Normal Retrotracheal Space Diameter at C5 on Radiography
The retrotracheal space is the soft-tissue interval located posterior to the trachea and anterior to the cervical vertebral bodies, best assessed on the lateral neck radiograph at the C5 level. Accurate measurement of this space is essential in pediatric patients, as abnormal widening can indicate a clinically significant retropharyngeal or paratracheal mass, abscess, or hemorrhage requiring prompt intervention.
Normal Reference Values
| Orientation | Age | Measurement |
|---|---|---|
| Lateral | 0-1 y/o | 2.0 cm |
| Lateral | 1-2 y/o | 1.5 cm |
| Lateral | 2-14 y/o | 1.2 cm |
Clinical Significance
In children, the retrotracheal space demonstrates predictable age-related maximal diameters at C5 on lateral radiography. Values exceeding the established upper limits for the patient’s age group should raise concern for pathological soft-tissue enlargement. Importantly, measurements can be falsely elevated if the radiograph is obtained in expiration or with the neck in flexion, leading to pseudo-widening — a critical technical pitfall to recognize before pursuing further workup.
When the retrotracheal space is genuinely widened, the differential diagnosis should be systematically approached. Common and important considerations include:
- Retropharyngeal abscess or cellulitis — most common infectious cause in children under 6 years
- Retropharyngeal hematoma — following trauma or bleeding diathesis
- Lymphadenopathy — reactive or neoplastic (e.g., lymphoma)
- Cervical spine fracture with prevertebral edema — always correlate with clinical history
- Neoplastic mass — neuroblastoma, rhabdomyosarcoma, or metastatic disease in the pediatric population
Reference: Hay PD, Jr. The Neck: A roentgenological study of the soft tissues: Consideration of the normal and pathological. III. Normal necks (infants and children). Ann Roentgenol Vol 9. New York: Hoever, 1930, p22.
Imaging Notes
The retrotracheal space at C5 is measured on a true lateral neck radiograph with the patient in full inspiration and the neck in neutral extension. The measurement is taken as the maximal anteroposterior soft-tissue width between the posterior tracheal wall and the anterior cortex of the C5 vertebral body. Consistent technique is paramount — expiratory or flexed-neck films may increase apparent soft-tissue thickness by up to 50%, mimicking pathology.
While radiography remains the first-line screening tool, equivocal or abnormal findings should prompt cross-sectional imaging with CT (with contrast) or MRI to further characterize the extent and nature of soft-tissue pathology, particularly when abscess or neoplasm is suspected.