Normal Haller Index: CT Measurement for Pectus Excavatum
The Haller Index (HI) is a CT-derived ratio used to quantify the severity of pectus excavatum, the most common congenital chest wall deformity. It is calculated by dividing the transverse (widest internal) diameter of the thorax by the shortest anteroposterior distance between the sternum and vertebral body on axial CT. Accurate measurement guides surgical decision-making and helps predict cardiopulmonary compromise.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Axial | <2.5 |
Clinical Significance
A normal Haller Index is less than 2.5, reflecting a symmetric, uncompressed thoracic cavity. As the index rises, the sternal depression increasingly displaces mediastinal structures, potentially impairing cardiac filling and reducing pulmonary reserve. Most surgical centers use a threshold of ≥3.25 as a primary criterion for operative intervention (Nuss or Ravitch procedure), though clinical symptoms, pulmonary function tests, and echocardiographic findings are always considered alongside the index.
A markedly elevated HI (>3.5–4.0) correlates with greater cardiopulmonary compromise and may predict more complex surgical repair. Pitfalls include asymmetric deformities, where a single axial slice may under- or overestimate severity, and patient positioning, which can alter AP diameter. Serial measurements should be taken at the level of maximum sternal depression for consistency.
- Pectus excavatum — primary indication; HI ≥3.25 supports surgical referral
- Marfan syndrome / connective tissue disorders — associated with exaggerated HI
- Cardiac compression / mitral valve prolapse — may accompany high HI values
- Restrictive pulmonary physiology — seen when thoracic volume is significantly reduced
- Post-operative assessment — HI used to confirm correction after Nuss bar placement
Reference: Haller JA, Kramer SS, Lietman SA. Use of CT scans in selection of patients for pectus excavatum surgery: a preliminary report. J. Pediatr. Surg. 1987;22(10):904-6.
Imaging Notes
The Haller Index is measured exclusively on axial CT at the level of maximum sternal depression. The transverse diameter is drawn between the inner aspects of the ribs at their widest point on the same slice. The anteroposterior diameter is the shortest distance from the posterior surface of the sternum to the anterior cortex of the vertebral body. Both measurements must be made on the same axial image to ensure ratio validity.
Standard chest CT without contrast is sufficient for index calculation; however, contrast-enhanced or cardiac-gated studies may be obtained when concurrent cardiac pathology is suspected. Multiplanar reformats can help identify the true level of maximum depression before selecting the reference axial slice, improving reproducibility across readers.