Posterior cranial fossa and cervical spine morphometric abnormalities in symptomatic Chiari type 0 and Chiari type 1 malformation patients with and without syringomyelia

Abstract

Background: To better understand how anatomical features of Chiari malformation type 0 (CM0) result in the manifestation of Chiari malformation type 1 (CM1) signs and symptoms, we conducted a morphometric study of the posterior cranial fossa (PCF) and cervical canal in patients with CM1 and CM0.

Methods: This retrospective study had a STROBE design and included 120 adult patients with MRI evidence of a small PCF (SPCF), typical clinical symptoms of CM1, and a diagnosis of CM1, CM0, or SPCF-TH0-only (SPCF with cerebellar ectopia less than 2 mm and without syringomyelia). Patients were divided by MRI findings into 4 groups: SPCF-TH0-only, SPCF-TH0-syr (CM0 with SPCF and syringomyelia), SPCF-CM1-only (SPCF with cerebellar ectopia 5 mm or more without syringomyelia), and SPCF-CM1-syr (CM1 with syringomyelia). Neurological examination data and MRI parameters were analyzed.

Results: All patient cohorts had morphometric evidence of a small, flattened, and overcrowded PCF. The PCF phenotype of the SPCF-TH0-only group differed from that of other CM cohorts in that the length of clivus and supraocciput and the height of the PF were longer, the upper CSF spaces of PCF were taller, and the area of the foramen magnum was smaller. The SPCF-TH0 groups had a more significant narrowing of the superior cervical canal and a smaller decrease in PCF height than the SPCF-CM1 groups.

Conclusions: Patients with SPCF-TH0 with and without syringomyelia developed Chiari 1 symptoms and signs. Patients with SPCF-TH0-syr (Chiari 0) had more constriction of their CSF pathways in and around the foramen magnum than patients with SPCF-TH0-only.

Keywords: Chiari malformation type 0; Chiari malformation type 1; Morphometric abnormalities; Posterior cranial fossa; Spinal canal; Syringomyelia.

Fig. 1

Morphometric measurements for assessing Chiari malformation. Linear, angular, and calculated variables. Linear variables (a–d). C-FM, F-FM, P-FM—distances from FM to corpus callosum, to fastigium, and to pons, respectively [21, 48]. ChD—distance between the Chamberlain line and tip of the dens axis [35]. CL—the length of the clivus [6]. FM—the anteroposterior diameter of the foramen magnum [21]. FV—distance between the fastigium and the floor of the fourth ventricle [46]. h—height of the osseous part PCF—distance from opistion to Twining line [6]. H—height of the skull above the Twining line. h ant.—anterior height of PCF [52]. M-FVV—distance between the M-line (Line M is drawn across the clivus vertex and perpendicular to the C-2 endplate) and fourth ventricle vertex [45]. obex-McR—the distance between the obex and the basion-opisthion line [14, 46]. pB-C2—perpendicular length between a line connecting the basion and the inferoposterior edge of the C2 to the ventral dural [21]. ROST—the anteroposterior distance of the soft tissue, shown as a hypointensity behind the odontoid process [15]. SC-ISCC, VER-ISCC—distance from the uppermost part of the superior colliculi and the uppermost part of the culmen of cerebellar vermis, respectively, to the inferior part of the splenium of corpus callosum [31]. SO—the length of supraocciput [6]. v—the anteroposterior width of the ventral subarachnoid space [6]. Y—the anteroposterior length of the PCF [4]. Z —the height of the PCF [4]. Angular variables (a, b, e). BA (basal angle)—angle formed by the nasion, dorsum sellae, and basion [35]. BoA (Boogaard angle)—angle formed by the dorsum sellae, basion, and opisthion [6]. C2DRv (odontoid retroversion angle)—angle between a line drawn along the inferior margin of C2 vertebral body and a line drawn from the mid-point of the inferior margin through the dens apex [21]. CAA (the clivoaxial angle)—angle between the dorsal surface of the clivus and the posterior surface of the odontoid process [15]. CAAm (the modified clivoaxial angle)—angle between the dorsal surface of the clivus and the posterior surface of the retro-odontoid soft tissue [15]. CLgr (the clivus gradient)—angle of the McRae’s line to the clivus [52]. C-SO—the angle between clivus and supra-occiput [4]. kink—cervicomedullary kinking. TA (tentorium angle)—angle formed by the tentorium and a line from the internal occipital protuberance to the opisthion [21]. TTw (tentorium-Twining angle) [4]—the angle at the intersection of the tentorium and the Twining line. Calculated variables: h/H ratio (d) was used to compare the skull compartments below (osseous part of the PCF) and above the Twining. S fm (f)—FM surface area [43] subdivided into the surface areas of the spinal cord (S sc), of the herniated cerebellar tonsils (S tt = S t₁ + S t₂), and of the CSF (S csf); S fm, S sc, St₁, and St₂ were calculated as the area of the ellipse: (π × semi-minor axis × semi-major axis). Also calculated were relative indicators – S tt/S fm and S csf/S fm ratios. S pf (e)—mid-sagittal PCF area [48] was delimited by the tentorium, the occipital bone, the McRae line, and clivus; subdivided into osseous part (S pf b, located below the Twining line) and extra-osseous part (S pf eb), and calculated as the sum of the areas of right-angled triangles. TR C1-4, TR C4-7, TR C1-7 (c)—the C1-C7, C1-C4, and C4-C7 taper ratio calculation [37]: the antero-posterior diameters of the spinal canal – apsc C1 – apsc C7 (apsc C3-7 not shown)—were plotted against the cervical level; a trend line was fitted by linear regression to the diameters between C1 and C7, and the slope of this line was calculated; the slope of the trend line was recorded as the taper ratio for that spine (mm/level). V cm (Fig. 1a)—volume of the cisterna magna [51] was calculated using formula: [height × width × depth]/6 (width of the cisterna magna not shown). V pf (d) – PCF volume was calculated using formula [4]: [4/3 × π×(X/2 × Y/2 × Z/2)], where X is the width of the PCF (not shown)

Fig. 2

Comparative characteristics of the PCF phenotype in control group and CM cohorts. a MRI parameters that differ between all CM group and CON (a down arrow indicates a decrease, and an up arrow indicates an increase in the parameter in all CM group in comparison with CON, p < 0.05), as well as a schematic representation of the main changes in the PCF phenotype (decrease, narrowing is highlighted by a thin arrow, increase by a wide arrow). b MRI parameters that differ between SPCF-syr and SPCF-only cohorts (a down arrow indicates a decrease, and an up arrow indicates an increase in the parameter in SPCF-syr cohort in comparison with SPCF-only cohort, p < 0.05), as well as a schematic representation of the main changes in the PCF phenotype (decrease, narrowing is highlighted by a thin arrow, increase by a wide arrow). c Reduction of the anteroposterior range in the upper part of the cervical spinal canal (SPCF-syr vs. SPCF-only, p < 0.05) and tendency to increase in the lower part leads to the formation of the “crossing” phenomenon. d MRI parameters that differ between SPCF-TH0 and SPCF-CM1 cohorts a down arrow indicates a decrease, and an up arrow indicates an increase in the parameter in SPCF-TH0 cohort in comparison with SPCF-CM1 cohort, p < 0.05), as well as a schematic representation of the main changes in the PCF phenotype (decrease, narrowing is highlighted by a thin arrow, increase by a wide arrow). e, f SPCF-TH0-only patient: woman, 53 years old, for a long time notes complaints of aching headaches, episodic double vision, mainly complicating the descent from the stairs, and attacks of dizziness, tinnitus and instability; on neurological examination—convergent strabismus on the left, left-sided brisk tendon reflexes and Babinski sign, instability in sensitized Romberg’s test. At the brain MRI: (e mid-sagittal T1 MRI) the lower pole of the cerebellar tonsils is located at the level of the foramen magnum (f axial T2 MRI through the plane of the foramen magnum) the cerebellar tonsils occupy the foramen magnum with compression of the brain stem, non-visible cisterna magna (posterior to the cerebellar tonsils); CL h41 mm, SO 32 mm, FM 32 mm, h 24 mm, CAAm 139 grad., pB-C2 10 mm, ROST 5 mm, S fm 509 mm². g Comparative characteristics of the PCF phenotype in SPCF-TH0-only and in other cohorts: (1) the smallest among other forms of CM, but statistically significant in comparison with CON, decrease in CL, SO and Spf; (2) change in the configuration of the PF (decrease in the osseous—below the Twining line—part, and increase in the extra-osseous—above the Twining line—part) while maintaining the total height and volume of the PF (Z and Vpf do not differ from CON); 3) the upper CSF spaces of the PCF (VER-ISCC) are narrower than in CON, but significantly wider in comparison with other forms of CM; (4) a decrease Sfm compared to CON and other forms of CM