Radiological Differentiation Between Intracranial Meningioma and Solitary Fibrous Tumor/Hemangiopericytoma

World Neurosurg. (2023) 170:68-83

Intracranial solitary fibrous tumor (SFT) is characterized by aggressive local behavior and high post-resection recurrence rates. It is difficult to distinguish between SFT and meningiomas, which are typically benign. The goal of this study was to systematically review radiological features that differentiate meningioma and SFT.

METHODS: We performed a systematic review in accordance with PRISMA guidelines to identify studies that used imaging techniques to identify radiological differentiators of SFT and meningioma.

RESULTS: Eighteen studies with 1565 patients (SFT: 662; meningiomas: 903) were included. The most commonly used imaging modality was diffusion weighted imaging, which was reported in 11 studies. Eight studies used a combination of diffusion weighted imaging and T1- and T2-weighted sequences to distinguish between SFT and meningioma. Compared to all grades/subtypes of meningioma, SFT is associated with higher apparent diffusion coefficient, presence of narrow-based dural attachments, lack of dural tail, less peritumoral brain edema, extensive serpentine flow voids, and younger age at initial diagnosis. Tumor volume was a poor differentiator of SFT and meningioma, and overall, there were less consensus findings in studies exclusively comparing angiomatous meningiomas and SFT.

CONCLUSIONS: Clinicians can differentiate SFT from meningiomas on preoperative imaging by looking for higher apparent diffusion coefficient, lack of dural tail/narrow-based dural attachment, less peritumoral brain edema, and vascular flow voids on neuroimaging, in addition to younger age at diagnosis. Distinguishing between angiomatous meningioma and SFT is much more challenging, as both are highly vascular pathologies. Tumor volume has limited utility in differentiating between SFT and various grades/subtypes of meningioma.

 

Brain infarctions after glioma surgery

Acta Neurochirurgica (2021) 163:3097–3108

Prevalence, radiological characteristics, and risk factors for peritumoral infarctions after glioma surgery are not much studied. In this study, we assessed shape, volume, and prevalence of peritumoral infarctions and investigated pos- sible associated factors.

Methods In a prospective single-center cohort study, we included all adult patients operated for diffuse gliomas from January 2007 to December 2018. Postoperative infarctions were segmented using early postoperative MRI images, and volume, shape, and location of postoperative infarctions were assessed. Heatmaps of the distribution of tumors and infarctions were created.

Results MRIs from 238 (44%) of 539 operations showed restricted diffusion in relation to the operation cavity, interpreted as postoperative infarctions. Of these, 86 (36%) were rim-shaped, 103 (43%) were sector-shaped, 40 (17%) were a combination of rim- and sector-shaped, and six (3%) were remote infarctions. Median infarction volume was 1.7 cm3 (IQR 0.7–4.3, range 0.1–67.1). Infarctions were more common if the tumor was in the temporal lobe, and the map shows more infarctions in the periventricular watershed areas. Sector-shaped infarctions were more often seen in patients with known cerebrovascular dis- ease (47.6% vs. 25.5%, p = 0.024). There was a positive correlation between infarction volume and tumor volume (r = 0.267, p < 0.001) and infarction volume and perioperative bleeding (r = 0.176, p = 0.014). Moreover, there was a significant positive association between age and larger infarction volumes (r = 0.193, p = 0.003). Infarction rates and infarction volumes varied across individual surgeons, p = 0.037 (range 32–72%) and p = 0.026.

Conclusions In the present study, peritumoral infarctions occurred in 44% after diffuse glioma operations. Infarctions were more common in patients operated for tumors in the temporal lobe but were not more common following recurrent surgeries. Sector-shaped infarctions were more common in patients with known cerebrovascular disease. Increasing age, larger tumors, and more perioperative bleeding were factors associated with infarction volumes. The risk of infarctions and infarction volumes may also be surgeon-dependent.

Early postoperative delineation of residual tumor after low-grade glioma resection by probabilistic quantification of diffusion-weighted imaging

J Neurosurg 130:2016–2024, 2019

In WHO grade II low-grade gliomas (LGGs), early postoperative MRI (epMRI) may overestimate residual tumor on FLAIR sequences. Consequently, MRI at 3–6 months follow-up (fuMRI) is used for delineation of residual tumor. This study sought to evaluate if integration of apparent diffusion coefficient (ADC) maps permits an accurate estimation of residual tumor early on epMRI.

METHODS From a consecutive cohort, 43 cases with an initial surgery for an LGG, and complete epMRI (< 72 hours after resection) and fuMRI including ADC maps, were retrospectively identified. Residual FLAIR hyperintense tumor was manually segmented on epMRI and corresponding ADC maps were coregistered. Using an expectation maximization algorithm, residual tumor segments were probabilistically clustered into areas of residual tumor, ischemia, or normal white matter (NWM) by fitting a mixture model of superimposed Gaussian curves to the ADC histogram. Tumor volumes from epMRI, clustering, and fuMRI were statistically compared and agreement analysis was performed.

RESULTS Mean FLAIR hyperintensity suggesting residual tumor was significantly larger on epMRI compared to fuMRI (19.4 ± 16.5 ml vs 8.4 ± 10.2 ml, p < 0.0001). Probabilistic clustering of corresponding ADC histograms on epMRI identified subsegments that were interpreted as mean residual tumor (7.6 ± 10.2 ml), ischemia (8.1 ± 5.9 ml), and NWM (3.7 ± 4.9 ml). Therefore, mean tumor quantification error between epMRI and fuMRI was significantly reduced (11.0 ± 10.6 ml vs -0.8 ± 3.7 ml, p < 0.0001). Mean clustered tumor volumes on epMRI were no longer significantly different from the fuMRI reference (7.6 ± 10.2 ml vs 8.4 ± 10.2 ml, p = 0.16). Correlation (Pearson r = 0.96, p < 0.0001), concordance correlation coefficient (0.89, 95% confidence interval 0.83), and Bland-Altman analysis suggested strong agreement between both measures after clustering.

CONCLUSIONS Probabilistic segmentation of ADC maps facilitates accurate assessment of residual tumor within 72 hours after LGG resection. Multiparametric image analysis detected FLAIR signal alterations attributable to surgical trauma, which led to overestimation of residual LGG on epMRI compared to fuMRI. The prognostic value and clinical impact of this method has to be evaluated in larger case series in the future.

 

Probabilistic versus deterministic tractography for delineation of the cortico-subthalamic hyperdirect pathway in patients with Parkinson disease selected for deep brain stimulation

J Neurosurg 126:1657–1668, 2017

Diffusion-weighted MRI (DWI) and tractography allows noninvasive mapping of the structural connections of the brain, and may provide important information for neurosurgical planning. The hyperdirect pathway, connecting the subthalamic nucleus (STN) with the motor cortex, is assumed to play a key role in mediating the effects of deep brain stimulation (DBS), which is an effective but poorly understood treatment for Parkinson disease. This study aimed to apply recent methodological advances in DWI acquisition and analysis to the delineation of the hyperdirect pathway in patients with Parkinson disease selected for surgery.

METHODS High spatial and angular resolution DWI data were acquired preoperatively from 5 patients with Parkinson disease undergoing DBS. The authors compared the delineated hyperdirect pathways and associated STN target maps generated by 2 different tractography methods: a tensor-based deterministic method, typically available in clinical settings, and an advanced probabilistic method based on constrained spherical deconvolution. In addition, 10 highresolution data sets with the same scanning parameters were acquired from a healthy control participant to assess the robustness of the tractography results.

RESULTS Both tractography approaches identified connections between the ipsilateral motor cortex and the STN. However, the 2 methods provided substantially different target regions in the STN, with the target center of gravity differing by > 1.4 mm on average. The probabilistic method (based on constrained spherical deconvolution) plausibly reconstructed a continuous set of connections from the motor cortex, terminating in the dorsolateral region of the STN. In contrast, the tensor-based method reconstructed a comparatively sparser and more variable subset of connections. Furthermore, across the control scans, the probabilistic method identified considerably more consistent targeting regions within the STN compared with the deterministic tensor-based method, which demonstrated a 1.9–2.4 times higher variation.

CONCLUSIONS These data provide a strong impetus for the use of a robust probabilistic tractography framework based on constrained spherical deconvolution, or similar advanced DWI models, in clinical settings. The inherent limitations and demonstrated inaccuracy of the tensor-based method leave it questionable for use in high-precision stereotactic DBS surgery. The authors have also described a straightforward method for importing tractography-derived information into any clinical neuronavigation system, based on the generation of track-density images.

Microembolism after endovascular coiling of unruptured cerebral aneurysms: incidence and risk factors

Microembolism after endovascular coiling of unruptured cerebral aneurysms

J Neurosurg 124:777–783, 2016

The incidence and risk factors of microembolic lesions on MR diffusion-weighted imaging (DWI) were analyzed after the endovascular coiling of unruptured intracranial aneurysms (UIAs).

Methods Data obtained from 271 consecutive patients (70 men and 201 women; median age 57 years; range 23–79 years) who presented with UIA for coil embolization between July 2011 and June 2013 were analyzed. Two independent reviewers examined the DWI and apparent diffusion coefficient maps obtained the following day for the presence of restrictive diffusion spots and counted the number of spots. Multivariate analysis was then performed to identify independent risk factors for developing microembolism following the coiling of an aneurysm.

Results Microembolic lesions were noted in 101 of 271 patients (37.3%). The results of the multivariate analysis showed that the following factors significantly influenced the risk for microembolism: age, diabetes, previous history of ischemic stroke, high-signal FLAIR lesions in the white matter, multiple aneurysms, and the insertion of an Enterprise stent (all ORs > 1.0 and all p values < 0.05). Previously known risk factors such as prolonged procedure duration, aneurysm size, and decreased antiplatelet function did not show any significant influence.

Conclusions The incidence of microembolism after endovascular coiling of UIA was not low. Lesions occurred more frequently in patients with vascular status associated with old age, diabetes, and previous stroke. Aneurysm multiplicity and the type of stent used for treatment also influenced lesion occurrence.

Diffusion-weighted imaging–detected ischemic lesions associated with flow-diverting stents in intracranial aneurysms

Diffusion-weighted imaging–detected ischemic lesions associated with flow-diverting stents in intracranial aneurysms

J Neurosurg 122:627–636, 2015

It was initially considered safe for flow-diverting stents to cover the ostia of branching vessels during endovascular procedures for the treatment of intracranial aneurysms. As more recent evidence suggests, however, their use is not always free of ischemic concerns in terms of covered arterial ostia. The authors sought to determine the frequency of silent and clinically evident diffusion-weighted imaging (DWI)–detected abnormalities related to stent placement as a means of elucidating potential clinical risks.

Methods This is a prospective single-center study on a series of patients with intracranial aneurysms that were treated with flow-diverting stents. All patients systematically underwent an MRI protocol that included DWI before treatment, between 24 and 48 hours postprocedure, and 3 months postembolization. Effectiveness of anticoagulation treatment was assessed for all patients. Lesions seen on DWI were correlated to the parent artery and the side-branch territories and were statistically analyzed in relation to their time of occurrence and clinical presentation. The authors compared the DWI findings in these patients to findings obtained in patients treated with a stent-assisted coiling technique during the same time period.

Results Over the course of 18 consecutive months, 38 consecutive patients (7 males and 31 females) with 49 intracranial aneurysms were treated using flow-diverting stents. Overall, 81.6% of the DWI spots found remained clinically silent during the follow-up period. Five ischemic clinical complications (13.2%) occurred in the postprocedural period. No statistically significant correlation could be established between DWI spots or aneurysm location and clinical complications or follow-up modified Rankin Scale score at 3 months. The complication rate was 7.8% (n = 3) at the 3-month follow-up, and mortality was 0%. Compared with stent-assisted coiling, use of flow-diverting stents showed a statistically significant correlation with silent DWI findings postintervention.

Conclusions Lesions seen on DWI resulting from the procedure are far more common than anticipated, but the technique remains safe and effective, providing an interesting alternative for “difficult” aneurysms, regardless of location. Late-occurring DWI-detected lesions distal to side arterial branches imply a local pressure gradient drop, related to flow competition by collateral networks. Further research is needed to assess the extent and significance of these events.

White matter fiber tractography: why we need to move beyond DTI

DTI

J Neurosurg 118:1367–1377, 2013

Diffusion-based MRI tractography is an imaging tool increasingly used in neurosurgical procedures to generate 3D maps of white matter pathways as an aid to identifying safe margins of resection. The majority of white matter fiber tractography software packages currently available to clinicians rely on a fundamentally flawed framework to generate fiber orientations from diffusion-weighted data, namely diffusion tensor imaging (DTI). This work provides the first extensive and systematic exploration of the practical limitations of DTI-based tractography and investigates whether the higher-order tractography model constrained spherical deconvolution provides a reasonable solution to these problems within a clinically feasible timeframe.

Methods. Comparison of tractography methodologies in visualizing the corticospinal tracts was made using the diffusion-weighted data sets from 45 healthy controls and 10 patients undergoing presurgical imaging assessment. Tensor-based and constrained spherical deconvolution–based tractography methodologies were applied to both patients and controls.

Results. Diffusion tensor imaging–based tractography methods (using both deterministic and probabilistic tractography algorithms) substantially underestimated the extent of tracks connecting to the sensorimotor cortex in all participants in the control group. In contrast, the constrained spherical deconvolution tractography method consistently produced the biologically expected fan-shaped configuration of tracks. In the clinical cases, in which tractography was performed to visualize the corticospinal pathways in patients with concomitant risk of neurological deficit following neurosurgical resection, the constrained spherical deconvolution–based and tensor-based tractography methodologies indicated very different apparent safe margins of resection; the constrained spherical deconvolution– based method identified corticospinal tracts extending to the entire sensorimotor cortex, while the tensor-based method only identified a narrow subset of tracts extending medially to the vertex.

Conclusions. This comprehensive study shows that the most widely used clinical tractography method (diffusion tensor imaging–based tractography) results in systematically unreliable and clinically misleading information. The higher-order tractography model, using the same diffusion-weighted data, clearly demonstrates fiber tracts more accurately, providing improved estimates of safety margins that may be useful in neurosurgical procedures. We therefore need to move beyond the diffusion tensor framework if we are to begin to provide neurosurgeons with biologically reliable tractography information.

Postoperative ischemic changes following resection of newly diagnosed and recurrent gliomas and their clinical relevance

Postoperative ischemic changes following resection of newly diagnosed and recurrent gliomas and their clinical relevance

J Neurosurg 118:801–808, 2013

The aim of surgical treatment of glioma is the complete resection of tumor tissue with preservation of neurological function. Inclusion of diffusion-weighted imaging (DWI) in the postoperative MRI protocol could improve the delineation of ischemia-associated postoperative neurological deficits. The present study aims to assess the incidence of infarctions following resection of newly diagnosed gliomas in comparison with recurrent gliomas and the influence on neurological function.

Methods. Patients who underwent glioma resection for newly diagnosed or recurrent gliomas had early postoperative MRI, including DWI and apparent diffusion coefficient (ADC) maps. Postoperative areas of restricted diffusion were classified as arterial territorial infarctions, terminal branch infarctions, or venous infarctions. Tumor entity, location, and neurological function were recorded.

Results. New postoperative ischemic lesions were identified in 26 (31%) of 84 patients with newly diagnosed gliomas and 20 (80%) of 25 patients with recurrent gliomas (p < 0.01). New permanent and transient neurological deficits were more frequent in patients with recurrent gliomas than in patients with newly diagnosed tumors. Patients with neurological deficits had a significantly higher rate of ischemic lesions.

Conclusions. Postoperative infarctions occur frequently in patients with newly diagnosed and recurrent gliomas and do have an impact on postoperative neurological function. In this patient cohort there was a higher risk for ischemic lesions and for deterioration of neurological function after resection of recurrent tumors. Radiogenic and postoperative tissue changes could contribute to the higher risk of an ischemic infarction in patients with recurrent tumors.

Subcortical Injury Is an Independent Predictor of Worsening Neurological Deficits Following Awake Craniotomy Procedures

Subcortical_Injury_Is_an_Independent_Predictor_of

Neurosurgery 72:160–169, 2013

Tailored craniotomies for awake procedures limit cortical exposure. Recently we demonstrated that the identification of eloquent areas increased the risk of postoperative deficits. However, it was not clear whether the observed neurological deficits were caused by proximity of functional cortex to the tumor [cortical injury] or subcortical injury.

OBJECTIVE: We hypothesize that subcortical injury during tumor resection is an important predictor of postoperative neurological deficits compared to cortical injury.

METHODS: A retrospective review of 214 patients undergoing awake craniotomy was carried out in whom preoperative functional magnetic resonance imaging (fMRI) and cortical mapping (CM) were performed. A radiologist blinded to the clinical data reviewed and graded the postoperative changes on diffusion-weighted MR-imaging (DWI).

RESULTS: Of the 40 cases who developed new intraoperative neurological deficit, 36 (90%) occurred during subcortical dissection, 3 (7.5%) during both subcortical and cortical dissection, and 1 (2.5%) during cortical dissection. Neurological dysfunction acquired during subcortical dissection was an independent predictor of postoperative deficits both in the immediate postoperative period (P< .001) and at the 3-month follow-up (P < .001). Significant DWI restriction in the subcortical white matter was predictive of neurological deficits both immediately and at 3 months, P = .011 and P < .001, respectively. New or worsening deficits were seen in 38% of patients; however, at 3 months 13% had a mild persistent neurological deficit.

CONCLUSION: Subcortical injury with significant DWI changes result in postoperative neurological decline despite our efforts to preserve cortical areas of function. This underscores the importance of preserving subcortical fiber tracts during awake craniotomy procedures.

Diffusion-weighted magnetic resonance imaging of symptomatic nerve root of patients with lumbar disk herniation

Neuroradiology. DOI 10.1007/s00234-010-0801-7

Diffusion-weighted imaging (DWI) can provide valuable structural information that may be useful for evaluating pathological changes of the lumbar nerve root. Diffusion-weighted magnetic resonance (MR) neurography has recently been introduced as an alternative way to visualize nerves, but to date, quantitative DWI and MR neurography have not been applied to evaluate the pathology of lumbar nerve roots.

Methods Our purpose was to visualize lumbar nerve roots and to analyze their morphology by MR neurography, and to measure the apparent diffusion coefficient (ADC) of lumbar nerve roots compressed by herniated disks using 1.5-T MR imaging. Ten consecutive patients (median age, 48.0 and range, 20–72 years) with monoradicular symptoms caused by a lumbar herniated disk and 14 healthy volunteers were studied. Regions of interests were placed on the lumbar roots at dorsal root ganglia (DRG) and distal spinal nerves on DWI to quantify mean ADC values. The spinal nerve roots were also visualized by MR neurography.

Results In the patients, mean ADC values were significantly greater in the compressed DRG and distal spinal nerves than in intact nerves. MR neurography also showed abnormalities such as nerve swelling at and below the compression in the symptomatic nerve root. Increased ADC values were considered to be because of edema and Wallerian degeneration of compressed nerve roots.

Conclusion DWI is a potential tool for analysis of the pathophysiology of lumbar nerve roots compressed by herniated disks.