Optic Nerve Sheath Diameter as a Predictor of Intracranial Hypertension

Objective

The goal of this study is to determine the diagnostic utility of bedside ultrasound use to assess optic nerve sheath diameter as a predictor of intracranial hypertension in clinically affected dogs.

Study Summary

Intracranial pressure (ICP) elevation can be life threatening when it leads to decreased cerebral perfusion or brain herniation and early recognition is essential.  The optic nerve is surrounded by the dural sheath which communicates with the subarachnoid space surrounding the brain and human studies have suggested that the optic nerve sheath diameter (ONSD) may distend sonographically within seconds after the development of intracranial hypertension. Bedside ocular ultrasound is now commonly used in humans to rapidly to detect ONSD and assess elevated intracranial pressures, however this has not yet been assessed in veterinary medicine.

This is a prospective observational study, which aims to assess the utility of bedside ultrasonographic assessment of ONSD in dogs. Two groups of dogs will be enrolled. A control group will consist of dogs presented with no evidence of intracranial disease and who have no abnormal neurologic findings.  Ideally, these dogs will be having head CT or MRI for non-neurologic reasons including nasal, mandibular, maxillary or extracalvarial soft tissue disease, which will confirm the absence of intracranial disease. A clinically affected group of dogs will also be enrolled that are suspected, based on history and neurologic assessment, to have intracranial disease as a primary differential diagnosis and are suspected to have elevated ICP.

Inclusion Criteria

  • Dogs > 10kg
  • Clinically affected group: known or suspected head trauma, intracranial mass effect (neoplasia, haemorrhage, or inflammation) on advanced imaging (MRI or CT), clinical signs suggesting intracranial hypertension (altered mentation with a Cushing's response or modified Glasgow coma score <15)
  • Control group: dogs undergoing brain or head MRI/CT for any reason with no suspicion of intracranial mass or hypertension

Exclusion Criteria

  • Dogs with pre-existing intraocular disease which may effect the optic nerve sheath size (glaucoma, intraocular implants, uveitis, optic neuritis)
  • Dogs that will not tolerate unsedated ocular ultrasound 

Incentives

  • Both groups: the study will cover the cost of ocular ultrasound and ophthalmic examination (tonometry, schirmir tear test, fluorescein stain, fundic examination)
  • Control group: cost of Neurological internal consultation & examination
  • Cost of advanced imaging (MRI/CT), hospitalization or treatment of intracranial hypertension is not included in the study

Samples Required

  • Ocular ultrasound
  • Neurological examination
  • Ophthalmic examination

For Further Information Please Contact

Dr. Vicky Sabine, PhD
Clinical Research Coordinator
Email address: clinical.research@uoguelph.ca
Work cell #: 226-218-0338

Funded by OVC Pet Trust