BackgroundThis is a pilot study to evaluate the effects of fentanyl on intraocular pressure (IOP) and pupil size (PS) in dogs premedicated with medetomidine and methadone.MethodsSixteen dogs with a median (first quartile–third quartile) age of 3.5 (1.25–6) years and a mean (sd) weight of 18.6 (9.2) kg were included. Baseline readings of IOP and PS were recorded before all dogs were premedicated intramuscularly with medetomidine (10 µg/kg) and methadone (0.5 mg/kg). Both measurements were repeated 15 and 30 minutes later. Following this, the dogs were randomly assigned into two groups. The fentanyl group received intravenous fentanyl (10 µg/kg), while the control group received the same volume of saline solution intravenously. IOP and PS measurements were measured and recorded in both groups at one, five and ten minutes after intravenous injection. Data were analysed with one-way and two-way repeated-measures analysis of variance or their non-parametric equivalents.ResultsPS was significantly decreased 15 and 30 minutes following intramuscular premedication and IOP was significantly increased in the fentanyl group at all time points following intravenous administration.ConclusionsMedetomidine, methadone and fentanyl combinations are not recommended for use in patients where an increase in IOP or decrease in PS is undesirable.

Basilar invagination is a poorly described condition in veterinary medicine where the tip of the odontoid process projects into a normal foramen magnum. This report describes the clinical, radiological, and surgical treatment of a basilar invagination associated with instability of the atlantoaxial joint due to an incomplete ossification of the atlas in a cat. At presentation, the clinical signs included obtundation and non-ambulatory tetraparesis with postural reaction deficits in hindlimbs and left forelimb. Radiographic examination revealed cranial displacement of the axis with the dens impinging the basioccipital bone, and computed tomography confirmed the impaction of the axis on the atlas due to an incomplete ossification of the left half of the neural arch with the intercentrum. Magnetic resonance imaging confirmed severe spinal cord compression and myelopathy at this level. The cat underwent surgery for atlantoaxial arthrodesis using a ventral approach to C1-C2. Recovery after surgery was uneventful. Follow-up a year after surgery finds the cat free of neurological signs. An incomplete ossification of the atlas can lead to atlantoaxial instability and basilar invagination in the cat. Diagnosis can be made based on its radiological characteristics, the cranial displacement of the odontoid process in contact with the basioccipital bone being its main feature. This case was successfully treated by atlantoaxial arthrodesis.