Chiari-like malformation and syringomyelia in American Brussels Griffon dogs

Abstract

Background: Although Chiari-like malformation (CM) and syringomyelia (SM) have been described in many small breed dogs, the prevalence and clinical manifestations of this complex have not been documented in a large cohort of American Brussels Griffon (ABG) dogs.

Objectives: To characterize the clinical and magnetic resonance imaging (MRI) features of CM and SM in the ABG breed.

Animals: Eighty-four American Kennel Club registered ABG dogs were recruited.

Methods: Prospective study. Complete histories and neurologic examinations were obtained before MRI. Images were blindly reviewed and calculations were made by using OsiriX. All analyses were performed by Student's t-test, Spearman's correlation, ANOVA, and chi-square test where appropriate.

Results: Chiari-like malformation and SM were present in 65% and 52% of dogs, respectively. Twenty-eight percent of dogs had neurologic deficits and 20% had neck pain. Mean central canal (CC) transverse height was 2.5 mm with a mean length of 3.6 cervical vertebrae. Neurologic deficits were significantly associated with a larger syrinx (P = .04, P = .08) and syrinx size increased with age (P = .027). SM was associated with a smaller craniocervical junction (CCJ) height (P = .04) and larger ventricles (P = .0001; P < .001).

Conclusions and clinical importance: Syringomyelia and CM are prevalent in American Brussels Griffon dogs. Syrinx size is associated with neurologic deficits, CM, larger ventricles, a smaller craniocervical junction height, neurologic deficits, and cerebellar herniation. Fifty-two percent of dogs with a SM were clinically normal.

Keywords: Central canal; Foramen magnum; Magnetic resonance imaging; Syrinx.

Figure 1

Sagittal T2‐weighted magnetic resonance images illustrating the Chiari‐like malformation (CM) grades used in this study based on British Veterinary Association grading scheme (Table 1). (A) CM grade 1 has no malformation with a normal shaped cerebellum. (B) CM grade 2 has an indented cerebellum but signal consistent with cerebrospinal fluid exists between the caudal cerebellar vermis and the foramen magnum (FM). (C) CM grade 3 exhibits a cerebellum impacted or herniated into the FM.

Figure 2

Sagittal T2‐weighted magnetic resonance images illustrating central canal, syrinx dorsoventral height (mm), or both in the sagittal (A) and transverse (B) planes measured by using OsiriX 3.6i.

Figure 3

At the level of the interthalamic adhesion, the area of the lateral ventricles was calculated as a percentage of the cerebral area by measuring the area of the cerebral hemispheres in the transverse plane and the area of the lateral ventricles in the transverse and sagittal planes (% ventricular area).

Figure 4

The lateral ventricles were subjectively graded using transverse T2‐weighted magnetic resonance images at the level of the rostral mesencephalon; a scale of 1 to 3 was assigned using the following definitions: (A) Grade 1: <20% of the cerebrum, (B) Grade 2: >20% but <50%, (C) Grade 3 >50%.

Figure 5

The length of the cerebellar protrusion beyond the foramen magnum was measured (A). The height of the craniocervical junction was measured and expressed as a percentage of caudal cranial fossa height for standardization (CCJ/caudal cranial fossa percentage). Height was measured from the caudal aspect of the foramen magnum at the level of the rostral border of arch of atlas. Height measurements were made perpendicular to the skull base (B).