Reliability of transcranial sonography for assessment of brain midline shift in adult neurocritical patients: a systematic review and meta-analysis

Transcranial sonography in the critical patient

Transcranial ultrasonography is a non-invasive, bedside technique that has become a widely implemented tool in the evaluation and management of neurocritically ill patients. It constitutes a technique in continuous growth whose fundamentals (and limitations) must be known by the intensivist. This review provides a practical approach for the intensivist, including the different sonographic windows and planes of insonation and its role in different conditions of the neurocritical patients and in critical care patients of other etiologies.

Neuro Point-of-Care Ultrasound

As the scope of point-of-care ultrasound (POCUS) expands in clinical medicine, its application in neurological applications offers a non-invasive, bedside diagnostic tool. With historical insights, detailed techniques and clinical applications, the chapter provides a comprehensive overview of neurology-based POCUS. It examines the applications, emphasizing its role when traditional neuroimaging is inaccessible or unsafe as well advocating for its use as an adjunctive tool, rather than a replacement of advanced imaging. The chapter covers a range of uses of neuro POCUS including assessment of midline shift, intracranial hemorrhage, hydrocephalus, vasospasm, intracranial pressure, cerebral circulatory arrest, and ultrasound-guided lumbar puncture.

Reliability of Third Ventricle Assessment by Transcranial Ultrasound: A Computational Model of the Effect of Insonation Angle

INTRODUCTION

Transcranial sonography (TCS) is a bedside examination which is currently used in multiple neurocritical care settings. Third ventricle ultrasound is usually a simple technique, though a large insonation angle could lead to an overestimation of third ventricular diameter. The aim of this study was to use a mathematical model to evaluate the impact of probe inclination on the false positive rate when using TCS to evaluate third ventricle enlargement.

METHODS

Using R software, we simulated a pool of 100,000 fictitious patients with a normal third ventricle size (diameter from 0 to 9 mm) in daily follow-up for ventricle enlargement for 30 consecutive days using TCS. Each day, a different, random insonation angle (α) was generated and a corresponding measured diameter calculated as: measured diameter=real diameter/cos α. If the measured diameter was >9.0 mm, the simulation registered a "misdiagnosis" episode and the simulation loop was interrupted; otherwise, the simulation continued to its thirtieth iteration.

RESULTS

Of the 100,000 "patient" simulations, 30,905 (30.9%) had an erroneous TCS diagnosis of ventricular enlargement. Angles of insonation >35 degrees contributed to 79.3% of the total misdiagnoses of ventricular enlargement (false positive rate, 3.71%), whereas misdiagnosis was rare when the insonation angle was ≤15 degrees (1.30% of the total misdiagnoses; false positive rate, 0.06%).

CONCLUSION

Using probe inclinations <15 degrees, erroneous diagnosis of third ventricular enlargement was rare. Our results suggest that TCS has a low rate of false positives when the angle of insonation is minimized.