Focusing and orienting spatial attention differently modulate crowding in central and peripheral vision

The allocation of attentional resources to a particular location or object in space involves two distinct processes: an orienting process and a focusing process. Indeed, it has been demonstrated that performance of different visual tasks can be improved when a cue, such as a dot, anticipates the position of the target (orienting), or when its dimensions (as in the case of a small square) inform about the size of the attentional window (focusing). Here, we examine the role of these two components of visuo-spatial attention (orienting and focusing) in modulating crowding in peripheral (Experiment 1 and Experiment 3a) and foveal (Experiment 2 and Experiment 3b) vision. The task required to discriminate the orientation of a target letter "T,'' close to acuity threshold, presented with left and right "H'' flankers, as a function of target-flanker distance. Three cue types have been used: a red dot, a small square, and a big square. In peripheral vision (Experiment 1 and Experiment 3a), we found a significant improvement with the red dot and no advantage when a small square was used as a cue. In central vision (Experiment 2 and Experiment 3b), only the small square significantly improved participants' performance, reducing the critical distance needed to recover target identification. Taken together, the results indicate a behavioral dissociation of orienting and focusing attention in their capability of modulating crowding. In particular, we confirmed that orientation of attention can modulate crowding in visual periphery, while we found that focal attention can modulate foveal crowdin

The role of hemodynamic assessment in the management of cerebral AVMs

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Direct surgery for brainstem tumors

Updating a previous report, the authors offer a review of 45 patients between age 2 and 63 treated by direct surgical excision for brainstem tumours of various description. Since 1986 all candidate patients were examined by NMR imaging in addition to CT scanning, sometimes with the further addition of digital-subtraction vertebral angiography. By Epstein and McLeary's criteria, 24 of the tumours were focal, 12 were cervicomedullary and 9 were diffuse. The most frequent histological diagnosis was glioma (36 cases between low-grade astrocytoma, anaplastic astrocytoma and glioblastoma); the balance was provided by cavernoma (6 cases), haemangioblastoma (2 cases), and lipoma (2 cases). Gross total resection was achieved in 28 patients, namely all those with ependymoma or vascular tumours and 14 of 17 with low-grade astrocytoma. Resection was subtotal in 16 cases and confined to a generous biopsy in one. There was no operative mortality, but 2 deaths occurred in the early postoperative period. At discharge, neurological status was unchanged or improved in 35 cases. At 3-month follow-up examination, 12 patients were improved, 27 were unchanged and 3 were worsened. By January 1990 (6 to 72 months postoperatively) 27 of the first 40 patients treated were alive: 13 had resumed normal life, 6 were self-sufficient and 8 were disabled. The authors conclude that present-day microsurgical resection of intra-axial brainstem tumours is associated with low mortality and morbidity and affords favourable results for which they credit high-quality NMR imaging, efficient microsurgery, adequate anesthesia, and competent postoperative intensive care

Endosellar meningiomas: report of 2 cases and review of the literature

Two cases of endosellar meningiomas are presented. The clinical and radiological picture is not always sufficiently specific to distinguish meningiomas from other types of sellar lesions, but pre-operative diagnosis is of fundamental importance in choosing the best surgical approach. In both cases, the transsphenoidal approach was used, and due to the dense consistency of the tumors, only biopsies were performed. One of the two patients was reoperated on using the sub-frontal approach for radical removal of the tumor. In the authors' experience, craniotomy proved to be the more favorable approach than the transsphenoidal route for radical excision of endosellar meningiomas. Literature on the classification of sellar meningiomas for radiological diagnosis and surgical strategy of endosellar meningiomas is reviewed

Temporal dissociation between the focal and orientation components of spatial attention in central and peripheral vision

Selective attention, i.e. the ability to concentrate one's limited processing resources on one aspect of the environment, is a multifaceted concept that includes different processes like spatial attention and its subcomponents of orienting and focusing. Several studies, indeed, have shown that visual tasks performance is positively influenced not only by attracting attention to the target location (orientation component), but also by the adjustment of the size of the attentional window according to task demands (focal component). Nevertheless, the relative weight of the two components in central and peripheral vision has never been studied. We conducted two experiments to explore whether different components of spatial attention have different effects in central and peripheral vision. In order to do so, participants underwent either a detection (Experiment 1) or a discrimination (Experiment 2) task where different types of cues elicited different components of spatial attention: a red dot, a small square and a big square (an optimal stimulus for the orientation component, an optimal and a sub-optimal stimulus for the focal component respectively). Response times and cue-size effects indicated a stronger effect of the small square or of the dot in different conditions, suggesting the existence of a dissociation in terms of mechanisms between the focal and the orientation components of spatial attention. Specifically, we found that the orientation component was stronger in periphery, while the focal component was noticeable only in central vision and characterized by an exogenous nature

Brain tumors in children under 3 years of age: recent experience (1987-1997) in 39 patients

Brain tumors in children under 3 years of age differ in clinical presentation and pathological behavior from those in older patients. In this study, we reviewed data from 39 children (24 males and 15 females) under 3 years of age who were treated for intracranial brain tumors since the introduction of magnetic resonance imaging. The purpose was to assess correlations between clinicoradiological and treatment-related factors, and their impact on prognosis. The following factors were analyzed: sex, age, duration of symptoms, intracranial hypertension on admission, tumor location, surgical removal and histology. Associations between these factors and correlations with prognosis were determined using bivariate analyses (chi(2) test) and Kaplan-Meier survival curves. Collins' concept of a period of risk recurrence was tested. Mean follow-up was 41 months (range 0-136). In March 1998, 20 children were still alive (51.2%) with a mean survival time of 65 months (range 2-136). The incidence of supratentorial tumors was significantly higher in children less than 1 year old (p = 0.027). Lateral tumors were 9/10 (90%) supratentorial versus only 7/26 (27%) midline tumors (p = 0.001). Outcome (dead or alive) was significantly better (p = 0.037) for low-grade astrocytomas (9/12 = 75% survival) when compared to ependymomas (2/6 = 33%) and primitive neuroectodermal tumors (3/12 = 25%). Total tumor removal was achieved in 20 cases and was associated with a better outcome (65 vs. 33% survival; p = 0.049). Survival analysis confirmed a worse prognosis for children with ependymomas and primitive neuroectodermal tumors (p = 0.011) and revealed a worse survival for children with intracranial hypertension on admission (p = 0.047). Total tumor removal was associated with a longer survival, although not significantly (p = 0. 077). Finally, we found no exceptions to Collins' law

Conservative treatment of a traumatic direct low-flow carotid-cavernous sinus fistula: a case report

A case of a 17-year-old boy presenting with a traumatic carotid-cavernous sinus fistula (CCSF), associated with an intracavernous pseudo-aneurysm, is reported. On angiography, the CCSF proved to be a direct and low-flow shunt. Conservative management was chosen and definitive closure of the fistula was obtained in two months by daily self-compression of the common carotid artery

Surgical management of ventral and ventrolateral foramen magnum meningiomas: report on a 64-case series and review of the literature.

Foramen magnum meningioma poses a challenge for neurosurgeons. Prognosis has generally improved with diagnostic and surgical advances over the past two decades; however, it may ultimately depend more on the surgeon's ability to tailor the approach and interpret intraoperative risks in single cases. The series comprised 64 patients operated on for ventral and ventrolateral foramen magnum meningioma. All patients underwent preoperative magnetic resonance imaging and received surgery via the dorsolateral route, rendering the series homogeneous in neuroradiological workup and surgical treatment. Particular to this series was that the majority of patients were of advanced age (n = 29; age, >65 years), had serious functional impairment (n = 30, Karnofski score <70), and large tumors (mean diameter, 3.5 cm). Total tumor removal was achieved in 52 (81 %) patients; operative mortality was nil. Early outcome varied depending on difficulties encountered at surgery (cranial nerve position and type of involvement in particular) and type of preoperative dysfunction. Long-tract signs and cerebellar deficits improved in 74 and 77 % of cases, respectively, but only 27 % of cranial nerve deficits did so. Surgical complications most often involved the cranial nerves: cranial nerve impairment, especially of the 9th through the 12th cranial nerves, due to stretching or encasement was noted in 44 cases. At final outcome assessment, two thirds of the cranial nerve deficits cleared, and all but two patients returned to a normal productive life. One patient was reoperated on during the follow-up period. Foramen magnum meningiomas behave like clival or spinal tumors depending on their prevalent extension. A dorsolateral approach tailored to tumor position and extension and meticulous surgical technique allow for definitive control of surgical complications. Scrupulous postoperative care may prevent dysphagia, a major persistent complication of surgery. Long-term observation of indolent tumor behavior at follow-up suggests that incomplete resection may be a viable surgical treatment option

Assessment and surgical management of posterior fossa epidermoid tumors: report of 28 cases

OBJECTIVE: The management of a series of 28 patients operated on for posterior fossa epidermoids is reviewed, emphasizing the need for long-term follow-up. We discuss the rationale for a comprehensive classification system that may allow the comparison of results from homogeneous series. METHODS: We grouped the tumors to differentiate the surgical management according to various tumor sites and the degree of extension. Twenty patients harbored tumors located in the cerebellopontine angle, five patients harbored tumors in the fourth ventricle, and three patients harbored tumors in the posterior fossa basal. In 17 patients, extensions of tumors outside the posterior fossa included the following regions: the suprasellar/chiasmatic (n = 5), the parasellar/temporobasal (n = 5), and the mesencephalic/pineal (n = 7). Tumor extension was also defined by the number of regions involved. Pre- and postoperative magnetic resonance imaging and computed tomographic findings collected in 17 and 28 patients, respectively, were carefully evaluated. RESULTS: Clinical features and surgical approaches varied according to location and growth pattern. Fifty-seven percent of the tumors were completely removed. A higher total removal rate was achieved in patients with tumors confined to the primary location. One patient (3%) died in the perioperative period. Approximately half of the patients presented with transient mild focal deficit impairments resulting from the manipulation of the nervous structure over a wide area. There was a higher rate of surgical complications with fourth ventricle and mesencephalic extended cerebellopontine angle tumors. The mean follow-up period was 8.6 years. Thirty percent of the patients with subtotal removal experienced symptomatic recurrences after 8.1 years, whereas all patients with total removal were still asymptomatic. The recurrence-free survival rate was 95% at 13 years for patients with total removal compared with 65% for patients with subtotal removal. Problems of identification of tumor regrowth are discussed. CONCLUSION: By assessing posterior fossa epidermoids, we determined that location and extension play a major role in the prognosis. Our data suggest that more aggressive surgery is called for at first operation, and that a second operation should be planned when regrowth becomes symptomatic and/or tends to extend outside its original site

Radiological and surgical aspects of pure spinal epidural cavernous angiomas. Report on 5 cases and review of the literature

BACKGROUND: Cavernous angiomas (CAs) that are localized completely in the spinal epidural space are uncommon vascular malformations. Although they have increasingly been reported in the literature in recent years, diagnostic and surgical features are not clearly defined. METHODS: We report five patients with pure spinal epidural cavernous angiomas (PSECAs) and review the literature, focusing on their radiologic and surgical characteristics. We also compare these tumors with other extra-axial CAs as well as with their intra-axial counterparts. RESULTS: PSECAs, like all other extra-axial CAs, differ from intra-axial ones on MRI: the hemorrhagic variant is less frequent, hemosiderin rim is rare, the signal is different, and contrast enhancement is the rule. They are very similar to spinal meningiomas but they differ in their growth pattern and morphology, since they infiltrate intervertebral foramina and have an oval shape. In PSECA, intraoperative bleeding is rarely profuse, in contrast to other extra-axial CAs, especially those of the cavernous sinus. CONCLUSIONS: On MRI, PSECAs and other extra-axial CAs constitute a homogeneous group since they enhance significantly. At operation, since there is rarely enough bleeding to limit removal, radical excision of PSECAs can be achieved with good results