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David A. Besachio, Ziyad Khaleel and Lubdha M. Shah


Posterior odontoid process inclination has been demonstrated as a factor associated with Chiari malformation Type I (CM-I) in the pediatric population; however, no studies to date have examined this measurement in the adult CM-I population. The purpose of this study was to evaluate craniocervical junction (CCJ) measurements in adult CM-I versus a control group.


The odontoid retroflexion, odontoid retroversion, odontoid height, posterior basion to C-2 line measured to the dural margin (pB-C2 line), posterior basion to C-2 line measured to the dorsal odontoid cortical margin (pB-C2* line), and clivus-canal angle measurements were retrospectively analyzed in adult patients with CM-I using MRI. These measurements were compared with normative values established from CT scans of the cervical spine in adults without CM-I.


A statistically significant difference was found between 55 adults with CM-I and 150 sex-matched controls (125 used for analysis) in the mean clivus-canal angle and the mean pB-C2 line.


These data suggest that there are sex-specific differences with respect to measurements at the CCJ between men and women, with women showing a more posteriorly inclined odontoid process. There were also differences between the CM-I and control groups: a more acute clivus-canal angle was associated with CM-I in the adult population. These CCJ findings could have an influence on presurgical planning.

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Ziyad L. Khaleel, David A. Besachio, Erica F. Bisson and Lubdha M. Shah


Posterior odontoid process inclination has been associated with Chiari malformation Type I in the pediatric population. There are varying reports to support a reliable range of odontoid inclination angles in control adults. The purpose of this study is to estimate the normal measurements in adults for odontoid retroflexion, retroversion, height, and the pB–C2 line (a line drawn through the odontoid tip from the ventral dura perpendicular to a second line from drawn the basion to the inferoposterior aspect of C-2 vertebral body) to establish a normative reference in this population.


After obtaining institutional review board approval, the authors performed a retrospective analysis of non–contrast enhanced cervical spine CT scans obtained in 150 consecutive control adults. Three neuroradiologists measured odontoid retroflexion, odontoid retroversion, odontoid height, and the pB–C2 line. The cohort was divided into sex and two age groups. Comparisons of the means with unpaired 2-tailed t-test were performed.


A total of 125 subjects met the inclusion criteria; 80 were men and 45 were women (mean age 52 years, range 18–89 years). The odontoid retroflexion angle ranged from 70° to 89° (mean 79.3° ± 4.9°), and the odontoid retroversion angle ranged from 57° to 87° (mean 71.9° ± 5.3°). The range and mean of odontoid height were 17–27 mm and 22 ± 1.8 mm, respectively. The mean pB–C2 line was 6.5 ± 2.1 mm with a range of 0–11.2 mm. The results were also compared with previously published pediatric data.


The current study demonstrates that the odontoid process in adults is anatomically different from that in children: it is longer, more posteriorly inclined, and has a greater pB–C2 line. Therefore, utilization of these parameters with previously published cutoffs in the pediatric population is not appropriate for surgical planning in adults.

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Toba N. Niazi, Lubdha M. Shah, Steven S. Chin and Meic H. Schmidt

Tailgut cysts are developmental cysts that arise from remnants of the embryonic postanal gut and are typically located within the presacral, retrorectal space. Isolated cases of aberrant locations, including prerectal, perirenal, perianal, retrovesical, and subcutaneous locations, have been reported. Malignant transformations with the presence of adenocarcinomas or carcinoids have been recognized within these entities. It is well recognized that anterior sacrococcygeal abnormalities are present and are frequently caused by the slow-growing nature of the tailgut cysts and related mass effect; however, the authors are aware of no reports in the literature of isolated tailgut cysts within the thecal sac in direct contact with neural elements, without extension into the peritoneal cavity. In this case, a 28-year-old woman presented with progressive back pain, frequent urinary tract infections, and bowel dysfunction. She was found to have a purely intradural tailgut cyst with malignant transformation consistent with carcinoid. No peritoneal extension of her disease was found. The authors hypothesize that this is a rare developmental aberration that has not been commonly recognized and potentially has implications for embryological development.