CNS Tumors

Question 1

Basic principles

Answer 1

o Can be metastatic (50%) or primary (50%)
o Metastatic tumors characteristically present as multiple, well circumscribed lesions at the gray-white junction –> lung, breast and kidney are common sources
o Primary tumors are classified according to cell type of origin –> e.g. astrocytes, meningothelial cells, ependymal cells, oligodendrocytes or neuroectoderm
o In adults, primary tumors are usually supratentorial
—> Most common tumors in adults are glioblastoma multiforme, meningioma and schwannoma
o In children, primary tumors are usually infratentorial
—> Most common tumors in children are pilocytic astrocytoma, ependymoma and medulloblastoma
o Primary malignant CNS tumors are locally destructive, but rarely metastasize

Question 2

Glioblastoma multiforme

Answer 2

Malignant, high grade tumors of astrocytes
o Most common primary malignant CNS tumor in adults
o Usually arises in the cerebral hemisphere –> characteristically crosses the corpus callosum = “butterfly” lesion
o Characterized by regions of necrosis surrounded by tumor cells (pseudopalisading) + endothelial cell proliferation
o Tumors cells are GFAP positive
o Poor prognosis

Question 3

Meningioma

Answer 3

Benign tumor of arachnoid cells
o Most common benign CNS tumor in adults
o More commonly seen in women, rare in children
o Express estrogen receptor
o May present as seizures –> tumor compresses but does not invade the cortex
o Imaging reveals a round mass attached to the dura
o Histology shows a whorled pattern
o Psammoma bodies may be present

Question 4

Schwannoma

Answer 4

Benign tumor of schwann cells
o Involves cranial or spinal nerves –> within the cranium most frequently involves cranial nerve VIII at the cerebellopontine angle = presents as loss of hearing + tinnitus
o Tumor cells are S-100 positive
o Bilateral tumors are seen in neurofibromatosis type 2

Question 5

Oligodendroglioma

Answer 5

Malignant tumor of oligodendrocytes
o Imaging reveals a calcified tumor in the white matter, usually involving the frontal lobe
o May present with seizures
o “fried egg” appearance of cells on biopsy

Question 6

Pilocytic astrocytoma

Answer 6

Benign tumor of astrocytes
o Most common CNS tumors in children –> usually arises in the cerebellum
o Imaging reveals a cystic lesion with a mural nodule
o Biopsy shows Rosenthal fibers (thick eosinophilic processes of astrocytes) + eosinophilic granular bodies
o Tumor cells are GFAP positive

Question 7

Medulloblastoma

Answer 7

Malignant tumor derived from the granular cells of the cerebellum (neuroectoderm)
o Usually arises in children
o Histology reveals small, round blue cells –> Homer-Wright rosettes may be present
o Poor prognosis –> tumor grows rapidly and spreads via CSF
—> Metastasis to the cauda equine = “drop metastasis”

Question 8

Ependymoma

Answer 8

Malignant tumor of ependymal cells
o Usually seen in children
o Most commonly arises in the 4th ventricle –> may present with hydrocephalus
o Perivascular pseudorosettes are a characteristic finding on biopsy

Question 9

Craniopharyngioma

Answer 9

Tumor that arises from epithelial remnants of Rathke’s pouch
o Presents as a supratentorial mass in a child or young adult –> may compress the optic chiasm leading to bitemporal hemianopsia
o Clacifications are commonly seen on imaging –> derived from “tooth like” tissue
o Bening, but tends to recur after resection