Radiographic Findings by Diagnosis: Situs and Complex Congenital Abnormalities

Key Points

▪

The chest radiograph can assist with establishing “situs” by identifying the orientation of the apex, the side of the aortic arch, and the stomach (gastric air bubble).
▪

The chest radiographic findings of complex disorders reflect not only the underlying abnormality but also often the interventions and their successes and complications.
▪

The classic physiology of Eisenmenger syndrome is represented on the chest radiograph by enlargement and centralization (“pruning”) of the pulmonary arterial vasculature, diminished pulmonary venous vasculature, and right heart enlargement.

Situs

Situs refers to the position/arrangement of the thoracic and abdominal organs ( Figs 20-1 to 20-5 ). The posteroanterior/frontal chest radiograph is able to depict the location of the heart, the left ventricular apex, the aorta, and the gastric air bubble, and it may thereby determine situs.

There are three patterns of situs and one variable pattern:

1.

Situs solitus
2.

Dextrocardia
3.

Situs inversus
4.

Situs ambiguous/indeterminate situs/heterotaxy

Situs Solitus

Situs solitus is the term for the normal arrangement of thoracic and abdominal organs ( Table 20-1 ).

□

Dextrocardia: (where the apex is) heart in the right side of the chest; refers to “reversal of the heart” position in the chest or of its structures. The incidence is less than 1:10,000
□

DextroVERSION: ventricular loop
□

Dextrocardia of embryonic arrest (situs solitus and a right-sided heart): heart located rightward in the chest, with the other organs in their normal positions (left gastric air bubble, left aortic arch). With dextrocardia of embryonic arrest/situs solitus with a right-sided heart, there is a 98% incidence of associated congenital heart disease, and 80% of affected individuals have anatomically corrected transposition of the great arteries. The next most frequent association of situs solitus and a right-sided heart is with a ventricular septal defect and pulmonary stenosis.
□

Dextrocardia situs inversus: reversal/mirroring of the orientation of the heart chambers. The incidence is less than 1:30,000 (3.3% of cases of dextrocardia).
□

Dextrocardia situs inversus totalis: reversal/mirroring of all visceral organs as well as the heart. Ninety to 95% of patients with situs inversus totalis do not have associated congenital heart disease, and they lead normal lives. Five to 10% of patients with situs inversus totalis have associated congenital heart disease, most commonly transposition of the great arteries. Primary ciliary dyskinesia/Kartagener syndrome is present in 25% cases of situs inversus totalis. The incidence is less than 1:15,000,000 (0.02% of cases of dextrocardia situs inversus).
□

Situs inversus: left-right inversion/reversal of organ position
□

Situs inversus with levocardia: 95% associated with congenital heart disease

Table 20-1

Situs Solitus

Right-Sided	Left-Sided
Thoracic Organ
Right atrium	Left atrium
Trilobed lung	Bilobed lung
	Aorta
Abdominal Organ
Liver	Stomach
Gallbladder	Spleen
Inferior vena cava

Situs Ambiguous/Heterotaxy/Indeterminate Situs

The gastric air bubble and the aortic “knob” are on different sides; therefore, the situs is not predictable (“ambiguous”). Manifestations of ambiguous situs include the following:

□

Errors of cardiac looping
- •
  
  Tetralogy of Fallot
- •
  
  Transposition of the great arteries
- •
  
  Pulmonic stenosis
- •
  
  Atrial septal defects and ventricular septal defects
□

“Derangement” of abdominal organ symmetry
- •
  
  Isolated stomach or splenic reversal
- •
  
  Midline organs: stomach, liver, adrenal gland
□

Organ malformation
- •
  
  Asplenia/polysplenia
- •
  
  Horseshoe kidney or adrenal gland
□

Caval abnormalities
- •
  
  Inferior vena caval interruption with azygous continuation (nearly always)
- •
  
  Bilateral superior vena cava or inferior vena cava