Two cases of SMA syndrome after neurosurgical injury to the frontal aslant tract

Utility of Surgical Simulation for Tubular Retractor Surgery Using Three-Dimensional Printed Intraventricular Tumor Models: Case Series

OBJECTIVE

The utility of the tubular retractor for deep-seated tumors, including intraventricular tumors, has recently been reported. However, the surgical field's depth and narrowness can lead to blind spots, and it is crucial to prevent damage to the cortex and white matter fibers in eloquent areas. Therefore, preoperative simulation is critical for tubular retractor surgery. In this study, we investigated the benefits of threedimensional (3D)-printed intraventricular tumor models for tubular retractor surgery.

METHODS

Nine patients with intraventricular central neurocytoma who underwent tubular retractor surgery at our institution between March 2013 and August 2023 were retrospectively reviewed. Fusion images and 3D-printed intraventricular tumor models were developed from preoperative computed tomography (CT) and magnetic resonance imaging (MRI). The puncture points of the tubular retractor were simulated using fusion images and 3D-printed intraventricular tumor models by 11 neurosurgeons (3 experts in brain tumors, 2 experts in areas other than brain tumors, and 6 residents). The dispersion of puncture points among 8 neurosurgeons (excluding brain tumor experts) was compared in each simulation model.

RESULTS

These cases were categorized into two groups based on the dispersion of puncture points simulated by fusion images. Puncture point dispersion was markedly smaller in all cases when using 3D-printed intraventricular tumor models compared to simulations solely based on fusion images.

CONCLUSIONS

In intraventricular tumor surgery using a tubular retractor, 3D-printed intraventricular tumor models proved more beneficial in preoperative simulation compared to fusion images.

Connectome imaging to facilitate preservation of the frontal aslant tract

Supplementary motor area (SMA) syndrome is characterized by contralateral akinesia and mutism, and frequently occurs following resection of tumors involving the superior frontal gyrus. The frontal aslant tract (FAT), involved in functional connectivity of the supplementary area and other related large-scale brain networks, is implicated in the pathogenesis of, and recovery from, SMA syndrome. However, intraoperative neuromonitoring of the FAT is inconsistent and poorly reproducible, leading to a high rate of postoperative SMA syndrome. We report the cases of two patients harboring lesions of the superior frontal gyrus: one cavernoma and one low grade glioma. Connectome imaging revealed involvement of functional networks implicated in SMA syndrome, as well as displacement of the FAT. A connectome-guided awake craniotomy was performed in both cases, and a combinatorial approach using awake language mapping and connectome-imaging guidance facilitated gross total resection of both patient's lesions without inducing SMA syndrome postoperatively. Functional and structural connectivity imaging through connectomics allows the identification of areas not traditionally considered eloquent, such as the SMA and FAT, and can help facilitate their preservation. Conserving the functional and structural connectivity of broader brain regions that are not traditionally deemed eloquent can improve patient outcomes.

The role of language-related functional brain regions and white matter tracts in network plasticity of post-stroke aphasia

The neural mechanisms underlying language recovery after a stroke remain controversial. This review aimed to summarize the plasticity and reorganization mechanisms of the language network through neuroimaging studies. Initially, we discussed the involvement of right language homologues, perilesional tissue, and domain-general networks. Subsequently, we summarized the white matter functional mapping and remodeling mechanisms associated with language subskills. Finally, we explored how non-invasive brain stimulation (NIBS) promoted language recovery by inducing neural network plasticity. It was observed that the recruitment of right hemisphere language area homologues played a pivotal role in the early stages of frontal post-stroke aphasia (PSA), particularly in patients with larger lesions. Perilesional plasticity correlated with improved speech performance and prognosis. The domain-general networks could respond to increased "effort" in a task-dependent manner from the top-down when the downstream language network was impaired. Fluency, repetition, comprehension, naming, and reading skills exhibited overlapping and unique dual-pathway functional mapping models. In the acute phase, the structural remodeling of white matter tracts became challenging, with recovery predominantly dependent on cortical activation. Similar to the pattern of cortical activation, during the subacute and chronic phases, improvements in language functions depended, respectively, on the remodeling of right white matter tracts and the restoration of left-lateralized language structural network patterns. Moreover, the midline superior frontal gyrus/dorsal anterior cingulate cortex emerged as a promising target for NIBS. These findings offered theoretical insights for the early personalized treatment of aphasia after stroke.

A modified neural circuit framework for semantic memory retrieval with implications for circuit modulation to treat verbal retrieval deficits

Word finding difficulty is a frequent complaint in older age and disease states, but treatment options are lacking for such verbal retrieval deficits. Better understanding of the neurophysiological and neuroanatomical basis of verbal retrieval function may inform effective interventions. In this article, we review the current evidence of a neural retrieval circuit central to verbal production, including words and semantic memory, that involves the pre-supplementary motor area (pre-SMA), striatum (particularly caudate nucleus), and thalamus. We aim to offer a modified neural circuit framework expanded upon a memory retrieval model proposed in 2013 by Hart et al., as evidence from electrophysiological, functional brain imaging, and noninvasive electrical brain stimulation studies have provided additional pieces of information that converge on a shared neural circuit for retrieval of memory and words. We propose that both the left inferior frontal gyrus and fronto-polar regions should be included in the expanded circuit. All these regions have their respective functional roles during verbal retrieval, such as selection and inhibition during search, initiation and termination of search, maintenance of co-activation across cortical regions, as well as final activation of the retrieved information. We will also highlight the structural connectivity from and to the pre-SMA (e.g., frontal aslant tract and fronto-striatal tract) that facilitates communication between the regions within this circuit. Finally, we will discuss how this circuit and its correlated activity may be affected by disease states and how this circuit may serve as a novel target engagement for neuromodulatory treatment of verbal retrieval deficits.

Beyond Broca's and Wernicke's: Functional Mapping of Ancillary Language Centers Prior to Brain Tumor Surgery

Functional MRI is a well-established tool used for pre-surgical planning to help the neurosurgeon have a roadmap of critical functional areas that should be avoided, if possible, during surgery to minimize morbidity for patients with brain tumors (though this also has applications for surgical resection of epileptogenic tissue and vascular lesions). This article reviews the locations of secondary language centers within the brain along with imaging findings to help improve our confidence in our knowledge on language lateralization. Brief overviews of these language centers and their contributions to the language networks will be discussed. These language centers include primary language centers of "Broca's Area" and "Wernicke's Area". However, there are multiple secondary language centers such as the dorsal lateral prefrontal cortex (DLPFC), frontal eye fields, pre- supplemental motor area (pre-SMA), Basal Temporal Language Area (BTLA), along with other areas of activation. Knowing these foci helps to increase self-assurance when discussing the nature of laterality with the neurosurgeon. By knowing secondary language centers for language lateralization, via fMRI, one can feel confident on providing neurosurgeon colleagues with appropriate information on the laterality of language in preparation for surgery.