Focused ultrasound in neurosurgery: a historical perspective.

Focused ultrasound (FUS) has been under investigation for neurosurgical applications since the 1940s. Early experiments demonstrated ultrasound as an effective tool for the creation of intracranial lesions; however, they were limited by the need for craniotomy to avoid trajectory damage and wave distortion by the skull, and they also lacked effective techniques for monitoring. Since then, the development and hemispheric distribution of phased arrays has resolved the issue of the skull and allowed for a completely transcranial procedure. Similarly, advances in MR technology have allowed for the real-time guidance of FUS procedures using MR thermometry. MR-guided FUS (MRgFUS) has primarily been investigated for its thermal lesioning capabilities and was recently approved for use in essential tremor. In this capacity, the use of MRgFUS is being investigated for other ablative indications in functional neurosurgery and neurooncology. Other applications of MRgFUS that are under active investigation include opening of the blood-brain barrier to facilitate delivery of therapeutic agents, neuromodulation, and thrombolysis. These recent advances suggest a promising future for MRgFUS as a viable and noninvasive neurosurgical tool, with strong potential for yet-unrealized applications.

The Neurocritical and Neurosurgical Care of Subdural Hematomas.

Subdural hematomas (SDHs), though frequently grouped together, can result from a variety of different etiologies, and therefore many different subtypes exist. Moreover, the high incidence of these lesions in the neurocritical care settings behooves practitioners to have a firm grasp on their diagnosis and management. We present here a review of SDHs, with an emphasis on how different subtypes of SDHs differ from one another and with discussion of their medical and surgical management in the neurocritical care setting. In this paper, we discuss considerations for acute, subacute, and chronic SDHs and how presentation and management may change in both the elderly and pediatric populations. We discuss SDHs that arise in the setting of anticoagulation, those that arise in the setting of active cerebrospinal fluid diversion, and those that are recurrent and recalcitrant to initial surgical evacuation. Management steps reviewed include detailed discussion of initial assessment, anticoagulation reversal, seizure prophylaxis, blood pressure management, and indications for intracranial pressure monitoring. Direct surgical management options are reviewed, including open craniotomy, twist-drill, and burr-hole drainage and the usage of subdural drainage systems. SDHs are a common finding in the neurocritical care setting and have a diverse set of presentations. With a better understanding of the fundamental differences between subtypes of SDHs, critical care practitioners can better tailor their management of both the patient's intracranial and multi-systemic pathologies.