Posterior cerebral artery Wada test: sodium amytal distribution and functional deficits

Selective Posterior Cerebral Artery Wada Better Predicts Good Memory and Naming Outcomes Following Selective Stereotactic Thermal Ablation for Medial Temporal Lobe Epilepsy Than Internal Carotid Artery Wada

The conventional intracarotid amobarbital (Wada) test has been used to assess memory function in patients being considered for temporal lobe epilepsy (TLE) surgery. Minimally invasive approaches that target the medial temporal lobe (MTL) and spare neocortex are increasingly used, but a knowledge gap remains in how to assess memory and language risk from these procedures. We retrospectively compared results of two versions of the Wada test, the intracarotid artery (ICA-Wada) and posterior cerebral artery (PCA-Wada) approaches, with respect to predicting subsequent memory and language outcomes, particularly after stereotactic laser amygdalohippocampotomy (SLAH). We included all patients being considered for SLAH who underwent both ICA-Wada and PCA-Wada at a single institution. Memory and confrontation naming assessments were conducted using standardized neuropsychological tests to assess pre- to post-surgical changes in cognitive performance. Of 13 patients who initially failed the ICA-Wada, only one patient subsequently failed the PCA-Wada (p=0.003, two-sided binomial test with p 0 =0.5) demonstrating that these tests assess different brain regions or networks. PCA-Wada had a high negative predictive value for the safety of SLAH, compared to ICA-Wada, as none of the patients who underwent SLAH after passing the PCA-Wada experienced catastrophic memory decline (0 of 9 subjects, p <.004, two-sided binomial test with p 0 =0.5), and all experienced a good cognitive outcome. In contrast, the single patient who received a left anterior temporal lobectomy after failed ICA- and passed PCA-Wada experienced a persistent, near catastrophic memory decline. On confrontation naming, few patients exhibited disturbance during the PCA-Wada. Following surgery, SLAH patients showed no naming decline, while open resection patients, whose surgeries all included ipsilateral temporal lobe neocortex, experienced significant naming difficulties (Fisher's exact test, p <.05). These findings demonstrate that (1) failing the ICA-Wada falsely predicts memory decline following SLAH, (2) PCA-Wada better predicts good memory outcomes of SLAH for MTLE, and (3) the MTL brain structures affected by both PCA-Wada and SLAH are not directly involved in language processing.

Transient phonemic paraphasia by bilateral hippocampus lesion in a case of limbic encephalitis

Although the hippocampus has not typically been identified as part of the language and aphasia circuit, recent evidence suggests that the hippocampus is closely related to naming, word priming, and anomic aphasia. A 59-year old woman with limbic encephalitis of possible autoimmune etiology, after recovery of consciousness, presented with severe memory impairment in both anterograde and retrograde modalities, episodes of fear, hallucination and convulsion, and transient fluent, phonemic paraphasia, together with small sharp waves diffusely by EEG. Brain MRI revealed bilateral symmetric, discrete lesions in the body to the infundibulum of the hippocampus.

The transient phonemic paraphasia noted in our patient may have been a result of primary damage in the hippocampus and its fiber connection to the Wernicke's area or secondary partial status epilepticus that might have originated in the hippocampus.

Multispectral molecular imaging of capillary endothelium to facilitate preoperative endovascular brain mapping

OBJECT

Brain mapping aims to localize neurological function to specific regions of the human brain. Preoperative endovascular brain mapping (PEBM) is a novel approach that allows clear visualization of nonfunctional (silent) brain parenchyma in real time during a resection. It has potential to improve neurosurgical guidance because brain shift does not alter the maps, and the map is visualized directly on the brain in situ rather than on a nearby image. Therefore, the risk of a new neurological deficit should be reduced. The authors report the first PEBM approach that combines selective molecular targeting of brain endothelium with multispectral (optical) imaging in preclinical animal models.

METHODS

Sprague-Dawley rats and New Zealand white rabbits were selectively catheterized, and a fluorescein isothiocyanate-derivatized tomato lectin-based imaging probe was administered into the carotid artery or posterior cerebral artery, measuring < 500 microm in diameter. After binding/uptake of the imaging probe, and removal of unbound probe, a craniotomy was performed to directly visualize the "brain map."

RESULTS

Selective localization of the imaging probe to the right hemisphere in rats or right posterior cerebral artery in rabbits was clearly visualized after craniotomy. Cross-sections of stained capillaries demonstrated that the imaging probe did not cause vascular occlusion. Gross regional selectivity of the imaging probe was documented by multispectral molecular imaging of intact brains, with discrete localization and endothelium-directed targeting validated by histological examination.

CONCLUSIONS

The authors have demonstrated the first molecular endothelium-targeted approach to PEBM that does not require manipulation of the intact blood-brain barrier or result in vascular occlusion. Furthermore, the presented multispectral molecular imaging technique appears to be a suitable methodology for the generation of region-selective brain maps of vascularized brain parenchyma. Further refinement of the PEBM approach, as well as the development of improved imaging probes, may result in clinical advancement of PEBM where direct visual discrimination of nonfunctional silent brain parenchyma at the time of resection could significantly improve neurosurgical outcomes.

Preoperative endovascular brain mapping for intraoperative volumetric image guidance: preliminary concept and feasibility in animal models

Object

The authors describe a novel concept for brain mapping in which an endovascular approach is used, and they demonstrate its feasibility in animal models. The purpose of endovascular brain mapping is to delineate clearly the nonfunctional brain parenchyma when a craniotomy is performed for resection. The nonfunctional brain will be stained with sharp visual margins, differentiating it from the functional, nonstained brain. The authors list four essential criteria for developing an ideal endovascular mapping agent, and they describe seven potential approaches for accomplishing a successful endovascular brain map.

Methods

Four Sprague–Dawley rats and one New Zealand white rabbit were used to determine initial feasibility of the procedure. The animals were anesthetized, and the internal carotid artery was catheterized. Four potential brain mapping agents were infused into the right hemisphere of the five animals. Afterward, the brains were removed and each was analyzed both grossly and histologically.

Fluorescein and FD&C Green No. 3 provided good visual clarity and margins, but required blood–brain barrier (BBB) manipulation. Tantalum particles enabled avoidance of BBB manipulation, but provided inadequate visual clarity, probably because of their size. A Sudan black “cocktail” provided excellent clarity and margins despite remaining in the brain capillaries.

Conclusions

This is a novel application of the endovascular approach, and has broad potential for clinical neurosurgical brain mapping. The animal models in this study establish the feasibility of the procedure. However, further study is required to demonstrate safety, minimize toxicity, investigate stain durability, and improve the characteristics of potential mapping agents. The authors are planning to conduct future studies for identification of mapping agents that do not require BBB manipulation or vascular occlusion.

Therapeutic advances in interventional neurology

Rapid advances in the field of interventional neurology and the development of minimally invasive techniques have resulted in a great expansion of potential therapeutic applications. We discuss therapeutic interventional neurology as applied in clinical practice in one of the two possible ways: 1) embolization leading to occlusion of blood vessels; and 2) revascularization leading to reopening of blood vessels. These procedures can be applied to a broad range of cerebrovascular diseases. In the first section of this review, we will explore the evolution of these interventions to occlude aneurysms, arteriovenous malformations, neurovascular tumors, and injuries. In the second section, revascularization in acute ischemic stroke, stenosis, and dural venous thrombosis will be discussed.

Intracarotid Amytal memory test and hippocampal magnetic resonance imaging volumetry: validity of the Wada test as an indicator of hippocampal integrity among candidates for epilepsy surgery

OBJECT

Intracarotid Amytal testing (the Wada test) has been used to lateralize language and identify patients who may be at risk for memory impairment after temporal lobectomy. The goal of this study was to determine the validity of the Wada test in the assessment of pathological conditions of the hippocampus among candidates for epilepsy surgery. The authors examined the correlation between the functional integrity of the hippocampus, measured using the Wada test, and quantitative measures of hippocampal pathology, determined by obtaining volumetric measurements of the hippocampus with the aid of magnetic resonance (MR) imaging.

METHODS

The authors reviewed the relationship between memory scores on the Wada test and hippocampal volumes measured on preoperative MR images in 76 patients who underwent anteromedial temporal lobectomy and amygdalohippocampectomy for the treatment of medically refractory temporal lobe epilepsy. The data were analyzed with respect to their usefulness in lateralizing the seizure focus and predicting the long-term postoperative memory outcome. Right and left hippocampal volume measurements did not correlate with one another (p > 0.1). Similarly, following a left carotid artery injection of Amytal the patients' right hemisphere memory was not significantly related to their left hemisphere memory on the Wada test (p'> 0.1). On the other hand, the patients' right hemisphere memory significantly correlated with their right hippocampal volume (r = 0.51; p < 0.001) and their left hemisphere memory significantly correlated with their left hippocampal volume (r = 0.51; p < 0.001). Both right and left hemisphere memory scores correlated with the hippocampal volumetry ratio (r = 0.47 and r = 0.45, respectively; both p < 0.001). Lateralization of a seizure focus based on hippocampal volumetry results was significantly related to lateralization based on the results of the Wada test (r = 0.49; p < 0.01). The disparity between the Wada memory scores on ipsilateral and contralateral sides was significantly and inversely related to the change in verbal memory following temporal lobectomy (r = -0.28; p < 0.02). The preoperative hippocampal volumetry ratio also significantly and inversely correlated with the change in verbal memory after surgery (r = -0.31; p < 0.01).

CONCLUSIONS

The Wada memory test may be a valuable method of measuring the functional integrity of the hippocampus. The systematic study of MR imaging-acquired morphological data and Wada-acquired neuropsychological data may increase our understanding of the location of material-specific memory and the selection of eligible candidates for epilepsy surgery.

Selective Posterior Cerebral Artery Amobarbital Test: Its Role in Presurgical Memory Assessment in Temporal Lobe Epilepsy

PURPOSE

To evaluate the efficacy and risk of complications of selective posterior cerebral artery (PCA) amobarbital anesthesia in memory assessment of patients with epilepsy under consideration for temporal lobe resection.

METHODS

Thirty-two candidates for temporal lobectomy in whom conclusive memory assessment could not be obtained by the standard intracarotid amobarbital procedure were submitted to a selective PCA amobarbital test. A mean dose of 75 mg amobarbital was injected via microcatheter into the P2 segment of the PCA. Ten common objects were presented for naming and remembering while the anesthesia was judged efficient. After return to neurologic baseline, recall and recognition memory were assessed.

RESULTS

In all of the 32 patients, angiography and PCA anesthesia were successfully accomplished without serious adverse events. All but one of the patients remained alert and cooperative for memory testing under the anesthesia, and 28 of these patients showed adequate memory capacity of the hemisphere contralateral to the side targeted for surgery. So far, 19 patients have proceeded to surgery, and no case of global amnesia or serious, material-specific memory impairment has resulted. Three patients failed the PCA test (fewer than 67% items correctly recognized) and were excluded from surgery, partly on the basis of the PCA test results, but also supported by an overall evaluation of all the diagnostic procedures used.

CONCLUSIONS

The selective PCA amobarbital test appears justifiable when performed by interventional neuroradiologists and may significantly reduce the risk of erroneously excluding patients with epilepsy from temporal resection. Further corroboration of the safety of the procedure seems warranted.

Selective middle cerebral artery Wada tests as a part of presurgical evaluation in patients with drug-resistant epilepsies

PURPOSE

To analyze the role of selective middle cerebral artery (MCA) Wada tests in the presurgical workup of patients with drug-resistant focal epilepsies.

METHODS

Twenty MCA Wada test procedures were performed to identify eloquent cortex (a) in nine patients with hemispheric lesions involving the motor cortex (connatal MCA infarct, n = 5; unilateral cortical dysplasia, n = 3; Rasmussen encephalitis, n = 1), (b) five patients with circumscribed neoplastic or nonneoplastic lesions adjacent to the motor cortex or classic language areas, and (c) for purely electrophysiologic reasons, in two patients with electrical status epilepticus in sleep (ESES). Sodium amobarbital and [99mTc]-HMPAO were simultaneously injected via a microcatheter into the distal M1 segment (n = 7), the inferior MCA trunk (n = 3), or into MCA branches (n = 10).

RESULTS

Co-registered single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI;n = 18) showed that sodium amobarbital did not reach the target area in three procedures. Temporary neurologic deficits occurred in 12 procedures. Eleven patients were operated on with the following surgical approaches: functional hemispherectomy, n = 3; partial or extended lesionectomy, n = 4; anterior temporal lobectomy, n = 1; and multiple subpial transsections, n = 3. Seizure freedom (Engel class I) was achieved in five patients.

CONCLUSIONS

Selective MCA Wada tests can contribute to risk assessment concerning postsurgical motor deficits before functional hemispherectomy. Other indications are less clear: The identification of language areas is targeted primarily by electrical-stimulation mapping after subdural grid implantations, and selective MCA Wada tests in ESES patients yet have to be validated in larger patient groups.

The frontal lobe role in memory: a review of convergent evidence and implications for the Wada memory test

Functional imaging studies have implicated the frontal lobe in many of the memory processes often thought to be the domain of medial temporal structures. Results from fMRI studies of normal subjects have suggested that some components of memory formation, including those components tested during the Wada memory test, may involve frontal lobe regions. Specific behavioral disruptions during carotid amytal injections support a model for frontal lobe anesthesia in explaining results of the Wada memory test. Cortical stimulation data suggest that frontal lobe disruption is sufficient to cause memory disturbances. The convergence of evidence suggests frontal lobe memory may limit the predictive value of the Wada memory test in defining the risk of memory loss following temporal lobectomy.