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🧠 CHAPTER 8 — CENTRAL NERVOUS SYSTEM (CNS)
🧠 I. Anatomy Overview
Major Divisions Central Nervous System (CNS): Brain + Spinal cord. Peripheral Nervous System (PNS): Cranial nerves (12 pairs) and spinal nerves (31 pairs). Autonomic Nervous System (ANS): Sympathetic (fight-or-flight) and parasympathetic (rest-and-digest). Brain: Four Main Parts
- Cerebrum o Two hemispheres, connected by corpus callosum. o Functions: thought, memory, sensory perception, voluntary movement. o Divided into lobes: Frontal → reasoning, motor control. Parietal → sensory interpretation. Temporal → auditory processing, memory. Occipital → vision.
- Cerebellum o Coordinates movement, balance, and posture. o Located posteriorly under cerebrum.
- Diencephalon o Contains thalamus (sensory relay) and hypothalamus (temperature, appetite, autonomic regulation). o Pituitary gland (attached via infundibulum) regulates endocrine function.
- Brainstem o Midbrain, pons, medulla oblongata. o Controls vital centers: respiration, heart rate, consciousness (reticular formation). Ventricular System & CSF Pathway Lateral ventricles → foramen of Monro → third ventricle → aqueduct of Sylvius → fourth ventricle → central canal/subarachnoid space.
CSF produced by choroid plexus; absorbed via arachnoid villi into venous sinuses. Meninges Dura mater (outer tough layer). Arachnoid (middle layer). Pia mater (inner layer, adheres to brain surface). Between arachnoid and pia = subarachnoid space (contains CSF and vessels). Blood–Brain Barrier (BBB): Selective permeability barrier protecting neural tissue from toxins, but allows oxygen/glucose; disrupted in inflammation or tumor → contrast enhancement on imaging.
🧠 II. Imaging Modalities of the CNS
Modality Best Uses / Strengths CT (Computed Tomography) Initial emergency imaging for trauma, hemorrhage, stroke (hyperacute phase), hydrocephalus, calcification, bony injury. MRI Modality of choice for most CNS pathologies: tumors, demyelination, infarction (subacute to chronic), infection, spine lesions, congenital anomalies. Sonography Neonatal brains via fontanelle; evaluates hydrocephalus, intracranial hemorrhage in infants. Nuclear Medicine Brain perfusion/SPECT/PET for tumor metabolism, epilepsy focus, dementia. Angiography (CT/MR/DSA) Vascular pathologies (aneurysm, AVM, stroke evaluation, stenosis). Radiography Limited to skull/spine trauma when CT unavailable.
🧠 III. Congenital CNS Anomalies
Condition Pathogenesis / Imaging Features Anencephaly Failure of upper neural tube closure → absence of cranial vault and cerebral hemispheres. Detected on
Condition Cause / Pathophysiology Imaging Findings sclerosis (MS) (autoimmune destruction of myelin in CNS). hyperintense plaques (“Dawson fingers”); best seen on FLAIR sequences.
🧠 V. Vascular Disorders
Condition Description / Pathogenesis maging Modality & Findings Cerebrovascular accident (CVA / Stroke) Ischemic (occlusion of artery) or hemorrhagic (rupture of vessel). CT (non-contrast): first line. Ischemic: may appear normal early, later hypodense infarct. Hemorrhagic: hyperdense bleed. MRI DWI: detects early ischemia. Transient ischemic attack (TIA) Temporary focal ischemia; no permanent infarction. MRI DWI negative; MRA may show stenosis. Intracranial hemorrhage
- Epidural (arterial, lens-shaped),
- Subdural (venous, crescent- shaped),
- Subarachnoid (aneurysmal rupture → diffuse),
- Intracerebral (within brain parenchyma). CT differentiates type by location/density. Aneurysm / AVM Weakening of vessel wall or congenital shunting between arteries/veins. CT/MR angiography visualizes; risk of rupture → subarachnoid hemorrhage. Hydrocephalus (secondary) Obstruction (tumor, hemorrhage, infection) → ventricular enlargement, periventricular edema. CT/MRI diagnostic. Treated with shunt.
🧠 VI. Neoplastic Diseases
Type Common Tumors Imaging Characteristics Primary brain tumors
- Gliomas (astrocytoma, glioblastoma multiforme, oligodendroglioma) — most common in adults.
- Medulloblastoma — children, cerebellar vermis.
- Meningioma — benign extra-axial tumor; may calcify; strong contrast enhancement.
- Pituitary adenoma — in sella; can cause endocrine changes or optic chiasm compression. MRI = modality of choice. Glioblastoma: irregular ring enhancement, edema, mass effect. Meningioma: sharply marginated, extra-axial, enhances homogeneously. Metastases From lung, breast, melanoma. Multiple lesions at gray-white junction. MRI: multiple ring-enhancing masses with surrounding edema. Acoustic neuroma (vestibular schwannoma) Tumor of cranial nerve VIII. MRI IAC: enhancing mass in cerebellopontine angle. Ependymoma / Craniopharyngioma Pediatric; arise near ventricles or sella. MRI shows mixed solid–cystic lesions.
🧠 VII. Degenerative and Demyelinating Disorders
Condition Description / Key Imaging Points Multiple Sclerosis (MS) Autoimmune demyelination → periventricular plaques (T2/FLAIR bright). Enhancing lesions = active disease. MRI is
🧠 IX. Imaging of the Spine Modality Indications CT (^) Bony injury, vertebral fracture, spinal canal narrowing. MRI Disc herniation, cord compression, tumor, demyelination, infection. Myelography (CT- Myelo) When MRI contraindicated; evaluates spinal canal, nerve root impingement. Common Pathologies Herniated nucleus pulposus (HNP): Posterolateral disc herniation compresses nerve root → MRI shows disc protrusion. Spondylosis: Degenerative osteophyte formation; CT/MRI show narrowing of foramina. Spinal stenosis: Narrowing of spinal canal; MRI best. Meningioma / Ependymoma (spinal): Intradural masses; MRI shows well- circumscribed, enhancing lesions.
🧠 X. Imaging Correlation and Modality Choice (CAMRT Focus)
Pathology Preferred Modality Head trauma / hemorrhage CT (non-contrast). Ischemic stroke (early) MRI DWI. Tumors MRI (with contrast). MS / demyelination MRI FLAIR. Congenital anomalies MRI; prenatal US. Hydrocephalus CT or MRI; shunt evaluation. Neonatal brain Sonography. Aneurysm / AVM CTA / MRA / DSA. Spine trauma CT; MRI if cord involvement. Pituitary pathology MRI (sella).
🧠 XI. Key Radiographic Appearances Summary Table Condition Characteristic Imaging Sign Epidural hematoma Biconvex/lens hyperdensity on CT. Subdural hematoma Crescentic hyperdensity. Subarachnoid hemorrhage Hyperdense basal cisterns/sulci. Hydrocephalus Dilated ventricles, transependymal CSF flow. Meningioma Extra-axial, homogeneous enhancement, “dural tail”. Glioblastoma Irregular ring enhancement, edema. MS Periventricular “Dawson fingers.” Alzheimer’s Cortical atrophy, widened sulci. Chiari malformation Cerebellar tonsil herniation through foramen magnum. Dandy–Walker Enlarged 4th ventricle, absent vermis. CVA (ischemic) Hypodensity, loss of gray–white differentiation. AVM Tangle of vessels, flow voids on MRI.
🧠 XII. Summary of Typical Treatments
Disorder Type Treatment Examples Congenital Surgical repair (spina bifida closure, shunt for hydrocephalus). Infectious Antibiotics/antivirals, drainage of abscess. Vascular Thrombolytics (ischemic stroke), surgical clipping/coiling (aneurysm). Neoplastic (^) Surgical resection, radiotherapy, chemotherapy, stereotactic radiosurgery. Degenerative Supportive therapy (dopaminergic meds for Parkinson’s, cholinesterase inhibitors for Alzheimer’s). Trauma (^) Craniotomy, decompression, steroids for cord edema, rehabilitation.
