TRIGEMINAL NEUROPATHY

•  facial pain, numbness, weakness of masticatory muscles, trismus

•  diminished / absent corneal reflex

•  abnormal jaw reflex; atrophy of masticatory muscles

•  decreased pain / touch / temperature sensation

•  tic douloureux = paroxysmal facial pain (usually confined to V₂ and V₃) mainly ← neurovascular compression (tortuous elongated superior cerebellar artery / anterior inferior cerebellar artery / vertebrobasilar dolichoectasia / venous compression)

A.  BRAINSTEM LESION

1.   Vascular: infarct, AVM

2.   Neoplastic: glioma, metastasis

3.   Inflammatory: multiple sclerosis (1–8%), herpes rhombencephalitis

4.   Other: syringobulbia

B.  CISTERNAL CAUSES

1.   Vascular: aneurysm, AVM, vascular compression

2.   Neoplastic: acoustic schwannoma, meningioma, trigeminal schwannoma, epidermoid cyst, lipoma, metastasis

3.   Inflammatory: neuritis

C.  MECKEL CAVE + CAVERNOUS SINUS

1.   Vascular: carotid aneurysm

2.   Neoplastic: meningioma, trigeminal schwannoma, epidermoid cyst, lipoma, pituitary adenoma, base of skull neoplasm, metastasis, perineural tumor spread

3.   Inflammatory: Tolosa-Hunt syndrome

D.  EXTRACRANIAL

1.   Neoplastic: neurogenic tumor, squamous cell carcinoma, adenocarcinoma, lymphoma, adenoid cystic carcinoma, mucoepidermoid carcinoma, melanoma, metastasis, perineural tumor spread

2.   Inflammatory: sinusitis

3.   Other: masticator space abscess, trauma

HORNER SYNDROME

=  syndrome ← interruption of oculosympathetic pathway:

•  ipsilateral blepharoptosis; pupillary miosis; facial anhidrosis

Oculosympathetic pathway:

(a)  1^st order neuron: posterolateral hypothalamus → brainstem → intermediolateral column of spinal cord → exit at C8, T1, T2

(b)  2^nd order preganglionic neuron: ventral spinal root → arch over apex of lung → cervical sympathetic chain → superior cervical ganglion

(c)  3^rd order postganglionic neuron: with carotid artery → cavernous sinus → ophthalmic branch of cranial nerve V

A.  CENTRAL HORNER (uncommon)

Location:   hypothalamus, thalamus, brainstem, cervical cord

Cause:   infarction of PICA / distal vertebral artery

•  hypothalamic / brainstem / spinal cord signs

B.  PREGANGLIONIC HORNER

Location:   cervicothoracic cord, brachial plexus, anterior neck, mediastinum

Cause:   trauma, lung (Pancoast) / mediastinal tumor, lesion in cervical spinal cord / brachial plexus

C.  POSTGANGLIONIC HORNER

Location:   superior cervical ganglion, internal carotid artery, cavernous sinus, orbital apex

Cause:   ICA dissection / aneurysm, carotid-cavernous fistula / thrombophlebitis, inflammation (Tolosa-Hunt syndrome), skull base tumor

CLASSIFICATION OF CNS ANOMALIES

A.  DORSAL INDUCTION ANOMALY

=  defects of neural tube closure

1.   Anencephaly

2.   Cephalocele at 4 weeks

3.   Chiari malformation at 4 weeks

4.   Spinal dysraphism

5.   Hydromyelia

B.  VENTRAL INDUCTION ANOMALY

=  defects in formation of brain vesicles + face

1.   Holoprosencephaly: 5–6 weeks

2.   Septo-optic dysplasia: 6–7 weeks

3.   Dandy-Walker malformation: 7–10 weeks

4.   Agenesis of septum pellucidum

C.  NEURONAL PROLIFERATION & HISTOGENESIS

1.   Neurofibromatosis: 5 weeks–6 months

2.   Tuberous sclerosis: 5 weeks–6 months

3.   Primary hydranencephaly: > 3 months

4.   Neoplasia

5.   Vascular malformation (vein of Galen, AVM, hemangioma)

D.  NEURONAL MIGRATION ANOMALY

due to infection, ischemia, metabolic disorders

1.   Schizencephaly: 2 months

2.   Agyria + pachygyria: 3 months

3.   Gray matter heterotopia: 5 months

4.   Dysgenesis of corpus callosum: 2–5 months

5.   Lissencephaly

6.   Polymicrogyria

7.   Unilateral megalencephaly

E.  DESTRUCTIVE LESION

1.   Hydranencephaly

2.   Porencephaly

3.   Hypoxia: periventricular leukomalacia, germinal matrix hemorrhage

4.   Toxicosis

5.   Infections (TORCH)

(a)  Toxoplasmosis

(b)  Other: syphilis, hepatitis, zoster

(c)  Rubella

√  punctate / nodular calcifications

√  porencephalic cysts

√  occasionally microcephaly

(d)  Cytomegalovirus inclusion disease

√  typically punctate / stippled / curvilinear periventricular calcifications

√  often hydrocephalus

(e)  Herpes simplex

Absence of Septum Pellucidum

1.   Holoprosencephaly

2.   Callosal agenesis

3.   Septo-optic dysplasia

4.   Schizencephaly

5.   Severe chronic hydrocephalus

6.   Destructive porencephaly

Phakomatoses

[ phako , Greek = lens / lentil-shaped object]

=  NEUROCUTANEOUS SYNDROMES = NEUROECTODERMAL DYSPLASIAS

=  development of benign tumors / malformations in organs of ectodermal origin (CNS, eye, skin)

(a)  autosomal dominant:

1.   Neurofibromatosis (von Recklinghausen)

2.   Tuberous sclerosis (Bourneville)

3.   Retinocerebellar hemangioblastoma (Von Hippel-Lindau)

4.   Neurocutaneous melanosis

(b)  not autosomal dominant:

5.   Encephalotrigeminal angiomatosis (Sturge-Weber-Dimitri)

6.   Ataxia-telangiectasia

DEGENERATIVE DISEASES OF HEMISPHERES

=  progressive fatal disease characterized by destruction / alteration of gray and white matter

Etiology:   genetic; viral infection; nutritional disorders (eg, anorexia nervosa, Cushing syndrome); immune system disorders (eg, AIDS); exposure to toxins (eg, CO); exposure to drugs (eg, alcohol, methotrexate + radiation)

Myelinoclastic / Demyelinating Disease

=  disease that destroys normally formed myelin

◊  Usually affects older children / adults

(a)  infectious

1.   Progressive multifocal leukoencephalopathy

2.   Subacute sclerosing panencephalitis (SSPE)

3.   Acute disseminated encephalomyelitis (ADEM)

(b)  noninfectious

1.   Radiation

2.   Anoxia

3.   Hypertensive encephalopathy

4.   Disseminated necrotizing leukoencephalopathy (from methotrexate therapy)

(c)  others

1.   Multiple sclerosis (most frequent of primary demyelinating disease)

2.   Alzheimer disease (most common of diffuse gray matter degenerative diseases)

3.   Parkinson disease (most common of subcortical degenerative disease)

4.   Creutzfeldt-Jakob disease

5.   Menkes disease (sex-linked recessive disorder of copper metabolism)

6.   Globoid cell leukodystrophy

7.   Spongiform degeneration

8.   Cockayne syndrome

9.   Spongiform leukoencephalopathy

10.   Myelinoclastic diffuse sclerosis (= Schilder disease)

Dysmyelinating Disease

=  metabolic disorder (= enzyme deficiency) resulting in deficient / absent myelin sheaths

◊  Usually presents in first 2 years / 1^st decade of life!

◊  Associated with white matter atrophy

(a)  macrencephalic:

1.   Alexander disease (frontal areas affected first)

2.   Canavan disease (white matter diffusely affected)

(b)  hyperdense thalami, caudate nuclei, corona radiata

1.   Krabbe disease

(c)  family history (X-linked recessive)

1.   X-linked adrenoleukodystrophy

2.   Pelizaeus-Merzbacher disease

(d)  others

1.   Metachromatic leukodystrophy (most common hereditary leukodystrophy)

2.   Binswanger disease (SAE)

3.   Multi-infarct dementia (MID)

4.   Pick disease

5.   Huntington disease

6.   Wilson disease

7.   Reye syndrome

8.   Mineralizing microangiopathy

9.   Diffuse sclerosis

VASCULAR DISEASE OF BRAIN

Classification of Vascular CNS Anomalies

A.  VASCULAR MALFORMATION

(a)  arterial = arteriovenous malformation (AVM)

1.   Classic brain AVM

2.   Cerebral proliferative angiopathy

3.   Cerebrofacial arteriovenous metameric syndrome

2.   Vein of Galen malformation

(b)  capillary = capillary telangiectasia

1.   Capillary telangiectasia

2.   Facial port-wine stain

(c)  venous = venous malformation

1.   Developmental venous anomaly

2.   Sinus pericranii

(d)  lymphatic

1.   Cystic hygroma

(e)  combinations

1.   Sturge-Weber disease

2.   Rendu-Osler-Weber disease

B.  VASCULAR TUMOR

1.   Hemangioma

(a)  capillary hemangioma: seen in children, involution by 7 years of age in 95%

(b)  cavernous hemangioma: seen in adults, no involution

2.   Hemangiopericytoma

3.   Hemangioendothelioma

4.   Angiosarcoma

Blunt Cerebrovascular Injury

=  carotid (CA) + vertebral artery (VA) injuries during generalized multitrauma / direct craniocervical trauma

Prevalence:   1.1–1.6% of all blunt trauma

Mechanism:   partial / complete failure of arterial mural integrity ← longitudinal stretching of artery, direct blow to artery, piercing by bone fragment

Prognosis:   25–38% mortality if injury untreated

Cx:   (1)   Infarction ← intimal disruption / flap / hematoma

→  thromboembolism of platelet aggregates

→  critical luminal stenosis + occlusion

(2)  Brain ischemia ← steal phenomenon by AV fistula

(3)  Fatal exsanguination

Type of Arterial Injury

1.   Minimal intimal injury

√  nonstenotic luminal irregularity

DDx:  arterial spasm

2.   Raised intimal flap

√  linear intraluminal filling defect emanating from arterial wall

3.   Dissection with intramural hematoma

√  eccentric / circumferential mural thickening:

√  narrowed arterial lumen

√  increased arterial diameter

4.   Arterial occlusion

√  lack of intraluminal enhancement

5.   Pseudoaneurysm

√  eccentric outpouching from native arterial lumen:

√  minimal contour abnormality

√  large irregular saccular outpouching

√  focal ballooning of arterial lumen

6.   Transection with active hemorrhage

√  irregular collection of extravascular contrast material surrounding parent vessel

7.   Arteriovenous fistula

√  early venous enhancement during the arterial phase

√  enlargement of draining vein

DDx:  (1)  Atherosclerosis (presence of calcification, characteristic location, increasing age)

Location:   vessel origin, carotid bulb, cavernous carotid segment

(2)  Coiled / looped cervical ICA segment (5–15%)

(3)  Congenitally absent / small ICA (small / absent carotid canal)

Shunt Lesions of Cerebral Vasculature

1.   AV malformation

2.   AV fistula: pia, dura, carotid-cavernous sinus

3.   Vein of Galen malformation

Congenital Venous Lesions

1.   Developmental venous anomaly

2.   Cerebral cavernous malformation

3.   Sinus pericranii

Occlusive Vascular Disease

(a)  Embolic state:

√  single vascular territory

(b)  Hypoperfusive state:

√  multiple vascular territories

Cause:

1.   Vasospasm from subarachnoid hemorrhage

2.   Embolic infarction (50%)

(a)  thrombus (atrial fibrillation, valvular disease, atheromatous plaques of extracerebral arteries, fibromuscular dysplasia, intracranial aneurysm, surgery, paradoxic emboli, sickle cell disease, atherosclerosis, thrombotic thrombocytopenic purpura)

•  fluctuating blood pressures; hypercoagulability

√  cerebral petechial hemorrhage within cortical / basal gray matter during 2^nd week (from fragments of embolus) in up to 40%; initial ischemia is followed by reperfusion (= HALLMARK of embolic infarction)

√  “supernormal artery” on NECT = high-density material lodged in cerebral vessel near major bifurcations

√  atheromatous narrowing of vessels

(b)  fat

(c)  nitrogen

3.   Watershed / border zone infarct (10%)

4.   Hypertension

(a)  Hypertensive encephalopathy

√  diffuse white matter hypodensity (edema ← arterial spasm)

(b)  Hypertensive hemorrhage

Location:   basal ganglia (putamen, external capsule), thalamus, pons, cerebellum

(c)  Lacunar infarction

(d)  Subcortical arteriosclerotic encephalopathy

5.   Amyloidosis involvement of small- + medium-sized arteries of meninges + cortex

•  normotensive patient > 65 years of age

√  multiple simultaneous / recurrent cortical hemorrhages

6.   Vasculitis

(a)  Bacterial meningitis, TB, syphilis, fungus, virus, rickettsia

(b)  Collagen-vascular disease: Wegener granulomatosis, polyarteritis nodosa, SLE, scleroderma, dermatomyositis

(c)  Granulomatous angiitis: giant cell arteritis, sarcoidosis, Takayasu disease, temporal arteritis

(d)  Inflammatory arteritis: rheumatoid arteritis, hypersensitivity arteritis, Behçet disease, lymphomatoid granulomatosis

(e)  Drug-induced: IV amphetamine, ergot preparations, oral contraceptives

(f)  Radiation arteritis = mineralizing microangiopathy

(g)  Moyamoya disease

7.   Anoxic encephalopathy cardiorespiratory arrest, near-drowning, drug overdose, CO poisoning

8.   Venous thrombosis

Multiple Infarctions

◊  Typical in extracranial occlusive disease, cardiac output problems, small vessel disease; in 6% from a shower of emboli

Location:   usually bilateral + supratentorial (¾); supra- and infratentorial (¼)

Reversal Sign

=  inversion of the normal attenuation relationship between gray and white matter (gray matter of lower attenuation than adjacent white matter of thalami, brainstem, cerebellum) on NECT of brain

Pathogenesis:   not fully understood

Cause:  global cerebral injury with anoxic insult ← head trauma, nonaccidental trauma, hypoxia, drowning, status epilepticus, hypothermia, bacterial meningitis, strangulation

Prognosis:  poor ← irreversible brain damage; survivors with profound neurologic deficits + severe developmental delay

Diffusion Weighted Imaging (DWI)

Hyperintense Lesion on DWI

1.   Cerebral infarction

2.   Epidermoid inclusion cyst

3.   Abscess with pus

4.   Encephalitis of cortex

5.   Creutzfeldt-Jakob disease

6.   Trauma: axonal shearing injury

7.   Neoplasm: medulloblastoma

INNUMERABLE PUNCTATE HYPERINTENSE LESIONS ON DWI

=  Starfield pattern

1.   Diffuse axonal injury (trauma)

2.   Emboli: cardiogenic, septic, fat

3.   Vasculitis

4.   Minute hemorrhagic metastases

Hypointense Lesion on DWI

1.   CSF

2.   Tumor cyst: pilocytic, hemangioblastoma

3.   Tumor nodules: hemangioblastoma

False Penumbra on Perfusion CT

True penumbra:   successfully treatable with thrombolysis

√  mean transit time (MTT) ↑

√  cerebral blood flow (CBF) ↓

√  cerebral blood volume (CBV) ↔

False penumbra:   area of abnormal perfusion as in ischemic penumbra NOT treatable with thrombolysis

A.  Atherosclerosis at carotid bifurcation

=  upstream flow limitation WITHOUT significant intracranial collateral blood supply

√  carotid bulb disease by CT angiography

B.  Evolving ischemic condition / chronic infarct

=  delayed reperfusion + vascular collateralization of incomplete acute / chronic infarct

√  hypoattenuation in the same region

√  restricted diffusion on DWI + ADC map

C.  Vascular dysregulation

=  hyperemia on symptomatic side with apparent perfusion abnormality on contralateral normal side

•  clinical history!

Cause:

1.   Hypertensive encephalopathy (PRES)

√  perfusion abnormality ← vasospasm

√  hyperintensity on STIR sequence

√  no restricted diffusion

2.   Seizure, subarachnoid hemorrhage, hemiplegic migraine

•  seizure activity

√  no restricted diffusion

D.  Head tilt / angulation

E.  Variations in cerebrovascular anatomy

=  physiologic perfusion delay in circle of Willis variants, unequal blood supply between anterior + posterior circulation, congenitally absent ICA, etc.

CNS Vasculitis

A.  LARGE-VESSEL VASCULITIS

1.    Takayasu arteritis

2.   Giant cell arteritis = Temporal arteritis

B.  MEDIUM-SIZED–VESSEL VASCULITIS

1.   Polyarteritis nodosa

√  aneurysm / stenosis / occlusion of intracranial carotid arteries

2.   Kawasaki disease

√  nonspecific subdural effusion, cerebral infarction

√  reversible hyperintense lesion in splenium

C.  SMALL-VESSEL VASCULITIS

1.   IgA vasculitis = Henoch-Schönlein purpura

√  hypertensive encephalopathy

√  focal ischemic / hemorrhagic lesions

2.   Microscopic polyangiitis

√  cerebral hemorrhage + infarction, pachymeningitis

√  variable degree of small-vessel disease

3.   Granulomatosis with polyangiitis = Wegener granulomatosis

√  leptomeningeal enhancement

4.   Eosinophilic granulomatosis with polyangiitis = Churg-Strauss syndrome

√  macro- / microinfarctions + macro- / microhemorrhages

√  optic neuropathy

D.  VARIABLE-SIZED VESSEL VASCULITIS

1.   Behçet disease

2.   Cogan syndrome

√  nonspecific ischemic changes

√  obliteration / narrowing of vestibular labyrinth

E.  SINGLE-ORGAN VASCULITIS

1.   Primary angiitis of CNS (PACNS)

√  discrete / diffuse supra- and infratentorial lesions

√  ± areas of infarction and hemorrhage

F.  VASCULITIS OF SYSTEMIC DISEASE

1.   Systemic lupus erythematosus (SLE)

√  subcortical + periventricular white matter hyperintensity (60%)

√  cerebral atrophy (30%), intracranial hemorrhage (3%)

2.   Sjögren syndrome

√  extensive white + gray matter lesions + microbleeds

3.   Rheumatoid arthritis

√  pachymeningitis with leptomeningeal enhancement

√  cerebral vasculitis (rare)

4.   APLA (antiphospholipid antibody) syndrome

√  arterial / venous thrombosis, thrombocytopenia

5.   Scleroderma

√  nonspecific infarction, macro- and microhemorrhages

G.  VASCULITIS WITH PROBABLE ETIOLOGY

1.   Infection-induced vasculitis

2.   Acute septic meningitis

√  cerebral infarcts (5–15% in adults, 30% in neonates)

3.   Mycobacterium tuberculosis

√  vasculitis of smaller cerebral arteries → small infarcts in basal ganglia

4.   Neurosyphilis

√  predominantly MCA stroke in young adult

5.   Viral (in childhood):

›  HIV-related vasculitis

√  aneurysm, vessel occlusion, embolic disease, venous thrombosis

›  Varicella-zoster vasculopathy

√  uni- / bilateral basal ganglia infarcts

6.   Fungal: mucormycosis aspergillosis

7.   Parasitic: cysticercosis

8.   Malignancy-induced vasculitis

9.   Drug-induced vasculitis

›  cocaine

√  vasculitis, vasospasm, infarction, moyamoya-like

›  heroin

√  spongiform leukoencephalopathy

10.   Radiation-induced vasculitis

√  wall thickening + prominent wall enhancement in affected large arteries

11.   Reversible cerebral vasoconstriction syndrome: Call-Fleming syndrome, postpartum angiopathy, migrainous vasospasm, benign angiopathy of CNS, vasoactive substances (cannabis, selective serotonin recapture inhibitors, nasal decongestants)

BRAIN ATROPHY

Cerebral Atrophy

=  irreversible loss of brain substance + subsequent enlargement of intra- and extracerebral CSF-containing spaces (hydrocephalus ex vacuo = ventriculomegaly)

A.  DIFFUSE BRAIN ATROPHY

Cause:

(a)  Trauma, radiation therapy

(b)  Drugs: dilantin, steroids, methotrexate, marijuana, hard drugs, chemotherapy, alcohol, hypoxia

(c)  Demyelinating disease: multiple sclerosis, encephalitis

(d)  Degenerative disease: eg, Alzheimer disease, Pick disease, Jakob-Creutzfeldt disease

(e)  Cerebrovascular disease + multiple infarcts

(f)  Advancing age, anorexia, renal failure

√  enlarged ventricles + sulci

B.  FOCAL BRAIN ATROPHY

Cause:   vascular / chemical / metabolic / traumatic / idiopathic (Dyke-Davidoff-Mason syndrome)

C.  REVERSIBLE PROCESS SIMULATING ATROPHY

(in younger people)

Cause:   anorexia nervosa, alcoholism, catabolic steroid treatment, pediatric malignancy

√  prominent sulci

√  ipsilateral dilatation of basal cisterns + ventricles

√  ex vacuo dilatation of ventricles

√  thinning of gyri

√  focal areas of periventricular high signal intensity

√  increased iron deposition in putamen approaching the concentration in globus pallidus

√  dilatation of Virchow-Robin perivascular space

Cerebellar Atrophy

A.  WITH CEREBRAL ATROPHY

=  generalized senile brain atrophy

B.  WITHOUT CEREBRAL ATROPHY

1.   Olivopontocerebellar degeneration / Marie ataxia / Friedreich ataxia

•  onset of ataxia in young adulthood

2.   Ataxia-telangiectasia

3.   Ethanol toxicity: predominantly affecting midline (vermis)

4.   Phenytoin toxicity: predominantly affecting cerebellar hemispheres

5.   Idiopathic degeneration 2° to carcinoma (= paraneoplastic), usually oat cell carcinoma of lung

6.   Radiotherapy

7.   Focal cerebellar atrophy:   (a)   infarction

   (b)   traumatic injury

Hippocampal Atrophy

1.   Alzheimer Disease

2.   Mesial temporal sclerosis

•  complex partial seizures

3.   Normal in octogenarians

BRAIN HERNIATION

=  shift of normal brain from high to low pressure through rigid structures of skull ← ⇑ intracranial pressure

Cause:   mass effect by primary / metastatic tumor, trauma, infection (abscess) / inflammation, intracranial hemorrhage, subdural hematoma, ischemia / infarction, acute hydrocephalus, iatrogenic (after lumbar puncture / pneumocephalus following craniotomy)

Classification:

A.  SUPRATENTORIAL HERNIATION

1.   Uncal (transtentorial)

2.   Central

3.   Cingulate (subfalcine)

4.   Transcalvarial

5.   Tectal (posterior)

B.  INFRATENTORIAL HERNIATION

1.   Upward (upward cerebellar / upward transtentorial)

2.   Tonsillar (downward cerebellar)

Subfalcine / Cingulate Herniation (most common)

=  contralateral shift of midline structures under falx cerebri

=  herniation of cingulate gyrus across falx cerebri

Risk:     compression of one of anterior cerebral arteries

May be associated with:   transtentorial herniation

•  weakness / paresis of contralateral leg ← compression of parafalcine cortex

•  weakness ± sensory changes of contralateral leg ← infarction of paracentral lobule / superior frontal gyrus ← compression of ACA / pericallosal artery

•  somnolence ← raised intracranial pressure

√  early signs:

@    falx

√  shift of ipsilateral cingulate gyrus beneath falx

√  deviation of anterior falx with widened CSF space at contralateral side

N.B.:   posterior falx remains relatively undisplaced due to greater height + rigidity

@    cingulate gyrus

√  compression of contralateral cingulate gyrus

@    corpus callosum

√  depression of ipsilateral corpus callosum

√  depression / elevation of contralateral corpus callosum

@    ventricle

√  compression / effacement of ipsilateral ventricle with amputation of ipsilateral frontal horn

√  late signs:

√  displacement of lateral ventricle to opposite side

√  obstruction of foramen of Monro → contralateral dilatation of the lateral ventricle + subependymal edema

√  infarction of cingulate gyrus

√  compression of anterior cerebral artery → infarction of ACA territory

Assessment:   degree of greatest displacement of septum pellucidum / falx measured in mm relative to a straight line drawn through anterior and posterior falcine attachments on axial image

Prognosis:  good with shift of < 5 mm; poor with shift > 15 mm

Cx:     traumatic aneurysm of ACA / pericallosal artery

Transtentorial (Central) Herniation

=  herniation of brain up / down across tentorium cerebelli

Tentorium cerebelli = inelastic reflection of dura

Connected to:   occipital bone posteriorly, petrous temporal bone laterally, clinoid processes anteriorly

Content:   transverse sinus, straight sinus

Tentorial hiatus / incisura

Content:   cerebral peduncles + brainstem

Descending Transtentorial Herniation

=  downward herniation of brain toward posterior fossa

•  oculomotor nerve (cranial n. III) palsy:

•  ipsilateral dilated pupil (= mydriasis) due to uncal herniation → compression of parasympathetic fibers traveling on outside of CN III → unopposed sympathetic activity to iris sphincter m.

•  abnormal extraocular muscle function (except for superior oblique m., lateral rectus m., levator palpebrae superioris m.)

•  ipsilateral hemiparesis (on side of expanding lesion) (false localizing sign = Kernohan notch syndrome) due to severe lateral translation of midbrain against opposite tentorial edge → compression of opposite corticospinal tracts above decussation

•  permanent anterograde amnesia ← infarction of uncal / parahippocampal gyrus ← arterial compression

•  permanent visual field defect ← temporal / occipital lobe infarction ← compression of calcarine branch of PCA against tentorium

Location and degree of herniation:

(a)  anterior / uncal herniation (see below)

(b)  posterior: herniation of parahippocampal gyrus

(c)  total: herniation of entire hippocampus

√  compression of ipsilateral cerebral peduncle

√  compression of contralateral cerebral peduncle → notching of midbrain (= Kernohan notch)

√  compression of aqueduct of Sylvius → early dilatation of temporal horn → obstructive hydrocephalus

√  widening of contralateral temporal horn

√  widening (obliteration) of ipsilateral (contralateral) basilar (ambient + quadrigeminal) cisterns

Cx:

(1)  Occipital infarction ← compression of ipsilateral posterior cerebral artery against cerebral peduncle by uncus + parahippocampal gyrus

√  effacement / displacement of ipsilateral PCA

(2)  Duret hemorrhage = hemorrhage in median / paramedian mesencephalon / tectum ← stretching of pontine perforators ← downward displacement of pons

(3)  Respiratory arrest

UNCAL / ANTERIOR TRANSTENTORIAL HERNIATION

=  herniation of uncus (most medial part of temporal lobe) across tentorium cerebelli into suprasellar cistern

◊  Most common subtype of transtentorial herniation caused by lesions in anterior half of brain

√  uncus displaced into suprasellar cistern → pressure on midbrain + brainstem

√  truncation of six-pointed star appearance of suprasellar cistern

Risk:  (1)  compression of midbrain (brainstem)

  (3)  Kernohan notch syndrome

Ascending Transtentorial / Cerebellar Herniation

=  displacement of cerebellum through tentorial incisura superiorly = upward (superior vermian) displacement

Cause:    slowly growing cerebellar / brainstem process, infarction

•  nausea & vomiting → obtundation → coma

√  compression + anterior displacement of 4^th ventricle

√  occlusion of aqueduct → obstructive hydrocephalus

√  narrowing / effacement of ambient + quadrigeminal cistern

√  compression of pons against clivus

√  upward displacement of cerebellar vermis

√  superior displacement of tectum

√  “spinning top” appearance of midbrain due to bilateral compression on posterolateral aspect of midbrain

√  downward displacement of cerebellar tonsils

Cx:        (1)  basilar artery compression ← displacement of midbrain / pons against clivus

(2)  compression of vein of Galen / basal vein of Rosenthal → parenchymal congestion

(3)  compression of posterior cerebral + superior cerebellar arteries ← superior displacement of cerebellum

Alar / Transalar / Retroalar / Sphenoid Herniation

=  herniation of frontal lobe posteriorly across edge of sphenoid ridge

Associated with:   transtentorial + subfalcine herniation

•  paucity of clinical symptomatology, clinically occult

›  posterior / descending: frontal lobe mass

√  frontal lobe displaced posteriorly

√  posterior displacement of sylvian fissure, temporal lobe + horizontal segment of MCA

›  anterior / ascending: temporal lobe / insula lesion

√  temporal lobe displaced anteriorly

Transforaminal / Tonsillar Herniation

=  herniation of inferior mesial portions of cerebellum (= inferior tonsils) downward through foramen magnum

Commonly associated with:   ascending (⅔) or descending (⅓) transtentorial herniation

•  neck pain, nystagmus, vomiting (in conscious patient)

•  Cushing response (= irregular respiration, bradycardia, hypertension) as warning sign in unconscious patient

•  decerebrate posturing

Risk:     compression of medulla → respiratory arrest → cardiovascular collapse → coma → death

√  cerebellar tonsils at level of dens on axial images

√  cerebellar tonsils ≥ 5 mm below foramen magnum (= line connecting basion with opisthion) in adults; ≥ 7 mm in children on sagittal / coronal images

√  effacement of 4^th ventricle / aqueduct → hydrocephalus of 3^rd + lateral ventricles with transependymal CSF flow

√  ± concurrent upward displacement of vermis

Cx:     compression of vulnerable PICA → cerebellar infarction

Transcalvarial / External Herniation

=  brain protrusion through fracture / surgical site of skull

Displacement of Vessels

A.  ARTERIAL SHIFT

(a)  Pericallosal arteries

1.   Round shift = frontal lesion anterior to coronal suture

2.   Square shift = lesion behind foramen of Monro in lower half of hemisphere

3.   Distal shift = posterior to coronal suture in upper half of hemisphere

4.   Proximal shift = basifrontal lesion / anterior middle cranial fossa including anterior temporal lobe

(b)  Sylvian triangle

=  branches of MCA within sylvian fissure on outer surface of insula form a loop upon reaching the upper margin of the insula; serves as angiographic landmark for localizing supratentorial masses

Location of lesion:

B.  CEREBRAL VEINS

=  indicate the midline of the posterior part of the forebrain showing the exact location of the roof of the 3^rd ventricle

BRAIN MASSES

Classification of Primary CNS Tumors

Incidence:  9% of all primary neoplasms (5^th most common primary neoplasm); 5–10÷100,000 population per year; account for 1.2% of autopsied deaths

A.  TUMORS OF BRAIN AND MENINGES

(a)  Gliomas

ASTROCYTOMA (50%)

1.   Astrocytoma (astrocytoma grades I–II)

2.   Glioblastoma (astrocytoma grades III–IV)

OLIGODENDROGLIOMA

PARAGLIOMA

1.   Ependymoma

2.   Choroid plexus papilloma

GANGLIOGLIOMA

MEDULLOBLASTOMA

(b)  Pineal tumor

1.   Germinoma

2.   Teratoma

3.   Pineocytoma

4.   Pineoblastoma

(c)  Pituitary tumor

1.   Pituitary adenoma

2.   Pituitary carcinoma

(d)  Meningioma

(e)  Nerve sheath tumor

1.   Schwannoma

2.   Neurofibroma

(f)  Miscellaneous

1.   Sarcoma

2.   Lipoma

3.   Hemangioblastoma

B.  TUMORS OF EMBRYONAL REMNANTS

(a)  Craniopharyngioma

(b)  Colloid cyst

(c)  Teratoid tumor

1.   Epidermoid (0.2–1.8%)

2.   Dermoid

3.   Teratoma

CNS Tumors Presenting at Birth

1.   Hypothalamic astrocytoma

2.   Choroid plexus papilloma / carcinoma

3.   Teratoma

4.   Primitive neuroectodermal tumor

5.   Medulloblastoma

6.   Ependymoma

7.   Craniopharyngioma

CNS Tumors in Pediatric Age Group

Prevalence:

2.4÷100,000 (< 15 years of age); 2^nd most common pediatric tumor (after leukemia); 15% of all pediatric neoplasms; 15–20% of all primary brain tumors; M > F

•  increased intracranial pressure

•  increasing head size

A.  SUPRATENTORIAL (50%)

Age:   first 2–3 years of life

B.  INFRATENTORIAL (50%)

Age:   4–11 years

mnemonic:   “BE MACHO”

Brainstem glioma

Ependymoma

Medulloblastoma

AVM

Cystic astrocytoma

Hemangioblastoma

Other

Supratentorial Tumor with Mural Nodule

1.   Extraventricular ependymoma

2.   Pleomorphic xanthoastrocytoma

3.   Hemispheric pilocytic astrocytoma

4.   Ganglioglioma

5.   Dysembryoplastic neuroepithelial tumor (DNET)

Supratentorial Midline Tumors

1.   Optic + hypothalamic glioma (39%)

2.   Craniopharyngioma (20%)

3.   Astrocytoma (9%)

4.   Pineoblastoma (9%)

5.   Germinoma (6%)

6.   Lipoma (6%)

7.   Teratoma (3.5%)

8.   Pituitary adenoma (3.5%)

9.   Meningioma (2%)

10.   Choroid plexus papilloma (2%)

Classification by Histology

1.   Astrocytic tumors (33.5%)

2.   “Primitive” neuroectodermal tumor = PNET (21%)

›  Medulloblastoma (16%)

›  Ependymoblastoma (2.5%)

›  PNET of cerebral hemisphere (2.5%)

3.   Mixed gliomas (16%)

4.   Malformative tumors (11.5%)

›  Craniopharyngioma (5.5%)

›  Lipoma (4.5%)

›  Dermoid cyst (1%)

›  Epidermal cyst (0.5%)

5.   Choroid plexus tumors (4%)

6.   Ependymal tumors (4%)

7.   Tumors of meningeal tissues (3.5%)

›  Meningioma (3%)

›  Meningeal sarcoma (0.5%)

8.   Germ cell tumors (2.5%)

›  Germinoma (1.5%)

›  Teratomatous tumor (1%)

9.   Neuronal tumors

›  Gangliocytoma (1.5%)

10.   Tumors of neuroendocrine origin

›  Pituitary adenoma (1%)

11.   Oligodendroglial tumors (0.5%)

12.   Tumors of blood vessel

›  Hemangioma (1%)

Superficial Gliomas

=  peripherally located cortical neoplasms serving as a seizure focus

1.   Ganglioglioma

2.   Desmoplastic infantile ganglioglioma

3.   Gangliocytoma

4.   Dysplastic cerebellar gangliocytoma

5.   Pleomorphic xanthoastrocytoma

6.   Dysembryoplastic neuroepithelial tumor

Multifocal CNS Tumors

A.  METASTASES FROM PRIMARY CNS TUMOR

(a)  via commissural pathways: corpus callosum, internal capsule, massa intermedia

(b)  via CSF: ventricles / subarachnoid cisterns

(c)  satellite metastases

B.  MULTICENTRIC CNS TUMOR

(a)  true multicentric gliomas (4%)

(b)  concurrent tumors of different histology (coincidental)

C.  MULTICENTRIC MENINGIOMAS (3%) without neurofibromatosis

D.  MULTICENTRIC PRIMARY CNS LYMPHOMA

E.  PHAKOMATOSES

1.   Generalized neurofibromatosis:

meningiomatosis, bilateral acoustic neuromas, bilateral optic nerve gliomas, cerebral gliomas, choroid plexus papillomas, multiple spine tumors, AVMs

2.   Tuberous sclerosis:

subependymal tubers, intraventricular gliomas (giant cell astrocytoma), ependymomas

3.   Von Hippel-Lindau disease:

retinal angiomatosis, hemangioblastomas, congenital cysts of pancreas + liver, benign renal tumors, cardiac rhabdomyomas

Multifocal Deep Hemispheric Masses

1.   Primary CNS Lymphoma

2.   Gliomatosis cerebri

√  nonenhancing tumor extension (common)

CNS Tumors Metastasizing Outside CNS

mnemonic:   MEGO

Medulloblastoma

Ependymoma

Glioblastoma multiforme

Oligodendroglioma

Large Heterogeneous Intracerebral Mass

1.   High-grade glioma

√  increased relative cerebral blood volume (rCBV) in zone of edema on perfusion-weighted images

2.   Metastasis

√  reduced relative cerebral blood volume (rCBV) in zone of edema on perfusion-weighted images

Mass with Large Tumor Vessels and Edema

1.   Glioblastoma multiforme

2.   Meningioma

Avascular Mass of Brain

mnemonic:   TEACH

Tumor: astrocytoma, metastasis, oligodendroglioma

Edema

Abscess

Cyst, Contusion

Hematoma, Herpes

Calcified Intracranial Mass

1.   Oligodendroglioma (frequent, although rare tumor)

2.   Low-grade astrocytoma (in 10–20%)

mnemonic:   Ca2+ COME

Craniopharyngioma

Astrocytoma, Aneurysm

Choroid plexus papilloma

Oligodendroglioma

Meningioma

Ependymoma

HYPODENSE BRAIN LESIONS

Diffusely Swollen Hemispheres

A.  METABOLIC

1.   Metabolic encephalopathy: eg, uremia, Reye syndrome, ketoacidosis

2.   Anoxia: cardiopulmonary arrest, near-drowning, smoke inhalation, ARDS

B.  NEUROVASCULAR

1.   Hypertensive encephalopathy

2.   Superior sagittal sinus thrombosis

3.   Head trauma

4.   Pseudotumor cerebri

C.  INFLAMMATION / INFECTION

eg, herpes encephalitis, CMV, toxoplasmosis

Brain Edema

=  increase in brain volume ← increased tissue-water content (80% for gray matter + 68% for white matter is normal)

Etiology:

(a)  Cytotoxic edema

reversible increase in intracellular water content 2° to ischemia / anoxia (axonal pallor) → depletion of ATP → ion pump dysfunction across glial cell membrane → increase in intracellular Na+ and K+

•  characteristically seen in cerebral infarction

•  30–60 min after onset of symptoms

√  decreased ADC value (dark)

(b)  Vasogenic edema (most common form)

fluid leakage of water out of capillaries into extracellular interstitial space ← damage of capillary endothelium; increase in pinocytotic activity with passage of protein across vessel wall into intercellular space

•  associated with primary brain neoplasm, metastases, hemorrhage, inflammation, infarction

•  takes > 3–6 hours; requires residual / reestablished blood flow

√  lack of contrast enhancement means breakdown of blood-brain barrier is NOT the cause

√  increased ADC value (bright)

DDx:  blood-brain barrier break-down after 8–10 days

Types:

1.   Hydrostatic edema

rapid increase / decrease in intracranial pressure

2.   Interstitial edema

increase in periventricular interstitial spaces ← transependymal flow of CSF with elevated intraventricular pressure

3.   Hypo-osmotic edema

produced by overhydration from IV fluid / inappropriate secretion of antidiuretic hormone

4.   Congestive brain swelling

rapid accumulation of extravascular water as a result of head trauma; may become irreversible (brain death) if intracranial pressure equals systolic blood pressure

√  decreased distinction between gray + white matter

√  compressed slitlike lateral ventricles

√  compression of cerebral sulci + perimesencephalic cisterns

CT:

√  areas of hypodensity

◊  Edema is always greatest in white matter!

√  mass effect: flattening of gyri, displacement + deformation of ventricles, midline shift

√  return to normal: from nonhemorrhagic edema / brain atrophy, from white matter shearing injury

MR:

√  decreased intensity on T1WI

√  increased intensity on T2WI

√  enhancement with gadolinium

US:

√  generalized / focal increase of parenchymal echogenicity with featureless appearance

√  decreased resistive indices

Midline Cyst

1.   Cavum septi pellucidi

2.   Cavum vergae

3.   Cavum veli interpositi

4.   Colloid cyst anterior + superior to cavum septi pellucidi

5.   Arachnoid cyst in region of quadrigeminal plate cistern

√  curvilinear margins

Intracranial Nonneoplastic Cyst

Characteristics:

√  no detectable wall / associated soft-tissue mass

√  homogeneous signal intensity identical to CSF

√  absence of surrounding edema / gliosis

√  NO contrast enhancement

1.   Choroid plexus cyst (most common, abnormal DWI in ⅔)

2.   Ependymal cyst

3.   Neuroglial cyst

4.   Enlarged perivascular spaces (typically multiple, clustered around basal ganglia)

5.   Arachnoid cyst (typically extraaxial)

6.   Porencephalic cyst (communication with lateral ventricle, surrounding gliosis)

7.   Infectious cyst of neurocysticercosis (< 1 cm, partially enhancing)

8.   Epidermoid cyst

Cyst with Mural Nodule

1.   Ependymoma

2.   Pilocytic astrocytoma (childhood)

3.   Pleomorphic xanthoastrocytoma

4.   Ganglioglioma

5.   Glioblastoma multiforme

6.   Hemangioblastoma (posterior fossa, spinal cord)

Multiple Tiny CNS Cysts

A.  DIFFUSE DEGENERATIVE DISEASE

B.  DIFFUSE INFLAMMATORY PROCESS

C.  LOW-GRADE CYSTIC NEOPLASM

1.   Ganglioglioma

2.   Pyelocytic astrocytoma

3.   Pleomorphic xanthoastrocytoma

Anterior Temporal Cysts with Leukoencephalopathy

1.   Congenital CMV infection

2.   Leukoencephalopathy with subcortical temporal cysts and megalencephaly

3.   Vanishing white matter disease

Cystic Lesions on Head Ultrasound

A.  NORMAL VARIANTS

1.   Cavum septi pellucidi

2.   Cavum vergae

3.   Cavum veli interpositi

B.  CYSTIC LESIONS OF POSTERIOR FOSSA

Evaluate

›  size of 4^th ventricle + communication with 4^th ventricle

›  size of vermis + cerebellar hemispheres

›  mass effect on cerebellum

1.   Megacisterna magna

2.   Dandy-Walker continuum disorder

3.   Blake pouch cyst

4.   Arachnoid cyst

5.   Vein of Galen malformation

B.  SUPRATENTORIAL PERIVENTRICULAR CYSTS

1.   Connatal cyst

=  coarctation of lateral ventricles + frontal horn cysts

Location:   at / just below superolateral angles of frontal horns / body of lateral ventricles anterior to foramen of Monro

Cause:   normal variant ← approximation of walls of frontal horns; NOT sequelae of ischemia

2.   Subependymal cyst

3.   Choroid plexus cyst

4.   Periventricular leukomalacia

4.   Pseudoporencephaly

C.  SUPRATENTORIAL INTRA- / EXTRAAXIAL CYSTS

1.   Schizencephaly

2.   Ventriculomegaly: hydrocephalus, brain atrophy

3.   Holoprosencephaly

4.   Supratentorial arachnoid cyst

5.   Spontaneous intracranial hematoma

6.   Brain abscess (uncommon)

Cholesterol-containing CNS Lesions

1.   Epidermoid inclusion cyst

2.   Cholesterol granuloma

3.   Acquired epidermoid of middle ear

4.   Congenital cholesteatoma of middle ear

5.   Craniopharyngioma

Mesencephalic Low-density Lesion

1.   Normal: decussation of superior cerebellar peduncles at level of inferior colliculi

2.   Syringobulbia found in conjunction with syringomyelia, Arnold-Chiari malformation, trauma

√  CSF density centrally

√  intrathecal contrast enters central cavity

3.   Brainstem infarction

√  abnormal contrast enhancement after 1 week

√  well-defined low-attenuation region without enhancement after 2–4 weeks

4.   Central pontine myelinolysis

5.   Brainstem glioma

6.   Metastasis

√  well-defined contrast enhancement

7.   Granuloma in TB / sarcoidosis (rare)

Intracranial Pneumocephalus

A.  TRAUMA (74%):

(a)  blunt trauma

in 3% of all skull fractures; in 8% of fractures involving paranasal sinuses (frontal > ethmoid > sphenoid > mastoid) or base of skull

(b)  penetrating injury

B.  NEOPLASM INVADING SINUS (13%):

1.   Osteoma of frontal / ethmoid sinus

2.   Pituitary adenoma

3.   Mucocele, epidermoid

4.   Malignancy of paranasal sinuses

C.  INFECTION WITH GAS-FORMING ORGANISM (9%) in mastoiditis, sinusitis

D.  SURGERY (4%)

hypophysectomy, paranasal sinus surgery

E.  SUPRATENTORIAL CRANIOTOMY

Location:   in any compartment; most often in subdural space over frontal lobe

Duration after surgery:   2 days (100%), 7 days (75%), 2^nd week (60%), 3^rd week (26%), > 3 weeks (0%)

Mechanism of dural laceration:

(1)  ball-valve mechanism during straining, coughing, sneezing

(2)  vacuum phenomenon ← loss of CSF

Time of onset:   on initial presentation (25%), usually seen within 4–5 days, delay up to 6 months (33%)

Mortality:  15%

Cx:   (1)  CSF rhinorrhea (50%)

(2)  Meningitis / epidural / brain abscess (25%)

(3)  Extracranial pneumocephalus = air collection in subaponeurotic space

HYPERDENSE INTRACRANIAL LESIONS

Intracranial Calcifications

mnemonic:   PINEEAL

Physiologic

Infection

Neoplasm

Endocrine

Embryologic

Arteriovenous

Leftover Ls

A.  PHYSIOLOGIC INTRACRANIAL CALCIFICATIONS

B.  INFECTION

TORCH (toxoplasmosis, others [syphilis, hepatitis, zoster], CMV, rubella, herpes), healed abscess, hydatid cyst, granuloma (tuberculoma, actinomycosis, coccidioidomycosis, cryptococcosis, mucormycosis), cysticercosis, trichinosis, paragonimiasis

mnemonic:

CMV calcifications are circumventricular

Toxoplasma calcifications are intraparenchymal

C.  NEOPLASM

Craniopharyngioma (40–80%), oligodendroglioma (50–70%), chordoma (25–40%), choroid plexus papilloma (10%), meningioma (20%), pituitary adenoma (3–5%), pinealoma (10–20%), dermoid (20%), lipoma of corpus callosum, ependymoma (50%), astrocytoma (15%), after radiotherapy, metastases (1–2%, lung > breast > GI tract)

N.B.:   Astrocytomas calcify less frequently but are the most common tumor!

D.  ENDOCRINE Hyperparathyroidism, hypervitaminosis D, hypoparathyroidism, pseudohypoparathyroidism, CO poisoning, lead poisoning

E.  EMBRYOLOGIC Neurocutaneous syndromes (tuberous sclerosis, Sturge-Weber, neurofibromatosis), Fahr disease, Cockayne syndrome, basal cell nevus syndrome

F.  ARTERIOVENOUS Atherosclerosis, aneurysm, AVM, occult vascular malformation, hemangioma, subdural + epidural hematomas, intracerebral hemorrhage

G.  LEFTOVER Ls
Lipoma, lipoid proteinosis, lissencephaly

Physiologic Intracranial Calcification

1.   Pineal calcification

Age:  no calcification < 5 years of age, in 8–10% at 8–14 years of age, in 40% by 20 years of age; in ⅔ of adult population

√  amorphous / ringlike calcification < 3 mm from midline usually < 10 mm in diameter

√  ~ 30 mm above highest posterior elevation of pyramids

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