To study the diagnostic accuracy of ultrasonographic optic nerve sheath diameter (ONSD) measurement in evaluation of raised ICP in traumatic brain injury patients in ED : Comparison with CT imaging

Global Burden of Traumatic Brain Injury (TBI)-Traumatic brain injury (TBI) is a major contributor to death and disability globally, with significant social, economic, and healthcare implications. According to the Global Burden of Disease (GBD) Study, TBI affects more than 69 million people worldwide annually, with the incidence steadily rising due to increasing rates of motor vehicle accidents, falls, and interpersonal violence . Low- and middle-income countries bear a disproportionate share of this burden, accounting for more than 90% of trauma-related deaths.India, in particular, reports over 1.5 to 2 million TBIs annually, with a significant number occurring in young adults and economically productive age groups.TBI encompasses a broad spectrum of neurological injuries resulting from external mechanical forces, ranging from mild concussions to severe injuries with life-threatening complications. One of the most critical and potentially fatal consequences of TBI is raised intracranial pressure (ICP). Elevated ICP, if not recognized and managed early, can lead to cerebral herniation, brainstem compression, ischemia, and eventually death. Therefore, early detection and appropriate management of raised ICP are vital in reducing TBI-related morbidity and mortality.

Pathophysiology and Clinical Implications of Raised ICP-Intracranial pressure is normally maintained within a tightly regulated range (typically 7–15 mmHg in adults). In TBI, mechanisms such as cerebral edema, hematoma formation, impaired cerebrospinal fluid (CSF) drainage, and auto regulatory failure disrupt this equilibrium, leading to increased ICP[6] . Elevated ICP reduces cerebral perfusion pressure (CPP), jeopardizing oxygen and nutrient delivery to brain tissues. The progression of intracranial hypertension, particularly if rapid or sustained, is associated with worse neurological outcomes, prolonged hospital stays, and increased mortality rates.Clinically, raised ICP manifests through signs like altered mental status, vomiting, papilledema, asymmetric pupils, motor posturing, and Cushing’s triad. However, these clinical indicators are neither specific nor sensitive, particularly in early stages or in sedated and intubated patients, limiting their utility as sole diagnostic criteria.

Current Modalities for ICP Assessment-The gold standard for ICP monitoring is invasive intracranial pressure monitoring, typically via an intraventricular catheter or intraparenchymal probe. While accurate and sensitive, these procedures are technically complex, invasive, resource-intensive, and carry risks including infection, hemorrhage, and malfunction . Additionally, such modalities are often unavailable in many emergency departments, especially in low-resource or rural settings. Non-invasive alternatives have therefore been developed, including neuroimaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI). CT imaging is widely used in emergency settings to assess intracranial pathology. It can reveal indirect signs of elevated ICP such as midline shift, effaced sulci, compressed ventricles, obliteration of basal cisterns, and signs of impending herniation . However, CT scanning has several limitations. It exposes patients to ionizing radiation, may necessitate the transport of unstable patients, and does not allow for dynamic or continuous monitoring of ICP.MRI provides superior soft tissue detail and is more sensitive for detecting diffuse axonal injury and brainstem lesions. However, it is time-consuming, expensive, and rarely available on an emergent basis, especially in critical care or trauma bays.

Emerging Role of Ultrasonographic ONSD Measurement-Given the limitations of current diagnostic tools, there is a growing interest in point-of-care ultrasonography (POCUS), especially for the evaluation of critically ill patients. Among its many applications, optic nerve sheath diameter (ONSD) measurement via trans orbital ultrasonography has emerged as a promising, non-invasive method for estimating ICP. Anatomically, the optic nerve is an extension of the central nervous system, enveloped by the dura mater and surrounded by cerebrospinal fluid within the subarachnoid space. When ICP rises, pressure is transmitted along the CSF pathways, causing distension of the optic nerve sheath — a phenomenon that can be visualized and measured with high-frequency ultrasound[13,14] .Ultrasonographic measurement of ONSD is a bedside, real-time, repeatable, and radiation-free procedure that can be performed by trained emergency physicians and intensivists. Several studies have demonstrated a strong correlation between ONSD and invasively measured ICP or CT findings, with a threshold of 5.0–5.7 mm commonly suggested to indicate raised ICP.A systematic review by Dubourg et al. (2011) Involving over 500 patients found that ONSD measurement had a pooled sensitivity of 90% and specificity of 85% for detecting raised ICP[18] . Despite its potential, variability in techniques, cutoff values, and operator training has hindered its widespread adoption.

Research Gap and Justification for the Study-While several studies have validated the utility of ONSD measurement in ICU or neurocritical care settings, data from emergency departments, particularly in low-resource settings and among acutely head-injured patients, remain limited. Moreover, direct comparative studies between ONSD and CT imaging findings in the context of TBI are sparse, particularly in the Indian clinical context. Given the time-sensitive nature of raised ICP diagnosis, a reliable bedside tool like ONSD ultrasonography could significantly improve triage, management, and outcomes of TBI patients. However, for ONSD to be integrated into emergency protocols, its diagnostic accuracy must be validated in direct comparison with current standard modalities.

So we planned to conduct a cross sectional analytical study to evaluate the diagnostic accuracy of ultrasonographic ONSD measurement in identifying raised intracranial pressure in TBI patients presenting to the our emergency department of JLN Hospital Ajmer and to compare its performance with CT imaging findings. This could potentially establish ONSD ultrasonography as an adjunct or even alternative to CT in specific clinical contexts.