CNS Tumors Overview and Key Concepts

CNS Tumors - Basic Principles

• CNS tumors can be metastatic (50%) or primary (50%).
• Metastatic tumors appear as multiple, well-defined lesions at the gray-white junction. Common sources are lung, breast, and kidney.
• Primary tumors are categorized by cell type of origin (astrocytes, meningothelial cells, ependymal cells, oligodendrocytes, or neuroectoderm).
• In adults, primary tumors are usually supratentorial. The most common types are glioblastoma multiforme, meningioma, and schwannoma.
• In children, primary tumors are usually infratentorial.

Glioblastoma Multiforme (GBM)

• Malignant, high-grade astrocyte tumor in adults.
• Commonly arises in the cerebral hemisphere, often crossing the corpus callosum (butterfly lesion).
• Characterized by zones of necrosis and tumor cells with a pseudopalisading appearance and substantial endothelial cell proliferation.
• GFAP positive.
• Poor prognosis.

Meningioma

• Benign tumor of arachnoid cells.
• Most common benign CNS tumor in adults, especially women.
• Rare in children.
• Often presents as seizures due to compression, without invading the cortex.
• Imaging shows a round mass attached to the dura.
• Histology reveals a whorled pattern and may exhibit psammoma bodies.

Schwannoma

• Benign tumor of Schwann cells.
• Involves cranial or spinal nerves. A frequent involvement is cranial nerve VIII at the cerebellopontine angle, presenting as hearing loss and tinnitus.
• S-100 positive.
• Bilateral schwannomas can occur in neurofibromatosis type 2.

Oligodendroglioma

• Malignant tumor of oligodendrocytes.
• Imaging often reveals calcified tumors in white matter, commonly involving the frontal lobe, and may cause seizures.
• "Fried-egg" appearance of cells on biopsy.

Pilocytic Astrocytoma

• Benign astrocyte tumor.
• Most common CNS tumor in children.
• Typically arises in the cerebellum.
• Imaging reveals a cystic lesion with a mural nodule.

Medulloblastoma

• Malignant tumor derived from cerebellar granular cells (neuroectoderm).
• Typically occurs in children.
• Histologically features small, round blue cells, sometimes exhibiting Homer-Wright rosettes.
• Poor prognosis; tumor spreads rapidly via cerebrospinal fluid (CSF). Metastasis to the cauda equina is called "drop metastasis."

Ependymoma

• Malignant tumor of ependymal cells.
• Commonly occurs in children.
• Often develops in the fourth ventricle, which may lead to hydrocephalus.
• Perivascular pseudorosettes are a characteristic feature seen in biopsy specimens.

Craniopharyngioma

• Tumor originating from epithelial remnants of Rathke's pouch.
• Presents as a supratentorial mass in children and young adults, often compressing the optic chiasm, leading to bitemporal hemianopsia.
• Common imaging feature: Calcifications ("tooth-like" tissue).
• Benign, but often recurs after resection.

This quiz covers the fundamental principles of CNS tumors, including the distinctions between metastatic and primary tumors. It highlights common types of tumors, such as glioblastoma multiforme and meningioma, their characteristics, and origin cell types. Test your knowledge on the basics of CNS tumors and their clinical significance.