Hacking C, Ismail M, Thibodeau R, et al. Atlantodental interval. Reference article, Radiopaedia.org (Accessed on 26 Mar 2025) https://doi.org/10.53347/rID-40483
The anterior atlantodental interval is the horizontal distance between the posterior cortex of the anterior arch of the atlas (C1) and the anterior cortex of the dens in the median (midsagittal) plane 2. Posterior atlantodental interval (PADI) is the horizontal distance between the posterior cortex of the dens to the posterior arch of the C1 in the median (midsagittal) plane.
The lateral atlantodental interval is the horizontal distance between the lateral cortex of the dens and the medial cortex of the lateral masses of the atlas. The normal value is 3.4 mm in either right or left atlantodental interval. However, normal asymmetry between right and left atlantodental interval can vary up to 0.76 mm. Therefore, asymmetry in lateral atlantodental interval is not a sensitive or specific sign of atlanto-occipital dissociation injuries 2.
Interpretation
Normal values for anterior atlantodental interval (AADI) are:
radiographs
adults
males: <3 mm
females: <2.5 mm 1 (although some authors do not specifically differentiate from males)
children: <5 mm 4-7
CT
adults: <2 mm 1
children: <2.6 mm 5
Normal value for posterior atlantodental interval (PADI) is >15mm7.
1. Rojas C, Bertozzi J, Martinez C, Whitlow J. Reassessment of the Craniocervical Junction: Normal Values on CT. AJNR Am J Neuroradiol. 2007;28(9):1819-23. doi:10.3174/ajnr.a0660 - Pubmed
2. Chen Y, Zhuang Z, Qi W et al. A Three-Dimensional Study of the Atlantodental Interval in a Normal Chinese Population Using Reformatted Computed Tomography. Surg Radiol Anat. 2011;33(9):801-6. doi:10.1007/s00276-011-0817-7 - Pubmed
3. Marathe N, Mhatre P, Bhaladhare S, Dahapute A, Sharma A, Mallepally A. Plain Roentgenographic and CT Scan Morphometric Analysis of the Anterior Atlantodens Interval (AADI) and Posterior Atlantodens Interval (PADI) in the Indian Population. Surg Neurol Int. 2021;12:427. doi:10.25259/sni_679_2021 - Pubmed
4. Kaufman R, Carroll C, Buncher C. Atlantooccipital Junction: Standards for Measurement in Normal Children. AJNR Am J Neuroradiol. 1987;8(6):995-9. PMC8332327 - Pubmed
5. Bertozzi J, Rojas C, Martinez C. Evaluation of the Pediatric Craniocervical Junction on MDCT. AJR Am J Roentgenol. 2009;192(1):26-31. doi:10.2214/ajr.08.1058
6. Hinck V & Hopkins C. Measurement of the Atlanto-Dental Interval in the Adult. Am J Roentgenol Radium Ther Nucl Med. 1960;84:945-51. - Pubmed
7. Marathe N, Mhatre PP, Bhaladhare S, Dahapute A, Sharma A, Mallepally AR. Plain roentgenographic and CT scan morphometric analysis of the anterior atlantodens interval (AADI) and posterior atlantodens interval (PADI) in the Indian population. Surg Neurol Int. 2021 Aug 24;12:427. doi: 10.25259/SNI_679_2021. PMID: 34513190; PMCID: PMC8422433.
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