The anomalies of CCJ can be divided into congenital and acquired pathologies.
In order to evaluate the main abnormalities it is important to know the main craniometric lines: Waikenheim line (drawn parallel to the superior surface of the clivus and extending inferiorly to the upper cervical canal; the tip of the dens should be ventral and tangential to this line); Chamberlain line (it goes from the back edge of the palatine process of the hard palate to the posterior midpoint of the large occipital foramen); McRae line (from the basion to the opisthion) and McGregor line (from the posterior margin of the hard palate to the most caudal point of the occipital curve) [4].
(Fig. 2)
Among the bone-like malformations,
we describe platyblasia,
observed both in congenital (craniofacial anomalies,
osteogenesis imperfecta,
Arnold Chiari) that and acquired diseases (Paget's disease,
osteomalacia).
Platybasia consists of an asymptomatic flattening of the basicranium which occurs when the angle formed from the intersection of the plane of the clivus and the plane of the anterior cranial fossa is > 135 ° [5].
Basilar invagination is a congenital condition characterized by the migration of vertebral structures,
more commonly the odontoid process in the foramen magnum,
due to anomalies of foramen magnum (dens of axis goes 3 mm beyond the Chamberlain line).
It is found in some conditions such as rickets,
osteogenesis imperfecta,
Paget's disease,
hyperparathyroidism,
rheumatoid arthritis.
It is also found in some neural dysgenesis such as Arnold Chiari e syringomyelia [6-7].
(Fig. 3)
Also in basilar impression (acquired condition) we can observe the upward displacemente of vertebral elements into the foramen magnum that in this case is however completely normal [6].
Atlanto-occipital assimilation consists of the fusion of the first cervical vertebra with the occipital bone: therefore it represents a transition vertebra.
It can be complete (non-identifiable C1) or partial (partially identifiable C1); it is associated with basilar invagination [6].
(Fig. 4) (Fig. 5)
The multiple anomalies of the atlas are due to various defects in chondrogenesis: from total agenesis (Fig. 6) to partial or complete hypoplasia; possible finding is the cleft of the anterior and posterior arch of the atlas (Split atlas) [8].
The duplication of the dens of the axis is a rare condition caused by the lack of fusion of the nuclei of ossification within the first year of life [9].
(Fig. 7)
Klippel-Feil disease is a complex syndrome characterized by congenital fusion of one or more cervical vertebrae,
presence of a short neck and limitation of the movement of the head or neck.
(Fig. 8) This syndrome is the result of an abnormality segmentation of cervical somes that occurs from the third to the eighth week of gestation [10].
It is classified in: type I if there is a massive fusion of the cervical and upper thoracic vertebrae; type II if there is the fusion of one or two vertebrae with associated atlanto-occipital fusion,
hemivertebra or other abnormalities of the cervical rachis (Fig. 9); type III in presence of fusion of cervical vertebrae with lumbar or lower thoracic vertebrae [10-11].
Arnold Chiari is a malformation of the posterior cranial fossa,
characterized by hindbrain’s deformity and herniation of the cerebellar tonsils through the foramen magnum > 5 mm.
This structural anomaly can be asymptomatic or manifest with disorders of the cerebellum,
brainstem and sensory-motory disordes of cranial nerves and spinal cord affecting lower limbs [12].
It is typically classified in: Clear type I (herniation of the cerebellar tonsils > 5 mm) (Fig. 10) (Fig. 11),
Chiari type II (herniation of brain trunk,
IV ventricle and cerebellar tonsils > 5 mm) (Fig. 12),
Chiari III (encephalocele with erniation of cerebellum with or without brainstem) (Fig. 13) and Chiari IV (cerebellar hypoplasia/aplasia) [13].
Mucopolysaccharidosis (MPS) are a group of hereditary lysosomal disorders caused by a lack of enzymes degrading glycosaminoglycans (GAG) resulting in progressive damage of the affected tissues.
In literature were described 7 clinical types of MPS associated with 11 different enzyme deficiencies.
Transmission is autosomal recessive,
except for type II which is X-linked.
In patients with MPS the most important radiological CCJ findings are: dysplasia and hypoplasia of the odontoid process,
atlanto-axial instability/subluxation,
spinal stenosis,
thickening of periodontal tissues and ligaments.
(Fig. 14) (Fig. 15) These findings may involve in compressive cervical myelopathy that requires decompressive surgical treatment [14].
(Fig. 16) (Fig. 17) Among the non-traumatic acquired pathologies affecting CCJ we report Grisel’s syndrome,
rheumatoid arthritis and neoplasms.
Grisel's syndrome,
or “nasopharyngeal torticollis” is a non-traumatic atlantoaxial ratatory sub-luxation; it affects children and young adults (68% of cases <12 years old and 90% <21 years old) [15-16].
The physiological rotation range of the atlas (C1) on the axis (C2) is 25 ° - 53 ° on both sides [17].
Its pathogenesis is still not completely clear.
The most accredited hypothesis supports that in presence of an abnormal relaxation of ligaments,
an oronasopharyngeal inflammation spreading from the lymphatic system through the pharyngo-vertebral venous plexus [18-19],
would determine a muscular spasm and subsequent the onset of the disease [20].
The clinic is variable,
typically characterised by neck pain and stifness and symptoms related to the underlying infection [21].
The radiographic findings include the asymmetry of C1-C2 joint and the increase of the lateral mass of C1 (due to its rotation) with a contralateral reduction; however,
given the difficulties techniques in correctly performing this examination due to the patient's obligatory position,
the gold standard for the diagnosis is the CT with multiplanar reformations.
Grisel’s syndrome is classified into 4 types: type 1 (most common) is not a real subluxation,
but an articular fixity in absence of normal rotation movements (Fig. 18); type 2 is due to the anterior displacement of both lateral masses of the atlas from the dens of axis between 3 and 5 mm (Fig. 19); type 3 if the anterior displacement of both lateral masses of the atlas is greater than 5 mm; type 4 (rare) consists of rotary fixity with posterior displacement of the atlas [17,21].
The cervical rachis may be affected by rheumatoid arthritis,
especially if it is longstanding [22].
Its main characteristic is the joint damage caused by the presence of chronic synovial inflammation.
Most common pathological anomalies are: the presence of rheumatoid “pannus” at C1-C2 level,
erosion of the dens of axis or atlantoaxial dislocation [23-24].
This pathology,
asymptomatic in a percentage ranging from 10 to 50% of patients [25],
can sometimes be associated with cervicalgia,
caused either from the instability of the joint and the compression of the nerve roots [22].
MRI is the examination of choice in selected patients for the possibility to visualize at the early stage the alterations of the disease even in the absence of clinical signs: it allows to visualize a small rheumatoid “pannus” at C1-C2 level.
It is also very sensitive in the detection of the initial signs of synovitis,
bone erosions and possible involvement of the surrounding nervous structures.
CT also allows visualization of the rheumatoid “pannus” at the C1-C2 level,
although only in advanced stages of the disease [22,24].
(Fig. 20).
Neoplastic diseases affecting the CCJ include bone tumors,
tumors that originate from soft tissues and nerve structures of this region.
Extra-axial lesions of the cervical skull junction are reported,
such as meningiomas (Fig. 21),
neurinomas (Fig. 22),
chordoma and bone tumors (chondrosarcoma,
plasmacytoma,
osteoblastoma,
fibrous dysplasia,
giant cell tumors and metastatic tumors) (Fig. 23) (Fig. 24).
The clinic is variable,
however the pain is present in 70% of cases.
The role of diagnostic imaging is very import for the assessment of resectability of tumor (extension,
invasion of surrounding structures,
vascularization,
intramedullary component and craniovertebral stability) [26].