are summarized in Table 2. Although intravenous contrast is not needed for the identification of CAP with either modality,

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in clinical practice the differential diagnosis is usually broader and it may still be preferred to use a contrast enhanced protocol in order to maximize the information gained from these studies.

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With both modalities, contrast is needed to detect pericardial inflammation if there is a clinical

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concern for pericarditis. Assessment of coronary anatomy with CCT may be indicated in some cases. With CCT, contrast administration is needed to delineate the cardiac chambers for the

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assessment of chamber size, atrial or ventricular septal defects and valve morphology. With a CMR exam, contrast administration is needed for the detection of myocardial scar in the setting

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of cardiomyopathy.

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Image appearance

As previously mentioned, the pericardium can be identified on CCT and CMR imaging because

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it is differentiated from the adjacent myocardium by the epicardial and pericardial fat layers (Figure 2). However, it may be challenging to visualize the pericardium when there is absent epicardial or pericardial fat layers, particularly in young individuals. Therefore it is important to recognize indirect findings that suggest absence of the pericardium. Two common findings are levorotation of the heart (Figure 5) and interposition of lung tissue in regions of absent pericardium including the anterior space between the aorta and pulmonary artery and between the diaphragm and the base of the heart (Figure 6). On cine CMR many of the two-dimensional echocardiographic clues may apply, including RV dilation, excessive cardiac motion, “tear-drop” appearance of the heart, and abnormal atrial-ventricular angle.

ACCEPTED MANUSCRIPT High risk features of partial defects are summarized in Table 3 and may include (1) presence of a myocardial crease or hinge point as a result of external pressure exerted on the heart by the

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edge of a partial pericardial defect (Figure 7), (2) coronary artery compression on CCT or

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myocardial crease23 or (4) evidence of LAA herniation8.

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invasive angiography12, (3) evidence of ischemia on perfusion imaging in association with a

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General diagnostic approach and management

The diagnostic approach to CAP will vary according to the clinical scenario (Figure 8). CAP

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may be incidentally identified or suspected during routine screening evaluation or on non-cardiac testing, such as chest CT or CMR. It may also be detected in the course of an evaluation for

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chest pain or other cardiac symptoms. In the case of the asymptomatic individual with suspected

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CAP based on the physical exam, ECG, or chest x-ray, a transthoracic echocardiogram may suffice to support the clinical impression and exclude other cardiac pathology. However, in

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those with intractable chest pain more advanced imaging with CCT or CMR may be indicated in

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order to provide a definitive diagnosis, stratify risk of herniation and guide therapeutic decisions. Surgical management is based on small, uncontrolled observations, limiting any definitive recommendations. Most authors agree that partial defects, particularly if symptomatic and potentially pose a risk of cardiac herniation, should warrant surgical intervention. The features listed in Table 3 can be used to identify high-risk patients. Pericardioplasty is the most commonly cited procedure. In some reports, pericardiectomy has been employed with seemingly good clinical outcomes24. Patients with complete CAP are unlikely to benefit from surgical intervention.

ACCEPTED MANUSCRIPT Summary CAP is a rare cardiac abnormality that is typically clinically silent, but has been associated with

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cardiac related symptoms in some individuals. With the advent of widespread thoracic and

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cardiac imaging, detection in asymptomatic individuals has increased. Partial defects of the

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pericardium, especially partial LP absence, can be associated with morbidity and mortality by way of cardiac herniation. The diagnosis of CAP can be made by a combination of clinical and

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non-invasive imaging findings, but a high index of suspicion is necessary. While some patients may benefit from surgical intervention, for most it is an incidental finding and reassurance

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should be provided.

ACCEPTED MANUSCRIPT Acknowledgement

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The authors want to thank Vislava Tylman, MLS for her assistance obtaining hard copies of reference articles.

ACCEPTED MANUSCRIPT Table 1

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Imaging findings of congenital absence of the pericardium Chest x-ray  Levorotation of the heart, elongated left heart border, sharp aortopulmonary window or prominent pulmonary artery, radiolucency between the inferior heart border and diaphragm Echo findings  M-mode – paradoxical septal motion, accentuated movement of the posterior wall, absent separation of epicardium-pericardium  2D – right ventricular dilation, exaggerated mobility of the heart, “pendulum heart”, posterior orientation of the apex and unusual acoustic windows, lateral probe position, elongated atria with widened ventricles give “tear-drop” appearance of the heart, abnormal atrial-ventricular angle, bulging outward of the inferior-posterior wall (apical view)  Doppler – tricuspid regurgitation due to annular dilation or chordal rupture, decreased pulmonary vein and superior vena cava systolic flow CCT and CMR findings  Absence of the pericardial layer  Levorotation of the heart  Interposition of lung tissue in the anterior space between aorta and pulmonary artery or between the diaphragm and the base of the heart  Subepicardial myocardial crease due to external pressure from a foramen type pericardial defect

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Adapted with permission from Klein et. al.25

ACCEPTED MANUSCRIPT Table 2

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Proposed CCT and CMR protocols for evaluation of CAP CCT CMR  64-slice detector or better  Minimize slice thickness and in-plane resolution (5 to 6 mm thick, approach  Consider pre-medication with beta1 mm in-plane resolution as possible) blocker for heart rate control  Multi-planar SSFP and HASTE scouts  Nitroglycerin is not necessary unless coronary angiography needed  Dark blood T1-weighted whole heart stack in two planes, (1) axial and (2)  Intravenous contrast is not indicated sagittal or coronal (100% slice gap) unless pericarditis is suspected or coronary angiography needed  Cine SSFP in standard long-axis views, whole heart short-axis and  Prospective ECG triggered scan axial stacks (100% slice gap) during diastole  Intravenous contrast is not indicated  Sub-millimeter isotropic unless pericarditis or myocardial scar reconstruction suspected  Real time cine imaging to evaluate for paradoxical septal motion

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CAP = congenital absence of the pericardium; SSFP = steady-state free-precession; HASTE = half-Fourier acquisition single-shot turbo spin echo

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Potential high risk features of partial pericardial defects 1. Left ventricular myocardial crease or hinge point on echo, CCT or CMR 2. Coronary compression on invasive angiography or CCT 3. Inducible ischemia on stress perfusion imaging (SPECT, PET or CMR) 4. Evidence of left atrial appendage herniation SPECT = single photon emission computer tomography; PET = positron emission tomography

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Table 3

ACCEPTED MANUSCRIPT Figure Legend Figure 1. Chest x-ray findings in complete (A) and partial (B) absence of the pericardium. Note the interposition of

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lung tissue causing a prominent pericardial window (arrow in panel A). Arrow in panel B indicates herniated left 6 atrial appendage through a partial pericardial defect. Adapted with permission from Gatzoulis et al .

Figure 2. Axial CCT (A and B) and CMR (C and D) images with (B and D) and without (A and C) contrast. Note how

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the pericardium (asterisks) is easily visualized when flanked by epicardial and pericardial fat but difficult to see in the absence of one of these fat layers (arrows). Contrast administration (B and D) does not influence pericardial visualization.

Figure 3. Parasternal long-axis (left panel) and apical 4-chamber (right panel) echocardiographic images

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demonstrate unusual echo windows (A), "teardrop" appearance (B), abnormal atrial-ventricular angle (C), and 26 apparent biventricular dilation. Reproduced with permission from Abbas et al

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Figure 4. Parasternal long-axis echocardiogram view at end-diastole in a patient with suspected partial pericardial defect. Note the lateral deviation of the apex and hinge point (arrow) in the mid to apical inferolateral wall.

Figure 5. Axial T1-weighted image demonstrates excessive levoposition of the heart (arrows) with complete 6

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absence of the left pericardium. Reproduced with permission from Gatzoulis et al .

Figure 6. T1-weighted axial (A) and coronal (B) images demonstrate interposition of lung tissue in regions of

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absent pericardium including the anterior space between the aorta and pulmonary artery (arrow in A) and 6 between the diaphragm and the heart (asterisk in B). Adapted with permission from Gatzoulis et al .

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Figure 7. T1-weighted (A) and cine SSFP (B) images at end-diastole demonstrate inferolateral epicardial crease (arrow) in a patient with suspected partial pericardial defect. SSFP = steady-state free precession

Figure 8. Suggested evaluation and management of patients with suspected CAP according to patient

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presentation. CAP = congenital absence of the pericardium; ECG = electrocardiogram; CCT = cardiac computed tomography; CMR = cardiac magnetic resonance imaging

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Figure 1

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Figure 1. Chest x-ray findings in complete (A) and partial (B) absence of the pericardium. Note the interposition of lung tissue causing a prominent pericardial window (arrow in panel A). Arrow in panel B indicates herniated 6 left atrial appendage through a partial pericardial defect. Adapted with permission from Gatzoulis et al .

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Figure 2

Figure 2. Axial CCT (A and B) and CMR (C and D) images with (B and D) and without (A and C) contrast. Note how the pericardium (asterisks) is easily visualized when flanked by epicardial and pericardial fat but difficult to see in the absence of one of these fat layers (arrows). Contrast administration (B and D) does not influence pericardial visualization.

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Figure 3

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Figure 3. Parasternal long-axis (left panel) and apical 4-chamber (right panel) echocardiographic images demonstrate unusual echo windows (A), "teardrop" appearance (B), abnormal atrial-ventricular angle (C), and 26 apparent biventricular dilation . Reproduced with permission from Abbas et al

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Figure 4

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Figure 4. Parasternal long-axis echocardiogram view at end-diastole in a patient with suspected partial pericardial defect. Note the lateral deviation of the apex and hinge point (arrow) in the mid to apical inferolateral wall.

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Figure 5

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Figure 5. Axial T1-weighted image demonstrates excessive levoposition of the heart (arrows) with complete 6 absence of the left pericardium. Reproduced with permission from Gatzoulis et al .

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Figure 6

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Figure 6. T1-weighted axial (A) and coronal (B) images demonstrate interposition of lung tissue in regions of absent pericardium including the anterior space between the aorta and pulmonary artery (arrow in A) and 6 between the diaphragm and the heart (asterisk in B). Adapted with permission from Gatzoulis et al .

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Figure 7

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Figure 7. T1-weighted (A) and cine SSFP (B) images at end-diastole demonstrate inferolateral epicardial crease (arrow) in a patient with suspected partial pericardial defect. SSFP = steady-state free precession

ACCEPTED MANUSCRIPT Figure 8 Symptoma c Pa ent - Atypical chest pain - Palpita ons - Syncope / Dizziness

Abnormal CXR

Abnormal Chest CT/MRI

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Abnormal Exam/ECG/CXR

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Asymptoma c Pa ent - Screening evalua on - Non-cardiac tes ng

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Echo

Probable CAP

Definite CAP

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Alterna ve diagnosis

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Reassure / Addi onal tes ng according to clinical scenario

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CCT/CMR

High risk features?*

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Clinical surveillance

Surgical candidate?

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Consider surgical interven on

*See Table 3

Figure 8. Suggested evaluation and management of patients with suspected CAP according to patient presentation. CAP = congenital absence of the pericardium; ECG = electrocardiogram; CCT = cardiac computed tomography; CMR = cardiac magnetic resonance imaging

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ACCEPTED MANUSCRIPT mechanisms of abnormal interventricular septal motion in congenital total absence of the left pericardium. Heart 1997;77(3):247–51. Candan I, Erol Q, Sonel A. Cross sectional echocardiographic appearance in. 1986;405–7.

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