Transcranial Ultraound Useful Bedside Adjunct to Monitor Midline Shift in Patients with Decompressive Hemicraniectomy

A recent report by researchers in Kochi, India has shown that  transcranial ultrasound (TCS) can measure midline shift (MLS) with high accuracy and can serve as a valuable bedside tool to monitor intracerebral lesions, especially in a neurocritical care setting.

Brain midline shift (MLS) secondary to raised intracranial pressure or space-occupying lesions is a common neurological emergency. It is imperative to make an early diagnosis and reassess at periodic intervals in the neuro-ICU (intensive care unit) to decide on treatment options. It usually occurs in the setting of raised Intracranial Pressure (ICP) owing to various causes such as intracranial hemorrhage, traumatic brain injury, neoplasms and secondaries, hydrocephalus, cerebral edema, etc. Some of the above conditions result in a prolonged hospital stay. These patients require serial follow-up with multimodal investigations such as computed tomography (CT) or magnetic resonance imaging (MRI). Shifting a comatose patient repeatedly for neuroimaging and the cumulative radiation exposure becomes troublesome and time consuming. Bedside MRI is only available in the US in select centers. Usage of transcranial ultrasonography (TCS) helps in serially monitoring a patient at the bedside. Bedside monitoring, avoidance of radiation exposure, and cost effectiveness are additional advantages. With TCS, follow-up of the patient is convenient as it can also be done in an outpatient clinic. Ultrasound waves are used to image the intracranial structures and perform measurements. Due to the nature of ultrasound waves, it cannot be performed in patients with thick skulls, elderly individuals, or where a bone window does not exist.

Decompressive craniectomy is performed to reduce the ICP. Even after decompressive craniectomy, MLS may progress or change and require additional therapeutic interventions. Theoretically, such patients make ideal candidates for TCS as a large iatrogenic bone-free window is available for repeated measurements. Visualization of brain anatomy is much easier and more convenient in these patients.

In the study, which was published in neurology india, the authors included patients who had undergone decompressive craniectomy due to various reasons like ICH, traumatic brain injury, etc., and have a MLS. Trans cranial ultrasonography was assessed by a single consultant (Neuro Critical Care Intensivist) who was blinded for the CT scan measurement. CT scan measurement of MLS was assessed by a neuroradiologist using standard guidelines, who was blinded for the TCS results of MLS. The finding of a MLS >0.5 cm in the CT scan was considered a significant MLS.

The authors found that the biggest difference between CT MLS and TCS MLS was 0.2 cm. This was likely because the absence of cranium makes the ultrasound penetrate intracerebral contents with ease and gives a clear, high-resolution picture. The the correlation (r2) using Pearson's correlation coefficient between CT and TCS was 0.99 and P value of <0.00001. ICC calculated between CT-MLS and TCS MLS was 0.996, indicating an almost perfect agreement. Significant MLS was detected in 24/31 of the patients, which showed that the ability to detect significant MLS was good. The study showed that even with the limitations, it has the ability to detect a significant MLS in decompressive craniectomy patients. Although CT Brain is considered as the gold standard in assessing the prognosis of the patient in decompressive craniectomy, the TCS  provides an alternative method to serial CT scans.

 TCS definitely is useful in assessing MLS after the initial CT and is definitely a substitute for serial CT scans. The current study has shown that TCS can measure MLS with high accuracy and can serve as a valuable bedside tool to monitor intracerebral lesions. The authors hope that it would pave the way for further studies with large sample sizes and different intracerebral parameters as well as encourage neurocritical care specialists to utilize this bedside tool.

Reference

Maramattom, Boby V.; Abraham, Mathew; Sundararajan, Ananthram. Assessment of Midline Shift in Postdecompressive Craniectomy Patients in Neurocritical Care: Comparison between Transcranial Ultrasonography and Computerized Tomography. Neurology India 71(6):p 1167-1171, Nov–Dec 2023. | DOI: 10.4103/0028-3886.391386