Radiologic Evaluation of Intracranial Tumors
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Radiologic Evaluation of Intracranial Tumors Todd Gourdin M-IV Radiology Final Presentation August 2, 2007
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Available Modalities 1)X-ray 2)CT 3)MRI 4)Nuclear Medicine
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X-ray Primarily of historical interest since the onset of CT in 1974. Was useful for detecting increased intracranial pressure and intracranial calcifications.
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CT Most intracranial neoplasms are visible on CT Tumors may be hypodense, isodense, or hyperdense on a noncontrast CT depending on tumor histology and location
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Pilocytic Cerebellar Astrocytoma
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Small tumors or isodense tumors may be missed on noncontrast CT but highlight after contrast administration - Meningiomas and Neuromas enhance strongly with contrast while low-grade gliomas and epidermoid tumors do not enhance.
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Why not MRI them all??? MRI is generally preferable to CT for evaluating intracranial neoplasms CT is preferred for visualizing tumor calcification or intratumor hemorrhage.
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Commonly Calcified and Hemorrhagic Lesions Calcified Hemorrhagic Oligodendroglioma Glioblastoma multiforme Choroid Plexus tumor Oligodendroglioma Ependymoma Metastatic: Central neurocytoma Melanoma Craniopharyngioma Breast Teratoma Lung Chordoma
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MRI Usually the preferred method of imaging intracranial tumors due to better soft-tissue contrast MRI exploits increased water content of many neoplasms. This water content shows up as increased signal on T2 weighted images and decreased signal on T1 Images.
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Noncontrast MRI of Meningioma T2 T1
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Contrast(often IV Gadolinium) helps visualize small tumors that don’t cause much edema.
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Advanced MRI Techniques “This stuff is complicated!!!!”
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Proton Magnetic Resonance Spectroscopy Analyzes the biochemical makeup of a tumor to create a characteristic spectroscopic pattern. - Computer analysis of the pattern allows histologic type to be determined non-invasively.
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Figure 98-3 Proton magnetic resonance spectroscopy; the choline peak (3.22 p.p.m.) is elevated, the creatine peak (3.03 p.p.m.) is low and the N-acetyl aspartate peak (2.01 p.p.m.) is nearly undetectable; characteristic spectroscopic appearance of gliomas (choline—CHO; creatine—PCr/Cr; N-acetyl aspartate—NAA). “Grainger and Allison’s Diagnostic Radiology, 2001”
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Perfusion weighted MRI Technique used to determine the relative cerebral blood volume (rCBV) of intracranial structures. - Many tumors are highly vascularized allowing them to be distinguished from the background on a perfusion weighted MRI.
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Meningioma T2 Contrasted T1 Perfusion-Weighted
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MRI-guided Surgery A variety of techniques have been developed to incorporate MRI into the surgical process for intracranial tumor resection: MRI guided stereotactic biopsy Brain surface imaging Interventional MRI
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Brain Surface Imaging
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Nuclear Medicine SPECT(Single Photon Emission Computed Tomography) Gamma rays emitted during radionuclide decay are detected by a gamma camera that rotates about the patient’s head - The radionuclides must cross the blood-brain barrier
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Radionuclides preferentially taken up by intracranial neoplasms include: 201 TI Chloride 99m Tc MIBI 123 I a-methyl tyrosine 111 In octreotide - Can be used for example in distinguishing between benign lesions, low-grade gliomas, and high-grade gliomas
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SPECT of Normal Brain Radionuclide = 99m TC
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201 T1 SPECT Diagnosed by SPECT as a high-grade glioma and confirmed post-resection
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PET(Positron Emission Tomography) Similar to SPECT but the radioisotopes used decay to produce positrons These positrons quickly combine with an adjacent electron to produce two gamma rays that travel in opposite directions. Detection of these gamma rays allows calculation of their exact point of origin. Can evaluate different brain processes depending on the radioisotope selected
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Radionuclides useful for PET analysis of intracranial tumors include: Fluorodeoxyglucose C methionine F a-methyl tyrosine
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Advantages of PET over SPECT: - Can be used to quantify emission Better resolution Disadvantages of PET: Cost Limited availability Need for a cyclotron(particle accelerator)
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PET scan of Language Center Figure 98-4 H215O PET activation study during a language task in a young man with a right frontal glioma, before neurosurgical resection. Language activation is seen bilaterally and is distant from the tumour. “Grainger and Allison’s Diagnostic Radiology, 2001”
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Classification of Intracranial Neoplasms 1)Neuroepithelial Origin – astrocytoma, oligodendroglioma, ependymoma, mixed glioma, choroid plexus tumor, neuronal tumor, pineal tumor. -Gliomas(astrocytomas, oligodendroglioma, ependymoma) = approximately 50% of primary brain tumors -Graded from 1 -4 based on severity -Grade 4 = Glioblastoma Multiforme – most common primary intracranial neoplasm
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GBM Hallmark finding is tumor necrosis Often cross the midline Extremely poor prognosis
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2)Tumors of Nerve Sheath – Schwannoma, Neurofibroma - These are cranial nerve sheath tumors that show marked enhancement with IV contrast
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Bilateral schwannomas in NF type 2
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3)Meningeal tumors – meningioma Originate from “arachnoid cell rests” in the dura matter Commonly arise from parasagittal region, cerebral convexities, sphenoid ridge, and olfactory groove Often contain calcifications and enhance well with IV contrast Represents approximately 15% of primary intracranial tumors
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4)Lymphoma 2-3% of intracranial neoplasms Well defined, rounded lesions that appear hyperdense on noncontrast CT and enhace well with contrast Lymphomas may appear “atypical” in the immunocompromised
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Lymphoma on noncontrast/contrast CT
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5)Metastasis Usually multiple lesions which help distinguish them from supratentorial gliomas Often found at grey/white matter junction
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6)Additional classes include: germ cell tumors, dermoid/epidermoid cysts, sellar/pituitary tumors,
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Some famous people who have suffered from a brain tumor
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References Harvard University Dept. of Radiology www.brighamrad.harvard.edu LSU Dept. of Radiology www.medschool.lsuhsc.edu University of South Carolina Dept. of Radiology www.radiology.med.sc.edu Grainger and Allison’s Diagnostic Radiology: A Textbook
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Grainger and Allison’s Diagnostic Radiology: A Textbook of Medical Imaging, 4th ed. 2001 Churchill
Grainger and Allison’s Diagnostic Radiology: A Textbook of Medical Imaging, 4th ed. 2001 Churchill Livinstone Inc., 2001.
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