Familial dystopic os odontoideum: a report of three cases

Os odontoideum: database analysis of 260 patients regarding etiology, associated abnormalities, and literature review

Introduction

Since the first description of os odontoideum in 1886, its origin has been debated. Numerous case series and reports show both a possible congenital origin and origin from the secondary to craniovertebral junction (CVJ) trauma. We conducted a detailed analysis of 260 surgically treated cases to document the initial symptoms, age groups, radiographic findings, and associated abnormalities, aiming to enhance the confirmation of the etiology. A literature search (1970-2022) was performed to correlate our findings.

Methods and materials

A total of 260 patients underwent surgical management of a referral database of 520 cases (1978-2022). All patients were examined by plain radiography and myelotomography as needed until 1984, and since then, CT and MRI have been employed. History of early childhood (aged below 6 years) CVJ trauma was investigated, including obtaining emergency department's initial radiographs from the referral and subsequent follow-up. Associated radiographic and systemic abnormalities were noted, and the atlas development was followed.

Results

The age of the patients ranged from 4 to 68 years, mostly between 10 and 20 years. There were 176 males and 86 females. Orthotopic os odontoideum was identified in 24 patients, and 236 patients had dystopic os odontoideum. Associated abnormalities were found in 94 of 260 patients, with 73 exhibiting syndromic abnormalities and 21 having Chiari I malformation. Two sets of twins had spondyloepiphyseal dysplasia. Of 260 patients, 156 experienced early childhood trauma /. Among these, 54 initially presented with normal radiographs but later demonstrated anterior atlas hypertrophy. In addition, a smaller posterior C1 arch was observed, leading to the development of os odontoideum. Two children had initial CVJ trauma as documented by MRI, with subsequent classical findings of os odontoideum and atlas changes. Syndromic patients had an earlier presentation. The literature reviewed confirms the multifactorial etiology.

Conclusions

The early presentation and associated abnormalities (such as Down syndrome, Klippel-Feil syndrome, Chiari I malformation, spondyloepiphyseal dysplasia, Morquio syndrome, and others) along with case reports documenting familial, hereditary, and twin presentations strongly support a congenital origin. Likewise, surgical complications are more prevalent in syndromic patients (40%) compared to 15% in other cases, as reported in the literature. The documentation of normal odontoid in early childhood trauma cases followed by the later development of os odontoideum provides evidence supporting trauma as an etiological factor. This process also involves vascular changes in both the atlas and the formation of os odontoideum. Associated abnormalities exhibit an earlier presentation and are only seen in cases with a non-traumatic origin.

Os Odontoideum: A Single-Center Experience with Controversies in Management and Evolution of Treatment Strategies

Os odontoideum is an independent ossicle of variable size and shape separated from the body of C2. There are various theories on the etiology. Different hypothesis on etiology include traumatic and congenital. Because of the laxity of the ligaments associated with the anomalous odontoid, there can be associated instability at the craniovertebral junction. The authors presented their experience of treating these anomalies, their clinical presentations, evolution of the treatment strategies over years, and a brief review of literature on etiopathogenesis.

Weak Ligaments and Sloping Joints: A New Hypothesis for Development of Congenital Atlantoaxial Dislocation and Basilar Invagination

OBJECTIVE

Developmental bony craniovertebral junction (CVJ) anomalies seem to have a genetic basis and also abnormal joint morphology causing atlantoaxial dislocation (AAD) and basilar invagination (BI).

METHODS

DNA extracted polymerase chain reaction single-stranded conformation polymorphism (SSCP) performed for mutation screening of FBN1 gene (n = 50 cases+ 50 age/sex-matched normal; total: 100). Samples with a deviated pattern of bands in SSCP were sequenced to detect the type of variation. Computed tomography (CT) scans of 100 patients (15-45 years old) compared with an equal number of age/sex-matched controls (21.9 ± 8.2 years). Joint parameters studied: sagittal joint inclination (SI), craniocervical tilt (CCT), coronal joint inclination (CI).

RESULTS

Thirty-nine samples (78%) showed sequence variants. Exon 25, 26, 27, and 28 showed variable patterns of DNA bands in SSCP, which on sequencing gives various types of DNA sequence variations in intronic region of the FBN1 gene in 14%, 14%, 6%, and 44% respectively. CT radiology:SI and CCT correlated with both BI and AAD (p < 0.01). The mean SI value in controls: 83.35° ± 8.65°, and in patients with BI and AAD:129° ± 24.05°. Mean CCT in controls: 60.2° ± 9.2°, and in patients with BI and AAD: 86.0° ± 18.1°. Mean CI in controls:110.3° ± 4.23°, and in cases: 125.15° ± 16.4°.

CONCLUSION

The study showed mutations in FBN1 gene (reported in Marfan syndrome). There is also an alteration of joint morphology, correlating with AAD and BI severity. Hence, we propose a double-hit hypothesis: the presence of weak ligaments (due to FB1 gene alterations) and abnormal joint morphology may contribute to AAD and BI.

Familial Os Odontoideum

BACKGROUND

To add to the confusion in the debate on pathogenesis of os-odontoideum, an additional report of its occurrence in two members of the same family is reported.

CASE DESCRIPTION

This is a report of a rare coincidence wherein both father (51 years old) and daughter (25 years old) were diagnosed to have os odontoideum and presented with crippling neurologic deficits.

CONCLUSIONS

Following atlantoaxial fixation, both recovered in their symptoms. Investigations revealed no genetic abnormality. Literature on the subject is briefly reviewed.

Os odontoideum: diagnosis and role of imaging

OBJECTIVE

To elucidate the imaging manifestations of os odontoideum, establish the diagnosis and guide surgical therapy.

METHODS

Clinical and imaging data, including X-ray, CT and MR of 24 patients with os odontoideum, were retrieved and reviewed retrospectively.

RESULTS

Os odontoideum with intact cortex was divided into round, conical and blunt tooth types. Four cases of orthotopic and 20 cases of dystopic os odontoideum were included. There was anterior displacement of the base of the dens in six cases, posterior displacement in nine cases and no displacement in nine cases. A widening of anterior atlanto-axial space was shown in 14 patients with varying degrees. Thickening of the soft tissue posterior to the dens was observed in 19 patients, spinal canal stenosis in 21 patients, cervical myelopathy in 10 patients and craniocervical junction malformation in 9 patients. Posterior C1-C2 pedicle screw fixation and fusion was performed in 12 patients and 4 patients underwent posterior occipito-cervical fixation and fusion.

CONCLUSION

Radiographically, os odontoideum is defined as an independent ossicle of variable size with smooth circumferential cortical margins separated from the axis. Imaging can be used to assess atlanto-axial instability, associated normal or abnormal anatomical structures and guide surgical therapy.

Atlantoaxial Subluxation Secondary to Unstable Os Odontoideum in a Patient With Arrested Hydrocephalus Due to Congenital Aqueductal Stenosis: A Case Report

BACKGROUND

In a small percentage of children born with congenital hydrocephalus, enlargement of the head and the presence of ventriculomegaly may halt and ultimately stabilize the condition designated as arrested hydrocephalus. Arrested hydrocephalus in children is typically due to congenital aqueduct stenosis, which can be described appropriately as a stasis existing within the channel between the third and fourth ventricles. Os odontoideum (OO) is an uncommonly occurring pathology at the craniovertebral junction. Although the clinical and radiologic features of its existence and the therapeutic options for its pathology have been widely discussed within the medical literature, its true etiology has been a source of divisive debate, proposing both a traumatic as well as a congenital mechanism. The etiology of OO has been heartily debated in the literature for several years as well. Most authors have come to support a posttraumatic causality. However, strong evidence exists to support a congenital origin to this rarely observed malformation.

METHODS

Within this case study we present a 24-year-old woman with atlantoaxial subluxation that exists secondary to an orthotropic OO. The patient had a history of arrested hydrocephalus due to congenital aqueductal stenosis beginning in early childhood. She presented with normal intelligence and was neurologically without deficits before the occurrence of an atlantoaxial dislocation. Unfortunately, the pathology was initially misdiagnosed as a decompensation state of the arrested hydrocephalus, and after 8 months the patient became wheelchair bound. Following this unfortunate event the correct diagnosis was ultimately uncovered. Subsequently a C2-1 instrumentation procedure resulted in excellent alignment and fusion.

CONCLUSIONS

To the best of our knowledge, this is the first example of an aqueduct stenosis in the setting of an existing OO, a combination that might be another clue in favor of a congenital etiology.

Os Odontoideum: A Comprehensive Clinical and Surgical Review

Os odontoideum (OO) is a rare anomaly of the odontoid process first described by Giacomini in 1886. There is considerable debate about the origin of this anomaly, whether congenital or acquired, though a growing body of evidence favors the latter. Using PubMed, we reviewed the literature on OO with regards to its etiology, clinical presentations, diagnostic modalities, and management. Manuscripts cited in reviews were also searched manually. Because the medical literature on this condition is limited, our understanding of the natural history and management of OO is still vague. The management guidelines for asymptomatic OO are preliminary. Therefore, we need more large-center studies to investigate this condition further.

Reduction of atlantoaxial dislocation prevented by pathological position of the transverse ligament in fixed, irreducible os odontoideum: operative illustrations and radiographic correlates in 41 patients

OBJECTIVE Os odontoideum (OO) is a craniovertebral junction (CVJ) abnormality in which an ossicle (small bone) is cranial to a hypoplastic dens by a variable gap. This abnormality can result in instability, which may be reducible or irreducible. What leads to irreducibility in OO is unclear. Therefore, the authors sought to better understand the causes of irreducibility in OO. METHODS A retrospective review was conducted, which identified more than 200 patients who had undergone surgical treatment for OO between 1978 and 2015 at the University of Iowa Hospitals and Clinics. Only the 41 patients who had irreducible OO were included in this study. All inpatient and outpatient records were retrospectively reviewed, and patient demographics, clinical presentation, radiographic findings, surgical treatment, and operative findings were recorded and analyzed. RESULTS The cohort of 41 patients who were found to have irreducible OO included both children and adults. A majority of patients were adults (61% were 18 years or older). Clinical presentation included neck pain and headache in the majority of patients (93%). Weakness, sensory disturbances, and myelopathy were invariably present in all 41 patients (100%). Down syndrome was much more common in the pediatric cohort than in the adult cohort; of the 16 pediatric patients, 6 had Down syndrome (38%), and none of the adults did. Of the 16 pediatric patients, 5 had segmentation failure (31%) in the subaxial spine, and none of the adults did. A form of atlantoaxial dislocation was seen in all cases. On CT imaging, atlantoaxial facets were dislocated in all 41 cases but did not have osseous changes that would have prevented reduction. On MRI, the transverse ligament was identified anterior and inferior to the ossicle and superior to the hypoplastic odontoid process in all cases in which these studies were available (i.e., post-MRI era; 36 of 36 cases). The ligament was hypointense on T2-weighted images but also had an associated hyperintense signal on T2 images. Intraoperatively, the transverse ligament was identified anterior and inferior to the ossicle and superior to the hypoplastic odontoid process in all 41 cases. CONCLUSIONS In the largest series to date of irreducible OO and the only study to examine variable factors that lead to irreducibility in OO, the authors found that the position of the transverse ligament anterior and inferior to the ossicle is the most common factor in the irreducibility of OO. The presence of granulation tissue and of the dystopic variant of OO is also associated with irreducibility. The presence of Down syndrome and segmentation failure probably leads to faster progression of ligamentous incompetence and therefore earlier presentation of instability and irreducibility. This is the first study in which intraoperative findings regarding the transverse ligament have been correlated with MRI.

First Gross Anatomic Findings of an Os Odontoideum

BACKGROUND

Os odontoideum is an uncommon abnormality of the craniovertebral junction where the tip of the odontoid process lacks continuity with the body of C2. The clinical presentation is variable, but severe neurologic impairment can result.

CASE DESCRIPTION

We report the gross and radiologic findings of a cadaver found to harbor an os odontoideum.

CONCLUSIONS

To our knowledge, there are no cadaveric reports in the literature regarding an os odontoideum. Such a case allows a rare window into the anatomy and relationships of this pathologic structure.

A rare case of os odontoideum from an Early Intermediate period tomb at the Huacas de Moche, Peru

Os odontoideum is an uncommon vertebral anomaly where there is a smoothly corticated ossicle independent from a shortened odontoid peg. An example of os odontoideum was observed in an Early Intermediate period skeleton excavated from the Huacas de Moche (Moche IV, AD 400-700), Peru. The affected individual is a middle adult male who presents additional minor developmental anomalies of the axial skeleton. This individual was interred with a middle adult female who also has developmental anomalies of the axial skeleton, including block cervical vertebra (Klippel-Feil). Os odontoideum is infrequently reported in the medical literature and there continues to be debate about whether it is acquired or congenital. Unlike clinical cases, archaeological cases present an opportunity to examine the entirety of the skeleton. In the present case, there does not appear to be macroscopic or radiographic evidence for a healed fracture, and since the individual has multiple minor axial developmental anomalies, a congenital etiology is plausible. This case is the first to be described from the archaeological context of South America and one of few paleopathological examples worldwide.

The odontoid process: a comprehensive review of its anatomy, embryology, and variations

BACKGROUND

The odontoid process is a critical component of the cranio-cervical junction. Therefore, clinicians who diagnose, treat, or operate this region need a strong background in regard to the embryology, anatomy, and anatomical variations that may be seen for the odontoid process.

METHODS

A literature review was performed, using standard search engines, to explore the morphology, embryology, and anatomical variants of the odontoid process.

CONCLUSIONS

A sound understanding of the development of the odontoid process, both in normal and in variant forms, as well as its phenotypical morphology is a prerequisite for the diagnosis and treatment of patients presenting with disorders affecting the cranio-cervical spine.

Craniocervical instability in the setting of os odontoideum: assessment of cause, presentation, and surgical outcomes in a series of 279 cases

BACKGROUND

Our clinical understanding of os odontoideum (OO) remains incomplete. Congenital and traumatic causes have been proposed and advocated. Clinical presentations range from asymptomatic to axial pain to myelopathy or vertebral-basilar ischemia. A consensus for surgical management exists for those found to have an unstable atlantoaxial complex or symptomatic cranial-vertebral junction compression.

OBJECTIVE

To evaluate the clinical presentation and surgical outcomes of patients with OO and an unstable atlantoaxial complex or symptomatic cranial-vertebral junction compression.

METHODS

Patients with a diagnosis of OO who underwent surgical management were included. Patients were excluded on the basis of previous C2 fracture, Fielding diagnostic criteria, and inadequate follow-up. History of trauma and presenting symptoms were assessed. Clinical and neurological improvements were measured with the use of patient satisfaction scores and the Japanese Orthopaedic Association scores. Fusion status was documented with the use of radiographs and computed tomographic imaging.

RESULTS

Of 279 patients, 112 reported a history of cranial-vertebral junction trauma, whereas 28 were diagnosed with congenital malformations. Clinically, 84.9% of patients presented with myelopathy, with pain presented in 42.6%. Atlantoaxial fixation was performed in 240 patients, occiput-to-C2 fixation in 35 patients, and extended occipito-cervical fixation in 4 patients. Mean follow-up was 40.3 months. Complications were reported in 2.4% of patients. Japanese Orthopaedic Association scores improved from a preoperative mean of 12.4 to 14.8. Two hundred thirty-five patients (77.7%) improved, with 30 patients experiencing no change in symptoms and 14 patients deteriorating. Fusion was achieved in 96.8% of patients.

CONCLUSION

Our data reveal that surgical treatment for OO using the indications and techniques delineated is associated with high satisfaction rates, improved functional scores, and high fusion rates with low complication rates.

Os odontoideum in identical twins: Comparative gene expression analysis

Background:

Os odontoideum is a well identified anomaly of the craniovertebral junction. Since its initial description, there has been a continuous debate regarding the nature of its etiology: Whether congenital or traumatic. We sought to compare the gene expression profiles in patients with congenital os odontoideum, those with traumatic os odontoideum and controls.

Methods:

We have evaluated a pair of identical twins both with os odontoideum. We identified two additional patients with and four subjects without os odontoideum. We analyzed the gene expression profiles in these patients using a custom TaqMan microarray and quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). The relative gene expression profiles in the two identical twins, the two nontwin patients with os odontoideum and the controls were assessed.

Results:

A total of 213 genes with significantly different expression between the twin os odontoideum patients and the subjects without os odontoideum were detected. CACNG6, PHEX, CACNAD3, IL2, FAS, TUFT1, KIT, TGFBR2, and IGF2 were expressed at levels greater than 100-fold more in the twins. There were six genes with significantly different expression profiles in the twins as compared with the nontwin os odontoideum patients: CMK4, ATF1, PLCG1, TAB1, E2F3, and ATF4. There were no statistically significant differences in gene expression in the four patients with os odontoideum and the subjects without. Trends, however, were noted in MMP8, KIT, HIF1A, CREB3, PWHAZ, TGFBR1, NFKB2, FGFR1, IPO8, STAT1, COL1A1, and BMP3.

Conclusions:

Os odontoideum has multiple etiologies, both traumatic and congenital and perhaps some represent a combination of the two. This work has identified a number of genes that show increased expression in a pair of twins with congenital os odontoideum and also demonstrates trends in gene expression profiles between a larger group of os odontoideum patients and non-os patients. A number of these genes are related to bone morphogenesis and maintenance.

Os odontoideum syndrome: pathogenesis, clinical patterns and indication for surgical strategies in childhood

Os odontoideum is a rare condition with a controversial pathogenesis and poorly understood natural history. Hypoplasia of the odontoid associated with an independent oval ossicle, with smooth margins widely separated from C2 and well above the superior facets of the axis, is termed "os odontoideum". The neurological manifestations arise from bulbospinal compression both at rest and during motion, due to the craniovertebral junction (CVJ) instability itself. Consequently, the surgical management of os odontoideum should aim at achieving both neural decompression and stabilization of the CVJ. The aims of this paper are to introduce the embryological steps involved in the CVJ development, to underline the updated theories propounded to interpret developmental and congenital disorders of the os odontoideum, to introduce the most updated surgical techniques and to discuss some exemplary cases selected from our personal experience.

Sequential imaging demonstrating os odontoideum formation after a fracture through the apical odontoid epiphysis: case report and review of the literature

INTRODUCTION

The mechanism of formation of an os odontoideum is controversial and likely multifactorial. One theory states that the apex of the odontoid separates from the body because of a fracture. The intact alar and apical ligaments pull the fractured segment superiorly. The independent vascular supply of the apex allows the fractured bone to remain viable and remodel into the smooth, corticated bone characteristic of an os odontoideum. However, there are no publications with direct radiographic evidence supporting the theory.

CASE REPORT

In this paper, the authors present a 7-year-old child with a fracture through the apical odontoid epiphysis, extending into the body of the dens. Serial imaging studies demonstrate progressive separation of the apex from the body of the odontoid. The fractured segment begins to remodel and assume the classic form of an os.

CONCLUSION

The authors consider this case to be radiographic evidence supporting an acquired/traumatic origin of os odontoideum. Further, the mechanism of fracture through a cartilaginous epiphysis may explain the formation of an os after "normal" x-ray images or following seemingly minor trauma.

Incidental os odontoideum: current management strategies

Os odontoideum was first described in the late 1880s and still remains a mystery in many respects. The genesis of os odontoideum is thought to be prior bone injury to the odontoid, but a developmental cause probably also exists. The spectrum of presentation is striking and ranges from patients who are asymptomatic or have only neck pain to those with acute quadriplegia, chronic myelopathy, or even sudden death. By definition, the presence of an os odontoideum renders the C1-2 region unstable, even under physiological loads in some patients. The consequences of this instability are exemplified by numerous cases in the literature in which a patient with os odontoideum has suffered a spinal cord injury after minor trauma. Although there is little debate that patients with os odontoideum and clinical or radiographic evidence of neurological injury or spinal cord compression should undergo surgery, the dispute continues regarding the care of asymptomatic patients whose os odontoideum is discovered incidentally. The authors' clinical experience leads them to believe that certain subgroups of asymptomatic patients should be strongly considered for surgery. These subgroups include those who are young, have anatomy favorable for surgical intervention, and show evidence of instability on flexion-extension cervical spine x-rays. This recommendation is bolstered by the fact that surgical fusion of the C1-2 region has evolved greatly and can now be done with considerable safety and success. When atlantoaxial instrumentation is used, fusion rates for os odontoideum should approach 100%.

The options of C2 fixation for os odontoideum: a radiographic study for the C2 pedicle and lamina anatomy

INTRODUCTION

Patients with os odontoideum always present instability in atlantoaxial joint and need atlantoaxial fixation. C2 pedicle or laminar screws fixation has proven to be efficient and reliable for atlantoaxial instability. However, os odontoideum is a congenital or developmental disease, featured with anomalous bony anatomies. The anatomic measurements and guidelines for C2 pedicle screw placement in general population tends to differ with those of os odontoideum patients, for whom C2 pedicle screws are often needed. The option and techniques of C2 fixation are still challenging and yet to be fully explored.

MATERIAL AND METHODS

We recruited 29 adult patients with os odontoideum and measured the dimension of C2 pedicle and lamina for each patient to examine how well do they match with the screws anatomically. In order to access the intra-observer reliability and inter-observer repeatability of the measurements, the intraclass correlation coefficient (ICC) was also calculated.

RESULTS

The results for reliability of the CT measurements showed excellent intraobserver (ICC = 0.95 and 0.96) and interobserver correlation coefficient (ICC = 0.93). The diameter and length of C2 pedicle were found to be 6.06 ± 1.37 and 24.05 ± 2.54 mm, while the corresponding figures of C2 laminar were 6.95 ± 0.82 and 25.60 ± 2.18 mm, respectively. In the measurements, all 29 cases had suitable diameter (larger than 5.5 mm) for C2 laminar screw (the laminar diameters ranged from 5.52 to 8.82 mm). In C2 pedicle measurements, the diameters of the 29 cases were from 3.50 to 9.86 mm, while 20 pedicles (34.5%) in 14 cases were less than 5.5 mm in diameter. Six had bilateral small pedicles where the diameter was less than 5.5 mm.

CONCLUSION

Anatomically, we found laminar screw is a better match in comparison with pedicle screw for C2 fixation in os odontoideum. The options for C2 fixation should be made based on careful preoperative imaging and thorough consideration. Preoperative reconstructive CT scan can offer great assistance for the choice of fixation in os odontoideum by revealing the anatomy of the C2 pedicles in detail.