Abnormal Situs and Cardiac Malposition

27 Abnormal Situs and Cardiac Malposition

With Kevin S. Roman

Definition and Classification

  • image Normally, body organs show asymmetric arrangement (Table 27.1). Situs refers to the pattern of arrangement of the body organs relative to the midline.
  • image Situs of the abdominal organs, bronchopulmonary system, and atria should be designated separately. The types of situs at three levels are concordant in the majority of cases (visceroatrial concordance rule), but there are rare exceptions (Fig. 27.1).

    • • Situs solitus: usual arrangement
    • • Situs inversus: mirror-image arrangement
    • • Heterotaxy: neither solitus nor inversus

      • – Characterized by jumbled arrangement of the abdominal organs
      • – Bronchopulmonary anatomy is symmetric or isomeric, both sides resembling the arrangement of the normal right or left side: bronchopulmonary right and left isomerisms.
      • – Atrial anatomy is also symmetric or isomeric, both sides showing the characteristic morphologies of the normal right or left atrium: right or left atrial isomerisms.

  • image Right isomerism refers to bilateral right-sided anatomy and is associated with asplenia.
  • image Left isomerism refers to bilateral left-sided anatomy and is almost always associated with polysplenia.
  • image Cardiac position is independent of body situs. Any cardiac position can be associated with any type of body situs.
  • image Cardiac malposition is defined as any combination of situs and cardiac position other than a combination of situs solitus and levocardia.
  • image Incidence of congenital heart diseases according to types of situs and position of the heart:

    • • Situs solitus: 8–10/1000

      • – Almost always in situs solitus with dextrocardia or mesocardia in which congenitally corrected transposition of the great arteries is the most common

    • • Situs inversus: frequent

      • – Approximately 10 to 50% in situs inversus with dextrocardia
      • – Almost always in situs inversus with levocardia or mesocardia

    • • Right isomerism: 100%
    • • Left isomerism: almost always (Tables 27.2, 27.3)

Table 27.1 Features Characterizing Normal Asymmetry of Body Organs

Right Left
Abdominal organs • Larger lobe of the liver • Spleen and stomach
Lung lobation • Three lobes • Two lobes
Main bronchus • Short, eparterial • Long, hyparterial
Pulmonary artery • Transverse course in front of the right main bronchus • Oblique course crossing over the left main bronchus (epbronchial course)

• Origin of the first branch proximally in the mediastinum • Origin of the first branch distally at the hilum
Atrium • Triangular appendage with wide junction demarcated by crista terminalis • Finger-like appendage with narrow junction not demarcated by crista terminalis

• Pectinate muscles extending to the atrioventricular junction • Pectinate muscles confined to the appendage

• Fossa ovalis with limbus • No fossa ovalis

Clinical Manifestations


Fig. 27.1 Types of visceral and atrial situs; GB, gallbladder; IVC, inferior vena cava; LA, left atrium; PA, pulmonary artery; RA, right atrium; SVC, superior vena cava.

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Jan 14, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Abnormal Situs and Cardiac Malposition
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Table 27.2 Common Congenital Cardiac Defects in Right and Left Isomerism

Right Isomerism Left Isomerism
Bilateral superior venae cavae 45% 45%
Bilateral systemic venous drainage 70% 60%
Absence of coronary sinus ~100% ~60%
Interruption of the inferior vena cava <2.5% 80%
Juxtaposition of the aorta and inferior vena cava ~90% Uncommon
Extracardiac type of total anomalous pulmonary venous connection with/without obstruction 50%, with obstruction in 50% Rare
Pulmonary venous connection to ipsilateral atriums 4% 45%
Atrioventricular septal defect 90% 50%
Atrial septum Functionally common atrium in 50%