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:
Well-differentiated = Low-grade Astrocytoma
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
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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)
CT:
MR:
Angio:
Prognosis: 3–10 years postoperative survival; may convert into more malignant form several years later
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:
Prognosis: postoperative survival of 2 years
= 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:
Location: originating in midline with extension into cerebellar hemisphere (29–53%), vermis (16–71%) >tonsils >brainstem (34%)
CT:
MR:
Angio:
Prognosis:
malignant transformation exceedingly rare
DDx of solid astrocytoma:
DDx of cystic astrocytoma:
= 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
Site: near ventricles (82%)
Imaging patterns:
CT:
MR:
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
DDx: fibrillary astrocytoma (dismal prognosis)
Hypothalamic Pilocytic Astrocytoma
= HYPOTHALAMIC GLIOMA
Prognosis: may regress spontaneously
Cerebral Pilocytic Astrocytoma
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
= 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
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
CT:
MR:
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