【正文】 is predominantly black and there is a large flow artefact running in the phaseencoding direction. These findings correspond to rapid blood flow, and the mass must therefore be an aneurysm. Angiogram of the same patient. It demonstrates that the flow in the aneurysm is not laminar, but that it swirls, gradually filling the lumen with contrast. HamartomaHamartomas masses of dysplastic tissue found almost exclusively in young children. One of the most mon locations is the floor of the third ventricle. This is a pathology specimen showing a small nodule hanging in the suprasellar cistern. They are benign lesions, but patients do succumb to them because of the bad location. These are CT images of a hamartoma suspended from the floor of the third ventricle. It does not enhance after the administration of intravenous contrast. MR images of a similar small nodule suspended from the floor of the third ventricle. Hamartoma (red arrow) posterior to the enhancing pituitary gland and stalk.The best images to see hamartomas on are enhanced sagittal T1weighted MR images. Here you can see the nonenhancing hamartoma attached to the tuber cinereum between the pituitary stalk and mamillary body. There really is no differential diagnosis. Hypothalamic and Chiasm GliomaOptic nerve glioma in a patient with neurofibromatosisGliomas can occur in any part of the brain and the optic chiasm is a mon location, particularly in patients with neurofibromatosis type 1. This enhanced CT shows an example of an optic nerve glioma in a patient with neurofibromatosis. There is a suprasellar mass which is indistinguishable from the optic chiasm. Further forward at the level of the orbits the optic nerve is abnormal on both sides. These consecutive coronal MRimages show the mass at the optic chiasm and the swollen optic nerves. On these axial images you can see the optic nerves and chiasm enhance after the administration of intravenous gadolinium. The way a patient is normally positioned, slices through the nerves themselves are not obtained. These slices can be used to make oblique images along the axis of the nerves. With these images as a result. Note the enhancement of the nerve after intravenous contrast with sparing of the meninges. Approximately 25% of optic nerve gliomas do not enhance, so a lack of enhancement should not prevent you from making the diagnosis. This is another example of a rightsided optic nerve glioma with enhancement after gadolinium. Note the normal pituitary gland and stalk. GerminomaGerminoma (Courtesy of Dr. Susan Blaser)The following case concerns a 9yearold male with a history of headache, nausea and vomiting.Sagittal T1 images before and after intravenous contrast show a mass in the midline, on the floor of the third ventricle. The mass enhances after gadolinium.Continue with next images. T2 and T1 weighted sagittal images of the same patient show a similar mass in the epiphysial area. This is a germinoma an intracranial germ cell tumor that occurs primarily in children and adolescents. These are typical localisations.These lesions crawl along the floor of the 3rd ventricle. ChordomaChondromas are the most mon lesions of the clivus, also a favored location for metastases and chondrosaras. This patient has a normal pituitary gland. Posterior to this is a large, fungating mass positioned at the level of the clivus. The CT shows some calcifications in this area. The differential diagnosis for this mass would be chondroma or chondrosara. Chordomas tend to occur in the midline, whereas chondrosaras tend to occur off the midline. MetastasesThe patient on the left is a patient with lung cancer who presented with a sixth cranial nerve palsy. The abnormality is in the clivus, which should have a high signal intensity on this sagittal T1weighted image (as in the image on the left). A low signal intensity means the normal fatty marrow has been replaced by some other tissue. In this case by tumor metastasis. Also lymphomas, myelomas or diffuse bone abnormalities can give this appearance. Therefore always take a minute to look at the clivus. So again in order to analyse a sellar or parasellar mass on MRI we use the following anatomic approach: 1. First identify the pituitary gland and sella turcica. 2. Then determine the epicenter of the lesion and whether it is in the sella or above, below or lateral to the sella. 3. If it is in the sella, determine whether or not the sella is enlarged. 4. Once the location of the mass is clear, analyze the signal intensity patterns: is the lesion cystic or solid? 5. Does it contain any abnormal vessels? 6. Are there any calcifications? And so on. 7. Finally establish a Differential Diagnosis. 寧可累死在路上，也不能閑死在家里！寧可去碰壁，也不能面壁。是狼就要練好牙，是羊就要練好腿。什么是奮斗？奮斗就是每天很難，可一年一年卻越來越容易。不奮斗就是每天都很容易，可一年一年越來越難。能干的人，不在情緒上計(jì)較，只在做事上認(rèn)真；無能的人！不在做事上認(rèn)真，只在情緒上計(jì)較。拼一個(gè)春夏秋冬！贏一個(gè)無悔人生！早安！—————獻(xiàn)給所有努力的人.學(xué)習(xí)好幫手