Haller index

The Haller index, also known as pectus index, is a simple mathematical way to assess and describe the chest cage on CT of the chest and is used in the detection of pectus excavatum as well as preoperative and postoperative assessment^1,5.

Technique

The Haller index is calculated by dividing the transverse diameter of the chest by the anterior-posterior distance on CT of the chest on the axial slice that demonstrates the smallest distance between the anterior surface of the vertebral body and the posterior surface of the sternum ^1,5. Some authors have found that both radiographic (plain film) and CT calculated Haller indices are strongly correlated and thus recommend the use chest radiography instead of CT to minimize the radiation exposure ².

The following values are used: 

• normal chest: < 2.0
• mild excavatum: 2.0-3.2.
• moderate excavatum: 3.2-3.5
• severe excavatum: >3.5 ¹

Corrective surgery is considered for a Haller index of greater than or equal to 3.25 ⁵.

Factors affecting index

A number of factors have been identified as affecting the Haller index including at what level it is measured as well as the age and sex of the patient. 

Vertebral level

The Haller Index is affected by the vertebral level at which it is measured and is largest cranially ³. For consistency, therefore, it is recommended to calculate the largest Haller index in pectus excavatum patients by obtaining the AP diameter at the deepest point of the sternum ¹.

Age

Young age also reduces the values, with 0 to 2-year-olds having smaller Haller index than older children ⁵.

Increasing age also changes the shape of the chest cage and affects the vertebral levels by various degrees:

• cranial levels show larger Haller index in older subject
• mid-thoracic levels remain unaltered
• caudal vertebral levels show only slight increase ³

Sex

Females have greater haller index than males in early childhood (from 0-6 years of age) and in teenage years (12-18 years of age) ⁵.

History and etymology:

The Haller index is named after J. Alex Haller, Jr. MD who first described it in 1987 ⁵.