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Straight Back Syndrome

General Considerations

  • Loss of normal kyphotic curve of thoracic spine associated with an abnormally short anterior-posterior dimension to the chest causing compression of the heart

Clinical Findings

  • Most are asymptomatic
  • Systolic ejection murmur, possibly made louder by chest compression
  • About half of cases are associated with mitral valve prolapse
  • Palpitations
  • Chest pain

Imaging Findings

  • Loss of the normal kyphosis of the thoracic spine
  • The cardiothoracic ratio is usually less than 50%
  • In some cases, there may be a leftward shift of the heart and prominence of the main pulmonary artery
  • There is a narrow AP diameter of the thorax as measured on the lateral chest radiograph from the anterior border of T8 to the posterior border of the sternum (“a” below)
    • In most cases, the absolute measurement of a narrow AP diameter in 10-11 cm or less
  • Or the measurements can be expressed as a ratio of that AP diameter to the lateral diameter of the chest cage at the level of the diaphragm (“b” below)
    • The ratio should be less than 1/3

From Clinical Topics in Japan
Straight Back Syndrome and Respiratory Failure
JMAJ 49 (4): 176-179, 2006.
Masayuki Kambe


Differential Diagnosis

  • Pectus excavatum defect


  • Monitor if mitral valve prolapse is present


  • Good, even if associated with mitral valve prolapse

Straight Back Syndrome. If the ratio of the distance between the anterior body of T8 and the posterior sternum (yellow arrow) to the transverse diameter of the thorax measured at the level of the diaphragm (red arrow), is less than 1/3, then suspect Straight Back Syndrome. The normal kyphotic curve of the thoracic spine is lost and, in fact, is lordotic in this patient (white arrow).
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The Straight-Back Syndrome: Radiographic Manifestations. HL Twigg, AC de Leon, JK Perloff, and M Majd. February 1967 Radiology, 88, 274-277.


Clinical Topics in Japan. Straight Back Syndrome and Respiratory Failure. M Kambe. JMAJ 49 (4): 176-179, 2006.