Linear magnetic resonance imaging measurements of the hippocampal formation differ in young versus old dogs

Abstract

Age-related hippocampal formation (HF) atrophy has been documented on MRI studies using volumetric analysis and visual rating scales.This retrospective cross-sectional study aimed to compare linear MRI measurements of the HF between young (1-3 years) and old (>10 years) non-brachycephalic dogs, with normal brain anatomy and cerebrospinal fluid (CSF) analysis. Right and left hippocampal formation height (HFH), height of the brain (HB) and mean HFH/HB ratio were measured by two observers on a transverse T2 fluid-attenuated inversion recovery sequence containing rostral colliculi and mesencephalic aqueduct.119 MRI studies were enrolled: 75 young and 44 old dogs. Left and right HFH were greater (p<0.0001) in young, while HB was greater in old dogs (p=0.024). Mean HFH/HB ratio was 15.66 per cent and 18.30 per cent in old and young dogs (p<0.0001). No differences were found comparing measurements between epileptic and non-epileptic dogs.Old dogs have a greater HB; this may represent the different study populations or a statistical phenomenon. Ageing affects HF linear measurements. A reduction of mean HFH/HB ratio between 18.30 per cent and 15.66 per cent should be considered a physiological age-related process of the canine lifespan. The use of mean HFH/HB ratio could be considered for quantifying brain atrophy in elderly dogs.

Keywords: age-related changes; brain; dog; hippocampal formation; hippocampus; magnetic resonance imaging (mri).

Figure 1

Transverse T2 FLAIR MRI of the brain of a 3-year and 3-month-old jack russell terrier at the level of the mesencephalon, containing both the rostral colliculi (asterisks) and mesencephalic aqueduct (hashtag). Red line=height of the brain. Blue lines=right and left hippocampal formation height.

Figure 2

Transverse T2 FLAIR MRI of the brain at the level of the mesencephalon in 2-year and 6-month-old (A) and 12-year (B) labrador retriever dogs. The hippocampal formation size appears greater in the young dog (A) compared with the old one (B). FLAIR, fluid-attenuated inversion recovery.

Figure 3

Bland-Altman plots indicating bias and 95 per cent limits of agreement between: (A) right hippocampal formation height (HFH) measured by the same observer (AG, neurologist resident) 1 year apart (intraobserver agreement) in young and old dogs; (B) left HFH measured by the same observer (AG, neurologist resident) 1 year apart (intraobserver agreement) in young and old dogs; (C) height of the brain (HB) measured by the same observer (AG, neurologist resident) 1 year apart (intraobserver agreement) in young and old dogs; (D) mean HFH (mHFH) measured by two different observers (AG and OT, a board-certified veterinary radiologist) (interobserver variability) in young and old dogs; (E) HB measured by two different observers (AG and OT, a board-certified veterinary radiologist) (interobserver variability) in young and old dogs.