Pericardium

The pericardium is a conical, flask-like, fibroserous sac which contains the heart and the roots of the great vessels and defines the middle mediastinum. 

Gross anatomy

The pericardium is made of two sacs in one. The outer sac is the fibrous pericardium and the inner sac is the double-layered serous pericardium. Layers of serous pericardium are divided by the pericardial space, which only contains 15-50 mL of serous fluid. They have quite different structures:

• fibrous pericardium: tough connective tissue continuous with and bound to the central tendon of the diaphragm, the roots of the great vessels, the pretracheal layer of the deep cervical fascia and the sternum via the superior (to manubrium) and inferior sternopericardic ligaments (to xiphoid process)
• serous pericardium: composed of a single layer of flattened mesothelial cells forming a closed sac and forms two continuous layers:
  • visceral serous pericardium (or epicardium): covers heart and great vessels
  • parietal serous pericardium: lines the fibrous pericardium and is inseparable

The serous pericardium is invaginated by the heart and great vessels forming two sinuses:

• oblique sinus: formed by the superior and inferior vena cavae and the four pulmonary veins (blind-ending) and thus sits posterior to the left atrium
  • may be mistaken for oesophageal masses or bronchogenic cysts ³
• transverse sinus: lies between the aorta/pulmonary artery anteriorly and the atria posteriorly, surrounding the ascending aorta; there are several recesses that may be mistaken for dissection or lymphadenopathy ³
  • ​superior aortic recess
  • right pulmonic recess
  • left pulmonic recess
  • postcaval recess

Relations

• anteriorly: body of the sternum, cartilages of left third-to-seventh ribs, pleura and lungs, and thymus (in children)
• posteriorly: oesophagus, descending thoracic aorta, pleura and lungs
• laterally: pleura and lungs, phrenic nerves
• inferiorly: blends with central tendon of diaphragm

Blood supply

• arterial supply
  • internal thoracic artery and its pericardiacophrenic and musculophrenic branches
  • branches from the descending thoracic aorta
• venous drainage: pericardiacophrenic veins

Innervation

• phrenic nerves: to fibrous and parietal serous layers
• vagus nerve
• sympathetic trunks: for pain, muscles and vessels of heart

Variant anatomy

• pericardial agenesis

Radiographic appearance

CT

• pericardium appears as a thin high-density line between the lower-density mediastinal and epicardial fat
• fibrous and serous pericardium cannot be delineated and the upper limits of normal for pericardial thickness is 2 mm ²
• often not imaged over the left ventricle ³

MRI

• T1WI and T2WI: appears as a low signal rim between the higher-signal mediastinal and epicardial fat ^2-3

Related pathology

• pericardial agenesis
• pericardial effusion
  • fetal pericardial effusion
• pericardial tamponade
• pneumopericardium
• pericarditis
• pericardial cyst
• pericardial calcification
• pericardial tumours
  • pericardial teratoma
    • fetal pericardial teratoma