Aabir Chakraborty

Preliminary investigation into the use of ultrasound elastography during brain tumour resection

Introduction Differentiation of brain tumours from normal brain, during surgical resection is, in part, based on their differing mechanical properties. Brain tumours have variable stiffness characteristics. Surgical evaluations on stiffness are, at best, subjective. Ultrasound elastography is a non-invasive method for imaging mechanical properties of tissues such as stiffness at depth. It is hypothesized that this technique may assist in differentiating tumour from the brain in an intraoperative setting. Methods This study evaluated the feasibility of the intraoperative use of ultrasound elastography during brain tumour resection. A total of 24 patients were recruited for the study. Surgical findings on tumour stiffness were compared with the elastogram findings. Furthermore, visibility of the brain-tumour interface on ultrasound echography compared with ultrasound elastography was analysed. Results Ultrasound elastography was found to have a sensitivity of 100% and specificity of 75% at detecting that tumour had a different stiffness to the brain when compared with surgical findings. The technique was also found to have a 100% sensitivity and specificity at the detection of intratumoral stiffness heterogeneity compared with surgical findings. The presence of fluid-filled cysts limited the quality of the elastograms. Ultrasound elastography did not detect the brain-tumour interface as accurately as conventional echography. Conclusion These findings suggest that ultrasound elastography in combination with conventional B-mode ultrasound may be a useful adjunct to differentiate tumour from the brain.

A novel technique of detecting MRI-negative lesion in focal symptomatic epilepsy: Intraoperative ShearWave Elastography

Focal symptomatic epilepsy is the most common form of epilepsy that can often be cured with surgery. A small proportion of patients with focal symptomatic epilepsy do not have identifiable lesions on magnetic resonance imaging (MRI). The most common pathology in this group is type II focal cortical dysplasia (FCD), which is a subtype of malformative brain lesion associated with medication‐resistant epilepsy. We present a patient with MRI‐negative focal symptomatic epilepsy who underwent invasive electrode recordings. At the time of surgery, a novel ultrasound‐based technique called ShearWave Elastography (SWE) was performed. A 0.5 cc lesion was demonstrated on SWE but was absent on B‐mode ultrasound and 3‐T MRI. Electroencephalography (EEG), positron emission tomography (PET), and magnetoencephalography (MEG) scans demonstrated an abnormality in the right frontal region. On the basis of this finding, a depth electrode was implanted into the lesion. Surgical resection and histology confirmed the lesion to be type IIb FCD.

Intra-operative Ultrasound Elastography and Registered Magnetic Resonance Imaging of Brain Tumours: A Feasibility Study

Following craniotomy, the decision to resect a brain tumour is based on (1) the surgeons interpretation of preoperative imaging, such as MRI, (2) correlating the imaging to the surgical field, (3) visual inspection of the surgical field, and (4) palpation thus providing biomechanical information on tumour and brain. There is a degree of subjectivity in the use of palpation for biomechanical evaluation. Ultrasound elastography is a technique for determining more objective biomechanical information at depth in the form of relative strain, thus indirectly stiffness, within an ultrasound scan plane. In addition, neuro-navigation techniques assist in correlating preoperative imaging to the surgical field. We present two cases where ultrasound elastography with co-registered MRI, using neuro-navigation, was used intra-operatively during brain tumour resection. Correlation with the co-registered MRI was excellent in both patients. Strain contrast between brain and tumour was evident in elastograms produced in both patients; the tumour had a lower strain, hence was stiffer compared with brain. When strain applied was increased slip between tumour and brain was detected. All these findings corresponded with the surgical findings. Ultrasound elastography with co-registered MRI is a promising imaging technique, which can be used intra-operatively to provide biomechanical information prior to resection.

Slip elastography: A novel method for visualising and characterizing adherence between two surfaces in contact

Identification of the anatomical location and mechanical properties such as adherence at the tissue tumour interface may be of clinical benefit in determination of tumour resectability and prognosis. There are currently no imaging modalities in routine clinical practice that can provide this information. This paper presents the development of a new imaging technique based on ultrasound elastography, called slip elastography, for determination of the anatomical location and measurement of the adherence between two surfaces. The theoretical basis of slip and its definition in relation to shear are described. In vitro testing with gelatine phantoms to determine the optimal parameters for shear strain estimation and slip boundary measurement and to test reliability are also described. The results suggest that slip elastography can reliably identify the anatomical location of a slip boundary and can measure the externally applied axial force required to initiate slip at that boundary in vitro. The vector based shear strain estimator was the most robust and worked with minimal angular dependence with minimal non-slip shearing artefact.

Temporising extradural haematoma by craniostomy using an intraosseous needle

We report a novel application of intraosseous needle drainage, alleviating raised intracranial pressure due to extradural haematoma. The potential application of this technique in preventing secondary brain injury and herniation during transfer to a neurosurgical unit is discussed.

Temporising an extradural haematoma by intraosseous needle craniostomy in the District General Hospital by non-neurosurgical doctors – A case report:

We report the case of a 69-year-old man admitted to the emergency department of a UK district general hospital with an extradural haematoma following closed head injury. He deteriorated rapidly before transfer to the regional neurosurgical centre and was treated with decompression of the extradural haematoma through an EZ-IO™ intraosseous needle in our department, with telephone guidance from the neurosurgeon. We believe this to be the first reported use of this technique in a district general hospital.

Reply from authors to letter on Temporising an extradural haematoma by intraosseous needle craniostomy in the District General Hospital by non-neurosurgical doctors - a case report

We are grateful to Dr Wiles for his comments and are pleased that this report has provoked interest and discussion of new strategies in the emergency management of a group of patients in extremis. Our primary principle at all stages has been to have our patient’s interests as the paramount consideration – we have only attempted a technique where the individual circumstances meant that it seemed to be the most appropriate option at the time. After making this intervention, we felt it could be of interest to the wider medical community to learn of our experience, so that other clinicians could be aware of this potential treatment option under certain circumstances. To be clear, this technique has not been used as part of a clinical trial, and we do not advocate it as standard practice. This is an off-label application of an approved device, where the relevant NICE guidance advises ‘balancing the risks and benefits to the patient’ and advises consideration of ethical and legal implications. We were satisfied that the balance of risks and benefits was reasonable in the cases presented and would welcome a broader discussion of ethical and legal implications involved. Perhaps, it is worth noting that the majority of emergency neurosurgery is performed without the benefit of Class 1 evidence, reflecting the difficulty of designing and implementing effective clinical trials in this area. We entirely agree that any future trial of this technique would need to be conducted in the context of standard ethical approvals. Finally, we are grateful to Dr Wiles for highlighting the CT report which was indeed incorrect. The initial CT report at the referring hospital diagnosed an extradural haematoma, but further analysis of the images shows they are more in keeping with acute subdural haematoma. The authors regret that this was not made clear in the original manuscript.