Neuroradiology and Neuroendovascular Interventions Abstract Neuroradiology is an area of radiology that focuses exclusively on radiology used to diagnose and characterize neurologic diseases, disorders, and injuries. Neuroradiologic examinations may include noninvasive measures such as plain radiographs, computed tomography, and magnetic resonance imaging; they may also encompass more invasive procedures such as cerebral angiograms and myelograms. Neuroendovascular interventions are procedures carried out by neuroradiologists and neurosurgeons who specialize in this type of treatment, including angioplasty, embolization, and stenting. Nurses caring for these patients must possess specific knowledge of these procedures and their indications in order to provide patients with the specialized care they require. Keywords: cerebral angiography, computed tomography, embolization, magnetic resonance imaging, myelography, radiography, stenting Neuroradiology is a discipline of radiology that focuses on diagnosis of, and intervention for, abnormalities of the central and peripheral nervous systems. This field comprises many imaging and diagnostic modalities, some of which are discussed in this chapter. Neuroendovascular procedures to treat abnormalities of the nervous system are also described herein. Radiographs, commonly referred to as plain films or X-rays, are gross two-dimensional structural images obtained without the use of a contrast medium. Most fundamental radiologic modality Decreasing role in neuroradiology due to advances in computed tomography (CT) and magnetic resonance imaging (MRI) Lesions or fractures of bony structures, including the following: Skull or spine fractures Facial trauma Abnormal structure or positioning of bones, as in flexion-extension injuries Sinusitis None (pregnancy is considered a relative risk; potential risk must be weighed against possible benefit) Screening per hospital policy Noninvasive None Myelography is an imaging technique that uses a contrast agent to reveal abnormalities within the spinal cord. The subarachnoid space is accessed via insertion of a spinal needle between L3 and L4 or L4 and L5 Contrast medium is injected directly into the subarachnoid space, and radiographs are taken of relevant spinal levels (cervical, thoracic, or lumbar) Disk herniation Spinal stenosis Bone displacement Spinal cord compression secondary to tumor or vascular malformation Actual or suspected intracranial mass (with or without increased intracranial pressure), as this introduces the potential for brain stem herniation. See also Chapter 3: Principles of Intracranial Pressure Noncommunicating hydrocephalus Coagulopathies Impaired renal function Known allergic reaction to contrast agents Informed consent required Review of previous laboratory studies, including coagulation profile Review of medications (anticoagulants such as warfarin should be suspended several days before myelogram) Patient should be nil per os (NPO), or nothing by mouth, for 2 hours before procedure Patient should be sedated Take precautions for patients with contrast agent allergy per institutional policies and procedures, if warranted (Box 14.1 Hospital Policy and Procedure) Box 14.1 Hospital Policy and Procedure Follow institutional guidelines, policies, and protocols regarding contrast allergy prep and anticoagulation reversal. A regular CT can be completed with or without contrast, but computed tomography angiography (CTA) is always performed with contrast. Patients with contrast allergies may undergo any neuroradiologic modality, as long as they are properly prepared Headaches (i.e., positional or “low-pressure” headache) Worse when patient is in an upright position Usually improves with time, rest, and hydration Epidural blood patch may be helpful Infection Reaction to sedation or contrast medium Extravasation of contrast (Box 14.2 Clinical Alert: Metformin and Contrast Agents) Box 14.2 Clinical Alert: Metformin and Contrast Agents Metformin should not be given to patients receiving radiologic contrast agents May cause renal failure CT is the most commonly used neuroimaging modality in the neurosciences. In CT imaging, X-ray beams are projected into the body in a single slice. A stationary detector then measures and reconstructs signals from multiple points of view, and images are generated from those signals and the attenuation of the radiation (▶ Fig. 14.1). Fig. 14.1 Axial computed tomogram of the head. CTA is a computed tomogram of the vascular system that combines the CT procedure described above with injected contrast material. The resulting CT angiogram provides detailed images of the patient’s blood vessels. As it applies to imaging techniques, the term attenuation refers to the intensity of a radiation beam as it passes through matter. Greater density equals greater attenuation, so objects with greater density will have greater attenuation and therefore will appear whiter/lighter Conversely, less density equals less attenuation, resulting in a darker/blacker appearance on CT (▶ Table 14.1). Substance Appearance on CT Bone White (+++) Blood (acute) White (++) Gray matter (brain parenchyma) Light gray (++) White matter (brain parenchyma) Gray (+++) Water or CSF Dark gray/light black (++) Air Black (+++) Abbreviations: CSF, cerebrospinal fluid; CT, computed tomography. +++ represents full appreciation of stated color; ++ represents moderate appreciation of stated color. Acute intracranial hemorrhage Space-occupying lesions Bony structural abnormalities Bony alignment, fractures, or dislocation of the spine Hydrocephalus Ischemic or hemorrhagic stroke (CTA is the gold standard for management of stroke) Pregnancy is a relative risk Contrast allergy, requires a contrast allergy work-up per institutional policy and protocol (Box 14.1 Hospital Policy and Procedure) Impaired renal function (a contraindication only if contrast is ordered) Noninvasive, no preparation is required for basic nonenhanced CT Follow institutional guidelines and policies regarding administration of contrast agent and testing for allergy to contrast agent Patient is placed on a flat surface and rolled into scanner up to the level to be examined Test usually takes less than 5 minutes Cross-sectional images can be viewed in sagittal, axial, and coronal views Delayed allergic reaction to contrast agent Acute renal failure secondary to contrast-induced nephrotoxicity Occurs in about 2% of general population, in 4.1% of patients with renal insufficiency (whose serum creatinine is >1.5 mg/dL), and in 12% of patients with both renal insufficiency and diabetes mellitus Extravasation of contrast material, which can damage tissue or cause compartment syndrome Magnetic resonance imaging is a sophisticated noninvasive imaging technique that combines radiofrequency waves with magnetic fields to visualize various anatomical structures, providing valuable details about their composition and location. MRI involves creation of a magnetic field that aligns the hydrogen ions in the body, which are otherwise randomly organized in the absence of a magnetic stimulant. Radio waves are introduced into the field, and signal energy from excitation of the ions to resting is measured and reconstructed into a visual matrix that features different shades of gray. Water and cerebrospinal fluid (CSF) are dark on T1-weighted MRI (▶ Fig. 14.2) and are white on T2-weighted MRI (▶ Fig. 14.3). Enhancement is the result of shortened T1, which is induced by the addition of a contrast agent (Box 14.3 T1-Weighted MRI and T2-Weighted MRI). Fig. 14.2 T1-weighted coronal magnetic resonance image of the head. Fig. 14.3 T2-weighted coronal magnetic resonance image of the head. Box 14.3 T1- and T2-Weighted MRI T1 and T2 are defined as constant measurement of time that represents the relaxation time needed for magnetized substance to return to equilibrium T1 = longitudinal relaxation time T2 = transverse relaxation time Different types of MRI may be indicated depending on the type of information sought. These types include the following: Magnetic resonance angiography (MRA) Noninvasive imaging study that uses a combination of radiofrequency waves and magnetic fields to define cerebral vasculature (▶ Fig. 14.6) May require the use of gadolinium (a contrast agent) Images are obtained by changing the protocol of signal acquisition to enhance the vasculature of the brain Magnetic resonance venography MRI of the venous system (▶ Fig. 14.5) Magnetic resonance spectroscopy MRI used to define the compounds within the brain tissue that contain protons Differentiates between abscess and neoplasm, tumor and multiple sclerosis plaques, tumor and radiation treatment necrosis, postoperative enhancement and tumor recurrence Diffusion-weighted imaging Differentiates between vasogenic edema, cytotoxic edema, and acute ischemic brain tissue or cells Perfusion-weighted imaging Evaluates microvascular circulation Functional MRI Tool for preoperative brain mapping to identify eloquent areas of the brain, such as speech and motor cortices (▶ Fig. 14.6) MRI with navigation systems Allows the surgeon to visualize the anatomical target in relation to surrounding normal structures Improves accuracy of lesion localization Fig. 14.4 Magnetic resonance angiography shows postoperative patency of anastamosis (arrow).. Fig. 14.5 Magnetic resonance venography. Fig. 14.6 Sagittal functional magnetic resonance image of the head. Tumor Infection Stroke Vascular abnormalities Demyelinating processes Hydrocephalus Inflammatory processes Visualization of soft tissue (e.g., spinal cord, spinal nerves, disk spaces, CSF flow, ligament integrity) (▶ Fig. 14.7). Fig. 14.7 Sagittal magnetic resonance image of cervical spine. Pregnancy is relatively contraindicated (potential risk must be weighed against possible benefit) Implanted metallic devices, such as pacemakers, defibrillators, spinal cord stimulators, or medication pumps; foreign bodies such as removable or permanent body piercing (dermal anchor piercing) (▶ Table 14.2) Clinical instability (potential risk must be weighed against possible benefit; Box 14.4 Clinical Alert: Clinical Instability and MRI) Box 14.4 Clinical Alert: Clinical Instability and MRI Clinically unstable patients may not be candidates for MRI for the following several reasons: Need for mechanical ventilation Use of infusion pumps (antiarrhythmic or vasopressor drugs) Very difficult to assess condition while patient is in cylinder Rapidly deteriorating neurologic status Difficulty maintaining airway Compatiblesa Incompatible Programmable shunt valves Deep brain stimulators Most intrathecal pumps Most surgical clips, plates Pacemakers Spinal cord stimulators Metal workers (anyone with history of working with metal should have orbital films done prior to MRI) Jewelry, body piercings (including dermal implants) Bullets, shrapnel Abbreviation: MRI, magnetic resonance imaging. Note: This is a partial list only. For a complete list of compatible devices, see http://www.mrisafety.com, the official site of the Institute for Magnetic Resonance Safety, Education, and Research. aSettings may become altered during MRI and should be checked afterward. Screening form per hospital policy (Box 14.5 MRI Safety) Sedation for patients with known claustrophobia NPO for patients undergoing sedation for 6 hours prior to MRI, or for as long as indicated by institutional policy and protocol Comprehensive metabolic profile with glomerular filtration rate per institutional policy; renal function screening if gadolinium will be administered Follow institutional guidelines for patient safety and patient selection Box 14.5 MRI Safety Nursing obligation is first-level screening only MRI safety falls on the MRI technician and the radiologist For more information on materials allowed in MRI scanners, see the following: http://www.MRIsafety.com http://www.IMRSER.org Allergic reaction to contrast agent Cerebral angiography has long been considered the best tool for diagnosis and evaluation of cerebrovascular anomalies (▶ Fig. 14.8). Fig. 14.8 Normal cerebral angiogram. Digital subtraction angiography (DSA) is a modification of the standard cerebral angiography process DSA allows for visualization of a specific artery by eliminating surrounding structures from view, facilitating treatment such as embolization, stenting, angioplasty, clot removal, and thrombolytic therapy (discussed in greater detail below) Evaluation of vascular malformations Fistulas (▶ Fig. 14.9) Aneurysms Arteriovenous malformations (AVMs) Vascular flow studies (pre- or postoperatively) Vascular flow studies may reveal stenosis, occlusion, or vasospasm DSA is the gold standard for evaluation of the vasculature of the brain and neck Used for the intervention or treatment of vasospasm, arterial or venous trauma, stroke, aneurysms, fistulas, vascular tumors, AVMs, and stenosis. Fig. 14.9 Fistula draining into a venous pouch on digital subtraction angiography.
14.1 Neuroradiology
14.2 Imaging
14.2.1 Radiography
Indications for Radiography
Contraindications
Method
Complications
14.2.2 Myelography
Indications for Myelography
Contraindications
Method
Complications
14.2.3 Computed Tomography
Computed Tomography Angiography
Attenuation
Indications for Computed Tomography and Computed Tomography Angiography
Contraindications
Method
Complications
14.2.4 Magnetic Resonance Imaging
Types of Magnetic Resonance Imaging
Indications for Magnetic Resonance Imaging
Contraindications
Method
Complications
14.2.5 Diagnostic Cerebral Angiography
Digital Subtraction Angiography
Indications for Digital Subtraction Angiography
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