Dr. Siddharth Narendran, S16890, Dr. Virna Shah
Introduction:
Raised Intracranial Pressure (ICP) is a dreaded complication of neurological disease that often leads to adverse outcomes. Clinical signs of raised ICP are often unreliable or too late to manifest and may lead to unacceptable delay in therapeutic intervention. Neuroimaging by computed tomography (CT) or magnetic resonance imaging (MRI) scans entail transfer of a critically ill patient out of the Intensive Care Unit (ICU), besides being an impracticable tool for repeat examinations at frequent intervals as may be necessary in patients with raised ICP. Invasive measurement by an intraventricular or intraparenchymal catheter is the gold standard and used extensively in the management of traumatic brain injury; however, it may not be feasible in a heterogenous group of medical patients
The optic nerve sheath is an anatomical extension of the dura mater and the subarachnoid space around the optic nerve is continuous with the intracranial subarachnoid space. Any pressure rise within the intracranial compartment impacts on the optic nerve head as swelling of the optic disc and papilledema. However, papilledema evolves over time and may be a delayed manifestation, besides requiring a skilled observer for precise identification. Dilatation of the optic nerve sheath has been shown to be a much earlier manifestation of ICP rise. The optic nerve sheath is fairly easy to visualize by ultrasonography (US) by insonation across the orbit in the axial plane.
Materials and Methods:
We carried out a combined historical (earlier test findings) and prospective (optic nerve US) study on all consecutive patients who presented to our department between January and June 2017 with suspected papilledema on fundoscopy. Inclusion criteria were compliance to undergo the full procedure of ocular US and the availability of a comprehensive medical examination. Exclusion criteria were a history of any central nervous system or ocular disease, previous ocular surgery or trauma. Ultrasonography was performed in a standardized fashion after obtaining informed consent from the patients. Approval to conduct the study was obtained from the institutional review board. The retrieved data included the patient’s medical history and the findings of a physical and neurological examination. The comprehensive ophthalmologic examination included funduscopy, brain and orbit imaging by magnetic resonance imaging (MRI) and an MR venogram.
All enrolled patients underwent optic nerve US (A-mode and B-mode). The B-scan provides a bidimensional anatomic image of the optic nerve head, and the A-scan enables the cross-sectional measurement of the ONW. Detection of the ‘doughnut’ or ‘crescent’ sign in the B-Mode or a positive 30-degree test was considered positive US findings. The 30-degree test is based on the assumption that when the eye turns, the optic nerve and its sheaths are stretched, thus distributing the increased subarachnoid fluid over a greater area. The analysed data were comprised of the results of imaging studies, LP values and long-term follow-up evaluations.
Results :
Thirty patients ( 20 female and 10 male ) were included in the study. Mean age was 32 years (range 16 – 58 years). . Detection of the ‘doughnut’ or ‘crescent’ sign in the B-Mode was considered positive US finding. Crescent sign was positive in 85 % of the individuals. Ultrasonography detected papilledema with a high degree of sensitivity (95%) with a positive likelihood ration of 1.91
Conclusion:
In conclusion, we demonstrated that US, which is a cheap and noninvasive modality, identified papilloedema
with a high sensitivity and a moderate specificity. Our study supports the use of US as a screening tool in patients with bilateral swelling of the optic nerve head when the results are taken together with a complete
ophthalmological examination.
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