A Case of Occipitocervical Fixation for Orthotopic Os Odontoideum in a 2-year-old Child with Progressive Floppy Infant

Yosuke HASHIMOTO; Hisaaki UCHIKADO; Takehiro MAKIZONO; Chihiro TAKASHIMA; Gohsuke HATTORI; Shoko SHIMOKAWA; Motohiro MORIOKA

doi:10.2176/jns-nmc.2025-0362

Abstract

Floppy infants caused by craniocervical instability in childhood are extremely rare. Furthermore, due to underdeveloped bone structures, treatment for it is extremely difficult.

The patient was a 2-year-old boy who was referred at the age of 1 year for psychomotor developmental delay. The cause was unknown, so he was placed under observation. At the age of 2 years, he remained a floppy infant and had not yet acquired motor skills, so he was referred again. Neurologically, he was in a state of progressive motor paralysis of the limbs. Magnetic resonance imaging revealed damage to the medulla oblongata, and he was diagnosed with orthotopic os odontoideum. A C1 laminectomy was performed, with posterior fixation from a C2 translaminar screw to the occipital bone. The progression of the condition has halted, and the patient is currently undergoing rehabilitation.

Here, we report the pathological diagnosis, surgical treatment, and orthotopic os odontoideum timing, a condition presenting with progressive craniocervical instability in infants.

Introduction

Os odontoideum (OO) is a congenital or post-traumatic abnormality of the second cervical vertebrae in which the odontoid process is separated from the body of the axis by a transverse gap.¹⁾ There are 2 types of OO: normal position orthotopic and dystopic.²⁾ Most cases of OO are asymptomatic and are discovered incidentally.²⁾ However, chronic atlantoaxial dislocation (AAD) in infants with OO is extremely rare.

Here, we report a case of orthotopic OO presenting with progressive quadriplegia and a floppy infant.

Case Report

A 1-year-old boy was referred to our hospital due to motor and mental retardation. A mild floppy infant with delayed head positioning and poor sucking ability was observed. Magnetic resonance imaging (MRI) revealed stenosis of the foramen magnum; the patient was followed up (Figure 1A). At 2 years of age the boy was referred again due to further progression of floppy quadriplegia with difficulty in maintaining a sitting position and difficulty in standing due to spastic gait, and MRI revealed medullary stenosis and upper cervical spinal cord syringomyelia with myelomalacia (Figure 1B). Three-dimensional computed tomography (3D-CT) revealed an orthotopic-type OO in addition to AAD, and non-union of the midline septum of odontoid process was observed (Figure 1C).

Figure 1

A. MRI at 1 year of age showed stenosis of the foramen magnum. B. MRI at 2 years of age showed medullary myelomalacia and syringomyelia. C. Three-dimensional computed tomography (3D-CT) sagittal reconstruction showed atlantoaxial dislocation (AAD) and orthotopic Os odontoideum (OO) due to anterior C1 dislocation. 3D-CT coronal reconstruction showed non-union of the midline septum of the odontoid process.

MRI: magnetic resonance imaging

The anterior and posterior arches of C1 were not fused, and the anterior-posterior diameter of the C1 canal was 6 mm (Figure 2A). A two-stage surgery was planned for the patient with progressive floppy infant. To prevent progression of symptoms, we first performed instrumentation surgery without bone grafting and then planned to wait for bone growth before performing bone grafting and re-fixation surgery. The C2 laminar was developed, measuring to more than 3 mm (Figure 2B); therefore, a C2 translaminar screw was planned as an anchor screw, and occipitocervical fixation with C1 laminectomy was planned.

Figure 2

A. Three-dimensional computed tomography (3D-CT) showed hypoplasia of the anterior and posterior arch of the C1 atlas. The anterior-posterior diameter of the C1 spinal canal was 6 mm. B. The transverse diameter of the C2 laminar was 3.27-3.54 mm.

Occioital-C2 (O-C2) fixation was performed under general anesthesia with the patient in the prone position using a face-guard system (prone view). During surgery, the airway was checked using the C-arm, and O-C2 fixation was performed to prevent the mandibular line from projecting posteriorly to the anterior wall of the C2 body. Postoperative lateral X-ray image showed that reduction was achieved with O-C2 fixation (Figure 3A). 3D-CT showed that the occipital plate and the C2 rod were fixed, and there was no deviation of the C2 translaminar screw (Figure 3B). MRI performed one week after the surgery showed sufficient decompression of the upper cervical cord (Figure 3C). The patient's postoperative and perioperative period was uneventful, and the patient is progressing well. Postoperative external fixation was performed using a Philadelphia collar, and rehabilitation treatment was provided. At the six-month follow-up after the surgery, the patient was able to suck and swallow. He is currently undergoing rehabilitation using a walker. Although no instrument backout was observed on the X-ray, strict follow-up is required.

Figure 3

A. Postoperative lateral radiograph after occipitocervical (C2) fixation. B. Postoperative three-dimensional computed tomography (3D-CT) showed rod connection of the occipital plate and C2 anchor screw. The C2 anchor screw showed bilateral translaminar screws. C. Magnetic resonance imaging one week after surgery shows decompression of the upper cervical cord.

Discussion

Embryology and anatomy

When the odontoid process begins to ossify, 2 centers appear prenatally on each side of a midline that fuses into a single mass by birth.³⁾ At birth, the subdental synchondrosis, a cartilaginous band, separates the odontoid process from the body of the axis.³⁾ This band lies invaginated within the body of the axis and ultimately contributes to the body of the axis. The subdental synchondrosis is present in most children younger than 4 years and disappears by the age of 8 years.²^,³⁾ Fielding et al.³⁾ described two anatomic types of OO: orthotopic and dystopic. In orthotopic OO, the ossicle is in the normal anatomic position of the odontoid process and moves with the anterior arch of C1. Dystopic OO is characterized by an ossicle that is located near the base of the occipital bone adjacent to the foramen magnum. The ossicle may be partially fused to the occiput, with a variable relationship to the anterior arch of C1.²⁾ Based on the above, in addition to the fact that this disease occurs in infants aged 1-2 years, 3D-CT findings suggest that this is congenital OO.

Surgical treatment of OO in infancy

Menezes reported that OO under the age of 5 years that was treated surgically was rare, with only 10 cases out of 260 (3.8%), and pointed out that in early-onset cases, congenital factors such as Down syndrome were the cause.⁴⁾ In a multicenter study of 102 cases of childhood OO (mean, 3.7 years; range, 2.0-11.8 years), 29% had neurological symptoms, and surgical treatment was reported to be effective.²⁾ Fifty of the 71 surgically treated cases (70%) were C1-2 fusions, and the rest were O-C fusions.⁵⁾ Alves et al.⁶⁾ also recommend that occipital bone fixation should be avoided as much as possible in children of growing age groups. In patients with AAD under 5 years of age, semi-rigid O-C fixation (19 cases) was chosen over C1-2 fixation (7 cases) due to the poor development of C1.⁷⁾ In recent years, with the development of instrumentation surgery, rigid fixation has become safer.⁸⁾ A method has been devised to avoid complications such as vertebral artery injury by using a translaminar screw in the C2 cervical spine.⁹⁾ C2 anchor screws and translaminar screws are safe and effective in children.¹⁰⁾

Conclusions

For infants with AAD who exhibit neurological symptoms, surgical internal fixation should be planned without delay. Furthermore, for orthotopic OO, occipitocervical fixation is more appropriate than atlantoaxial fixation. In this case, a translaminar screw is safe and effective for C2 anchor screws.

Disclaimer

Author Shoko Shimokawa is one of the Editorial Board members of the Journal. This author was not involved in the peer-review or decision-making process for this paper.

Conflicts of Interest Disclosure

All authors have no conflict of interest.

Informed Consent

Informed consent was obtained from the patient.

References

Corresponding author

Register with J-STAGE for free!