Measurement of stretch-evoked brainstem function using fMRI

Knowledge on the organization of motor function in the reticulospinal tract (RST) is limited by the lack of methods for measuring RST function in humans. Behavioral studies suggest the involvement of the RST in long latency responses (LLRs). LLRs, elicited by precisely controlled perturbations, can therefore act as a viable paradigm to measure motor-related RST activity using functional Magnetic Resonance Imaging (fMRI). Here we present StretchfMRI, a novel technique developed to study RST function associated with LLRs. StretchfMRI combines robotic perturbations with electromyography and fMRI to simultaneously quantify muscular and neural activity during stretch-evoked LLRs without loss of reliability. Using StretchfMRI, we established the muscle-specific organization of LLR activity in the brainstem. The observed organization is partially consistent with animal models, with activity primarily in the ipsilateral medulla for flexors and in the contralateral pons for extensors, but also includes other areas, such as the midbrain and bilateral pontomedullary contributions.

Fulminant Guillain Barre syndrome with recurrent lung collapse

Fulminant Guillain-Barré syndrome (GBS) is a rapidly progressive form of polyneuropathy in which patients demonstrate eventual flaccid quadriplegia and an absence of brainstem function. Most patients present initially with a mild upper respiratory or gastrointestinal illness and have non-diagnostic cerebral imaging studies. Here we report the case of child aged 7 who was admitted initially with complaints of weakness of lower limbs lasting for 4-5 hours. He had difficulty in standing and walking, associated with pain in both lower limbs. Flaccid weakness rapidly progressed over 12 hours to involve both upper limbs along with difficulty in swallowing and nasal regurgitation of feeds. He was intubated and mechanically ventilated for respiratory failure. Over the period of time, after confirmation with all the test reports and symptoms, other differential diagnoses were ruled out and fulminant GBS was considered and hence plasmapheresis was started. Over the period of 3 months his muscle power slowly improved. During discharge, he was able to lift limbs against minimal resistance, turn sideways on bed, sit up with minimal support and likewise stand with support.

Measurement of stretch-evoked brainstem function using fMRI

ABSTRACTKnowledge on the organization of motor function in the reticulospinal tract (RST) is limited by the lack of methods for measuring RST function in humans. Behavioral studies suggest the involvement of the RST in long latency responses (LLRs). LLRs, elicited by precisely controlled perturbations, can therefore act as a viable paradigm to measure motor-related RST activity using functional Magnetic Resonance Imaging (fMRI).Here we present StretchfMRI, a novel technique developed to study RST function associated with LLRs. StretchfMRI combines robotic perturbations with electromyography and fMRI to simultaneously quantify muscular and neural activity during stretch-evoked LLRs without loss of reliability. Using StretchfMRI, we established the muscle-specific organization of LLR activity in the brainstem. The observed organization is partially consistent with animal models, with activity primarily in the ipsilateral medulla for flexors and in the contralateral pons for extensors, but also include other areas, such as the midbrain and bilateral pontomedullary contributions.

Brainstem death and prolonged disorders of consciousness

Advances in resuscitation and the advent of modern intensive care techniques to support the circulation challenge the simple definition of death in terms of loss of spontaneous circulation (‘cardiac death’). Instead, death is now better regarded as an irreversible loss of the capacity for consciousness combined with irreversible loss of the capacity to breathe. Since the brainstem is required for both consciousness and spontaneous breathing, irreversible loss of brainstem function (e.g. after trauma, haemorrhage, or hypoxia/ischaemia) defines the state of ‘brainstem death’. Clinical criteria for the diagnosis of brainstem death have been published, but practice varies around the world. Brainstem death lies at the extreme end of this spectrum and is, by definition, permanent. Unlike those with brainstem death, patients with prolonged disorders of consciousness may survive for many years without physiological support. The care of such patients has huge social, societal, ethical, and economic implications.

Brain Death

The fundamental neurologic principle that all brainstem function must have irreversibly ceased—in the overwhelming proportion, but not exclusively from massive damage to both cerebral hemisphere—must be understood before brain death testing proceeds. Brain death is a non- functioning destroyed (“dead”) brain with absent breathing and no circulation if support is not provided.

How should we use imaging in the determination of brainstem death?

Brainstem death is defined as the “irreversible cessation of brainstem function”, either due to primary intracranial events or extracranial factors such as hypoxia. The importance of accurate and timely diagnosis of brainstem death in critical care should not be understated, as it allows the withdrawal of treatment when it is no longer deemed to beneficial. Additionally, it may facilitate the process of organ donation. Overall, the diagnosis of brainstem death has four common principles across the world: (1) neurological criteria based on clinical assessment; (2) evidence of irreversible brain damage from known aetiology; (3) demonstrating an absence of a reversible cause; and (4) the use of ancillary studies. The latter in particular has been a controversial issue, with much debate continuing on how imaging should be used. We discuss three key questions surrounding the role of imaging in the diagnosis of brainstem death as well as important issues the radiology community should consider.