 Today, brain tumors and masses. We have a young adult teenager with an intracranial mass. An axial T1-weighted image without contrast shows bithylamic hypointensity with mass effect, although the ventricles are not very enlarged. Following contrast administration, there is little to scant enhancement. A T2-weighted image shows the lesion across the midline with surrounding perilesial edema. The flare sequence adds little more to the diagnosis. Let's begin with our first question. Question number one. The most common primary brain tumor of the adult is A, neurocytoma, also known as central neurocytoma. B, meningioma. C, polycytic astrocytoma. D, glioblastoma multiforme. E, anaplastic astrocytoma. Take a minute, generate your answer or pause. Question number two. The most common glial neoplasm is A, ependymoma. B, glioblastoma multiforme. C, astrocytoma. D, oligodendroglioma. You can pause. Take a moment to generate your answer. Question number three. Who or world health organization grade one neoplasmic lesions include all of the following except amen and geoma. B, pituitary adenoma. C, schwannoma. D, epidermoid. Might have to think about this one a little bit. Let's go to question number four. Which of the following statements is false? A, glioblastoma is a world health organization grade four lesion. B, pleomorphic xanthoastrocytoma is a grade three lesion. C, polycytic astrocytoma is most commonly a grade one lesion. D, anaplastic astrocytoma is a grade three lesion. E, pillow mixoid astrocytoma is a grade two lesion. Let's attack the answers, shall we? Let's go to question number one. Most of you would have said that glioblastoma multi-forming was the most common primary brain tumor of the adult. If the choice was glioneoplasm, then that would be true. But glioblastoma is a subset making up about 50 to 52% of all glioneoplasms. Therefore, by subsetting it, meningioma, which is 27% of all intracranial primary tumors, is the correct answer. The correct answer is B, not E, not E. Neurocytoma is far less common. And polycytic astrocytoma is another subset of astrocytic neoplasm seen in young individuals. Question number two. The most common glioneoplasm is, I just gave you that answer, glioblastoma multi-forming making up at least 50% or more of all glioneoplasms, which is most unfortunate. Question number three. Who, or World Health Organization, grade one neoplastic lesions include all of the following except. The answer is epidermoid. Epidermoid is not a neoplasm. It is a developmental inclusion. The other three are neoplasms, and they are who grade one lesions. Finally, question number four. This is the toughest of the questions, and they do ramp up in difficulty. Which statement is false? Yes, glioblastoma is a grade four. Pleomorphic xanthroastrocytoma is not a who grade three. It is a who grade two. And that is the false answer. Polycytic astrocytoma, while there is a grade two variant, it is far less common. It is almost always a grade one lesion with a very good prognosis. D, anoplastic astrocytoma is a grade three, and E, pillow myxoid astrocytoma is a grade two on par with the PXA or pleomorphic xanthroastrocytoma. So the answer, the false answer to this question is B. A few items to discuss as we introduce brain tumors. First, as a basic approach, the first thing I do is where is the lesion, extraxial, intraaxial, or intraventricular? Where is the lesion? Is it supertentorial, more common in adults, or infratentorial, more common in children, with the exception of the corioplexus tumor? How old is the patient? Child, adult, infant, neonate. What about the sex of the patient? Often irrelevant, but relevant in some cases like meningioma, which is more common in females. Let's talk about the approach to astrocytomas and brain tumors by histology, using the central brain tumor registry of the United States, which includes over 37,000 primary central nervous system tumors. Meningioma, at 27.4%, is the most common. But all types of glioma combined. If you're given the choice glioma, you answer glioma over meningioma. How does glioma break down? Well, GBM, 52% of gliomas. Astrocytoma, 22% of gliomas. Oligo, 4%, a big drop-off. Endomomas, 2.2%. Nerve sheath tumors, 7.5%. Potuitary tumors, 6.6%. Lymphoma, 2.7%. Embryonal tumors, like medullo, 1.9%, and all other, 12.6%. The other thing I try and do with brain tumors is not only do I divide them up, intraaxial, extraaxial, intraventricular, but I also try and figure out whether they are primary intraaxial, secondary intraaxial, primary extraaxial, secondary extraaxial. The extraaxial non-glial neoplasms include meningioma, schwannoma, and pituitary neoplasms. The intraaxial neoplasms are going to be overwhelmingly glial, but there will be some others. Let's stop right there and move on to our next case. Shall we?