Normal Dublin’s Distance Size: Radiography, CT & MRI
Dublin’s Distance refers to the measured gap between the mandible and the upper cervical spine — specifically from the mandible to the atlas (C1) and to the axis (C2) — assessed on lateral cervical imaging. These measurements serve as indirect indicators of craniocervical alignment and the patency of the upper airway and retropharyngeal space. Accurate assessment is particularly relevant in trauma, congenital anomalies, and surgical planning of the craniocervical junction.
Normal Reference Values
| Orientation | Location | Measurement |
|---|---|---|
| Lateral | Mandible – Atlas Distance | 2-5 mm |
| Lateral | Distance Mandibule – Axis | 9-12 mm |
Clinical Significance
Under normal conditions, the mandible-to-atlas distance measures 2–5 mm and the mandible-to-axis distance measures 9–12 mm on a true lateral projection. Deviation from these ranges can signal craniocervical instability, basilar invagination, or retropharyngeal soft-tissue swelling compressing the upper cervical structures.
Reduction in Dublin’s Distance — particularly narrowing of the mandible–atlas interval — may indicate upward migration of the odontoid process (cranial settling) or atlantoaxial instability. Conversely, increased distance can be associated with retropharyngeal hematoma, abscess, or soft-tissue edema following trauma or surgery. These measurements are especially useful in pediatric patients and in conditions such as rheumatoid arthritis and Down syndrome where craniocervical instability is prevalent.
- Basilar invagination — odontoid projects superiorly, reducing mandible–atlas space
- Atlantoaxial instability — may alter alignment and interval measurements
- Retropharyngeal abscess or hematoma — increases apparent distance due to soft-tissue mass
- Cranial settling in rheumatoid arthritis — progressive reduction of Dublin’s Distance
- Post-traumatic craniocervical dissociation — abnormal distraction or compression alters both intervals
Reference: Fessler R, Sekhar L. Atlas of Neurosurgical Techniques, Spine and Peripheral Nerves. TNY. (2006).
Imaging Notes
On lateral radiography, Dublin’s Distance is measured from the posterior cortex of the mandibular symphysis to the anterior arch of the atlas and separately to the anterior body of the axis. Patient positioning is critical — the head must be in neutral position without rotation or flexion to avoid spurious measurements. On CT, sagittal reformats through the midline provide the most reproducible measurements, allowing simultaneous assessment of bony landmarks and surrounding soft tissue. MRI sagittal sequences (T1 or T2) are preferred when soft-tissue pathology or ligamentous injury is suspected, enabling direct visualization of the retropharyngeal space and craniocervical ligaments alongside the distance measurements.