Measurement of brainstem diameter in small-breed dogs using magnetic resonance imaging

Abstract

Measurement of brainstem diameters (midbrain, pons, and medulla oblongata)is of potential clinical significance, as changes in brainstem size may decrease or increase due to age, neurodegenerative disorders, or neoplasms. In human medicine, numerous studies have reported the normal reference range of brainstem size, which is hitherto unexplored in veterinary medicine, particularly for small-breed dogs. Therefore, this study aims to investigate the reference range of brainstem diameters in small-breed dogs and to correlate the measurements with age, body weight (BW), and body condition score (BCS). Herein, magnetic resonance (MR) images of 544 small-breed dogs were evaluated. Based on the exclusion criteria, 193 dogs were included in the midbrain and pons evaluation, and of these, 119 dogs were included in the medulla oblongata evaluation. Using MR images, the height and width of the midbrain, pons, and medulla oblongata were measured on the median and transverse plane on the T1-weighted image. For the medulla oblongata, two points were measured for each height and width. The mean values of midbrain height (MH), midbrain width (MW), pons height (PH), pons width (PW), medulla oblongata height at the fourth ventricle level (MOHV), medulla oblongata height at the cervicomedullary (CM) junction level (MOHC), rostral medulla oblongata width (RMOW), and caudal medulla oblongata width (CMOW) were 7.18 ± 0.56 mm, 17.42 ± 1.21 mm, 9.73 ± 0.64 mm, 17.23 ± 1.21 mm, 6.06 ± 0.53 mm, 5.77 ± 0.40 mm, 18.93 ± 1.25 mm, and 10.12 ± 1.08 mm, respectively. No significant differences were found between male and female dogs for all the measurements. A negative correlation was found between age and midbrain diameter, including MH (p < 0.001) and MW (p = 0.002). All brainstem diameters were correlated positively with BW (p < 0.05). No significant correlation was found between BCS and all brainstem diameters. Brainstem diameters differed significantly between breeds (p < 0.05), except for MW (p = 0.137). This study assessed linear measurements of the brainstem diameter in small-breed dogs. We suggest that these results could be useful in assessing abnormal conditions of the brainstem in small-breed dogs.

Keywords: age; body weight; brainstem; canine; medulla oblongata; midbrain; pons; size.

Figure 1

Median plane of the brainstem (A,C,E,G) and transverse plane of the midbrain (B), pons (D), and medulla oblongata (F,H) in T1-weighted MRI images. (A) Midbrain height (MH) was measured from the midpoint of the interpeduncular fossa to the margin of the cerebral aqueduct, perpendicular to the interpeduncular fossa (dotted line). (B) Midbrain width (MW) was measured by connecting both bilateral commissures of the medial geniculate body and the brachium of the caudal colliculus. (C) Pons height (PH) was measured from the ventral margin of the pons to the margin of the fourth ventricle, perpendicular to the tangent line (white line) of the most ventral point of the pons. (D) Pons width (PW) is the maximum width connecting both bilateral middle cerebellar peduncles. (E) Medulla oblongata height at the fourth ventricle level (MOHV) was measured from the kinking point at the level of the obex to the ventral margin of the medulla, perpendicular to the long axis of the medulla. (F) Rostral medulla oblongata width (RMOW) was measured from one end to the other of the bilateral cochlear nuclei. CN VIII (asterisk), the vestibulocochlear nerve, extends from the cochlear nuclei. (G) Medulla oblongata height at the CM junction (MOHC) is the diameter measured at the level of the CM junction. (H) Caudal medulla oblongata width (CMOW) is the widest width of the medulla at the level of the CM junction. M, midbrain; P, pons; MO, medulla oblongata; GB, geniculate body.

Figure 2

Scatter plots of the linear regression analysis of the relationship between BW and brainstem diameter. All brainstem diameters showed significant positive correlations with BW. (A) Positive correlation between MH and BW (R² = 0.027, p < 0.05). (B) Positive correlation between MW and BW (R² = 0.024, p < 0.05). (C) Positive correlation between PH and BW (R² = 0.034, p < 0.05). (D) Positive correlation between PW and BW (R² = 0.138, p < 0.001). (E) Positive correlation between MOHV and BW (R² = 0.157, p < 0.001). (F) Positive correlation between RMOW and BW (R² = 0.356, p < 0.001). (G) Positive correlation between MOHC and BW (R² = 0.215, p < 0.001). (H) Positive correlation between CMOW and BW (R² = 0.074, p < 0.05).

Figure 3

Scatter plots of the linear regression analysis of the relationship between the BW/BCS index and brainstem diameter. All brainstem diameters were significantly positively correlated with the BW/BCS index. (A) Positive correlation between MH and BW/BCS (R² = 0.035, p < 0.05). (B) Positive correlation between MW and BW/BCS (R² = 0.034, p < 0.05). (C) Positive correlation between PH and BW/BCS (R² = 0.053, p < 0.05). (D) Positive correlation between PW and BW/BCS (R² = 0.198, p < 0.001). (E) Positive correlation between MOHV and BW/BCS (R² = 0.181, p < 0.001). (F) Positive correlation between RMOW and BW/BCS (R² = 0.468, p < 0.001). (G) Positive correlation between MOHC and BW/BCS (R² = 0.227, p < 0.001). (H) Positive correlation between CMOW and BW/BCS (R² = 0.123, p < 0.001).

Figure 4

Scatter plots of the linear regression analysis of the relationship between age and brainstem diameter. Only MH and MW correlated negatively with age. The other values, including PH, PW, MOHV, MOHC, RMOW and CMOW, had no significant correlation with age. (A) Negative correlation between MH and age (R² = 0.245, p < 0.001). (B) Negative correlation between MW and age (R² = 0.049, p < 0.05).

Figure 5

Box plots of the difference in brainstem diameters between breeds. There were statistically significant differences between breeds in (A) MH (p < 0.001), (C) PH (p = 0.006), (D) PW (p = 0.003), (E) MOHV (p < 0.001), (F) RMOW (p = 0.004), (G) MOHC (p < 0.001), and (H) CMOW (p = 0.008). There were no statistically significant differences between breeds in (B) MW (p = 0.137).