Imaging of the Brain and Spinal Cord

Learning objectives include discussing radiologic imaging modalities for the brain and spinal cord, identifying common anatomical structures, and identifying common pathological conditions that can be detected through imaging.

Diagnostic Imaging Modalities

Cranial Ultrasound (CUS)
- Uses sound waves to create images of the brain and cerebrospinal fluid.
- Valuable for evaluating brain development in the first year of life.
- Serves as initial screening.
- Often complementary to CT and MRI imaging.
- Advantages: safe, inexpensive, portable, easily repeatable.
- Indications: abnormal head circumference, hemorrhage/brain abnormalities in preterm/term infants, ventriculomegaly/hydrocephalus, vascular abnormalities, suspected hypoxic ischemic injury, patients using hypothermia/ECMO, congenital malformations, symptoms of central nervous system disorders (e.g., seizures, facial malformations), congenital/acquired brain infections, suspected/known head trauma, craniosynostosis, follow-up/surveillance of prior documented abnormalities (including prenatal), and screening before surgery.
X-rays
- Produce images of internal structures using electromagnetic radiation (x-rays).
- Bones and organs absorb varying amounts of x-rays, creating images on film or digital detectors.
- A last resort in trauma imaging if a CT isn't available.
- Advantages: inexpensive, readily available, and faster than other imaging techniques. Useful for detecting fractures, decalcification, birth defects, infections, and pituitary tumors.
- Indications: skull fractures, bone decalcification, birth defects, infections, pituitary tumors, and other metabolic/endocrine disorders that affect bone structure within the skull. Includes a magnified technique for evaluating lesions on the scalp that are palpable.
CT Scan (Computed Tomography)
- Creates cross-sectional images of the body.
- Uses x-rays and a ring of radiation detectors to capture images, allowing for reconstruction of the internal structure.
- Spiral CT technology allows contiguous slices to be acquired.
- Advantages: fast, high image quality; good for anatomical regions; useful in cases where a patient cannot fully cooperate.
- Measurement units: Hounsfield Units
  - Air: approximately -1000 HU
  - Lung: approximately -500 to 0 HU
  - Water: approximately 0 HU
  - Fat: approximately 0 to 100 HU
  - Soft tissue: approximately 20 to 80 HU
  - Bone: approximately +1000 to +613 HU
MRI (Magnetic Resonance Imaging)
- Uses a strong magnetic field to produce detailed images of soft tissues and organs.
- Radio waves realign atoms to generate radio signals, used by a computer to create images.
- Advantages: non-invasive, does not use ionizing radiation, excellent detail; particularly useful for soft tissues; multiple planes.
- Types: T1-weighted, T2-weighted, Fluid-Attenuated Inversion Recovery (FLAIR), proton density.
- Contraindications: metal implants, some allergies to contrast agents, pregnancy.

Additional Details

Normal Ultrasound Anatomy: Images show various structures (e.g., ventricles, bones) for evaluation and comparison, enabling detection of irregularities.
Advantages of MRI: Safe, inexpensive, portable, quick to perform with repeatability.
Different Window Level: Different window levels (e.g., brain, soft tissue, bone) highlight specific aspects of the image (e.g., hemorrhage, hematoma, skull fractures).
CT Neuroimaging: Standard procedure for axial plane scanning for brain analysis with 5mm slices; useful for angiography of head/neck.
Head CT Approach: Method to assess normal anatomy, assess pathology indicators and structures with bone/soft tissue windows.
Skull Bones and Sutures: Frontal, parietal, occipital, sphenoid, temporal, all ossify individually, coalesce at sutures, inner and outer layers
Sutures: Coronal, sagittal, lambdoid, squamosal, metopic (varies with presence in adults). Pterion (clinical significance regarding meningeal arteries).
CSF Spaces: Brain-surrounding fluid spaces, including sulci, fissures, basal cisterns and ventricles; lower density than grey/white matter—appearance darker on CT images.
Fissures/Ventricles: Interhemispheric fissure (separates hemispheres), Sylvian fissure (frontal/temporal separation), lateral ventricles.
Brain Parenchyma & Lobes: Grey matter, white matter, differences in density (grey—grey matter; white—white matter; densities differ).
Brain Lobes: Paired, bilaterally symmetrical anatomical areas; do not perfectly correlate with overlying bones.
Grey Matter Structures: Cortex, insula, basal ganglia, and thalamus
Insula: Deep structure, often highlighted to evaluate issues (e.g., strokes).
Basal Ganglia and Thalamus: Deep brain matter, with possible indications/indications (e.g., movement disorders).
White Matter Structures: Deep to the grey matter, important for connectivity.
Internal Capsules/Corpus Callosum: Tracts that connect cortical structures and cerebral hemispheres.
Posterior Fossa: Cerebellum, brain stem regions.
Cerebral Vascular Territories: Supplied by anterior, middle, and posterior cerebral arteries, and vertebrobasilar arteries in the posterior fossa. (Specific areas supplied by each artery)
Calcified Structures: Choroid plexus; pineal gland; basal ganglia; falx; calcified structures on imaging can indicate normalcy, but can be confused with acute hemorrhage
Trauma: Acute brain hemorrhage appears bright; subarachnoid, intraventricular hemorrhage examples. Epidural, subdural hematoma.
Imaging Modalities for Spine: Fractures, dislocations, degenerative disorders (e.g., osteoarthritis) and scoliosis.
MRI Imaging Facts: Various modalities (T1, T2, FLAIR, proton density) useful in evaluation of the tissues; advantages of non-invasive approach.