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Nervous System Disorders

Incidence: 70–75% of all primary intracranial tumors; most common brain tumor in children (40–50% of all primary pediatric intracranial neoplasms)

Distribution: proportional to amount of white matter

Location:

  1. in adults: central white matter of cerebrum (15–30% of all gliomas)
  2. in children: cerebellum (40%), brainstem (20%), supratentorial (30%)

Well-differentiated = Low-grade Astrocytoma!!navigator!!

Incidence: 9% of all primary intracranial tumors; 10–15% of gliomas

Age: 20–40 years; M >F

Path: benign nonmetastasizing; poorly defined borders with infiltration of white matter + basal ganglia + cortex; NO significant tumor vascularity / necrosis / hemorrhage; blood-brain barrier may remain intact

WHO Classification of Astrocytomas

Grade ICircumscribed astrocytomagenerally benign well-circumscribed tumor, specific unique histologic features for each tumor, pilocytic astrocytoma (most common), subependymal giant cell astrocytoma; no tendency to progress to higher grade; low rate of recurrence
Grade IIAstrocytomadiffusely infiltrating; well-differentiated; minimal pleomorphism or nuclear atypia; no vascular proliferation / necrosis
Grade IIIAnaplastic astrocytomapleomorphism and nuclear atypia; increased cellularity; mitotic activity; vascular proliferation + necrosis absent
Grade IVGlioblastoma multiformemarked vascular proliferation and necrosis; increased cellularity; anaplasia + pleomorphism; variable mitotic activity; cell type may be poorly differentiated, fusiform, round or multinucleated

Histo: homogeneous relatively uniform appearance with proliferation of well-differentiated multipolar fibrillary / protoplasmic astrocytes; mild nuclear pleomorphism + mild hypercellularity; rare mitoses

Location: posterior fossa in children, supratentorial in adults (typically lobar)

  • may develop a cyst with high-protein content (rare)

CT:

  • usually hypodense lesion with minimal mass effect + minimal / NO peritumoral edema
  • well-defined tumor margins
  • central calcifications (15–20%)
  • minimal / no contrast enhancement (normal capillary endothelial cells)

MR:

  • well-defined hypointense lesion with little mass effect / vasogenic edema / heterogeneity on T1WI
  • hyperintense on T2WI
  • little / no enhancement on Gd-DTPA
  • cyst with content hyperintense to CSF ← protein
  • hyperintense area within tumor mass ← paramagnetic effect of methemoglobin
  • inhomogeneous gadolinium-DTPA enhancement of tumor nodule

Angio:

  • majority avascular

Prognosis: 3–10 years postoperative survival; may convert into more malignant form several years later

Anaplastic Astrocytoma!!navigator!!

Incidence: 11% of all primary intracranial neoplasms; 25% of gliomas

Path: frequently vasogenic edema; NO necrosis / hemorrhage

Histo: less well differentiated with greater degree of hypercellularity + pleomorphism, multipolar fibrillary / protoplasmic astrocytes; mitoses + vascular endothelial proliferation common

Location: typically frontal + temporal lobes

MR:

  • moderate mass effect
  • well-defined slightly heterogeneous hypointense lesion on T1WI with prevalent vasogenic edema
  • hyperintense on T2WI
  • ± enhancement on Gd-DTPA

Prognosis: postoperative survival of 2 years

Cerebellar Astrocytoma!!navigator!!

= CEREBELLAR PILOCYTIC ASTROCYTOMA

2nd most frequent tumor of posterior fossa in children

Incidence: 10–20% of pediatric brain tumors

Histo: mostly grade I

Age: children >adults; no specific age peak; M÷F = 1÷1

Path:

  1. cystic lesion with tumor nodule (“mural nodule”) in cyst wall (50%); (midline astrocytomas cystic in 50%, hemispheric astrocytomas cystic in 80%)
  2. solid mass with cystic (= necrotic) center (40–45%)
  3. solid tumor without necrosis (<10%)
  • hydrocephalus, headache, vomiting, neck pain, 6th nerve palsy
  • blurred vision, diplopia, papilledema, nystagmus
  • cerebellar signs: truncal ataxia, dysdiadochokinesia appendicular dysmetria, gait disturbance

Location: originating in midline with extension into cerebellar hemisphere (29–53%), vermis (16–71%) >tonsils >brainstem (34%)

  • calcifications (20%): dense / faint / reticular / punctate / globular; mostly in solid variety
  • may develop extreme hydrocephalus (quite large when finally symptomatic)

CT:

  • round / oval cyst with density of cyst fluid >CSF
  • round / oval / plaquelike mural nodule with intense homogeneous enhancement
  • cyst wall slightly hyperdense + nonenhancing (= compressed cerebellar tissue)
  • uni- / multilocular cyst (= necrosis) with irregular enhancement of solid tumor portions
  • round / oval lobulated fairly well-defined iso- / hypodense solid tumor with hetero- / homogeneous enhancement

MR:

  • hypointense on T1WI + hyperintense on T2WI
  • enhancement of solid tumor portion

Angio:

  • avascular

Prognosis:

malignant transformation exceedingly rare

  • 40% 25-year survival rate for solid cerebellar astrocytoma
  • 90% 25-year survival rate for cystic juvenile pilocytic astrocytoma

DDx of solid astrocytoma:

  1. Medulloblastoma (hyperdense mass, noncalcified)
  2. Ependymoma (4th ventricle, 50% calcify)

DDx of cystic astrocytoma:

  1. Hemangioblastoma (lesion <5 cm)
  2. Arachnoid cyst
  3. Trapped 4th ventricle
  4. Megacisterna magna
  5. Dandy-Walker cyst

Pilocytic Astrocytoma!!navigator!!

= JUVENILE PILOCYTIC ASTROCYTOMA

= most benign histologic subtype of astrocytoma without progression to high-grade glioma

Incidence: 0.6–5.1% of all intracranial neoplasms

◊Most common pediatric CNS glioma; 85% of all cerebellar + 10% of all cerebral astrocytomas in children

Age: predominantly in children + young adults; 75% in first 2 decades of life; peak age between birth and 9 years of age; M÷F = 1÷1

Histo: biphasic pattern of compact bipolar pilocytic (hairlike) astrocytes arranged mostly around vessels + loosely aggregated protoplasmic astrocytes undergoing microcystic degeneration

Associated with: neurofibromatosis type 1

Location: in / near midline

  • common: cerebellum, optic nerve / chiasm, hypothalamus (around 3rd ventricle)
  • less common: cerebral hemispheres (adults), cerebral ventricles, velum interpositum, spinal cord

Site: near ventricles (82%)

Imaging patterns:

  1. Cyst with intensely enhancing mural nodule (67%)
    1. nonenhancing cyst wall (21%)
    2. enhancing cyst wall (46%)
  2. Solid mass (33%)
    1. central nonenhancing necrotic zone (16%)
    2. minimal / no cystic component (17%)

CT:

  • well-demarcated smoothly marginated round / oval mass with cystic features
  • occasional calcifications
  • intense enhancement (94%)
  • multilobulated / dumbbell appearance along optic pathway
  • mural tumor nodule located in wall of cerebellar cyst

MR:

  • T1-isointense + T2-hyperintense to normal brain
  • small rim of vasogenic edema (low biologic activity)
  • increased heterogeneous signal intensity on early Gd-DTPA-enhanced T1WI; homogeneous enhancement on delayed images

Prognosis: relatively benign clinical course, almost never recurs after surgical excision; 94% (79%) postsurgical 10-year (20-year) survival; NO malignant transformation to anaplastic form

DDx: metastasis, hemangioblastoma, atypical medulloblastoma

Brainstem Pilocytic Astrocytoma

  • nausea, vomiting, ataxia, torticollis
  • papilledema, nystagmus, 6th & 7th nerve palsy
  • exophytic extension from dorsal surface of brainstem
  • obliteration of 4th ventricle

DDx: fibrillary astrocytoma (dismal prognosis)

Hypothalamic Pilocytic Astrocytoma

= HYPOTHALAMIC GLIOMA

  • obesity, diabetes insipidus ← hypothalamic-pituitary dysfunction
  • diencephalic syndrome (= emaciation despite normal / slightly decreased caloric intake, alert appearance, hyperkinesis, irritability, normal / accelerated growth)
  • hemiparesis ← compression of corticospinal tracts
  • hydrocephalus

Prognosis: may regress spontaneously

Cerebral Pilocytic Astrocytoma

  • headache, seizure activity, hemiparesis
  • ataxia, nausea, vomiting

Location: temporal lobe

Optic Pathway Pilocytic Astrocytoma

= OPTIC NERVE GLIOMA

Location: optic nerve / chiasm

◊Most common tumor in NF1 population (15–21%); NF1 diagnosed in ⅓ of all optic pathway gliomas; NF1 diagnosed in 40–70% of all tumors in this region; 1.5–3.5% of all orbital neoplasms;⅔ of all neoplasms of the optic nerve

Age:<6 years; M÷F = 2÷1

  • visual loss / visual-field deficit, optic disk pallor, optic nerve atrophy ← axonal damage + ischemia
  • precocious puberty (39%) in NF1 patients

Pleomorphic Xanthoastrocytoma!!navigator!!

= superficially located supratentorial tumor that involves leptomeninges

Prevalence: 1% of all brain neoplasms

Age: average age of 26 years (range, 5–82 years)

Path: circumscribed tumor attached to meninges with infiltration into surrounding brain

Histo: pleomorphic spindled tumor cells (reactive to glial fibrillary acidic protein) with intracytoplasmic lipid (xanthomatous) deposits in a dense intercellular reticulin network; giant cells; eosinophilic granular bodies; WHO grade II tumor

  • long history of seizures (71%)

Location: supratentorial (98%): temporal (49%) / parietal (17%) / frontal (10%) / occipital (7%) lobe; thalamus; cerebellum; spinal cord

◊Its PERIPHERAL LOCATION is the single most consistent imaging feature

  • cystic (48%) supratentorial mass with mural nodule
  • intense enhancement of solid portions
  • CHARACTERISTIC involvement of leptomeninges (71%)
  • peritumoral vasogenic edema / calcification / skull erosion are uncommon

CT:

  • hypo- / isoattenuating mass

MR:

  • hypo- to isointense mass relative to gray matter on T1WI
  • hyper- to isointense mass on T2WI

Rx: surgical resection (unresponsive to chemotherapy + radiation therapy)

Prognosis: 81% (70%) 5-year (10-year) survival rate; high rate of recurrence; malignant transformation in 20%

DDx: meningioma, glioblastoma multiforme, oligodendroglioma, metastatic disease, infection

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