An intact action-perception coupling depends on the integrity of the cerebellum.

It is widely accepted that action and perception in humans functionally interact on multiple levels. Moreover, areas originally suggested to be predominantly motor-related, as the cerebellum, are also involved in action observation. However, as yet, few studies provided unequivocal evidence that the cerebellum is involved in the action perception coupling (APC), specifically in the integration of motor and multisensory information for perception. We addressed this question studying patients with focal cerebellar lesions in a virtual-reality paradigm measuring the effect of action execution on action perception presenting self-generated movements as point lights. We measured the visual sensitivity to the point light stimuli based on signal detection theory. Compared with healthy controls cerebellar patients showed no beneficial influence of action execution on perception indicating deficits in APC. Applying lesion symptom mapping, we identified distinct areas in the dentate nucleus and the lateral cerebellum of both hemispheres that are causally involved in APC. Lesions of the right ventral dentate, the ipsilateral motor representations (lobules V/VI), and most interestingly the contralateral posterior cerebellum (lobule VII) impede the benefits of motor execution on perception. We conclude that the cerebellum establishes time-dependent multisensory representations on different levels, relevant for motor control as well as supporting action perception. Ipsilateral cerebellar motor representations are thought to support the somatosensory state estimate of ongoing movements, whereas the ventral dentate and the contralateral posterior cerebellum likely support sensorimotor integration in the cerebellar-parietal loops. Both the correct somatosensory as well as the multisensory state representations are vital for an intact APC.

Effects of cerebellar lesions on working memory interacting with motor tasks of different complexities.

We examined the influence of focal cerebellar lesions on working memory (n-back task), gait, and the interaction between working memory and different gait tasks in a dual-task paradigm. The analysis included 17 young patients with chronic focal lesions after cerebellar tumor resection and 17 age-matched controls. Patients have shown mild to moderate ataxia. Lesion sites were examined on the basis of structural magnetic resonance imaging. N-back tasks were executed with different levels of difficulty (n = 1-4) during sitting (baseline), treadmill walking, and treadmill tandem walking (dual-task conditions). Patients exhibited decreased n-back performance particularly at difficult n-back levels and in dual-task conditions. Voxel-based lesion-symptom mapping revealed that decreased baseline n-back performance was associated with lesions of the posterolateral cerebellar hemisphere and the dentate nucleus. By contrast, decreased n-back performance in dual-task conditions was more associated with motor-related areas including dorsal portions of the dentate and the interposed nucleus, suggesting a prioritization of the motor task. During baseline walking, increased gait variability was associated with lesions in medial and intermediate regions, whereas for baseline tandem gait, lesions in the posterolateral hemispheres and the dentate nucleus became important. Posterolateral regions overlapped with regions related to baseline n-back performance. Consistently, we observed increased tandem gait variability with growing n-back difficulty in the dual-task condition. These findings suggest that dual-task effects in cerebellar patients are at least partially caused by a common involvement of posterolateral cerebellar regions in working memory and complex motor tasks.

Intracranial aneurysms: optimized diagnostic tools call for thorough interdisciplinary treatment strategies.

OBJECTIVE: Intracranial aneurysms (IAs) require deliberately selected treatment strategies as they are incrementally found prior to rupture and deleterious subarachnoid haemorrhage (SAH). Multiple and recurrent aneurysms necessitate both neurointerventionalists and neurosurgeons to optimize aneurysmal occlusion in an interdisciplinary effort. The present study was conducted to condense essential strategies from a single neurovascular centre with regard to the lessons learned. METHOD: Medical charts of 321 consecutive patients treated for IAs at our centre from September 2008 until December 2010 were retrospectively analysed for clinical presentation of the aneurysms, multiplicity and treatment pathways. In addition, a selective Medline search was performed. RESULTS: A total of 321 patients with 492 aneurysms underwent occlusion of their symptomatic aneurysm: 132 (41.1%) individuals were treated surgically, 189 (58.2%) interventionally; 138 patients presented with a SAH, of these 44.2% were clipped and 55.8% were coiled. Aneurysms of the middle cerebral artery were primarily occluded surgically (88), whereas most of the aneurysms of the internal carotid artery and anterior communicating artery (114) were treated endovascularly. Multiple aneurysms (range 2-5 aneurysms/individual) were diagnosed in 98 patients (30.2%). During the study period 12 patients with recurrent aneurysms were allocated to another treatment modality (previously clip to coil and vice versa). CONCLUSIONS: Our data show that successful interdisciplinary occlusion of IAs is based on both neurosurgical and neurointerventional therapy. In particular, multiple and recurrent aneurysms require tailored individual approaches to aneurysmal occlusion. This is achieved by a consequent interdisciplinary pondering of the optimal strategy to occlude IAs in order to prevent SAH.

Evaluation of hardware-related geometrical distortion in structural MRI at 7 Tesla for image-guided applications in neurosurgery.

RATIONALE AND OBJECTIVES: Geometrical distortion is a well-known problem in structural magnetic resonance imaging (MRI), leading to pixel shifts with variations up to several millimeters. Because the main factors of geometrical distortion are proportional to B(0), MRI spatial encoding distortions tend to increase with higher magnetic field strength. With the increasing prospects of utilizing ultra-high-field MRI (B(0) ≥ 7 Tesla) for neuroimaging and subsequently for image-guided neurosurgical therapy, the evaluation and correction of geometrical distortions occurring in ultra-high-field MRI are essential preconditions for the integration of these data. Hence, we conducted a phantom study to determine hardware-related geometrical distortion in clinically relevant sequences for structural imaging at 7 T MRI and compared the findings to 1.5 T MRI. MATERIAL AND METHODS: Hardware-related geometrical distortion was evaluated using a MRI phantom (Elekta, Sweden). Both applied scanner systems (Magnetom Avanto 1.5 T and Magnetom 7 T, Siemens Healthcare, Erlangen, Germany) were equipped with similar gradient coils capable of delivering 45 mT/m of maximum amplitude and a slew rate of 220 mT/m/ms. Distortion analysis was performed for various clinically relevant gradient echo and spin echo sequences. RESULTS: Overall, we found very low mean geometrical distortions at both 7 T and 1.5 T, although single values of up to 1.6 mm were detected. No major differences in mean distortion between the sequences could be found, except significantly higher distortions in turbo spin-echo sequences at 7 T, mainly caused by B(1) inhomogeneities. CONCLUSION: Hardware-related geometrical distortions at 7 T MRI are relatively small, which may be acceptable for image coregistration or for direct tissue-targeting procedures. Using a subject-specific correction of object-related distortions, an integration of 7 T MRI data into image-guided applications may be feasible.

Instable cervical spine injury in a toddler: technical note.

PURPOSE: Instable upper cervical spine injuries (CSI) in very young children are rare and consecutively only few data on the treatment and operative approaches exist in the literature. Hence, we suggest an operative strategy in the case of a 15-month-old infant treated for an instable CSI at the level of C2/3 at our department. Detailed steps of the operation with special consideration to the challenging anatomy of the immature spine are presented. METHODS: A toddler suffered a CSI without neurological deficits after a stair fall. Computer tomography (CT) and magnetic resonance imaging (MRI) of the cervical spine revealed an instable luxation fracture of C2/3. As repositioning in the halo vest immobilization failed, surgical fusion was indicated. RESULTS: Via a posterior midline approach, the lamina of C2 and C3 was conflated in a modified sublaminar wiring technique using non-resorbable sutures, sparing the ossification zones of the vertebral arches. Postoperative immobilization in a halo vest facilitated bony fusion of the laminae at C2/3 without lordotic displacement of the cervical spine. CONCLUSIONS: We consider the instable CSI of the immature cervical in the very young a challenging situation for every treating physician. The particular features of the growing spine require special attention to avoid damage to the growth centers of the vertebrae. To our knowledge, this is the first technical report giving detailed information of an operative approach to the severely injured immature cervical spine and postoperative management.

Surgical treatment of primary intracranial myxoma in a child following radiotherapy: case report and review of the literature.

INTRODUCTION: Myxomas are benign tumors of the mesenchymal origin and account for about half of the benign cardiac tumors. Occasionally, they occur at other locations, but the intracranial manifestation of a myxoma is exceptionally rare. As a secondary neoplasia following radiotherapy, myxoma has only been reported once in the literature. MATERIAL AND METHODS: A 12-year-old girl, who was previously treated for a medulloblastoma, was diagnosed with a new lesion at the left transverse sinus in the follow-up magnetic resonance imaging (MRI). Indication for surgery was made and complete removal could be achieved. RESULTS AND DISCUSSION: Histological examination revealed a myxoma. Further staging showed no other manifestation of the myxoma. The close relation to the radiation field of the posterior fossa makes it highly suggestive that the myxoma developed as a secondary neoplasia induced by radiotherapy. Treatment philosophy for this benign tumor entity is a completed resection of the lesion with regular follow-up MRI.