Phase‐Contrast Magnetic Resonance Imaging Identifies Low Cerebrospinal Fluid Velocity at the Foramen Magnum in Small Breed Dogs With an Enlarged Ventricular System

Background In small breed dogs, enlarged ventricles of the brain are a common finding on magnetic resonance imaging (MRI). In humans, enlarged lateral ventricles are usually the consequence of mesencephalic aqueduct stenosis. Cerebrospinal fluid (CSF) velocity measurements indicating obstruction are lacking in dogs. Objectives Measure CSF velocity in small breed dogs with ventricular enlargement. Animals Velocity of CSF in 17 small breed dogs with enlarged ventricles and 8 small breed dogs with normal‐sized ventricles was measured by phase‐contrast MRI at the mesencephalic aqueduct, foramen magnum (FM) and second cervical vertebra (C2). Methods Peak systolic (PSV) and diastolic (PDV) velocity, peak velocity (PV), difference between peak systolic and diastolic velocity (DPV), average velocity (AV) and maximum average velocity (MAV) were measured. Results Dogs with enlarged ventricles had lower PDV, PV, AV, and MAV at the dorsal subarachnoid space of the FM compared with dogs without enlargement ( p < 0.05). At the ventral subarachnoid space of FM, moderate decreases in PDV, PV, DPV, AV, and MAV were found with increasing severity of ventricular enlargement. Conclusion Ventricular enlargement may be associated with or result in altered CSF flow dynamics, particularly decreased velocity at the craniocervical junction. This relationship may, in turn, reflect underlying structural changes, such as skull shape or craniocervical abnormalities. Therefore, enlarged ventricles in small breed dogs should be considered pathological findings.