**8. Clinical implications of neuroimaging findings**

The analysis of the clinical implications of neuroimaging findings requires an important discussion about some limitations of the neuroimaging methods in order to critically interpret the results of the several PB studies.

The localization of human brain functions by studying the correlation between a behavioral disorder and the region of brain lesion has an historical and huge contribution to the understanding of brain function. Nevertheless, as well as all the neuroimaging techniques, the 'lesion method' has some noteworthy limitations.

Roden and Karnath pointed out that the lesion method usually assumes that after a focal lesion, the intact regions of the brain continue to function in the same manner as before the lesion (Roden & Karnath, 2004). However, with tasks controlled by spread and changeable circuits, the brain start to adapt rapidly following the lesion. This rearrangement is helpful for recovery, but makes it difficult to infer the original function of the healthy brain. Also, the design of the brain, its blood supply and the surrounding skull mean that some areas of the brain are injured more often than others what implicate that the locations of brain damage are not randomly distributed in the brain. Roden and Karnath highlighted that this

New Insights for a Better Understanding

standard brain that was used during spatial normalization.

1a 1b

of the Pusher Behavior: From Clinical to Neuroimaging Features 253

allow better representation of average neuro-anatomy, the MNI created an average brain template based on the MRI scans from several hundred individuals (Evans et al., 1993;Collins et al., 1994). However, the Talairach coordinate system is still the standard reference system used by the neuroimaging community and it is a common practice to report the results in terms of Talairach coordinates even when different brain templates have been used to analyze imaging data. Nevertheless, there is no simple way to transform multiple subject data from the MNI space to the Talairach space. It is actually possible that the coordinate location in MNI space of two subjects would map to different points of Talairach space (Chau & MacIntosh, 2005). The discrepancy becomes a problem when the data are analyzed in the MNI space but the results are reported using the Talairach space (Brett et al., 2002; Chau & MacIntosh, 2005; Laird et al, 2010). Certainly, there is no perfect solution to the conversion problem. According to Laird et al. (Laird et al, 2010), authors should be encouraged to make a clearer distinction between the basic coordinate system as defined by Talairach and Tournoux (1998) and the reference template corresponding to a

1: Scans from a PB patient with traumatic brain injury. Note the left subdural haematoma and mass

2: Scans from a PB patient with multiple hemorrhagic metastasis from a pelvis rabdomiosarcoma. The larger lesions were located in the right frontal and parietal lobes causing a mild falx displacement. (from

effect with midline shift and multiple areas of contusion over the left hemisphere.

2a 2b

Fig. 4. CT scans of patients showing different etiologies for PB.

Santos-Pontelli et al., 2005)

makes it difficult to interpret lesion overlay plots (Roden & Karnath, 2004). Moreover, if we test patients in the acute stage of their disease, we will not be able to accurately identify all of the brain regions that are damaged. However, if we wait for these initial issues to resolve, the issues associated with brain plasticity will become more evident.

1: Ischemic stroke of the left M1 segment of the middle cerebral artery and significant midline shift (midline shift of the septum pellucidum = 8mm; interthalamic adhesion = 6mm; pineal = 7mm). 2: Right thalamic hemorrhagic stroke with intraventricular hemorrhage and midline shift (midline shift of the septum pellucidum = 2mm; interthalamic adhesion = 5mm; pineal = 9mm).

Fig. 3. CT scans of PB patients in the acute stage.

Although lesion data do not provide the precision of fMRI activation foci, they can tell us which areas are necessary for controlling a cognitive function (Roden & Karnath, 2004). According to Roden and Karnath, simple overlay plots for patients who have a disorder can be inaccurate due to the fact that the regions that they highlight might reflect increased vulnerability of certain regions to injury (as discussed above), rather than any direct involvement with the disorder of interest. A control group of neurological patients who do not exhibit the deficit of interest is, therefore, fundamental for valid anatomical conclusions (Roden & Karnath, 2004). Each technique on its own has only limited explanatory power. However, the strengths and weaknesses of these tools are complementary.

In neuroimaging studies, it is a common practice to spatially normalize subject brains to a standard coordinate system in order to reduce intersubject variability, enable intersubject image averaging, and facilitate the reporting of reduced results in the form of stereotactic coordinates. Numerous registration methods exist, and the two most established are based on the Talairach atlas (Talairach & Tournoux, 1988) and the Montreal Neurological Institute (MNI) templates (Evans et al., 1993; Collins et al., 1994; Laird et al, 2010). The Talairach cannot reflect an excellent representation of the neuroanatomy for the general population atlas because it was created based on the postmortem brain of single subject. In order to

makes it difficult to interpret lesion overlay plots (Roden & Karnath, 2004). Moreover, if we test patients in the acute stage of their disease, we will not be able to accurately identify all of the brain regions that are damaged. However, if we wait for these initial issues to resolve,

the issues associated with brain plasticity will become more evident.

Fig. 3. CT scans of PB patients in the acute stage.

of the septum pellucidum = 2mm; interthalamic adhesion = 5mm; pineal = 9mm).

However, the strengths and weaknesses of these tools are complementary.

1: Ischemic stroke of the left M1 segment of the middle cerebral artery and significant midline shift (midline shift of the septum pellucidum = 8mm; interthalamic adhesion = 6mm; pineal = 7mm). 2: Right thalamic hemorrhagic stroke with intraventricular hemorrhage and midline shift (midline shift

Although lesion data do not provide the precision of fMRI activation foci, they can tell us which areas are necessary for controlling a cognitive function (Roden & Karnath, 2004). According to Roden and Karnath, simple overlay plots for patients who have a disorder can be inaccurate due to the fact that the regions that they highlight might reflect increased vulnerability of certain regions to injury (as discussed above), rather than any direct involvement with the disorder of interest. A control group of neurological patients who do not exhibit the deficit of interest is, therefore, fundamental for valid anatomical conclusions (Roden & Karnath, 2004). Each technique on its own has only limited explanatory power.

In neuroimaging studies, it is a common practice to spatially normalize subject brains to a standard coordinate system in order to reduce intersubject variability, enable intersubject image averaging, and facilitate the reporting of reduced results in the form of stereotactic coordinates. Numerous registration methods exist, and the two most established are based on the Talairach atlas (Talairach & Tournoux, 1988) and the Montreal Neurological Institute (MNI) templates (Evans et al., 1993; Collins et al., 1994; Laird et al, 2010). The Talairach cannot reflect an excellent representation of the neuroanatomy for the general population atlas because it was created based on the postmortem brain of single subject. In order to allow better representation of average neuro-anatomy, the MNI created an average brain template based on the MRI scans from several hundred individuals (Evans et al., 1993;Collins et al., 1994). However, the Talairach coordinate system is still the standard reference system used by the neuroimaging community and it is a common practice to report the results in terms of Talairach coordinates even when different brain templates have been used to analyze imaging data. Nevertheless, there is no simple way to transform multiple subject data from the MNI space to the Talairach space. It is actually possible that the coordinate location in MNI space of two subjects would map to different points of Talairach space (Chau & MacIntosh, 2005). The discrepancy becomes a problem when the data are analyzed in the MNI space but the results are reported using the Talairach space (Brett et al., 2002; Chau & MacIntosh, 2005; Laird et al, 2010). Certainly, there is no perfect solution to the conversion problem. According to Laird et al. (Laird et al, 2010), authors should be encouraged to make a clearer distinction between the basic coordinate system as defined by Talairach and Tournoux (1998) and the reference template corresponding to a standard brain that was used during spatial normalization.

1: Scans from a PB patient with traumatic brain injury. Note the left subdural haematoma and mass effect with midline shift and multiple areas of contusion over the left hemisphere. 2: Scans from a PB patient with multiple hemorrhagic metastasis from a pelvis rabdomiosarcoma. The larger lesions were located in the right frontal and parietal lobes causing a mild falx displacement. (from Santos-Pontelli et al., 2005)

Fig. 4. CT scans of patients showing different etiologies for PB.

New Insights for a Better Understanding

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In this context, the PB neuroimaging studies greatly advanced our understanding of this interesting behavior. Although without a major precision, the qualitative analysis can be hepful to identify a patient that has a tendency to develop PB by the analysis of his/her neuroimage scan., specially in patients with thalamic lesions. In addition, the knowledge that several lesion locations can elicit PB reinforces the concept that this behavior can be accompanied by several neurologic deficits and all the neurologic condition can be critical for the functional prognosis of PB.

As discussed by Roden and Karnath (Roden & Karnath, 2004), the strength of cognitive neuroscience comes from using convergent tools to investigate the same theoretical question. Although there are neuroimaging studies regarding the PB, it remains an issue of future studies to investigate several aspects of PB using brain activation techniques (funcional magnetic resonance, single-photon emission computed tomography, positron emission tomography, magnetoencephalography, event related potential) and transcranial magnetic stimulation techniques in order to better understand this intriguing behavior.

#### **9. Acknowledgement**

The authors acknowledge the Coordenaçao de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Fundaçao de Amparo à Pesquisa do Estado de Sao Paulo (FAPESP) for the financial support.

#### **10. References**


In this context, the PB neuroimaging studies greatly advanced our understanding of this interesting behavior. Although without a major precision, the qualitative analysis can be hepful to identify a patient that has a tendency to develop PB by the analysis of his/her neuroimage scan., specially in patients with thalamic lesions. In addition, the knowledge that several lesion locations can elicit PB reinforces the concept that this behavior can be accompanied by several neurologic deficits and all the neurologic condition can be critical

As discussed by Roden and Karnath (Roden & Karnath, 2004), the strength of cognitive neuroscience comes from using convergent tools to investigate the same theoretical question. Although there are neuroimaging studies regarding the PB, it remains an issue of future studies to investigate several aspects of PB using brain activation techniques (funcional magnetic resonance, single-photon emission computed tomography, positron emission tomography, magnetoencephalography, event related potential) and transcranial magnetic stimulation techniques in order to better understand this intriguing behavior.

The authors acknowledge the Coordenaçao de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Fundaçao de Amparo à Pesquisa do Estado de Sao Paulo (FAPESP)

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**14** 

*Italy* 

**Neurosonological Evaluation of** 

*Department of Neurology-Stroke Unit-Arcispedale Santa Maria Nuova, Reggio Emilia* 

Stroke is a condition with an high mortality rate and a relevant burden of disability and social costs. Indeed it is the third cause of death and the first cause of disability in western countries. About 80% of strokes is ischemic and due to the occlusion of a large or small cerebral artery. Therefore the rationale of thrombolysis is the reopening of the occluded vessel within a short time window from symptoms onset, mainly by using iv rtPA but also by using local delivery of rtPA and/or mechanical disruption of the thrombus. The basic assumption is simple and clear: a large vessel was abruptly occluded and the corresponding brain territory was deprived of oxygenated blood and nutrients. The brain metabolism during ischemia is flow- and time-dependent; there are precise perfusional thresholds for maintaining membrane pump activity; therefore the cell integrity and the duration of neuronal life is related to the time from the vessel occlusion, in a variable combination of individual ischemic tolerance and activation of the collateral circulation. The irreversibly damaged brain tissue is known as ischemic core and the suffering, but still viable, tissue is known as penumbra. The penumbra to core ratio is affected by several factors, but it is widely recognized that both occlusive pattern and time from symptoms onset are strong predictors of the presence of as much viable tissue as needed for the success of the reperfusion treatment. The clinical data and the neurological severity scales, as NIHSS (National Institute of Health Stroke Scale), do not reliably predict if there is a large vessel occlusion and for which extent in single cases. The clinical presentation can be the same for a very proximal large arterial occlusion and for a small perforating artery involvement, but the recanalization rate is strictly dependent on the occlusive pattern. Therefore, because the recanalization is a strong predictor of a good outcome, the prognosis depends on it and it

All efforts should be made to achieve the diagnosis of vessel occlusion ad brain perfusion condition as early as possible, in order not only to predict the prognosis but also to tailor the

In acute stroke time is brain, and therefore the diagnostic steps should be reliable, fast and not time consuming. Ultrasound techniques have these features for other body districts, also for extracranial vessels, but their use for the examination of the intracranial circulation has been hampered for many years, because of the attenuation effect of the skull. In the last twenty years this limitation has been demonstrated to be passed by neurosonological

can be early inferred by the diagnosis of the occlusive pattern.

**1. Introduction** 

treatment.

**the Acute Stroke Patients** 

Giovanni Malferrari and Marialuisa Zedde

