Thomas Mindermann

Erratum to: Gamma Knife, CyberKnife or micro-multileaf collimator LINAC for intracranial radiosurgery?

The original version of this article unfortunately contained mistakes. Contrary to what is written in the article, it should read “in certain instances the dose rate may be as much as 5 times higher” in CK technology than in Gamma Knife technology (instead of “at least 5 times higher”). Also, the correct reference 6 should be: 6. Kaul D, Badakhshi H, Gevaert T, Pasemann D, Budach V, Tulaesca C, Gruen A, Prasad V, Levivier M, KufeldM (2014) Dosimetric comparison of different treatment modalities for stereotactic radiosurgery of meningioma. Acta Neurochir. doi:10.1007/s00701-014-2272-9

Delayed diagnosis of myocardial infarction due to deep brain stimulation

Dear Editor, We report the case of a patient in whom diagnosis of myocardial infarction was delayed because of deep brain stimulation (DBS). To our knowledge, this is the first case reported in the literature. Increasing numbers of DBS devices are implanted worldwide for various indications. DBS seems to be compatible with cardiac pacemakers (1) and with routine electrocardiogram (ECG) (3). Because of stimulation artifacts, routine ECG is usually performed with stimulators turned off. ECG tracings with stimulators turned on may cause problems with ECG readings (2, 3). In emergency situations interference of stimulation artifacts with ECG readings may cause significant problems if the stimulation cannot be turned off in time. To illustrate such potential problems, we present the following case.

Radiosurgery for mesial temporal lobe epilepsy

There are several microsurgical approaches for mesial temporal lobe epilepsy (MTLE) of which the selective amygdalohippocampectomy (SAH) has evolved as the most popular intervention based on a comparably high success rate and low complication rates [6]. In addition, minimally invasive techniques have been evaluated such as stereotactic radiosurgery (SRS) and thermal ablation methods based on stereotactic radiofrequency or laser-induced thermal therapy. MRI-guided focused ultrasound ablation may be another potential method. In this issue, the group of Liscak from Prague reports on their 20-year-long experience with Gamma Knife radiosurgery (GKRS) for MTLE [8]. Like many other centers [1, 2, 7], the authors do not seem to be very happy with their results. On the other hand, neuropsychological outcomes following GKRS for MTLE seem to be favorable [4]. Not surprisingly, GKRS for MTLE is far from being generally accepted, and it has been the subject of editorials before [3]. There are several peculiarities that need to be considered regarding radiosurgery for MTLE. In SAH, a larger volume resection seems to correlate to a better seizure control rate. In GKRS, a larger target volume also seems to correlate to a better seizure control rate, yet at the cost of more and more severe adverse radiation effects (AREs). Because of the target’s location between the brain stem and visual pathways, AREs following radiosurgery for MTLE may be severe and are potentially life threatening. They may require emergency surgery. On the other hand, the transient MR changes are the desired effect of functional radiosurgery indicating neuromodulation. They occur following radiosurgery for movement disorders or obsessive compulsive disorders where they do not indicate a problem. In the treatment of tumors or AVMs, they would be considered a complication that one tries to avoid at almost any cost. Like in other functional disorders, they are actually the desired effect following radiosurgery for MTLE. Ideally, the transient MR changes of the temporal lobe indicate the process of the desired neuromodulation [5] and not radionecrosis, and they seem to correlate with the success rate. Therefore, the dilemma that radiosurgeons face in the treatment of MTLE is to apply a high enough dose leading to what is usually considered an ARE resulting in neuromodulation rather than radionecrosis and at the same time cover a large enough target volume without putting the patient at risk of an excessive ARE. Unfortunately, this dilemma has not yet been resolved. An interesting and elegant approach may be the use of radiosurgery as a second-line treatment in case of persisting or recurrent seizures following SAH or anterior temporal lobectomy [9]. In such cases, the residual target volume is smaller than in firstline treatments, which should reduce the risk of excessive AREs. It would not be surprising if in the future radiosurgery for MTLE were to be reserved for failed surgery cases. The comparison of radiosurgery and open surgery for MTLE is subject to an ongoing prospective, international, multicenter study, the ROSE Trial (Radiosurgery or Open Surgery for Epilepsy). Until the results of this trial are out, radiosurgery for MTLE has to be considered experimental and should only be performed within the strict guardrails of scientific trials approved by ethical committees. * Thomas Mindermann tmindermann@hin.ch; http://www.mindermann.ch

On government-regulated access to diagnostic imaging in neurosurgery

The authors of BThe role of computed tomography in the screening of patients presenting with symptoms of an intracranial tumor^ [1] present their study investigating a government-regulated diagnostic pathway to detect brain tumors in patients who are referred to radiology services by mostly primary caretakers. Because of limited availability of MRI time, Danish government regulations seem to stipulate that patients in whom a brain tumor is suspected may undergo a contrast-enhanced CT scan within 7 days of referral to a radiology service if an MRI is not available within that 7day period. In that context, the authors investigate if the sensitivity and specificity of contrast-enhanced CT scans is sufficient to detect intracranial tumors in such patients. While the study’s question is interesting, there are a number of issues that need to be addressed. Is this really the way to go ahead for the health care system of a developed country? From a neurosurgical point of view, one of the great advantages of health care in developed countries is the chance of early detection of intracranial space-occupying lesions (SOL). A good number of SOL are detected by MRI when patients are still oligosymptomatic or even before the lesions lead to focal deficits. In the present study, many of those tumors such as small meningiomas have been designated to the non-tumor patient group. Is that really appropriate? CT imaging for skull base and posterior fossa tumors is undoubtedly less than optimal. Therefore, many of such tumors may be missed on CT scans. Typically, such tumors tend to be small in comparison to supratentorial lesions and they are best treated at an early stage. Good examples are meningiomas of the cavernous sinus, of the tuberculum sellae, and of the sphenoid wing. We all have seen patients in whom meningiomas of the cavernous sinus have been missed on earlier MRIs. How are they to be detected on CT scans? All of those tumors may be treated at an early stage invasively or noninvasively with optimal long-term results sparing the patients subsequent focal deficits such as blindness, ophthalmoplegia, or worse. Small vestibular schwannomas and schwannomas of other cranial nerves are another group of tumors which may easily be missed on a CT scan. The same is true for pituitary adenomas, cerebellar hemangioblastomas, ependymoma of the posterior fossa, chordomas, chondrosarcomas, cavernomas, and small brain metastases. All patients with one or more lesions mentioned above would be designated to the study’s nontumor patient group and the lesions would most probably be missed on CT scans. Will all of those patients with false-negative CT scans receive an MRI follow-up or an adequate clinical follow-up? This is most doubtful. It is more likely that those patients will return to their primary caretaker who will then manage their further medical care. Based on the current study [1], the primary caretaker will rightly argue that the patients did undergo sufficient imaging and that no tumor or other relevant intracranial lesion had been detected. While this governmentregulated diagnostic pathway may be appropriate for larger and less benign supratentorial tumors, it will inevitably lead to less involvement of neurosurgeons at an early stage in an entire set of important intracranial lesions. In addition, one may question if it is really appropriate to submit pediatric patients to CT scanning just because an MRI is not readily available as it was the case in the present study. A great deal of improved outcomes in neurosurgery is owed to early detection of intracranial lesions and early intervention. The deeper the lesions are located, the less they are likely to be detected on CTscans and the worse is the outcome for patients if they are missed at an early stage. Should we really forgo the advantages of early tumor detection and treatment for plain regulatory reasons of a given health care system? Should pediatric patients really be exposed to radiation * Thomas Mindermann tmindermann@hin.ch

Proton-beam therapy or photon-beam radiosurgery for WHO grade I meningiomas?

Proton-beam therapy (PBT) has been in use since the early 1960s [1]. Typically, PBT has been applied in rare or paediatric neoplasms because of its costs, its specific physical properties and its rare availability. PBT’s share of radiotherapy was 0.6% in the US in 2012 [4]. In this issue of Acta Neurochirurgica, Vlachogiannis et al. [3] present their experience with PBT in 170 patients with WHO grade I meningiomas. As opposed to the classical use of PBT, their patients have neither a rare tumour type nor do they belong to the paediatric age group. Reports on PBT for more common tumours from a neurosurgical viewpoint such as meningiomas add to the competitive field of non-invasive treatments for such tumours. Until recently, PBT did not have to stand much competition from other non-invasive treatment options such as stereotactic singlesession photon-beam radiosurgery (RS) because of the rarity of the tumours treated or the paediatric age group undergoing PBT.Accordingly, PBT has been considered as part of radiation oncology, performed by radiation oncologists dealing with a rather narrow niche in terms of tumours and patients. This is going to change with the inroad of PBT into the field of more common neurosurgical neoplasms in adult patients. With the treatment of classical neurosurgical neoplasms, PBT will have to face competitive challenges and critical questions, which so far it may not have confronted. The neurosurgeon Lars Leksell developed the concept of RS and the first dedicatedmachine for such treatments, the Gamma Knife (GK). The neurosurgeon John R. Adler developed the second dedicated machine for RS, the CyberKnife (CK). RS was introduced by neurosurgeons against the resistance of radiation oncologists. Because of that resistance and in advocacy of their new concept, neurosurgeons amassed an unparalleled knowledge and experience in RS for intracranial neoplasms. As a consequence, RS is nowadays one of the best-documentedmedical treatments, withmore than 15,000 publications on Gamma Knife radiosurgery (GKRS) alone. Ideally, neurosurgeons approach tumours such as intracranial meningiomas with a concept in mind including microsurgery, RS or the combination of both. Therefore, any new treatment for classical neurosurgical neoplasms of adult patients will have to prove at least equality of results with well-established neurosurgical treatment options such as RS, stand the test of everyday clinical practice and compete with the comparably low costs of RS. Until today, the Bgold standard^ for any radiation treatment of WHO grade I meningiomas remains GKRS. Altogether, more than 100,000 patients with WHO grade I meningiomas have been treated with single-session GKRS worldwide and multicentre studies with up to 5,300 benign meningiomas in one study alone have been published, revealing excellent long-term results [2]. In addition, studies on GKRS for meningiomas exist for specific anatomical locations such as cavernous sinus, parasagittal location, skull base, foramen magnum, etc., and for specific technical aspects such as volume-staging, conformality index as a predictor to perifocal oedema formation, etc. This is an unparalleled knowledge base from which neurosurgeons may draw in planning their RS treatments. Over the years, the excellent results and the broad acceptance of RS for meningiomas has led to modifications in the surgical treatment of meningiomas. Often, a radical resection of a larger tumour or a smaller tumour in challenging locations may be avoided by leaving a tumour remnant for radiosurgery and thereby reducing the patients’ risks. Today, many meningiomas * Thomas Mindermann tmindermann@hin.ch

Do cochlear implants play a role in the induction of brain tumors

In this issue of Acta Neurochirurgica, Kalkoti et al. [2] report two cases of glioblastoma multiforme (GBM) diagnosed in patients with cochlear implants (CIs). These are the first two cases in the literature making a connection between CI and the development of brain tumors. As the authors report in their paper, until today more than 500,000 patients have received CI worldwide. At the same time, the overall incidence of primary malignant brain tumors is about 7 per 100,000 person-years, and the prevalence is about 29 per 100, 000 inhabitants in the USA [1, 3]. The most common brain tumors are meningiomas in patients older than 20 years of age. The second most common brain tumors are nerve sheath tumors and glioblastomas in patients 35–44 years of age, and glioblastomas are the second most common brain tumors in all patients older than 45 years of age [1, 3]. Glioblastomas are more common in male patients with a female-to-male ratio of 1:1.6 [1, 3]. Therefore, 1 GBM in 250,000 patients with CI is not necessarily an alarming finding from an epidemiological point of view. However, if one takes the demographics of this publication into account, the two cases may deserve a closer look. One of the patients was a 60-year-old male and the other a 42-year-old female. While the 60-year-old male patient fits the expected demographic pattern of patients with glioblastomas, the 42-year-old female patient does not quite as well. For this and other reasons, the authors’ observation should not be easily dismissed as anecdotical. So far, a number of adverse effects have been associated with CI but not the induction of brain tumors. Therefore, it is likely that a possible connection between CI and the induction of brain tumors has been underreported so far because no one ever thought about the possibility of a causal relationship. Another point that deserves attention is the latency period from the implant of the CI to the diagnosis of GBM in these two patients, which was 7 and more than 23 years, respectively. This latency period is suggestive of a causal relationship just like the GBMs’ occurrence in close proximity to the CI transmitting devices on the skull bone. Furthermore, we know that the external application of alternating electrical fields (AEFs) to the skull i n t e r f e r e s w i t h t h e a b i l i t y o f d e e p s e a t e d int raparenchymal tumor cel ls to repl icate [4] . Obviously, this kind of treatment has an effect at the subcellular level, influencing the cells’ mitotic processes. The question arises whether the application of continuous, long-term, external electrical fields to the brain as seen in CI may have a detrimental effect on the brain parenchyma, placing patients at higher risk for brain tumor induction. In conclusion, because of the demographics, tumor location, latency period, and long-term application of electrical fields to the brain, as reported in these two patients with CI, the authors may have found a problem deserving our attention. A heightened vigilance of the neurosurgical community may be indicated since neurosurgeons are the most likely specialists to see patients with CI and brain tumors. * Thomas Mindermann tmindermann@hin.ch

Intraoperative MRI in transsphenoidal surgery

Over the years, several preand intraoperative diagnostic techniques have been introduced to optimize the results of transsphenoidal surgery for pituitary adenomas. Preoperative diagnostic measures routinely consist of a CT scan and an MRI of the sellar region for visualization of the paranasal sinuses and the tumor and for data acquisition for intraoperative measures such as neuronavigation and intraoperative MRI (iMRI); an endocrine workup; and in some instances blood sampling from the inferior petrosal sinuses with an associated venography. Intraoperative diagnostic measures may consist of fluoroscopy, neuronavigation, intraoperative ultrasound [3], intraoperative inferior petrosal sinus sampling [2], endoscopy, intraoperative frozen sections for histology, or iMRI. Currently, there are two different iMRI techniques in use: low-field iMRI and high-field iMRI. The authors of this issue’s contribution “Follow-up and longterm outcome of nonfunctioning pituitary adenoma operated by transsphenoidal surgery with intraoperative high-field magnetic resonance imaging”[1] are to be commended for sharing their experience with high-field iMRI. The authors present their impressive surgical experience with endocrine inactiveor non-functioning pituitary adenomas (NFA). In 85 of the more than 1,000 cases that have undergone transsphenoidal surgery at their institution, they have performed first-time surgery with the assistance of a high-field iMRI. In some of those patients, the authors have used intraoperative endoscopy in addition. Although the authors can draw from an extraordinary caseload, some questions remain unanswered. Why was high-field iMRI used in merely less than 10 % of the cases with first-time transsphenoidal surgery for NFA? Could this have anything to do with the fact that its use is rather time-consuming? Does high-field iMRI really add so much more information in comparison to low-field iMRI? Does this justify its use over the comparably easy and quick-to-use low-field iMRI? In addition, one last question remains: why was a lateral tumor extension of Knosp grades 3 and 4 or a sphenoidal tumor extension of modified Hardyor Wilson-Hardy grades 3 and 4 present in merely less than 10 % of the patients with NFAwho underwent first-time transsphenoidal surgery when this number is more than 40 % in another study dealing with iMRI [4] and when that percentage seems so much more convincing? In other words, may there have been a selection bias? Unfortunately, this potential limitation may have an impact on the validity of the study’s results and its conclusions. While there are several studies on the use of low-field and high-field iMRI in transsphenoidal surgery, there is no direct comparison of the two methods. This is understandable, since a department of neurosurgery is unlikely to purchase both machines. On the other hand, such a comparison would be of great interest. While the goal is always to improve the success rate of pituitary surgery, at the same time the intraoperative cost and expenditure should be kept reasonable.

Observation of Shift Phenomena when Using 3T MRI Scanners in Stereotactic Radiosurgery

Background: Given the high mechanical accuracy of the Leksell Gamma Knife®, the most sensitive technical factor having an influence on the overall precision of radiosurgery is still imaging (mainly MRI). The new generation of MRI scanners, with field strengths up to 3.0 T, deliver promising image quality with regard to anatomical resolution and contrast, but critical features are the sensitivity to susceptibility and chemical shift effects which both create artifacts. Changes in the magnetic properties of the ferromagnetic plates can cause additional problems in the z direction. Methods: All sequences from all scanners to be investigated were defined automatically and manually (upper, middle and lower block) in light-guided plates. After the procedure of definition the geometric imaging quality of the 3.0-T MRI-Scanner (Siemens ‘Trio’) was analyzed and compared to a Siemens Magnetom ‘Expert’ 1.0 T and to a Philips ‘Gyroscan’ 1.5 T. The analyses were performed in three steps: (1) the evaluation of the magnitude of error was performed within transversal slices in two orientations (axial/coronal) using a cylindrical phantom with an embedded grid; (2) the deviations were determined for 21 targets in a slab phantom with known geometrical positions within the stereotactic frame, and (3) distortions caused by chemical shift and/or susceptibility effects were analyzed in a head-phantom. In-house developed software was used for data analyses. Results: For all scanners tested, the 3D-volume scan is the most sensitive to a z shift. For scan times > 10 min the shift can increase to several millimeters in the z direction. SE sequences are rather insensitive but show up with a small shift in the y direction. The 3.0-T MRI-Scanner was analyzed using sequences in axial and coronal orientations. The mean deviation was < 0.3 mm in the axial and < 0.4 mm in the coronal orientation. For the known targets the maximum deviation came up to 1.18 mm (far from the center). Due to inhomogeneities an additional shift in the z direction up to 1.5 mm was observed for a dataset which was shown compressed by 1.2 mm. By optimizing the parameters in the protocol these inaccuracies could be reduced to < 1.1 mm. Conclusions: The 3.0-T scanner showed sophisticated anatomical contrast and resolution in comparison to the established 1.0- and 1.5-T scanners. However, due to the high field strength the field within the head coil is very sensitive to inhomogeneities and therefore 3.0-T imaging data still have to be handled with care. Long scan times especially for the 3D-volume sequences lead to a warming up and to a change in the magnetic properties of the ferromagnetic plates which cause an additional effect on the main-field B0 thus disturbing the z gradient.