X-ray anatomy of the craniovertebral zone and cervical spine
The high complexity of the anatomical structure of the craniovertebral zone explains the need to identify the main radiographic guidelines used in its evaluation.
On the roentgenograms of the craniovertebral zone in the lateral projection, the ratios of the skull base structures to each other, as well as the ratio of the base of the skull to the upper cervical vertebrae, are evaluated. It is necessary to remember the basic condition for a correct evaluation of the anatomical relationships in this zone: images of all necessary structures - the hard palate and the perforated plate in the front, the occipital bone - at the rear should be stored on the radiographs.
When assessing the central part of the skull base, the following indicators are analyzed:
- The sphenoidal angle (Figure 58, a) is formed by the intersection of the lines drawn relative to the planum sphenoidale and the Blumenbachian ramp of the base of the brain. Normally the value of the sphenoidal angle lies in the range from 90 ° to 130 °;
- the angle of inclination of the large occipital foramen (BZO) (Figure 58, b) is formed by the intersection of the entry line in the BZO (McRue line) and the line connecting the posterior edge of the hard palate with the posterior edge of the BZO (Chamberlen line). Normally, the angle of inclination of the BZO is from 0 ° to 18 °.
On the roentgenogram of the skull in the anteroposterior projection drawn through the open mouth ("per os"), the ratio of the faces of the pyramids of the temporal bones is evaluated, the lines tangent to them are normally on the same line or intersect at an angle upwards of at least 160 ° .
The relationship between the skull (in general) and the vertebral canal is estimated according to the following indices:
- the craniovertebral angle is formed by the intersection of the lines tangent to the ramp of the base of the brain and the posterior surface of the C2-vertebra tooth. The angle characterizes the magnitude of the physiological craniovertebral kyphosis, which is normally 130 ° -165 °.
- The sphenovertebral angle is formed by the intersection of the lines tangent to the perforated plate (the base of the anterior cerebral fossa) and the posterior surface of the C-vertebra tooth. Normally its value lies in the range from 80 ° to 105 °.
- Chamberlain's index is determined by the distance between the tip of the vertebra C tooth and the line connecting the posterior edge of the hard palate with the posterior edge of the BZO (the so-called Chamberlain line). Normally, the Chamberlain line crosses the top of the axis or is located within 3 mm above or below it;
- MacGregor's score is determined by the distance between the vertex of the C2 vertebra and the so-called. Basal line connecting the posterior edge of the hard palate with the occipital tubercle (the so-called Mae Gregor line). Normally, the lines of Chamberlain and Mae Gregor coincide, or the Mae Gregor line is 2-4 mm lower. Evaluation of the ratio of the large occipital opening and the cranial section of the vertebral canal makes it possible to assess the stability of the craniovertebral zone. A lateral radiograph is used to determine the following parameters (Figure 58, 59): the angle of entry into the large occipital foramen is formed by the intersection of the line tangential to the posterior surface of the C vertebra tooth and the line connecting the posterior edge of the C body with the posterior edge of the large occipital foramen. Normally, this angle ranges from 25 ° to 55 °.
- the anterior craniovertebral (blue supradental) distance is measured between the anterior margin of the BZO (base) and the apex of the tooth C, vertebrae. Normally, the supradental distance is 4-6 mm in children and reaches 12 mm in adults;
- the posterior craniovertebral distance is measured between the upper surface of the posterior half-arc of the atlas Q and the occipital bone. In the middle position of the head this index is in the norm of 4-7 mm, but with its inclination forward and back can vary from 0 to 13 mm;
- the ratio of the basion and the tip of the tooth C2 of the vertebra: a perpendicular drawn from the basion to the line of entry into the vertebral canal, normally crosses the vertebra C2;
- the ratio of the size of the entrance to the vertebral canal to the full size of the large occipital foramen (ratio CB / AB), should normally be at least 1/2, often 3/4. The distance C B is estimated as the smallest distance "available" for the cranial region of the spinal cord - SAC (see abbreviations).
The main spondilometric parameters characterizing the anatomy of the cervical spine proper are evaluated by lateral radiographs performed at the average physiological position of the head. Investigation of SHOP in functional positions of sagittal and lateral inclinations is conducted to reveal its hidden pathology, most often - instability or hypermobility of individual vertebral-motor segments.
Retrodental distance is measured between the posterior surface of the tooth C2 and the anterior surface of the posterior half of the atlas of C1. Normally, the retro -dental distance should be equal to or greater than 2/3 of the distance between the inner contours of the anterior and posterior half-arches C4, a decrease in this index is noted with atlantoaxial instability associated with the instability of the Crueuillet anterior joint.
The line connecting the posterior wall of the vertebral canal between C1 and C3 vertebrae by the name of the author who described it is called the Swischuk line. Normally, the base of the spinous process of C2 should be located no more than 1 mm behind the indicated line (the so-called Swischuk test). The violation of these relationships is characteristic of atlantoaxial instability associated with instability of the Cruevelia anterior joint or with corpore-dental instability C2.
The ratio of the sagittal value of the vertebral canal measured at the C4 vertebral body level to the anteroposterior size of this body in foreign literature is described as the Pavlov index, and in the domestic one as the Tchaikovsky index. According to foreign data, in the norm this indicator should exceed the value of 0.8, and its decrease indicates the presence of congenital stenosis of the cervical spinal canal. In the domestic literature, the value of the index exceeding 1.0 is considered normal, with values from 0.8 to 1.0, the condition is considered as compensated, and at a value less than 0.8 - as decompensated stenosis of the spinal canal.
Among other indicators of the normal, physiological state of the cervical spine, the following should be noted:
- cores of ossification of the apophyses of the cervical vertebra bodies appear in 10-12 years;
- the natural wedge shape of the cervical vertebrae remains up to 10 years;
- the maximum retropharyngeal distance at the level of C2 C4 vertebral bodies should not exceed 7 mm, at the level of C5-C7 vertebrae - 20 mm;
- at the level of the C2-C3 segment in children, physiological mobility of the vertebrae in the range from 0 to 3 mm is possible, which is estimated as pseudo-stability of this segment;
- the fusion of the body and tooth C2 occurs according to roentgenological data at the age of 3 to 6 years. However, on magnetic resonance tomograms, the shadow of the corporeal-dental synchondrosis persists in much later terms, including that it can be detected in adults;
- the Crucial joint gap does not exceed 3-4 mm;
- the supradental distance is 4-6 mm in children and reaches 12 mm in adults;
- the ratio of the distance between the basion and the posterior half-arc atlant to the distance between the front arch of the atlas and opistion is described in the literature as the Power index, the indicator characterizes the stability of the craniovertebral zone and is normally equal to or less than 1.0.