The patient was admitted to hospital with gait disturbance, spasticity of the lower extremities, ataxia and urinary dysfunction. The symptoms had appeared 1 year prior to admission and the patient's condition was progressively deteriorating.
The patient was admitted to hospital with gait disturbance, spasticity of the lower extremities, and ataxia. She also mentioned urinary dysfunction, namely urgency. The symptoms had appeared 1 year prior to admission and the patient's condition was progressively deteriorating.
Clinical examination revealed bilateral pyramidal signs with right predominance, bilateral Babinski signs, right Barré sign and increased reflexes bilaterally with right predominance, without sensory deficiency.
The complete biochemical workout was unremarkable. The patient's medical history included a total right hip arthroplasty and osteoarthritis of the right knee. She also mentioned a head trauma 45 years previously that did not require hospitalisation.
The imaging findings are typical of os odontoideum (OO). The plain lateral radiograph shows absence of the odontoid process. It also reveals that Wackenheim's clivus baseline falls tangentially to the anterior aspect of the os instead of the posterior aspect of the tip of the odontoid process. The axial CT scans and mid-sagittal reconstructions reveal that the tip of the odontoid lies well below C1 and that the ossicle is well corticated. There is also a retrodental soft tissue mass indenting the spinal cord. The anterior arch of the atlas is hypertrophic. The mid-sagittal T2-weighted TSE and enhanced T1-weighted Spin Echo with fat-suppression MR images demonstrate atrophy and myelomalacia of the cord, the presence of the OO, a retrodental soft tissue mass and linear enhancement due to venous stasis.
The os odontoideum (OO) is a well-defined ossicle lying at the tip of the odontoid process and is about one-half the size of a normal dens (1). There is evidence that OO is an acquired rather than a congenital lesion, as it has been shown to be present after trauma in patients with a previously normal process (1). This can not be proved in the present case, as there is no imaging study before trauma.
OO is easily differentiated from condylus tertius (an ossified remnant at the distal end of the clivus) and the Bergman ossicle, since the odontoid process is normal in height in both these conditions. OO can be distinguished from an acute odontoid fracture radiographically by noting (a) the presence of a rounded or oval ossified mass possessing smooth, thin cortical borders and being smaller in size than expected for a complete odontoid process, and (b) a wide gap between the ossicle and the body of C2. However, the differentiation between an OO and an old type 2 fracture of the odontoid process may be problematic on a lateral x-ray (2). In patients with OO, the axis body has a well-corticated convex upper margin, and the anterior atlas appears hypertrophic and rounded, rather than half-moon shaped. In contrast, type 2 odontoid fracture is typically associated with a flattened uncorticated margin to the upper axis body and a normal, half-moon-shaped anterior atlas arch. In fact, it has been proposed that OO might be the result of a non-union of a type 2 odontoid fracture (3).
Because the gap between the OO and the axis body lies at or above the level of the superior articular facet of the axis, incompetence of the cruciate ligament and atlantoaxial instability can exist (4). The instability may lead to narrowing of the spinal canal and cord compression at the level of C1. In addition to the degree and/or the direction of instability, the decreased space available for the cord can also result in a reactive soft tissue lesion (5). This soft tissue retrodental mass has been reported to disappear after fixation of the unstable segment, thus obviating the need for transoral removal of the mass.
The patient in this case was referred for surgery including both a transoral approach for removing the OO and a posterior atlantoaxial fusion.
Os odontoideum
The patient is a 61-year-old female who was admitted due to an unsteady gait, spastic paralysis of the lower limbs, ataxia, and urinary incontinence for 1 year, with progressive deterioration. Based on the provided X-ray, CT, and MRI images, the following observations can be noted:
Based on the radiological findings and the patient’s clinical symptoms, the following diagnoses and differential diagnoses are considered:
Taking into account the patient’s age, progressively worsening neurological dysfunction, characteristics of the isolated bony fragment on imaging, changes in the superior margin of the C2 vertebral body, and the absence of a normal odontoid process, the most likely diagnosis is: Os Odontoideum with atlantoaxial instability and spinal cord compression.
To further clarify the diagnosis, additional past imaging data or medical history would be beneficial to exclude a nonunion of an old odontoid fracture. Furthermore, dynamic X-ray evaluation may be performed if necessary to assess atlantoaxial mobility and quantify the degree of instability.
Whether undergoing surgery or conservative management, a personalized rehabilitation program should be developed based on the patient’s specific condition. In principle, rehabilitation should restore bodily function gradually, while ensuring adequate cervical spine protection.
This report is a reference analysis based on the currently available imaging and clinical history. It cannot replace an in-person clinical evaluation or the opinion of a professional physician. Patients should seek further diagnostic tests and medical advice in a hospital setting to develop a definitive treatment and rehabilitation plan.
Os odontoideum
