6

All patients should be stabilized according to the “A, B, Cs” (A, airway; B, breathing; C, circulation). Most important in determining neurological injuries are the history and neurological examination. After the initial evaluation, the secondary survey includes lateral cervical spine x-rays. Some institutions have supplemented lateral cervical x-rays with CT scans with reconstructed views to rule out obvious fractures and malalignments. The quality of the lateral reconstructed cervical spine views depends on the thickness of the slice and their overlap; the smaller the thickness, the better the quality of reconstruction. Additional x-rays or films are taken as needed.

Plain Films

Skull x-rays may show nontraumatic abnormalities, such as congenital skull defects, skull lesions, or even foreign bodies.1

Traumatic linear fractures must differentiate from vessel grooves and suture lines. Vessel grooves are thicker, and may curve and branch. Suture lines are wide and jagged and follow the course to meet other sutures.² Traumatic linear fractures are often associated with epidural hematoma (EDH) or subdural hematoma (SDH).³

CT, computed tomography; EDH, epidural hematoma; SDH, subdural hematoma.

Traumatic depressed skull fractures are best evaluated by CT scan using bone windows. It is important to determine if there is trauma to underlying brain if the depression is greater than the thickness of the skull, or 8 to 10 mm.

The fracture may appear within the suture of the calvarium called diastasis, or widening of the suture line. On follow-up films, the fracture may grow if associated with dural tear. This is rarely seen in pediatric patients and less so in the adult population (Table 6–1).

Skull x-rays also demonstrate foreign bodies, postoperative changes, and extracranial material, such as reservoirs, plates, or screws, and intracranial material, such as shunt tubing, coils, or clips.

Spine x-rays may show nontraumatic abnormalities, such as congenital defects, degenerative processes, or pathological fractures.

Traumatic findings include fractures, dislocation, subluxation, and rotation. The completed cervical spine evaluation must be seen from the craniocervical junction through T1. If the entire view is not seen, then a swimmer’s view must be obtained with the arm above the head so that there is less tissue to shoot through. A consistent process must be adhered to every time a cervical spine x-ray is obtained. On a lateral x-ray, look for smooth contours of the anterior and posterior marginal line, as well as the alignment of the spinolaminar line. The alignment of the posterior spinous line is an approximation. When reviewing the posterior elements, attention should be paid to the fanning of the spinous processes. After the bone is inspected, the soft tissue should be reviewed. Prevertebral soft tissue swelling may be an indicator of damage as well. Approximations of normal width of the prevertebral tissue is 6 mm at C3 and 12 mm at C6.² The lateral cervical spine x-ray should include measurement of the atlantodental interval as an indicator of atlantoaxial subluxation; it should be 2.5 to 3 mm in adults. Other areas of concern are the normal cervical lordotic curvature and loss of vertebral height, or fracture lines, or change in disk height. The same areas should be reviewed in the thoracic and lumbar spine. If there is a mechanism of injury that leads to cervical spine radiographs, then it is usually a good idea to x-ray the thoracic and lumbar spines (Table 6–2).

X-rays in the neurosurgical intensive care unit (NICU) may be done after the application of a halo or tongs for traction to evaluate reduction after each addition of weights or each manipulation of the device. X-rays will look for postoperative instrumentation placement. Dynamic films, or flexion and extension films, evaluate motion. These are most often used for cervical spine clearance, but they are also used to evaluate subluxation with spondylolisthesis and compression fractures. For cervical spine clearance, the patient must be alert and cooperative. Dynamic films cannot be used if there is more than 3.5 mm subluxation seen on the lateral film or if the patient is not neurologically intact.

CT Scan of the Brain

CT scan is the best imaging tool for studying bone or other calcific structures. It is based on attenuation of the electron density of the material in the path of the x-ray beam. It is good for the initial assessment of head injury and neurological deficits, as well as for patients who cannot have magnetic resonance imaging (MRI). However, CT scan is prone to artifact from the densest material and cannot differentiate between soft tissues of similar densities; therefore, it is less advantageous for posterior fossa evaluation. It is contraindicated with contrast enhancement if the patient is in renal failure and blood urea nitrogen (BUN) > 2.0, or if there is a first-trimester pregnancy. CT scans can be completed with or without contrast. If you suspect a bleed inside the skull, do not use contrast on initial exam. Noncontrasted CT scans can also be utilized to evaluate hardware placement and function with deep brain stimulators, intracranial pressure (ICP) monitors and drains, external ventricular drain, and subdural catheters and as follow-up for residual or reaccumulation of hemorrhage. Contrasted CT scans are helpful when evaluating residual tumor or abscess, when MRI is not accessible or tolerated by the patient.

The CT scan measures exposures in Hounsfield units from – 1000 to 4000, progressing from dark (hypodense) to bright (hyperdense), for example, air→fat→water→CSF→brain tissue→subacute blood→liquid blood→clotted blood→bone→contrast→metals.4

CT scans can demonstrate deleterious changes for the neurological patient. This is useful when the neurological exam is compromised by sedation or overmedication. Some CT scan signs of increased intracranial pressure are the following:⁵

• Loss of sulci
  
• Compressed ventricles, loss of fourth ventricle
  
• Loss of cisterns
  
• Midline shift

As the condition worsens, the patient may progress to herniation (Table 6–3).

Brain CT scans are useful for the evaluation of neurological deficits, both new onset and progressive, and for following the progression of known pathology, such as hydrocephalus, infarction, edema, and intra- and extra-axial hemorrhage. Contrasted CT scans evaluate neurological deficits when there is a suspected mass or infection.

MRI, magnetic resonance imaging.

Some characteristic CT scan findings for bleeds are:6

• Epidural hematoma Biconvex or lentiform appearance, often underlying fractures, located between skull and dura; may be limited by suture lines; usually seen in acute phase when lesion is hyperdense; areas of hypodensity indicate active bleeding
  
• Subdural hematoma Crescent shaped, between brain and dura; may be acute (hyperdense), subacute (nearly isodense), or chronic (hypodense); areas of hypodensity indicate active bleeding in an acute SDH; may see areas of calcification in chronic SDH
  
• Subarachnoid hemorrhage (SAH) Seen within the cisterns and sulci
  
• Intracerebral hemorrhage (ICH) Seen in putamen, caudate, cerebellum, and brainstem where hypertensive hemorrhages are likely to occur spontaneously

EDHs are seen less frequently than SDHs and are usually the result of bleeding from the lacerated middle meningeal artery or the dural venous sinus.

SDH is usually the result of bleeding from bridging cortical veins.

SAH should be suspected before or after an accident or in association with the worst headache of the patient’s life. Most CT scans should be repeated in 12 to 24 hours. ICHs tend to reoccur after 6 to 12 hours.

CT Scan of the Spine

Other Types of CT Scans

MRI

MRI Protocols

• T1-weighted image
  
  
  
  • Echo time (TE) < 50, repetition time (TR) < 1000
    
  • Progressing in intensity from hypointense, to isointense, to hyperintense (from dark to bright): bone→calcium→CSF→gray matter→white matter→fat/ melanin/blood > 48 hours old4
    
  • Most pathology is dark (hypointense = low signal).
    
  • Good for detecting gadolinium contrast enhancement
  
  
• T2-weighted image
  
  
  
  • TE > 80, TR > 2000
    
  • Progressing from dark to bright: fat→bone→white matter→gray matter→CSF→edema/water
    
  • Notice that fat becomes dark on a T2-weighted image, whereas it is bright on a T1-weighted image.
    
  • Most pathology is light.
    
  • Gadolinium contrast enhancement does not cause much change in intensity of signal.
    
  • Good for detecting pathological areas with edema, inflammation, or water (Table 6–4)
  
  
• Diffusion-weighted image
  
  
  
  • Based on movement of water in tissues
    
  • Freely diffusing water (CSF) appears dark, whereas restricted diffusion seen with intracellular edema–associated cell swelling from infarction appears bright.
    
  • Acute infarction appears bright within minutes.

MRI of the Brain

MRI of the brain should be the first advanced scan in numerous conditions, such as

MRI of the Spine

MRI is also very useful in the spine, especially when soft tissue evaluation is essential. It is the evaluation of choice after taking the patient’s history and performing a physical exam for herniated disc and nerve root impingement, congenital abnormalities, stroke, hemorrhage, ligamentous injury, spinal cord injury, and spinal cord hemorrhage. In the spine, MRI contrast and noncontrasted films are the imaging modality of choice for tumors, including drop metastases; infection, including paravertebral lesions; fistulas; the extent of tumor removal; and postoperative infection.6

In facilities with a neurosurgical intensive care unit, an MRI scanner must be available 24 hours a day. It is used emergently in patients with incomplete spinal cord injury or worsening neurological deficit, as well as clinical evidence without radiographic proof of spinal cord injury.⁵

Other Uses of MRI

MRI is used without contrast in determining peripheral nerve injury. Just as CT angiography provides detailed anatomy of the vessels in the brain and the large vessels of the spine, MRI angiography (MRA) demonstrates normal and pathological vascular anatomy such as carotid-cavernous fistulas, as well as vascular malformations, including aneurysms and arteriovenous malformations (AVMs). The venous phase of circulation can also be specifically probed when looking for venous sinus thrombosis. MRI has been employed in neuroscience for decades. It was once referred to as nuclear magnetic resonance (NMR), but the term was changed because of the connotation attached to nuclear. MRI examines the characteristic molecules in tissue samples. Magnetic resonance spectroscopy does the same thing on a much larger scale; it produces a graph based on the chemical shift and is used primarily in the brain to help distinguish tumor from infection.2

Additional Imaging in the NICU

The angiogram is an invasive test having a 0.5 to 2% risk of major morbidity or mortality.3 It also carries the risk of ionizing radiation. Although still the “gold standard” in many vascular cases, it has been replaced in some large institutions with CTA and MRA. In the community neurosurgical setting, it remains the procedure of choice to investigate cerebral AVM, aneurysm, and carotid-cavernous fistulas, to determine tumor blood supply and embolization of arterial feeders, to administer an injection for vasospasm, and to evaluate vessel injury (e.g., with gunshot wounds) and pseudoaneurysm development. In the spine the angiogram can be used to evaluate spinal AVM and dural fistulas.

Nuclear medicine scans, such as bone and tagged white blood scans, are used to evaluate osteoblastic activity seen in infection, tumor, and abnormal metabolism. They also can be used to differentiate between old and new fractures.

Transcranial Doppler scans have become extremely useful tools in both trauma and cerebral vascular disease. Such a scan can be performed at bedside to determine if there is vasospasm in the intracranial circulation, as well as the efficacy of thrombolysis in acute stroke. A transcranial Doppler is used to determine brain death.

Ultrasound has become critical in the evaluation of extracranial circulation, both carotid and vertebral, for the degree of stenosis, as well as in the evaluation of the neonatal brain.

Radiology in the NICU