Background: Measurements of the optic nerve sheath diameter (ONSD) using bedside ultrasound (US) have been shown to correlate with clinical and radiologic signs and symptoms of increased intracranial pressure (ICP).

No abstract

IntroductionPoint-of-care ultrasound (POCUS) is expanding across all medical specialties. As the benefits of US technology are becoming apparent, efforts to integrate US into pre-clinical medical education are growing. Our objective was to describe our process of integrating POCUS as an educational tool into the medical school curriculum and how such efforts are perceived by students.MethodsThis was a pilot study to introduce ultrasonography into the Harvard Medical School curriculum to first- and second-year medical students. Didactic and hands-on sessions were introduced to first-year students during gross anatomy and to second-year students in the physical exam course. Student-perceived attitudes, understanding, and knowledge of US, and its applications to learning the physical exam, were measured by a post-assessment survey.ResultsAll first-year anatomy students (n=176) participated in small group hands-on US sessions. In the second-year physical diagnosis course, 38 students participated in four sessions. All students (91%) agreed or strongly agreed that additional US teaching should be incorporated throughout the four-year medical school curriculum.ConclusionPOCUS can effectively be integrated into the existing medical school curriculum by using didactic and small group hands-on sessions. Medical students perceived US training as valuable in understanding human anatomy and in learning physical exam skills. This innovative program demonstrates US as an additional learning modality. Future goals include expanding on this work to incorporate US education into all four years of medical school.

The current gold standard for the diagnosis of elevated intracranial pressure (ICP) remains invasive monitoring. Given that invasive monitoring is not always available or clinically feasible, there is growing interest in non-invasive methods of assessing ICP using diagnostic modalities such as ultrasound or magnetic resonance imaging (MRI). Increased ICP is transmitted through the cerebrospinal fluid surrounding the optic nerve, causing distention of the optic nerve sheath diameter (ONSD). In this issue of Critical Care, Geeraerts and colleagues describe a non-invasive method of diagnosing elevated ICP using MRI to measure the ONSD. They report a positive correlation between measurements of the ONSD on MRI and invasive ICP measurements. If the findings of this study can be replicated in larger populations, this technique may be a useful non-invasive screening test for elevated ICP in select populations.The recognition that elevated intracranial pressure (ICP) is transmitted through the optic nerve and its sheath has been known for many years. This physiological process is the basis for the physical exam finding of papilledema on fundoscopic examination. Recently, interest has turned to measurement of the optic nerve sheath diameter (ONSD) through noninvasive imaging technologies to provide surrogate markers for early elevated ICP. In this issue of Critical Care, Geeraerts and colleagues [1] present their research correlating magnetic resonance imaging (MRI) measurements of ONSD with ICP. In a retrospective review of 38 patients with traumatic brain injury requiring both invasive ICP monitoring and MRI, they found a significant positive relationship between ONSD measured by MRI and ICP (r = 0.71). The best cut-off value to detect an ICP > 20 cmH 2 O based on a receiver operating characteristic curve was found to be ONSD = 5.82 mm with a sensitivity of 90% and a specificity of 92%. A cut-off value of 5.30 mm yielded a sensitivity of 100%.The optic nerve is surrounded by cerebrospinal fluid (CSF), which is contiguous with intracranial CSF. Increased ICP is transmitted through this subarachnoid space causing distention of the dural optic nerve sheath, especially the retrobulbar segment [2]. The optic nerve and its surrounding sheath can be imaged and measured on MRI using a fatsuppressed T2-weighted sequence [3,4].MRI has been used to demonstrate increased ONSD in idiopathic intracranial hypertension [5], and interestingly, decreased ONSD in CSF hypotension [6]. The ONSD has also been shown on MRI to decrease after drainage of subdural hematomas [7]. The research presented by Geeraerts and colleagues is unique in its comparison of ONSD with simultaneous direct measurements of ICP through invasive monitoring.Their findings generally correlate with a growing body of research using bedside ultrasound measurements of ONSD to detected elevated ICP. Original research with lumbar intrathecal infusions performed by Hansen and Helmke [8] demonstrated rapid changes in the ONSD with alteration of CSF pressures. In em...