Radiation Oncology: A Question-Based Review

13
General Central Nervous System

Steven H. Lin and Anita Mahajan

image 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 is the most common type of primary CNS tumor?

Glioma ( ~40%) > meningioma (15%–20%)

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?

1.     Children: juvenile pilocytic astrocytoma (JPA) (20% <14 yo vs. 12% >14 yo)

2.     Adults: glioblastoma

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?

1.     Nuclear Atypia

2.     Cellularity and Mitosis

3.     Endothelial proliferation

4.     Necrosis

(Mnemonic: AMEN)

What CNS tumors tend to have CSF spread?

Medulloblastomas and other blastomas (except astroblastoma/glioblastoma multiforme [GBM]), CNS lymphoma, choroid plexus carcinomas, germ cell tumors, and mets

What CNS tumors have Flexner-Wintersteiner rosettes?

Pineoblastoma and RB (any PNET)

What CNS tumors have psamomma 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.

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.

image Workup/Staging


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 structure produces CSF?

CSF is produced in the choroid plexus.

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 trasverse 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

image 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