Investigation of choice for posterior fossa tumors?

Ans. d (MRI). (Ref. Allison & Grainger, Diagnostic Radiology, 4th ed., 2327).BRAIN TUMOR IMAGING# Tumors of brain are usually better demonstrated on MRI than on CT due to greater inherent soft tissue contrast.# An additional advantage of MRI is its ability to provide direct multiplanar imaging which helps to define the relation- ship of the tumor to adjacent structures & thus helps in planning of surgery & facilitates the distinction between intra- axial & extra-axial tumors.# MRI is vastly superior to CT in evaluating posterior fossa tumors as CT is frequently hampered by 'beam - hardening artifact' from the base of skull.# Positron emission tomography (PET) and single-photon emission tomography (SPECT) have ancillary roles in the imaging of brain tumors, primarily in distinguishing tumor recurrence from tissue necrosis that can occur after irradiation.# Functional imaging with PET, MRI, magnetoencephalography may be useful in surgical/radiosurgical planning.Guidelines for the Use of CT, Ultrasound, and MRI in CNSConditionRecommended TechniqueHemorrhageAcute parenchymalCT, MRSubacute/chronicMRISubarachnoid hemorrhageCT, CTA, lumbar puncture angiographyAneurysmAngiography > CTA, MRAIschemic infarction Hemorrhagic infarctionCT or MRIBland infarctionMRI > CT, CTA, angiographyCarotid or vertebral dissectionMRI/MRAVertebral basilar insufficiencyCTA, MRI/MRACarotid stenosisCTA > Doppler ultrasound, MRASuspected mass lesionNeoplasm, primary or metastaticMRI + contrastInfection/abscessMRI + contrastImmunosuppressed with focal findingsMRI + contrastVascular malformationMRI +/- angiographyWhite matter disordersMRIDemyelinating diseaseMRI +/- contrastDementiaMRI > CTTraumaAcute traumaCT (noncontrast)Shear injury/chronic hemorrhageMRIHeadache/migraineCT (noncontrast) / MRISeizureFirst time, no focal neurologic deficitsCT as screen +/- contrastPartial complex/refractoryMRI with coronal T2W imagingCranial neuropathyMRI with contrastMeningeal diseaseMRI with contrastSpineLow back painNo neurologic deficitsMRI or CT after 4 weeksWith focal deficitsMRI > CTSpinal stenosisMRI or CTCervical spondylosisMRI or CT myelographyInfectionMRI + contrast, CTMyelopathyMRI + contrast > myelographyArteriovenous malformationMRI, myelography/angiographyEducational points:# Glial tumors account for 50-60% of primary brain tumors, meningiomas for 25%, schwannomas for 10%, and other CNS tumors for the remainder.0# Gliomas and primary CNS lymphomas are associated with an increased risk for deep vein thrombosis and pulmonary embolism.# Tumors with astrocytic cytologic features are the most common primary intracranial neoplasms.# Pilocytic astrocytoma (Spindle-shaped cells), is the most common childhood brain tumor and is typically benign.- It frequently occurs in the cerebellum. Q# For primary glial tumors, radiation is generally administered to the tumor mass, as defined by contrast enhancement on a CT or MRI scan, plus a 2-cm margin.- A total dose of 5000-7000 cGy is administered in 25-35 equal fractions, 5 days per week.# The lung is the most common origin of brain metastases. Q# Temozolomide, an orally administered alkylating agent, has replaced nitrosureas, including carmustine (BCNU) and lomustine (CCNU), as the most widelx used chemotherapeutic agent for high-grade gliomas.