Chiari malformations were first described by pathologist Hans Van Chiari in 1891 and classified as types I–IV ().4
Our patient had a type I Chiari malformation (CIM). The CIM consists of caudal displacement of the cerebellar tonsils at least 3 mm into the upper cervical spinal canal.5
Patients with the CIM may present with a variety of symptoms and signs ranging from a slight headache to severe myelopathy and brainstem compromise. The most common symptom is pain, usually occipital and upper cervical in location, and often induced or exacerbated by Valsalva manoeuvres such as laughing, sneezing and coughing, which may provoke dynamic cord compression. Our patient had similar attacks of headache and neck pain for more than 10 years.
Types of Chiari malformations
Basilar invagination refers to a developmental anomaly in which the vertebral column is situated in an abnormally high position due to decreased height of the skull base. The odontoid process becomes higher than the normal level into the foramen magnum. The diameter of foramen magnum shortens and the volume of posterior fossa becomes smaller, following with the hindbrain herniation and the compression of medulla oblongata, cerebellum and cervical nerve roots. Basilar invagination may be caused by congenital or acquired anomalies of occiput, atlas and axis, as well as acquired skull-base softening. The tip of the odontoid process projects more than 5 mm above Chamberlain's palato-occipital line.6
Ventral spinal cord compression occurs with Wackenheim's clivus-canal angle less than 150 °.6
The atlanto-occipital joint axis angle is more obtuse than the average range (124–127 °).6
The tip of the odontoid process was 4.7 mm above Chamberlain's line in our patient (). Nevertheless, both of the angles reached the standards: the clivus-canal angle was 126.86 ° () and the atlanto-occipital joint axis angle was 146.62 ° in this case ().
The clinical presentation of basilar invagination is diverse too. A constellation of symptoms and signs that reflect dysfunction of the brain stem, cerebellum, cervical spinal cord, upper cervical nerve roots, lower cranial nerves and the vascular supply point to the craniocervical border.6
The main symptoms in this case were recurrent attacks of headache, vertigo and cervical radicular pain.
Total or partial aplasia of the posterior arch of atlas is relatively uncommon. Geipel7–10
found it in 4% of 1613 autopsies. The posterior arch of the atlas begins its ossification at the seventh week of intrauterine life.11
This ossification process starts from two centres in the lateral masses and proceeds to the midline.12
At birth, the posterior arches are nearly fused except for several millimeters of cartilage, while the complete ossification is expected to occur between 3 and 5 years of age. Congenital aplasia of the posterior arch of atlas is thought to be due to a failure of the normal posterior arch chondrification process. Currarino et al13
developed classification types (A–E) for congenital aplasia of the posterior arch of atlas (), 97% of which were type A. The incidence of the general population harbouring types B–E was estimated 0.69%. Our patient had a type B anomaly, which was a small gap.
Figure 2 Classification of posterior arch defects of the atlas. Type A: failure of posterior midline fusion with a small gap remaining. Type B: unilateral clefts. Defects may range from a small gap to a complete absence of the hemi-arch. Type C: bilateral defects (more ...)
This case illustrates the lack of recognition of Chiari malformation and basilar invagination in adult patients. It is important, especially for radiologists and physicians, to keep in mind the possibility of basilar invagination and the related deformities.
- This case illustrates the lack of recognition of Chiari malformation and basilar invagination in adult patients.
- It is important, especially for radiologists and physicians, to keep in mind the possibility of basilar invagination and the related deformities.
- The stability of atlantoaxis in adolescence may be due to the connective tissue bridging the small bony defect, which was found in autopsies and operations.