Intraoperative High-Field Magnetic Resonance Imaging in Transsphenoidal Surgery of Hormonally Inactive Pituitary Macroadenomas

Consensus guideline for the diagnosis and management of pituitary adenomas in childhood and adolescence: Part 1, general recommendations

Tumours of the anterior part of the pituitary gland represent just 1% of all childhood (aged <15 years) intracranial neoplasms, yet they can confer high morbidity and little evidence and guidance is in place for their management. Between 2014 and 2022, a multidisciplinary expert group systematically developed the first comprehensive clinical practice consensus guideline for children and young people under the age 19 years (hereafter referred to as CYP) presenting with a suspected pituitary adenoma to inform specialist care and improve health outcomes. Through robust literature searches and a Delphi consensus exercise with an international Delphi consensus panel of experts, the available scientific evidence and expert opinions were consolidated into 74 recommendations. Part 1 of this consensus guideline includes 17 pragmatic management recommendations related to clinical care, neuroimaging, visual assessment, histopathology, genetics, pituitary surgery and radiotherapy. While in many aspects the care for CYP is similar to that of adults, key differences exist, particularly in aetiology and presentation. CYP with suspected pituitary adenomas require careful clinical examination, appropriate hormonal work-up, dedicated pituitary imaging and visual assessment. Consideration should be given to the potential for syndromic disease and genetic assessment. Multidisciplinary discussion at both the local and national levels can be key for management. Surgery should be performed in specialist centres. The collection of outcome data on novel modalities of medical treatment, surgical intervention and radiotherapy is essential for optimal future treatment.

Trouillas's Grading and Post-Surgical Tumor Residue Assessment in Pituitary Adenomas: The Importance of the Multidisciplinary Approach

BACKGROUND

We aim to assess the role of a multidisciplinary approach in pituitary adenomas (PitNETs) classification, evaluate criteria concordance, and compare intraoperative assessments with post-operative MRIs for tumor remnants.

METHODS

Clinical, radiological, histological, and intra- and post-operative data of the treated PitNETs were extracted from prospectively created records. PitNETs were graded according to Trouillas, and the evaluation of the tumor remnants was recorded.

RESULTS

Of 362 PitNETs, 306 underwent surgery, with Trouillas grading assigned to 296. Eight-nine radiologically non-invasive PitNETs progressed to grades 1b (27), 2a (42), or 2b (20) due to proliferative or surgical invasiveness criteria. Twenty-six radiologically invasive tumors were graded 2b due to proliferative criteria. Surgical resection details and post-surgical MRI findings revealed that residual tumors were more common in grades 2a and 2b. During surgery, small tumor remnants were documented in 14 patients which were not visible on post-surgical MRI. Post-surgical MRIs identified remnants in 19 PitNETs not seen during surgery, located in lateral recesses of the sella (4), retrosellar (2), or suprasellar regions (7), along the medial wall of the cavernous sinus (6).

CONCLUSIONS

The Pituitary Board allows for the correct grading of PitNETs to be obtained and an accurate identification of high-risk patients who should undergo closer surveillance due to tumor remnants.

Intraoperative Ultrasonography in Pituitary Surgery Revisited: An Institutional Experience and Systematic Review on Applications and Considerations

OBJECTIVE

The primary objective of this systematic review is to evaluate the effectiveness of intraoperative ultrasound (IOUS) in improving outcomes in patients undergoing pituitary surgery.

METHODS

A systematic review was performed by searching MEDLINE (PubMed), Web of Science, Scopus, and Embase electronic bibliographic databases from conception to 2022.

RESULTS

The included studies yielded a total of 660 patients, with 488 patients undergoing IOUS. Outcome were available for 341 patients treated with IOUS and 157 patients who were treated without the IOUS application, and the remission rates following surgery were 76% and 59%, respectively. Only 2 studies reported remission rates for both groups, and meta-analysis for these studies showed significant superiority of intraoperative ultrasonography (Random effect, odds ratio 4.99, P < 0.01). Regarding extent of resection, IOUS resulted in 71% gross total resection, while absence of IOUS yielded a gross total resection rate of 44%. Among studies with available follow-up on IOUS, the recurrence rate was 3%. Pituitary dysfunction (34%), cerebrospinal fluid leak (31%), and central nervous system infection (8%) were the most common complications in the IOUS group. The mean follow-up was 19.97 months in studies reporting follow-up time.

CONCLUSIONS

The application of the IOUS is both safe and effective and could improve the outcome of pituitary surgeries. IOUS can assist surgeons in the identification of pituitary tumors and their surrounding anatomy and can help minimize the risk of complications associated with this complex surgical procedure.

Non-functioning pituitary macroadenoma following surgery: long-term outcomes and development of an optimal follow-up strategy

Objectives

Recurrence and regrowth of non-functioning pituitary macroadenomas (NFPMs) after surgery are common but remain unpredictable. Therefore, the optimal timing and frequency of follow-up imaging remain to be determined. We sought to determine the long-term surgical outcomes of NFPMs following surgery and develop an optimal follow-up strategy.

Methods

Patients underwent surgery for NFPMs between 1987 and 2018, with a follow-up of 6 months or more, were identified. Demographics, presentation, management, histology, imaging, and surgical outcomes were retrospectively collected.

Results

In total, 383 patients were included; 256 were men (256/383; 67%) with median follow-up of 8 years. Following primary surgery, 229 patients (229/383; 60%) achieved complete resection. Of those, 28 (28/229; 11%) developed recurrence, including six needed secondary surgery (6/229; 3%). The rate of complete resection improved over time; in the last quartile of cases, 77 achieved complete resection (77/95; 81%). Reoperation-free survival at 5, 10 and 15 years was 99%, 94% and 94%, respectively. NFPMs were incompletely resected in 154 patients (154/383; 40%); of those, 106 (106/154; 69%) had regrowth, and 84 (84/154; 55%) required reoperation. Surgical reintervention-free survival at 5, 10 and 15 years was 74%,49% and 35%, respectively. Young age and cavernous sinus invasion were risk factors for undergoing reoperation (P < 0.001 and P < 0.0001, respectively) and radiotherapy (P = 0.003 and P < 0.001, respectively). Patients with residual tumour required reoperation earlier than those underwent complete resection (P = 0.02). Radiotherapy to control tumour regrowth was delivered to 65 patients (65/383; 17%) after median time of 1 year following surgery. Radiotherapy was administered more in patients with regrowth of residual disease (61/106; 58%) than those who had NFPMs recurrence (4/28; 14%) (P ≤ 0.001) Following postoperative radiotherapy, one patient (1/65; 2%) had evidence of regrowth, seven (7/65; 11%) had tumour regression on imaging, and no patients underwent further surgery.

Conclusions

NFPMs recurrence and regrowth are common, particularly in patients with residual disease post-operatively. We propose a follow-up strategy based on stratifying patients as "low risk" if there is no residual tumour, with increasing scan intervals, or "high risk" if there is a residual tumour, with annual scans for at least five years and extended lifelong surveillance after that.

Skull-Base Surgery—A Narrative Review on Current Approaches and Future Developments in Surgical Navigation

Surgical navigation technology combines patient imaging studies with intraoperative real-time data to improve surgical precision and patient outcomes. The navigation workflow can also include preoperative planning, which can reliably simulate the intended resection and reconstruction. The advantage of this approach in skull-base surgery is that it guides access into a complex three-dimensional area and orients tumors intraoperatively with regard to critical structures, such as the orbit, carotid artery and brain. This enhances a surgeon’s capabilities to preserve normal anatomy while resecting tumors with adequate margins. The aim of this narrative review is to outline the state of the art and the future directions of surgical navigation in the skull base, focusing on the advantages and pitfalls of this technique. We will also present our group experience in this field, within the frame of the current research trends.

Identification of tumor residuals in pituitary adenoma surgery with intraoperative MRI: do we need gadolinium?

OBJECTIVE

To evaluate the diagnostic accuracy of high-resolution T2w intraoperative magnetic resonance imaging (iMRI) for detecting pituitary adenoma remnants compared to contrast-enhanced T1-weighted images.

METHODS

42 patients underwent iMRI-guided resection of large pituitary macroadenomas and fulfilled the inclusion criteria for this retrospective analysis. Intraoperative and postoperative imaging evaluation of tumor residuals and localization were assessed by two experienced neuroradiologists in a blinded fashion. The diagnostic accuracy of T2w and contrast-enhanced T1w images were evaluated.

RESULTS

The diagnostic accuracy for detecting tumor residuals of high-resolution T2w images showed highly significant association to contrast-enhanced T1w images (p < 0.0001). Furthermore, identification rate of tumor remnants in different compartments, e.g., cavernous sinus, was comparable. In total, coronal T2w images provided a diagnostic sensitivity of 97.7% and specificity of 100% compared to the gold standard of contrast-enhanced T1w images. The postoperatively expected extent of resection proved to be true in 97.6% according to MRI 3 months after resection.

CONCLUSIONS

High-resolution T2w intraoperative MR images provide excellent diagnostic accuracy for detecting tumor remnants in macroadenoma surgery with highly significant association compared to T1w images with gadolinium. The routine-use and need of gadolinium in these patients should be questioned critically in each case in the future.

Pituitary surgery and volumetric assessment of extent of resection: a paradigm shift in the use of intraoperative magnetic resonance imaging

OBJECTIVE

The aim of this study was to quantitatively assess the role of intraoperative high-field 3-T MRI (3T-iMRI) in improving the gross-total resection (GTR) rate and the extent of resection (EOR) in endoscopic transsphenoidal surgery (TSS) for pituitary adenomas.

METHODS

Radiological and clinical data from a prospective database were retrospectively analyzed. Volumetric measurements of adenoma volumes pre-, intraoperatively, and 3 months postoperatively were performed in a consecutive series of patients who had undergone endoscopic TSS. The quantitative contribution of 3T-iMRI was measured as a percentage of the additional rate of GTR and of the EOR achieved after 3T-iMRI.

RESULTS

The cohort consisted of 50 patients (51 operations) harboring 33 nonfunctioning and 18 functioning pituitary adenomas. Mean adenoma diameter and volume were 21.1 mm (range 5–47 mm) and 5.23 cm3 (range 0.09–22.14 cm3), respectively. According to Knosp's classification, 10 cases were Grade 0; 8, Grade 1; 17, Grade 2; 12, Grade 3; and 4, Grade 4. Gross-total resection was the surgical goal (targeted [t]GTR) in 34 of 51 operations and was initially achieved in 16 (47%) of 34 at 3T-iMRI and in 30 (88%) of 34 cases after further resection. In this subgroup, the EOR increased from 91% at 3T-iMRI to 99% at the 3-month MRI (p < 0.05). In the 17 cases in which subtotal resection (STR) had been planned (tSTR), the EOR increased from 79% to 86% (p < 0.05) and GTR could be achieved in 1 case. Intrasellar remnants were present in 20 of 51 procedures at 3T-iMRI and in only 5 (10%) of 51 procedures after further resection (median volume 0.15 cm3). Overall, the use of 3T-iMRI led to further resection in 27 (53%) of 51 procedures and permitted GTR in 15 (56%) of these 27 procedures; thus, the GTR rate in the entire cohort increased from 31% (16 of 51) to 61% (31 of 51) and the EOR increased from 87% to 95% (p < 0.05).

CONCLUSIONS

The use of high-definition 3T-iMRI allowed precise visualization and quantification of adenoma remnant volume. It helped to increase GTR and EOR rates in both tGTR and tSTR patient groups. Moreover, it helped to achieve low rates of intrasellar remnants. These data support the use of 3T-iMRI to achieve maximal, safe adenoma resection.

Transsellar Ultrasound in Pituitary Surgery With a Designated Probe: Early Experiences

BACKGROUND

Anatomic orientation in transsphenoidal surgery can be difficult, and residual tumors are common. A major limitation of both direct microscopy and endoscopic visualization is the inability to see below the surface of the surgical field to confirm the location of vessels, nerves, tumor remnants, and normal pituitary tissue.

OBJECTIVE

To present our initial experience with a new forward-looking, custom-designed ultrasound probe for transsellar imaging.

METHODS

The center frequency of the prototype tightly curved linear array, bayonet-shaped probe is 12 MHz. Twenty-four patients with pituitary adenomas were included after informed consent.

RESULTS

With the use of transsellar ultrasound, we could confirm the location of important neurovascular structures and improve the extent of resection in 4 of 24 cases, as rated subjectively by the operating surgeons. Image quality was good. In 17 patients (71%), biochemical cures and/or complete resections were confirmed at 3 months.

CONCLUSION

We found the images from our custom-designed ultrasound probe to be clinically helpful for anatomic orientation during surgery, and the technology is potentially helpful for improving the extent of resection during transsphenoidal surgery. This quick and flexible form of intraoperative imaging in transsphenoidal surgery could be of great support for surgeons in both routine use and difficult cases. The concept of transsellar intraoperative ultrasound imaging can be further refined and developed.

An advanced navigation protocol for endoscopic transsphenoidal surgery

OBJECTIVE

To report our clinical experience with an advanced navigation protocol that provides seamless integration into the operating workflow of endoscopic transsphenoidal surgery.

PATIENTS AND METHODS

From 32 consecutive cases of endoscopic transsphenoidal surgery, an optimal setup of continuous electromagnetic instrument navigation was created. Additionally, our standard multimodality image navigation of T1-weighted magnetic resonance (MR) images for soft tissue, MR angiogram for vascular structures, and computed tomography (CT) for solid bone was advanced by the addition of a CT surface rendering for fine paranasal sinus structures. The anatomic structures visualized and their clinical impacts were compared between standard and advanced visualization protocol. Bone-windowed CT images served as reference. The accuracy of the navigation setup was assessed by intraoperative landmark tests. Potential tissue shift was calculated by comparing pre- and postoperative MR angiograms of 20 macroadenomas.

RESULTS

After a learning curve of 2 cases (1 ferromagnetic interference and 1 dislocation of the patient reference tracker), the advanced navigation protocol was feasible in 30 cases. Advanced multimodality imaging was able to visualize significantly finer paranasal sinus structures than multimodality image navigation without CT surface rendering, equal to bone-windowed CT images (P < 0.001, McNemar test). This was found helpful for orientation in cases of complex sphenoid sinus anatomy. The accuracy of the advanced navigation setup corresponded to standard optic navigation with skull fixation. A tissue shift of median 2 mm (range 0-9 mm) was observed in the posterior genu of the internal carotid arteries after tumor resection.

CONCLUSIONS

The advanced navigation protocol permits continuous suction-tracked navigation guidance during endoscopic transsphenoidal surgery and optimal visualization of solid bone, fine paranasal sinus structures, soft-tissue and vascular structures. This may add to the safety of the procedure especially in cases of anatomical variations and in cases of recurrent adenomas with distorted anatomy.

Intraoperative high-field MRI for transsphenoidal reoperations of nonfunctioning pituitary adenoma

OBJECT

The loss of anatomical landmarks, frequently invasive tumor growth, and tissue changes make transsphenoidal reoperation of nonfunctioning pituitary adenomas (NFAs) challenging. The use of intraoperative MRI (iMRI) may lead to improved results. The goal of this retrospective study was to evaluate the impact of iMRI on transsphenoidal reoperations for NFA.

METHODS

Between September 2002 and July 2012, 109 patients underwent reoperations in which 111 transsphenoidal procedures were performed and are represented in this study. A 1.5-T Magnetom Sonata Maestro Class scanner (Siemens) was used for iMRI. Follow-up iMRI scans were acquired if gross-total resection (GTR) was suspected or if no further removal seemed possible.

RESULTS

Surgery was performed for tumor persistence and regrowth in 26 (23%) and 85 (77%) patients, respectively. On the initial iMRI scans, GTR was confirmed in 19 (17%) patients. Remnants were located as follows: 65 in the cavernous sinus (71%), 35 in the suprasellar space (38%), 9 in the retrosellar space (10%). Additional resection was possible in 62 (67%) patients, resulting in a significant volume reduction and increased GTR rate (49%). The GTR rates of invasive tumors on initial iMRI and postoperative MRI (poMRI) were 7% and 25%, respectively. Additional remnant resection was possible in 64% of the patients. Noninvasive tumors were shown to be totally resected on the initial iMRI in 31% of cases. After additional resection for 69% of the procedures, the GTR rate on poMRI was 75%. Transcranial surgery to resect tumor remnants was indicated in 5 (5%), and radiotherapy was performed in 29 (27%) patients. After GTR, no recurrence was detected during a mean follow-up of 2.2 ± 2.1 years.

CONCLUSIONS

The use of iMRI in transsphenoidal reoperations for NFA leads to significantly higher GTR rates. It thus prevents additional operations and reduces the number of tumor remnants. The complication rates do not exceed the incidences reported in the literature for primary transsphenoidal surgery. If complete tumor resection is not possible, iMRI guidance can facilitate tumor volume reduction.

Determining the utility of intraoperative magnetic resonance imaging for transsphenoidal surgery: a retrospective study

OBJECT

Intraoperative MRI (iMRI) provides updated information for neuronavigational purposes and assessments on the status of resection during transsphenoidal surgery (TSS). The high-field technique additionally provides information about vascular structures at risk and precise information about extrasellar residual tumor, making it readily available during the procedure. The imaging, however, extends the duration of surgery. To evaluate the benefit of this technique, the authors conducted a retrospective study to compare postoperative outcome and residual tumor in patients who underwent conventional microsurgical TSS with and without iMRI.

METHODS

A total of 143 patients were assessed. A cohort of 67 patients who had undergone surgery before introduction of iMRI was compared with 76 patients who had undergone surgery since iMRI became routine in TSS at the authors' institution. Residual tumor, complications, hormone dependency, biochemical remission rates, and improvement of vision were assessed at 6-month follow-up. A volumetric evaluation of residual tumor was performed in cases of parasellar tumor extension.

RESULTS

The majority of patients in both groups suffered from nonfunctioning pituitary adenomas. At the 6-month follow-up assessment, vision improved in 31% of patients who underwent iMRI-assisted surgery versus 23% in the conventional group. One instance of postoperative intrasellar bleeding was found in the conventional group. No major complications were found in the iMRI group. Minor complications were seen in 9% of patients in the iMRI group and in 5% of those in the conventional group. No differences between groups were found for hormone dependency and biochemical remission rates. Time of surgery was significantly lower in the conventional treatment group. Overall a residual tumor was found after surgery in 35% of the iMRI group, and 41% of the conventional surgery group harbored a residual tumor. Total resection was achieved as intended significantly more often in the iMRI group (91%) than in the conventional group (73%) (p < 0.034). Patients with a planned subtotal resection showed higher mean volumes of residual tumor in the conventional group. There was a significantly lower incidence of intrasellar tumor remnants in the iMRI group than in the conventional group. Progression-free survival after 30 months was higher according to Kaplan-Meier analysis with the use of iMRI, but a statistically significant difference could not be shown.

CONCLUSIONS

The use of high-field iMRI leads to a significantly higher rate of complete resection. In parasellar tumors a lower residual volume and a significantly lower rate of intrasellar tumor remnants were shown with the technique. So far, long-term follow-up is limited for iMRI. However, after 2 years Kaplan-Meier analyses show a distinctly higher progression-free survival in the iMRI group. No significant benefit of iMRI was found for biochemical remission rates and improvement of vision. Even though the surgical time was longer with the adjunct use of iMRI, it did not increase the complication rate significantly. The authors therefore recommend routine use of high-field iMRI for pituitary surgery, if this technique is available at the particular center.

Tumor shrinkage after transsphenoidal surgery for nonfunctioning pituitary adenoma

OBJECT

Volume reduction of nonfunctioning pituitary adenomas has been described, for example, after radiotherapy and pituitary tumor apoplexy. Even when considerable remnants remain after surgery, spontaneous shrinkage and relief of mass lesion symptoms can sometimes occur. The aim of this study was to assess shrinkage of tumor residues after transsphenoidal surgery and to identify predictors of tumor shrinkage.

METHODS

A total of 140 patients with postoperative remnants of nonfunctioning pituitary adenomas treated at the Department of Neurosurgery, University Hospital Erlangen, Erlangen, Germany, were included in this study. All patients underwent transsphenoidal procedures with guidance by 1.5-T intraoperative MRI. The intraoperative images of remnants were compared with images taken at 3 months and at 1 year after surgery. The possible predictors analyzed were age; sex; preoperative and intraoperative tumor dimensions; tumor growth pattern; endocrinological, ophthalmological, and histological characteristics; and history of previous pituitary surgery. For statistical analyses, the Fisher's exact test, Mann-Whitney U-test, and multivariate regression table analysis were used.

RESULTS

Follow-up imaging 3 months after surgery showed tumor remnant shrinkage of 0.5 ± 0.6 cm3 for 70 (50%) patients. This reduction was 89% ± 20% of the residual volume depicted by intraoperative MRI. In 45 (64%) patients, the remnants disappeared completely. Age, sex, and preoperative tumor volume did not significantly differ between the shrinkage and no-shrinkage groups. Positive predictors for postoperative shrinkage were cystic tumor growth (p = 0.02), additional resection of tumor remnants guided by intraoperative MRI (p = 0.04), smaller tumor volume (p = 0.04), and smaller craniocaudal tumor diameter of remnants (p = 0.0014). Negative predictors were growth into the cavernous sinus (p = 0.009), history of previous pituitary surgery (p = 0.0006) and tumor recurrence (p = 0.04), and preoperative panhypopituitarism (p = 0.04). Multivariate regression analysis indicated a positive correlation between tumor shrinkage and smaller tumor remnants (p < 0.0001) and no history of previous pituitary surgery (p = 0.003). No spontaneous change in tumor remnant volume was detected between 3 months and 1 year postoperatively. During a mean follow-up time of 2.7 years, 1 (2%) patient with postoperative tumor shrinkage had to undergo another operation because of tumor progression.

CONCLUSIONS

Spontaneous volume reduction of nonfunctioning pituitary adenoma remnants can occur within 3 months after surgery. Predictors of shrinkage are smaller tumor remnant volume and no history of previous pituitary surgery.

Endoscopic endonasal transsphenoidal surgery for growth hormone-secreting pituitary adenomas

OBJECT

The aim of this study was to determine the preoperative predictors of the extent of resection and endocrinological remission following endonasal endoscopic removal of growth hormone (GH)-secreting pituitary adenomas.

METHODS

The authors analyzed a prospectively collected database of 24 consecutive acromegalic patients who underwent endoscopic endonasal transsphenoidal surgery. The extent of resection was evaluated on postoperative contrast-enhanced MR imaging. Endocrinological remission was defined as normal insulin-like growth factor I (IGFI) serum levels and either a nadir GH level of < 0.4 ng/ml after an oral glucose load or a basal GH serum level < 1 ng/ml.

RESULTS

The majority of acromegalic patients (83%) had macroadenomas > 1 cm in maximum diameter. Gross-total resection was achieved in 17 (71%) of 24 patients. Notably, endoscopic transsphenoidal surgery allowed complete resection of all lesions without cavernous sinus invasion, regardless of the suprasellar extent. Biochemical remission was achieved in 11 (46%) of 24 patients. A smaller tumor volume and a postoperative reduction in GH serum levels were associated with a higher rate of biochemical cure (p < 0.05). During a 23-month follow-up period 5 patients (21%) underwent Gamma Knife treatment of any residual disease to further reduce excess GH production. Twenty patients (83%) reported significant relief of their symptoms, while 3 (13%) considered their symptoms stable. Two patients (8%) with large macroadenomas experienced postoperative panhypopituitarism, and 2 patients (8%) suffered from CSF leaks, which were treated with lumbar CSF diversion.

CONCLUSIONS

A purely endoscopic endonasal transsphenoidal adenoma resection leads to a high rate of gross-total tumor resection and endocrinological remission in acromegalic patients, even those harboring macroadenomas with wide suprasellar extension. Extended approaches and angled endoscopes are useful tools for increasing the extent of resection.

Intraoperative magnetic resonance imaging in pituitary macroadenoma surgery: an assessment of visual outcome

✓Pituitary macroadenomas most frequently present with visual loss. Although transsphenoidal surgery remains the treatment of choice for patients with neurological manifestations, there have been several advances in its implementation over the last 5 years. Intraoperative magnetic resonance (MR) imaging has emerged as a novel quality control measure, with the potential to guide the surgeon to tumor remnants concealed from the operating microscope. Investigators have reported enhanced resections when using intraoperative MR imaging, leading to complete tumor removal in a larger proportion of cases. Further debulking of unresectable lesions may also prove beneficial in delaying symptom recurrence and facilitating radiotherapy, where distance between the tumor and optic chiasm is an important predictor of visual outcome. However, confirmation of such advantages is complicated by the fact that most macroadenomas are both indolent and hormonally silent, necessitating years of follow-up. Experienced pituitary surgeons will operate as safely with intraoperative MR imaging as without it, perhaps due to a balance between more elaborate resections and better visualization. Intraoperative MR imaging represents a new technique applied to an old problem in tumor surgery: complete, safe resection.

AN INTEGRATED RADIO FREQUENCY PROBE AND CRANIAL CLAMP FOR INTRAOPERATIVE MAGNETIC RESONANCE IMAGING

OBJECTIVE

To design an integrated radio frequency (RF) head probe and cranial clamp for intraoperative magnetic resonance imaging (MRI) that do not interfere with the operating procedures.

METHODS

A concept based on four inductively coupled rings was developed and applied for an intraoperative RF probe. The probe was integrated with a specially designed cranial clamp and incorporated into the intraoperative MRI system.

RESULTS

The design of the RF probe allows splitting the probe into two separate parts; the lower two rings and matching ring are permanently incorporated into the patient table, and the two upper rings can be removed to expose the patient's head during neurosurgery. The probe produces a homogeneous B1 field over the entire region of interest with sufficient sensitivity to obtain high quality images. The cranial clamp, made of MRI compatible materials, is asymmetrical to allow variable head positioning.

CONCLUSION

The described RF head probe and cranial clamp have been used successfully in more than 400 brain surgeries without compromising sterility of the operating area. Pre-, intra-, and postsurgical MRI scans have been obtained without a need to move a patient or reposition the head for imaging sessions. The images were of high quality and free of susceptibility or eddy currents artifacts. With minor modifications, the integrated RF probe and cranial clamp can be used successfully in other intraoperative MRI systems.