ANATOMY

The pericardium is a fibroserous sac, that encloses the heart, consisted of two main components:

• serous pericardium: smooth and glistening lining that is covered by mesothelium.
  • visceral layer (epicardium): surrounds the heart and great vessels.
  • parietal layer: lines the fibrous component.
• fibrous pericardium: strong and inelastic due to interlacing collagenous fibers.

Fig 1: Pericardium: anatomy.

The reflections of the serosal layers are arranged around two complex tubes, with the transverse sinus as the passage between them:

• one tube encloses the aorta and pulmonary trunk.
• the other tube encloses the superior vena cava, the inferior vena cava, and the four pulmonary veins.

Fig 2: Pericardium: anatomy.

Linked to the epipericardial fat and cardiac surface, the pericardium is easily recognizable during image acquisition as a linear image, while the sinus and recesses (low attenuation) are formed by extensions of the pericardial cavity when the visceral layer adapts to the entry of vessels into the heart or between them.

Fig 3: Pericardium: anatomy.

Fig 4: Pericardium: anatomy.

Superior aortic recess: the superior extent of the transverse sinus.

• Anterior portion: anterior to the aorta and pulmonary artery, forming a characteristic cleft as it indents between the great vessels, occasionally including the aortopulmonary window recess.
• Posterior portion: a well-defined crescentic fluid collection adjacent to the posterior wall of the ascending aorta usually at the level of the left pulmonary artery.

Fig 5: Pericardium | serosal | visceral | transverse sinus | superior aortic recess.

• High-riding superior pericardial recess: prominent superior aortic pericardial recess with cephalic extension in the right paratracheal region, which usually has no clinical significance and can potentially simulate lymph node enlargement or bronchogenic cyst, as well other mediastinal lesions.

Fig 6: High-riding superior pericardial recess. Images from chest CT (A, B, axial, C, sagittal) and MRI (D), T2W coronal, E, T2W axial) show a high-riding superior pericardial recess (arrow) as an incidental finding, that may mimic lymphadenomegaly, specially in oncological patients.

Inferior aortic recess: the inferior extent of the transverse sinus, between the ascending aorta and the right atrium. Its caudal extent is at the level of the aortic valve annulus.

Fig 7: Pericardium | serosal | visceral | transverse sinus | inferior aortic recess.

Right pulmonic recess: the lateral extent of the transverse sinus. Inferior to the proximal right pulmonary artery, it is bounded by the reflection of serous pericardium extending from the right pulmonary artery to the superior vena cava.

Fig 8: Pericardium | serosal | visceral | transverse sinus | right pulmonic recess.

Left pulmonic recess: the lateral extent of the transverse sinus. It is bounded superiorly by the left pulmonary artery; inferiorly by the left superior pulmonary vein; and medially by the ligament of Marshall.

Fig 9: Pericardium | serosal | visceral | transverse sinus | left pulmonic recess.

Posterior pulmonic recess: It arises from the superior margin of the oblique pericardial sinus, posterior to the right pulmonary artery and medial to the bronchus intermedius.

Fig 10: Pericardium | serosal | visceral | oblique sinus.

Right pulmonic venous recess: between the right superior and inferior pulmonary veins, posterior to the left atrium.

Left pulmonic venous recess: between the left superior and inferior pulmonary veins, posterior to the left atrium.

Post-caval recess: a diverticulum of the pericardial cavity proper, posterior to the superior vena cava, bounded by the right pulmonary artery and the right superior pulmonary vein.

Fig 11: Pericardium | serosal | visceral | pericardial cavity proper.

TURNING AROUND THE PERICARDIUM AND BEYOND…

Pericardial agenesis: rare condition that is frequently misdiagnosed due to a lack of symptoms and clinical awareness, characterized by the absence of the pericardium to varying degrees. If only a small portion of the pericardium is absent, it is known as a pericardial defect.

Fig 12: Pericardial defect. Axial images from chest CT show a "tongue" of lung tissue interposing between the main pulmonary artery and aorta (arrow), considered a very specific sign, associated with levoposition of the heart (B). For comparison, note the inset in A with the representation of a normal pericardium and its relationship with de adjacent lung (asterisk).

Pericardial cyst: classically, it is considered a congenital anomaly in which incomplete fusion during embryogenesis leads to herniation or weakness in the pericardial sac, forming a cyst or diverticulum, usually filled with clear fluid. Less frequently, it is acquired, such as after cardiothoracic surgery, pericarditis, trauma, or in patients on chronic hemodialysis. In most cases, pericardial cysts are incidental findings. Rarely, they can become symptomatic and require treatment or intervention.Statistically, pericardial cysts are most common at the right cardiophrenic angle (51 to 70%) and less common at the left cardiophrenic angle (22 to 38%). Mediastinal locations not adjacent to the diaphragm account for approximately 8 to 11%.

Fig 13: Pericardial cyst. Images from chest CT scan (A, coronal, B, axial, C, sagittal) and cardiac MRI (D, four-chamber view, E, short axis Triple IR) show a small thin-walled, sharply defined with lobulated contours image with and cystic appearance (homogeneously hypoattenuating on CT and with high signal on MRI), in right cardiophrenic angle (arrow).

Fig 14: Pericardial cyst. Images from chest CT scan (A, axial, B, coronal) show a thin-walled, sharply defined, oval, homogeneous and hypoattenuating image measuring 7.4 cm in diameter in right costophrenic angle (arrow). . Its attenuation is near that of water (~14 UH).

Calcification of pericardial cysts is extremely rare.

Fig 15: Calcified pericardial cyst. Axial images from chest CT scan show an oval image with peripheral calcifications (arrow), without enhancement after administration of intravenous contrast medium (B), in the upper portion of the anterior mediastinum, anterior to the great vessels.

Pericardial diverticulum: they are differentiated from congenital pericardial cysts by the presence of direct communication with the pericardial cavity. They can change in size depending on body position, with symptoms related to changes in the patient's position. Pericardial effusion, sometimes associated with heart lesions causing cardiac enlargement, is a frequent factor in the formation of diverticula.

Fig 16: Pericardial diverticulum. Images from chest CT scan (A, D, axial, B, E, coronal, C, F, sagittal) show a well-defined and low-attenuation image in the anterior mediastinum, anterior to the superior vena cava and on the right side of the ascending aorta, which presented complete spontaneous resolution in a 2-month follow-up (bottom line).

Fig 17: Pericardial diverticulum. Images from chest CT scan (A, B, axial, C, coronal, D, sagittal) show a a well-defined and low-attenuation outpouching image (arrow) arising from the anterior portion of the superior aortic recess, communicating with the pericardial cavity. Note that the diverticulum may mimic a lymphadenomegaly. Pitfall | Lymphadenomegaly. Axial images from chest CT scan show lymphadenopathy (arrow) resembling a pericardial recess in a patient with prostate cancer. Images (E) correspond to the August 2022 examination, while (F) refers to the March 2022 examination.

Pericardial effusion and thickness: Usually, the pericardial space contains only a small amount of pericardial fluid (normally between 10–50 mL), produced by the visceral pericardial cells. This fluid resembles an ultrafiltrate of plasma and serves to lubricate and reduce friction between the visceral and parietal pericardial surfaces.

• Pericardial effusion evaluated by axial methods:
  • Mid: < 10 mm
  • Moderate: 10-20 mm
  • Severe: > 20 mm
• Normally the pericardium is < 2 mm thick.

Fig 18: Evaluation of pericardial effusion and thickness using axial methods.

In normal situations, the pericardium has a small capacitance reserve that can accommodate only small increases in cardiac chamber size and/or pericardial fluid volume of about 150–250 mL before significant increases in pericardial pressure occur. Once the pericardial capacitance reserve is reached, any further increase in contained volume dramatically raises pericardial pressure as this occurs on the steep incline part of the pressure–volume curve.

Fig 19: The relationship between the speed of onset of pericardial effusion and the pressure developed due to pericardial distension and tamponade.

Fig 20: Pericardial effusion and pericardiocentesis. Images from chest X-ray (A) show a globular cardiac shadow enlargement (A) confirmed at CT scan (B, coronal, C, axial, D, sagittal) as pericardial effusion (asterisk). (E) axial and (F) sagittal images follow-up show soft tissues stranding (arrow) of the thoracoabdominal wall, anteroinferior to the xiphoid process of the sternum, and the lower portion of the anterior mediastinum related to the recent interventional procedure (pericardiocentesis) to drain the pericardial effusion.

Fig 21: Pericardial drain. Images from chest X-ray (A) and axial chest CT scan (B) show a pericardial drain (arrow) for pericardial effusion.

Fig 22: Acute pericarditis. 29-year-old male patient with acute chest pain. Images from cardiac CTA scan (A, four-chamber view, B, short-axis view MIP) and cardiac MRI (E, axial T1 FS G+, F, triple IR) show diffuse pericardial thickening with edema associated with discrete epipericardial fat stranding. There was no detectable coronary atheromatosis, nor coronary luminal narrowing (D).

Fig 23: Constrictive pericarditis | armoured heart | Panzerherz. Images from chest CT scan (A, axial, B, coronal MIP, C, D, volume-rendered three-dimensional) and cardiac MRI (E, four-chamber view, F, G, short-axis view) show circumferential pericardial calcification in the atrioventricular transition and basal segments of both ventricles (arrow), associated with local diastolic disfunction.

Pneumopericardium: represents gas within the pericardium, surrounding the heart. Underlying causes may include positive pressure ventilation, thoracic surgery or pericardial fluid drainage, trauma, infection with gas-producing organisms, and fistulas.

Fig 24: Pneumopericardium. Images from chest X-ray (A) and CT scan (B, C, volume-rendered three-dimensional reconstruction, D, coronal, E, axial, F sagittal) show spontaneous pneumopericardium (arrow) and discrete apical pneumothorax (arrowhead) in a patient with invasive mechanical ventilation and marked involvement of the small airways.

Epipericardial fat necrosis: It is related to the torsion of the epicardiac fat and is a self-limited condition. Combining the clinical presentation with the typical CT findings is usually sufficient to make an accurate diagnosis and obviate the need for unnecessary interventions.

Fig 25: Epipericardial fat necrosis. Images from chest CT scan (A, axial, B, coronal, C, sagittal) show an epicardiac, well-encapsulated, fat-containing, space-occupying abnormality, with internal soft-tissue heterogeneity and surrounding focal stranding associated with focal adjacent pericardial thickening on the right side (arrow). Note the pleural effusion on the right (arrowhead).

Fig 26: Epipericardial fat necrosis. Images from chest CT scan (A, axial, B, coronal, C, sagittal) show an epicardiac, well-encapsulated, fat-containing, space-occupying abnormality, with surrounding focal stranding associated with focal adjacent pericardial thickening on the left side (arrow). Note the pleural effusion on the left (arrowhead).

Shared-sheath aortic dissection: acute aortic dissection is a life-threatening condition, and a mediastinal hematoma dissecting the pulmonary artery sheath is considered a rare complication that can simulate pulmonary thromboembolism and vasculitis. This generally occurs because, just above the aortic valve, the ascending aorta and the pulmonary artery trunk share a common adventitia, which caudally becomes the visceral pericardium.

Fig 27: Shared-sheath aortic dissection. 54-year-old male patient with dyspnea and chest pain. Images from chest CTA scan (A, axial non-contrast, B-E, axial, F, axial MIP, G, coronal MIP, H-K, volume-rendering three-dimensional) show Stanford type A aortic dissection with secondary hematoma (asterisk) involving the pulmonary trunk and its branches, most evident on the right with luminal narrowing in its proximal segment (black arrow). Also note there is a small mediastinal hematoma in the para-aortic and sub-aortic regions (arrowhead) with intimal calcification displacement (white arrow).

Neoplasm

Fig 28: Intrapericardial paraganglioma. (A, B) Axial CT scans, (C) axial two-dimensional fluorine 18 (18F) fluorodeoxyglucose (FDG) PET/CT scan, and (D, E) volume-rendered three-dimensional reconstruction show a low-attenuation nodule (arrow), measuring 2.6 cm, with intense and heterogeneous postcontrast enhancement, central nonenhancing areas, and 18F-FDG uptake (maxim standardized uptake value, 9.3) surrounded by the inferior border of artic arch, the posterior border of ascending aorta, the upper border of the right main pulmonary artery, and the anterior border of the trachea and proximal left main bronchus. Note its relationship with the posterior portion of the superior aortic recess (arrowheads). (A) Photomicrograph shows encapsulated paraganglioma with tumor cells arranged in solid nests with sustentacular cells, vascular stroma, and abundant eosinophilic cytoplasm, without mitotic figures, involvement of intracapsular vessel, or areas of necrosis. (Hematoxylin-eosin stain; original magnification, ×100; inset original magnification, ×400.) (B) The tumor is diffusely positive for chromogranin-A. (Chromogranin-A immunohistochemical staining; original magnification, ×250.) (C) The sustentacular cells are prominent with S100 staining. (Original magnification, ×400).

Fig 29: Pericardial carcinomatosis and effusion. Male patient with lung cancer. Images from chest CT scan (A, axial, B-D, coronal oblique) show pericardial thickening associated with nodules distributed circumferentially. Note the left ventricular myocardial involvement (arrowhead).

Foreign body

Fig 30: Foreign body. 72-year-old male patient with previous myocardial revascularization (20 years ago). Images from coronary CT scan (A, B, axial, C, D, volume-rendered three-dimensional reconstruction) show a curvilinear image with high density next to the pericardium and epicardium in the apical lateral segment of the left ventricle (arrow), which may be related to a suture needle associated with the previous surgical manipulation.