Sarah Hubler, Christina Precht, Gertraud Schüpbach-Regula, Veronika M. Stein, Daniela Schweizer
Background
Enlargement of the brain’s ventricular system is a frequent finding in small breed dogs, often termed ventriculomegaly when unaccompanied by clinical signs. Its cause remains uncertain, but hypotheses include congenital aqueductal stenosis, reduced cerebrospinal fluid (CSF) absorption, and obstruction at the craniocervical junction. In humans, phase‐contrast magnetic resonance imaging (PC-MRI) provides valuable insight into CSF flow abnormalities. This study sought to determine whether small breed dogs with ventricular enlargement exhibit measurable CSF velocity alterations suggestive of obstruction.
Methods
This prospective case–control study examined 25 small breed dogs (<10 kg), including 17 with enlarged ventricles and 8 with normal ventricles. Using 3-Tesla PC-MRI, CSF velocities were quantified at the mesencephalic aqueduct, foramen magnum (FM), and second cervical vertebra (C2). Key velocity metrics—peak systolic (PSV), peak diastolic (PDV), peak velocity (PV), difference between systolic and diastolic peaks (DPV), average velocity (AV), and maximum average velocity (MAV)—were measured. Correlations between ventricular size, cephalic index (as a measure of brachycephaly), and CSF velocity were statistically analyzed.
Results
Dogs with ventricular enlargement demonstrated significantly lower PDV, PV, AV, and MAV in the dorsal subarachnoid space at the FM compared with dogs with normal ventricles (p < 0.05). These parameters decreased progressively with greater ventricular size and more pronounced brachycephaly. Moderate negative correlations were found between ventricular volume ratios and CSF velocities at the FM. Descriptive analysis of sagittal PC-MRI sequences revealed CSF flow obstruction—indicated by signal loss—ventral to the obex and extending to the FM in most affected dogs.
Limitations
The study’s limitations include a small sample size, particularly among control dogs, and the use of clinical rather than healthy subjects, introducing potential confounding effects of disease. Differences in body weight and challenges with peripheral pulse gating reduced the number of successful sagittal acquisitions. The study also did not fully evaluate craniocervical structural abnormalities that may influence CSF flow.
Conclusions
Phase‐contrast MRI identified decreased CSF velocity at the craniocervical junction in small breed dogs with ventricular enlargement, supporting an association between altered CSF dynamics and structural skull changes such as brachycephaly. The findings suggest that ventricular enlargement in these breeds represents a pathological condition rather than a benign variant. PC-MRI may serve as a useful clinical tool to detect CSF flow obstruction in disorders like hydrocephalus, Chiari-like malformation, and syringomyelia.
T2 weighted midsagittal image (A) of a 3 years old male Chihuahua diagnosed with idiopathic epilepsy. The red, yellow and orange lines mark the locations where the transverse phase-contrast measurements were carried out (red = mesencephalic aqueduct, yellow = foramen magnum, orange = second cervical vertebra). (B) Midsagittal phase-contrast sequence of the brain and upper cervical spine. The dark signal dorsal and ventral to the spinal cord and cerebellum represents the cerebrospinal fluid (CSF) phase shift due to moving protons (green arrows). The blue arrow points to a focal loss of signal ventral to the obex extending caudally to the foramen magnum. (C) transverse phase-contrast image at the level of the mesencephalic aqueduct. The red circle indicates mesencephalic aqueduct. (D) transverse phase-contrast image at the level of the foramen magnum. The yellow circles indicate the dorsal and ventral subarachnoid space of the foramen magnum. (E) transverse phase-contrast image at the level of the second cervical vertebra. The orange markings indicate the dorsal and ventral subarachnoid space of the second cervical vertebra.
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