3 Neuroimaging and the Neurosurgical Intensive Care Unit Patient
Abstract
Once the clinician has obtained a history and performed a detailed physical examination inclusive of a sophisticated neurologic exam, a differential diagnosis can be determined. For the patient in the neurosurgical intensive care unit, imaging is vital to confirm pathology to begin treatment when such treatment should be precise to gain the best outcome. All imaging modalities, whether X-ray, magnetic resonance imaging, or ultrasound, can add details for the clinician in an attempt to provide the best possible care.
Case Presentation
A 14-year-old boy sustains a head injury during a head-on collision with a tree while snowboarding without a helmet. He is brought to the emergency room, still awake and alert, but with a 4-cm laceration over his right temple and obvious cerebrospinal fluid (CSF) leaking from the injury site. A computed tomographic (CT) scan of the head shows a right temporal region skull fracture under the laceration, with the inner table of the skull depressed 1.5 cm into the cranial cavity.
See end of chapter for Case Management.
3.1 Introduction
The patient must be stabilized according to the ABCDEs. Most important to determine neurologic injuries is the history and neurologic exam. 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 base films and their overlap; the smaller the thickness the better the quality of reconstruction. Additional X-rays or films will be taken as needed.
3.2 X-rays of the Skull and Spine
Skull X-rays may show nontraumatic abnormalities, such as congenital skull defects, skull lesions, or even foreign bodies. 1
Traumatic linear fractures must be differentiated from vessel grooves and suture lines. Vessel grooves are thicker, and they may curve and branch. Suture lines are wide, jagged, and follow the course to meet other sutures. 2 Traumatic linear fractures are often associated with an epidural hematoma (EDH) or a subdural hematoma (SDH). 3
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 depression is greater than the thickness of the skull (8–10 mm). Contrecoup injuries of the brain must also be assessed. Do not confuse this with a bone shadow from bony prominences of the skull.
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 a dural tear. This is rarely seen in pediatric patients and less so in the adult population (► Table 3.1).
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. They are also useful in determining normal bony alignment and confirming stability of a fracture with the patient in a spinal orthosis.
Traumatic findings include fractures, dislocation, subluxation, or rotation. The completed cervical spine evaluation must see from the craniocervical junction through T1. If there is too much soft tissue shadow on lateral views, reorder the X-ray, obtaining the “swimmer’s view” X-ray (vs. standard lateral C-spine X-ray). 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, and 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 indicate pathology. Approximations of normal width of the prevertebral tissue are 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 2.5–3 mm in adults. Other areas of concern are the normal cervical lordotic curvature and loss of vertebral height, or fracture lines, or a 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 3.2).
X-rays in the neurosurgical intensive care unit may be done after the application of a halo or tongs for traction to evaluate reduction after each addition of weights or 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 are also used to evaluate subluxation with spondylolisthesis and compression fractures. For cervical-spine clearance the patient must be alert and cooperative; the cervical spine cannot be cleared if there is more than 3.5 mm subluxation seen on the lateral film or if the patient has neurologic deficits.
3.3 CT Scans
3.3.1 Brain CT Scan
A CT scan is the best imaging tool for studying bone, hemorrhage, or other calcified 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 neurologic deficits and patients who cannot have a magnetic resonance imaging (MRI) scan. However, a CT scan is prone to artifact from the densest material and cannot differentiate between soft tissues of similar densities and therefore 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) is > 2.0 or there is a first-trimester pregnancy. CT scans can be completed with or without contrast. If suspecting a hemorrhage, obtain a noncontrasted CT head initially. Noncontrast CT scans can also be used to evaluate hardware placement and function with deep brain stimulators, intracranial pressure monitors and drains, external ventricular drains, 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 light (hyperdense):
Air → fat → water → CSF → brain tissue → subacute blood → liquid blood → clotted blood → bone → contrast → metals 4
CT scans can demonstrate deleterious changes for the neurologic patient. This is useful when the neurologic exam is compromised by sedation or overmedication. The following are some CT scan signs of increased intracranial pressure 4 :
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 3.3).
Brain CT scans are useful for the evaluation of neurologic deficits, both new-onset and progressive, for following the progression of known pathology, such as hydrocephalus, infarction, edema, and intra-axial and extra-axial hemorrhage. Contrasted CT scans evaluate neurologic deficits when there is a suspected mass or infection.
The following are characteristic CT scan findings for bleeds 6 :
Epidural hematoma (EDH): Biconvex or lentiform appearance, often underlying fractures, located between the skull and dura, may be limited by suture lines, usually seen in the acute phase when the lesion is hyperdense, areas of hypodensity indicate active bleeding.
Subdural hematoma (SDH): Crescent shaped, between the brain and dura, may be acute (hyperdense), subacute (nearly isodense), or chronic (hypodense); areas of hypodensity indicate active bleeding in an acute SDH; areas of calcification may be seen in chronic SDH.
Subarachnoid hemorrhage (SAH): Seen within the cisterns and sulci.
Intracerebral hemorrhage (ICH): Seen in the 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 a lacerated middle meningeal artery or dural venous sinus. If there is a loss of sulcal and gyral patterns on axial views near the vertex, order coronal and sagittal views to assess for a vertex EDH. These can be associated with fractures that extend midline and may be associated with damage to the superior sagittal sinus.
SDH is usually the result of bleeding from bridging cortical veins. SDHs conform to the contours of the brain and usually do not cross the midline but may cross suture lines. It is important to correlate the SDH width with the midline shift and edema. When patients present with what may seem like a small chronic SDH on imaging with edema and midline shift out of proportion to the SDH size, one must consider other possibilities, such as intracranial hypotension, subdural empyema, or even metastatic disease.
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 recur after 6 to 12 hours. These patients can present posttrauma, and a careful history must be obtained to decipher if the patient ruptured an aneurysm, which led to a fall or motor vehicle collision, or if the fall/collision caused the SAH.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
