Therefore, in children, the diagnosis of os odontoideum is confirmed by showing relative motion between the odontoid and the body of the axis. In os odontoideum, there is a joint-like articulation between the odontoid and the body of the axis that appears radiologically as a wide radiolucent gap that may be confused with the normal neurocentral synchondrosis before 5 years of age. Two types have been described in the literature: Orthotopic and dystopic. The origin of os odontoideum remains debated in the literature with evidence for both acquired and congenital causes. The definition of an os odontoideum is uniform throughout the literature: An ossicle with smooth circumferential cortical margins representing the odontoid process that has no osseous continuity with the body of C2. It is the most common developmental anomaly of odontoid. TOF, flexion-extension, and PC-CSF flow study was done wherever indicated. Standard sagittal T1, T2 axial T1, T2 and gradient echo (GRE) and coronal T2W sequences were taken. The imaging parameters were: T1 and T2 turbo spin-echo with a repetition time (TR)/echo time (TE) of 400//110 ms, respectively section thickness/gap was 3.0/0.3 mm field of view (FOV) 260 × 220 mm and matrix size 288 × 256. Phase-contrast CSF flow study aids further in surgical decision-making and patient management.Īll patients were examined at our institution by using 1.5 T MR scanner in neutral positioning and spine coil. 2D and 3D time-of-flight (TOF) methods can help in detection of underlying vascular pathology. Dynamic MRI in flexion, extension, and neutral positions offers special role in diagnosis of AAD. Reconstruction was done with a slice thickness of 1.0 mm.ĭue to its multiplanar capabilities and excellent delineation of neural structures and ligaments, MRI has become the imaging modality of choice. Imaging parameters were as follows: 0.5 mm slice thickness, 0.75 s/rotation, 120 kV, and 300 mA. It also helps with craniometric measurements that cannot be accounted by plain radiographs.Īt our institution, CT was done on a 40-slice MDCT scanner. Multidetector computed tomography (MDCT) with isotropic resolution and multiplanar reformations has enabled better visualization of complex bony abnormalities. It forms Clivus Canal angle along the posterior surface of the axis body Craniometric measurements (A) Solid black: ADInormal is 13 mm Dotted white: Chamberlain's line and solid white: Mc Rae Line (B) White: Wecken-Heim Clivus base line: It should fall tangent to the posterior aspect of the tip of the odontoid.
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