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Neuroanatomie (Subject) / Alles (Lesson)

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• Differentiating a small neoplasm from a small infarct may be very difficult. When can followup imaging be obtained to help distinguish between the two. Virtually all infarcts will be smaller in size by 3 weeks. If lesion is same size or larger at 3 weeks, a neoplasm should be favored.
• Extra-axial mass refers to Everything outside the brain: Arachnoid. Meninges. Dural sinuses. Skull. Ventricles.
• White matter buckling? Extra-axial lesions may buckle white matter. Inward compression of white matter (thinning of fronds). Preserved gray-white matter differentiation.
• Tumors of high cellular density Usually small cell tumors (high nucleus:cytoplasm ratio, hyperdense and T2 hypointense): Lymphoma. Pineoblastoma. Neuroblastoma. Medulloblastom. Metastases: Melanoma. Lung carcinoma. Colon carcinoma. Breast carcinoma.
• Some specialized areas of the brain have no blood-brain barrier and will normally enhance Choroid plexus. Pituitary glands. Pineal glands. Tuber cinereum. Area postrema.
• Tumor enhancement generally means Aggressive, high-grade neoplasms tend to have fenestrated capillaries (blood-brain barrier breakdown) allowing for enhancement.
• Postop granulation tumor versus residual tumor? Granulation tissue generally forms 72 hours after surgery. Early (less than 72 hours) postop enhancement likely reflects residual tumor rather than granulation tumor.
• Diffuse white matter radiation injury Unenhancing geographic white matter T2 hyperintensity conforming to radiation ports. Develops 6 months postradiation therapy.
• Radiation necrosis Indistinguishable from recurrent tumor on conventional imaging. May demonstrate mass effect and enhancement. Radiation necrosis may have elevated lactate peak (necrosis) on MRS. Recurrent tumor may have elevated choline peak and depressed n-acetyl aspartate (NAA) peak.
• Astrocytoma grades and types Grade I (pilocytic astrocytoma, subependymal giant cell astrocytoma). Grade II (lack necrosis and endothelial proliferation). Grade III (anaplastic astrocytoma). Grade IV (necrosis and endothelial proliferation, Glioblastoma multiforme).
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• Female predominant brain tumors Meningioma (4:1). Neurofibroma. Pineocytoma. Pituitary tumor.
• Male predominant brain tumors Pineal germinoma (10:1). Pineal parenchymal tumor (4-7:1). Medulloblastoma (3:1). Glioblastoma multiforme (3:2). Choroid plexus papilloma (2:1). CNS lymphoma. Hamartoma of tuber cinereum.
• Two neoplasms that may exhibit bihemispheric spread through the corpus callosum. Glioblastoma multiforme. CNS lymphoma.
• Intra-axial Lesions With Marked Surrounding Edema Metastases. Abscess. Glioblastoma multiforme. Radiation necrosis. Hematoma (mild).
• Hemorrhagic Brain Tumors Primary: Glioblastoma multiforme (most common overall). Oligodendroglioma. Metastasis: RCC. Thyroid carcinoma. Choriocarcinoma. Melanoma.
• Cerebral Ring-Enhancing Lesions MAGIC DR. Metastasis. Abscess. Glioblastoma multiforme. Infarct. Contusion. Demyelinating disease. Resolving hematoma. radiation necrosis.
• This MR sequence may help distinguish acute infarct from low-grade neoplasm. DWI. Infarct exhibitis restricted diffusion.
• Gliomatosis cerebri Rare neoplastic infiltration of at least three lobes of the brain. Poor prognosis. Diffuse involvement of cerebral white matter with or without a mass.
• In an adult with a heterogeneous calcified mass within the periphery of a frontal lobe with calvarial erosion and relative absence of edema should suggest the diagnosis of Oligodendroglioma.
• Oligodendroglioma features Grade II tumor. Commonly located in the frontal lobes. Often extends to cortex and may erode calvarium. 70% calcify.
• Calcified Glial Tumors in Order of Frequency Old Elephants Age Gracefully: Oligodendroglioma. Ependymoma. Astrocytoma. Glioblastoma multiforme.
• CNS lymphoma imaging characteristics Hyperdense and T1 hypointensity on T2WIs with surrounding vasogenic edema. Subependymal spread is common. Bihemispheric involvement via corpus callosum may be seen.
• Ganglioglioma and Gangliocytoma Ganglioglioma contains glial cells and differentiated neurons. Most common tumor seen with chronic temporal lobe epilepsy. Gangliocytoma and ganglioneuroma are pure neuronal tumors without glial components. Floor of third ventricle is the most common location for gangliocytoma.
• Desmoplastic Infantile Ganglioglioma Rare variant of ganglioglioma seen in the first year of life. Very large heterogeneous mass with intense enhancement.
• Most common tumor associated with medically refractory partial complex seizures Dysembryoplastic neuroepithelial tumor. Always involves cortical gray matter. May have “soap bubble” appearance with exophytic extension beyond cortical gray matter margin.
• Congenital Brain Tumors in Infants Younger Than 60 Days Old Teratoma (most common): Two thirds are supratentorial. Primitive neuroectodermal tumors: Curvilinear, sparse calcification. Astrocytoma. Choroid plexus papilloma. Ependymoma. Medulloepithelioma. Germinoma. Angioblastic meningioma. Ganglioglioma.
• Most (80% to 85%) metastatic lesions occur supratentorially, with the exception of ___________, which has a predilection for the posterior fossa. Renal cell carcinoma.
• Most Common Intra-axial Metastases to the CNS Lung. Breast. Melanoma. Colon cancer.
• Most Common Extra-axial Metastases to the CNS Breast. Prostate. Lung. Neuroblastoma.
• Most Common Hemorrhagic Metastases to the CNS Melanoma. Renal. Thyroid. Choriocarcinoma.
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• Leptomeningeal carcinomatosis Malignant invasion of leptomeninges. May mimic meningitis. Commonly involves basal cisterns. May present with cranial nerve palsies. Common malignancies: Breast. Lung. Lymphoma. Leukemia. Primary CNS malignancies.
• Most common primary cerebellar neoplasm in adult population. Hemangioblastoma.
• Most reliable way to differentiate a medulloblastoma from an astrocytoma on cross-sectional imaging studies is Noncontrast CT scan. Astrocytoma will usually be hypodense. Medulloblastoma will almost never be hypodense.
• Posterior Fossa Masses in Children: Medulloblastoma Most common pediatric CNS malignancy. Majority (85%) arise from cerebellar vermis. Commonly extends into fourth ventricle causing hydrocephalus. Highly malignant neoplasm (WHO grade IV). Hyperdense on CT. Hypointense on T1WIs. Variable on T2WIs.
• Posterior Fossa Masses in Children: Pilocytic astrocytoma Location: Cerebellar vermis. Hemisphere. Cystic with enhancing nodule.
• Posterior Fossa Masses in Children: Ependymoma Location: 4th ventricle. Appearance: Foraminal extension. Heterogeneous on CT and MR. Intense but heterogeneous enhancement.
• Posterior Fossa Masses in Children: Brainstem glioma Location: Brainstem. Appearance: Expansile brainstem. Isodense to hypodense on CT. Hypointense on T1WIs. Hyperintense on T2WIs.
• Most common brain tumor seen in neurofibromatosis type 1 (NF1) Pilocytic astrocytoma.
• Cystic cerebellar mass with an enhancing mural nodule suggests two possible diagnoses, and the best discriminator between the two is Age. Pilocytic astrocytoma, peak age of birth to 9 years. Hemangioblastoma, peak age of 35 years.
• Capillary hemangioblastomas Benign neoplasms of endothelial origin. Most common primary cerebellar neoplasm in adults. 4% to 20% occur as part of von Hippel-Lindau syndrome. Occur most often in cerebellar hemispheres and spinal cord. Well-defined cystic mass with an intensely enhancing mural nodule.
• Dysplastic Cerebellar Gangliocytoma (Lhermitte-Duclos Disease) Likely a hamartoma. Half of patients have Cowden disease (phacomatosis, colonic polyps, cutaneous tumors, meningioma, glioma, thyroid, breast neoplasms). CT often is normal. Striated cerebellar mass on T1and T2 WIs.
• Meningioma Most common extra-axial neoplasm of adults. Peak age of 50 to 60 years. Occur more commonly within women. Multiple tumors are associated with neurofibromatosis. Common locations: Parasagittal or convexity locations (50%). Sphenoid wing (20%). Olfactory groove/planum sphenoidale (10%). Parasellar region (10%). Hyerdense, hyperenhancing mass with variable surrounding edema. Calcification occurs in 10% to 20% of cases. Angiographically, early dense tumor blush that persists well into venous phase,
• Cerebral Intraventricular Masses Choroid plexus papilloma (24%). Choroid plexus carcinoma (2%). Ependymoma (18%). Subependymoma (11%). Central neurocytoma (10%). Subependymal giant cell astrocytoma (6%). All other astrocytomas (9%). Meningioma (6%). Colloid cyst (4%). Metastasis (2%).
• Most Common Lateral Ventricle Masses, by Location and Age: 0 - 10 yo, Ventricle Body PNET (Primitive neuroectodermal tumor). Teratoma. Choroid plexus papilloma.
• Most Common Lateral Ventricle Masses, by Location and Age: 0 - 40 yo, Ventricle Trigone Choroid plexus papilloma.
• Most Common Lateral Ventricle Masses, by Location and Age: 10 - 40 yo, Foramen of Monro Subependymal giant cell astrocytoma. Pilocytic astrocytoma.
• Most Common Lateral Ventricle Masses, by Location and Age: 10 - 40 yo, Ventricle Body Ependymoma. Pilocytic astrocytoma. Central neurocytoma.
• Most Common Lateral Ventricle Masses, by Location and Age: > 40 yo, Ventricle Body Subependymoma.
• Most Common Lateral Ventricle Masses, by Location and Age: > 40 yo, Ventricle Trigone Meningioma. Metastasis.
• Choroid Plexus Papilloma Most commonly occurs in lateral ventricle, especially in children. Increased intracranial pressure and hydrocephalus due to: Increased tumor production of CSF. Impaired CSF resorption (tumoral hemorrhage). CSF obstruction (mass effect). WHO grade I. May engulf glomus of choroid plexus. Choroid plexus calcification in first decade of life suggests choroid plexus papilloma.

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