General Central Nervous System
BACKGROUND
What is the estimated annual incidence of primary CNS tumors in the U.S.?
~50,000–55,000 cases/yr of CNS tumors (per the National Program of Cancer Registries database)
What is the most common intracranial tumor?
Brain mets (20%–40% of all cancer pts develop brain mets)
What are the most common primary histologies associated with brain metastases?
Most common: lung, breast, melanoma
Which primary histologies are associated with hemorrhagic metastases?
Renal cell carcinoma, melanoma, and choriocarcinoma are associated with hemorrhagic mets.
Which primaries tend to metastasize to the posterior fossa?
GU/Pelvic primaries tend to go to the posterior fossa, where they are more likely to have a mass effect
What is the most common type of primary CNS tumor?
Glioma (~40%) > meningioma (15%–20%)
What % of CNS tumors are metastases vs. glioma vs. other?
Of all CNS tumors, roughly one-third are mets, one-third are gliomas, and one-third are other (meningioma, schwannoma, pituitary, lymphoma, etc.)
What % of adult astrocytomas are low grade vs. high grade?
25% low grade vs. 75% high grade
What is the most common histologic type of malignant CNS tumor in children? In adults?
Children: juvenile pilocytic astrocytoma (JPA) (20% <14 yo vs. 12% >14 yo)
Adults: glioblastoma
What is the most common benign intracranial tumor in adults?
Meningioma
What is the strongest risk factor for developing CNS tumors?
Ionizing RT in children (no threshold—glioma, meningioma, nerve sheath)
What CNS tumors are linked to the following?
1. NF-1
2. NF-2
3. Tuberous sclerosis
4. Von Hippel-Lindau
5. Li-Fraumeni
6. Cowden
7. Gorlin
8. Turcot
9. Retinoblastoma (RB)
10. Ataxia telangiectasia
11. MEN-1
1. Optic glioma, JPA
2. Bilat acoustic neuroma, spinal ependymoma
3. Subependymal giant cell astrocytoma, retinal hamartoma
4. Hemangioblastoma
5. Glioma
6. Meningioma
7. Medulloblastoma
8. Medulloblastoma, glioblastoma
9. Pineoblastoma
10. CNS lymphoma
11. Pituitary adenoma
What are the 4 factors used for grading in the WHO brain tumor grading system?
Nuclear Atypia
Cellularity and Mitosis
Endothelial proliferation
Necrosis
(Mnemonic: AMEN)
WHO grade I = no factors present
WHO grade II = atypia
WHO grade III = atypia, mitoses
WHO grade IV = endothelial proliferation or necrosis
Which CNS structures cross midline?
Glioblastoma multiforme (GBM), radiation necrosis, meningioma (extra-axial can spread along meninges to contralateral side), epidermoid cyst, multiple sclerosis
What CNS tumors tend to have CSF spread?
Medulloblastomas and other blastomas (except astroblastoma/GBM), CNS lymphoma, choroid plexus carcinomas, germ cell tumors, and mets
What is the pathway in which CSF flows?
CSF is produced by the choroid plexus → lateral ventricles → foramen of Monroe → third ventricle → cerebral aqueduct of Sylvius → fourth ventricle → foramen of Magendie, and 2 lateral foramina of Lushka
What CNS tumors have Flexner-Wintersteiner rosettes?
Pineoblastoma and RB (any PNET)
What CNS tumors have psammoma bodies?
Meningioma and pituitary tumors (uncommon)
What CNS tumor type exhibits Verocay bodies? Schiller-Duval bodies?
Schwannomas exhibit Verocay bodies, and yolk sac tumors exhibit Schiller-Duval bodies.
Which CNS tumors have Homer-Wright rosettes?
Neuroblastoma, medulloblastoma, pinealoblastoma, and PNET
What CNS tumor has pseudorosettes?
Ependymoma
What receptors are commonly overexpressed in gliomas?
EGFR (30%–50% in GBM tumors) and PDGFR (non-GBM tumors)
Neural stem cells express which marker? Why are they important?
CD133. Neural stem cells are thought to be precursors for astrocytomas.
What gene on chromosome 17 is frequently lost in both low-grade and high-grade gliomas?
The p53 gene is frequently lost in low- and high-grade gliomas.
What is the genetic mutation in NF-1, and for which sites does it predispose to gliomas?
In NF-1, the genetic mutation is 17q11.2/neurofibromin. It predisposes to optic/intracranial gliomas.
WORKUP/STAGING
Which structures enhance on the MRI sequences, T1, T2, and FLAIR?
T1 enhances fat and soft tissue, does not enhance fluid. T1 with contrast is generally the best way to visualize intracranial tumors. T2 enhances fluid (CSF, edema) and does not enhance fat. FLAIR removes the increased CSF signal on T2 and shows abnormal fluid (masses and edema).
Which structures enhance with contrast?
Mets, Abscess, GBM, Lymphoma, +/– AA or AO [anaplastic astrocytoma/anaplastic oligodendroglioma]) (Mnemonic: MAGLA), meningioma, pilocytic astrocytoma, gliosis, cerebritis
Which structures do not enhance with contrast?
Grade 2 low-grade gliomas, +/– AA or AO, rare for GBM to not enhance.
Which gyri contain the sensory and motor area?
The precentral gyrus contains the motor area, and the postcentral gyrus contains the somatosensory area. Medial = body, lower extremities, feet. Lateral = trunk, arms, head.
What brain region is associated with expressive aphasia?
The Broca motor area (dominant/left frontal lobe) is associated with expressive aphasia.
What brain region is associated with receptive aphasia?
The dominant/left temporal lobe at the post end of the lateral sulcus (Wernicke area) is associated with receptive aphasia.
Which CN exits on the dorsal side of the brain (midbrain)?
CN IV exits on the dorsal side of the brain.
What structures are in the cavernous sinus?
CNs III, IV, VI, V1, and V2; internal carotid artery
What common defect does tumor involving the cavernous sinus produce?
CN VI palsy (no abduction of the lateral rectus)
What components traverse the superior orbital fissure?
CNs III, IV, VI, and V1
What nerve passes through the foramen rotundum?
V2 passes through the foramen rotundum.
What nerve passes through the foramen ovale?
V3 passes through the foramen ovale.
What structures pass through the foramen spinosum?
The middle meningeal artery and vein as well as the nervus spinosus (branch of CN V3), pass through the foramen spinosum.
Through what structure do CNs VII–VIII traverse?
CNs VII–VIII traverse through the internal auditory meatus.
Through which foramen does CN VII traverse the skull base?
CN VII emerges through the stylomastoid foramen.
What passes through the jugular foramen?
CNs IX–XI pass through the jugular foramen.
How many spinal nerves are there in the spinal cord?
There are 31 spinal nerves in the spinal cord (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal).
Where does the cord end? Where does the thecal sac end?
The cord ends at L3–4 in children and L1–2 in adults. The thecal sac ends at S2–3 in both children and adults.
What tumors present with a dural tail sign?
Meningioma (60%), also chloroma, lymphoma, and sarcoidosis
TOXICITY
Name some acute RT complications in pts receiving RT for CNS tumors.
Alopecia, dermatitis, fatigue, transient worsening of neurologic Sx, n/v, otitis externa, seizures, and edema
What is the timing and mechanism of somnolence syndrome?
6–12 wks post-RT, due to transient demyelination of axons
What are some late complications of RT to the CNS? What is the timing for these?
Radionecrosis, leukoencephalopathy, retinopathy, cataracts, endocrine deficits, memory loss, learning deficits, and hearing loss; 3 mos to 3 yrs
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