Central nervous system MRI and cardiac implantable electronic devices

Accuracy of Patient-Specific Instrument for Cylindrical Axis Implementation in Kinematically Aligned Total Knee Arthroplasty

Background

In kinematically aligned total knee arthroplasty (KA-TKA), the cylindrical axis (CA) is very important in restoring the native joint line and kinematics of the pre-arthritic knee. This study aimed to determine the accuracy of patient-specific instrument (PSI) for restoring the CA for femoral bone resection in KA-TKA.

Methods

Thirty KA-TKAs were performed using a computed tomography (CT)-based PSI system. Data from preoperative CT were reconstructed into three-dimensional (3D) models using 3D-planning software. The CA was created by connecting the centers of each virtual sphere to the medial and lateral femoral condyles using computer software. Femoral bone resection of the distal and posterior condyles was performed parallel to the sagittal planes of the CA. The thickness of the CA-referenced bone resection was determined based on the thickness necessary for the respective regions of the femoral component. The PSI was manufactured to locate the guide pin for a conventional cutting block. The accuracy of PSI for KA-TKA was evaluated as the absolute error between the preoperatively predicted thickness and the intraoperative measurements in each of the four regions, as well as the difference in error between distal-medial (DM) and posterior-medial (PM) and between distal-lateral (DL) and posterior-lateral (PL).

Results

The differences in thickness of bone cut in the DM, DL, PM, and PL were 0.79 ± 0.39 mm (range, -1.20 to 1.50), 0.70 ± 0.42 mm (range, -1.50 to 1.50), 0.80 ± 0.46 mm (range, -0.80 to 1.50), and 0.75 ± 0.47 mm (range, -2.10 to 1.40), respectively. There was no significant difference in the thickness error between DM and PM (p = 0.959) and between DL and PL (p = 0.812).

Conclusions

In KA-TKA, PSI was effective for accurate femoral bone resection based on virtually planned thickness.

Feasibility, safety, and utility of brain MRI for patients with non-MRI-conditioned CIED

Feasibility, safety, and utility of brain MRI for patients with non-MRI-conditioned cardiac implantable electrical devices (CIEDs) remains controversial. While a growing number of studies have shown safe employment in select patients under strict protocols, there is an increasing clinical need for further off-label investigations. To assess the feasibility and utility of brain MRI in neurological and neurosurgical patients with non-MRI-conditioned CIEDs using off-label protocol. We retrospectively evaluated 126 patients with non-MRI-conditioned CIEDs referred to our hospital between 2014 to 2018 for MRI under an IRB-approved protocol. A total of 126 off-label brain MRI scans were performed. The mean age was 67.5 ± 13.0. Seventy percent of scans were performed on female patients. Indications for MRI are neurosurgical (45.2%), neurological (51.6%), and others (3.2%). MRI utilization for tumor cases was highest for tumor cases (68.3%), but employment was valuable for vascular (12.7%), deep brain stimulators (3.2%), and other cases (15.9%). In the tumor category, (37.2%) of the scans were performed for initial diagnosis and pre-surgical planning, (47.7%) for post-intervention evaluation/surveillance, (15.1%) for stereotactic radiosurgery treatment (CyberKnife). No clinical complications were encountered. No functional device complications of the CIED were identified during and after the MRI in 96.9% of the studies. A 49.6% of the off-label brain MRI scans performed led to a clinically significant decision and/or intervention for the patients. A 42.9% of obtained MRI studies did not change the plan of care. A 7.9% of post-scan decision-making data was not available. We demonstrate that off-label brain MRI scans performed on select patients under a strict protocol is feasible, safe, and relevant. Almost 50% of scans provided critical information resulting in clinical intervention of the patients.

State-of-the-art approach towards magnetic resonance imaging of the nervous system structures in patients with cardiac implantable electronic devices

INTRODUCTION

MRI generated forces are the source of potential complications in patients with cardiac implantable electronic devices (CIED). The technological progress, and growing clinical evidence concerning the operation of the contemporary MR non-conditional CIEDs during MRI, have started to significantly change our every-day clinical practice. Nevertheless, a lot of patients who could have an MRI performed safely, still have been refused the examination.

STATE-OF-THE-ART

In many clinical situations, an MRI examination in a patient with a CIED is reasonable, and is linked to a negligible risk of complications if performed under strict precautions. The MagnaSave Registry that evaluated the influence of nonthoracic MRI on the function of MR non-conditional CIEDs, and numerous studies involving thoracic and non-thoracic MRIs in patients with legacy CIEDs, have confirmed the feasibility and safety of such examinations. In this article, practical tips aimed towards improving the safety of MRI in MR conditional and non-conditional CIED patients are largely based on the very recently released (2017) HRS expert consensus statement.

CLINICAL IMPLICATIONS

Clinical data emphasize the necessity of making the MRI more accessible to CIED patients, also in the case of MR non-conditional systems or when the thorax MR imaging is clinically reasonable. This goal should be achieved by increasing the number of centers complying with respective recommendations and applying protocols that would guarantee the highest safety level.

FUTURE DIRECTIONS

Further studies are warranted to assess safety issues related to the main current contraindication to MRI, i.e., the presence of abandoned leads.

Diagnostic Challenge: Sequential Unilateral Cranial Neuropathies Due to Perineural Spread of Carcinoma

An 86-year old man developed sequential dysfunction of trigeminal (V1), facial, abducens, trigeminal (v2), oculomotor, and hypoglossal cranial nerves on the right over 20 months. Magnetic resonance imaging (MRI) showed a lesion in the right cavernous sinus. Although there was clinical suspicion that this was related to perineural spread of an extracranial tumour, a primary lesion was not discovered. Stereotactic biopsies of the intracranial lesion were non-diagnostic, and the patient succumbed to his tumour following a period of rapid growth. Postmortem examination showed the intracranial lesion to be a carcinoma with squamous features. This case highlights the challenges of diagnosis of intracranial perineural spread and the potential for transformation from indolent to aggressive tumour behaviour.