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Neuroanatomie (Subject) / Alles (Lesson)

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• Central neurocytoma Arises from septum pellucidum or ventricular wall. 50% occur in lateral ventricle near foramen of Monro. May be bilateral. Most patients (75%) are between 20 and 40 years. Well-circumscribed lobulated mass within lateral or third ventricles. Hyperdense at CT. Cystic elements (Swiss cheese) and calcification are common.
• Subependymoma WHO grade I. Most are asymptomatic. Well-circumscribed lobulated intraventricular mass. Isodense to hypodense at CT. Frequent calcification (33%) and cystic degeneration (20%). Low T1 and high T2 signal. Hypointensity on T1WIs and hyperintensity on T2WIs are seen on MR. Enhancement not as diffuse as in central neurocytoma.
• Subependymal giant cell astrocytoma Seen in 10% of patients with tuberous sclerosis (look for subependymal and cortical hamartomas). WHO grade I. Commonly calcifies. and slow-growing, with calcification a common feature. Almost always produces some degree of hydrocephalus.
• Colloid cyst Occurs in anterosuperior portion of third ventricle near foramen of Monro. Can cause acute hydrocephalus. Almost all are hyperdense. Variable T1 and T2 signal.
• Masses of the Anterosuperior Third Ventricle Colloid cyst. Meningioma. Choroid plexus papilloma. Hamartoma. Glioma. Vascular lesion. Granulomatous disease.
• Most common neoplasm of pineal region Germ cell tumors
• Calcified pineal mass in a female is more likely to be Pineocytoma. In a male more likely to be a germinoma.
• When calcification in the pineal region exceeds ____ in size, a pathologic pineal process should be suspected. 1 cm.
• Cerebral Germ cell tumors Well-defined, usually midline masses. 65% occur in pineal region (male more than female). 60% of all pineal masses. 35% are suprasellar (male = female). Germinoma is by far the most common. Commonly seen in children and young adults.
• Pineal region masses Germ Cell Tumors (60%): Germinoma. Teratoma. Embryonal carcinoma. Endodermal sinus tumor. Choriocarcinoma. Pineal Parenchymal Tumors (14%): Pineocytoma. Pineoblastoma. Other: Pineal cyst, glioma, tentorial meningioma, vein of galen malformation, arachnoid cyst, lipoma.
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• Pineoblastoma Similar to medulloblastoma, part of PNET spectrum. Majority occur in young children. Well-circumscribed, often lobular. Local invasion and frequent calcification. WHO grade IV. Rarely may occur with bilateral retinoblastomas, the so-called trilateral retinoblastoma.
• Pineocytoma Most commonly seen in adults (women more than men). Usually well demarcated, noninvasive, and slow growing. Often calcified. Rarely metastasizes. At imaging, cant be differentiated from pineal germinoma or pineoblastoma.
• Pineal cysts Are common. Signal similar to or slightly higher than CSF, likely due to lack of CSF puslation. No enhancement.
• Pituitary adenomas Most common sellar masses. Microadenomas (10 mm or smaller). Macroadenomas (>10 mm). 75% are hormonally active, most of which are microadenomas. Lateral gland generally contains prolactin and growth hormone secreting adenomas. Central gland generally contains ACTH, TSH, FSH secreting adenomas. Microadenomas best detected on coronal T1WIs: Focal hypointensity (on noncontrast studies).
• Craniopharyngioma Arise from squamous epithelial remnants of anterior lobe of pituitary gland. Commonly are symptomatic due to large size. Most common suprasellar mass in children. Peak incidence between 5 and 10 years of age and 50 and 60 years. Solid and cystic components are typical. Large cystlike sellar/suprasellar mass with enhancing rim and some calcification. T1 (liquid crystal) and T2 hyperintense cyst.
• Rathke cleft cyst Arise from squamous epithelial remnants of anterior lobe of pituitary gland. Usually asymptomatic. Cyst may contain mucus, serous fluid, or cellular debris. Variable signal intensities. May mimic craniopharyngioma.
• Schwannoma Arises from Schwann cells. Commonly affects vestibulocochlear (VIII) and trigeminal (V) nerves. Cystic degeneration is common, especially in larger lesions. T1 hypointense to gray matter and T2 hyperintense to gray matter. Intense enhancement.
• Most helpful imaging feature in distinguishing vestibular schwannomas Extension of enhancement along course of seventh and eighth nerves.
• Suprasellar Masses SATCHMO Sella (pituitary) tumor. Sarcoid. Aneurysm. Arachnoid cyst. Teratoma. Craniopharyngioma. Hypothalamic glioma. Hamartoma of tuber cinereum. Histiocytosis. Meningioma. Optic nerve glioma.
• Cerebellopontine Masses AMEN Acoustic (vestibular) schwannoma. Meningioma. Ependymoma. Neuroepithelial cyst (arachnoid, epidermoid).
• Epidermoid versus Dermoid Epidermoid: Common. 40 to 50 yo. Ectoderm. Off midline (cerebellopontine cistern, parasellar, posterior fossa). Follows CSF, except hyperintense on DWI. Lobulated with peripheral enhancement. Dermoid: Uncommon. 20 to 30 yo. Ectoderm and mesoderm. Midline (pericerebellar, suprasellar). Typical fat attenuation or signal.
• Intracranial lipomas Occur within all age groups. Most common locations: Interhemispheric falx (often associated with agenesis of corpus callosum). Quadrigeminal plate. Suprasellar regions. Chemical shift artifact or fat suppression. Presence of flow void or traversing cranial nerve favors lipoma and excludes dermoid.
• Arachnoid cysts Are intra-arachnoidal. 50% occur in middle cranial fossa. Other sites: Frontal convexity. Suprasellar and quadrigeminal cisterns. Posterior fossa. Follow CSF signal and density. May remodel adjacent bone. Do not restrict diffusion. Enlarged cisterna magna fills immediately at cisternography
• Hamartoma of tuber cinereum Rare congenital hamartoma. More common in boys. Precocious puberty, gelastic seizures, developmental delay, and hyperactivity. Well-circumscribed, round or oval mass centered at the tuber cinereum (base of infundibulum). Does not calcify or hemorrhage. Stalk connecting mass with tuber cinereum or mamillary bodies cinches diagnosis.
• Intracranial tuberculoma Granuloma with central caseous necrosis. Isodense or slightly hyperdense nodules or small mass lesions.
• Brain Coccidioidomycosis Occurs in southwestern United States. Focal parenchymal granulomas are rare. Hydrocephalus is common from complicating meningitis.
• Brain Blastomycosis Occurs in Ohio and Mississippi River valleys. Frequently presents with meningitis with parenchymal abscesses and granulomas less likely. Epidural granulomas and abscesses also occur usually from direct extension from bone infection.
• Brain Histoplasmosis Occurs in Midwest and southern United States. Meningitis is most common. Multiple or solitary granulomas may occur.
• CNS Aspergillosis Parenchymal disease usually takes the form of an abscess. Granulomas are unusual. Abscesses are often multiple with irregular ring enhancement. Subcortical or cortical infarcts and hemorrhage from blood vessel invasion may occur.
• CNS Mucormycosis Invades brain usually by direct extension from sinuses, nose, or oral cavity. Almost all patients are diabetic or immunocompromised. Tends to invade blood vessels. Lesions are often in the base of the brain, adjacent to diseased sinuses. Infarcts, intra-axial or extra-axial hemorrhage, and meningeal enhancement can be seen with CT or MR.
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• CNS Candidiasis Usually causes meningitis. Granulomas and small abscesses may occur. Meningeal enhancement or multiple small enhancing granulomas or microabscesses are usually seen.
• Most frequently reported CNS fungal infection. Cryptococcosis.
• CNS Cryptococcosis 50% occur in immunocompetent patients. Common infection in patients with AIDS. Usually presents as meningitis. Granulomas can occur and are usually multiple. Abscesses are less common. CT scans can be normal. Cryptococcomas are small, usually multiple, solid-enhancing, peripheral parenchymal nodules. Gelatinous pseudocysts can be seen.
• Gelatinous pseudocyst Cystic lesion usually in basal ganglia. Perivascular spaces filled with cryptococcal organisms. Usually found only in immunocompromised.
• Cysticercosis Caused by larvae of pork tapeworm Taenia solium. Ingested eggs hatch in intestine and larvae are hematogenously distributed, forming cysticerci. 3 stages of CNS disease: Early phase, edema and/or nodular enhancement. Later, peripheral viable cysts. Scolex may be seen as small mural nodule. Late phase, peripheral calcifications without edema or enhancement.
• Echinococcosis Caused by dog tapeworm. More commonly involves liver and lungs, but brain can rarely be involved. Cysts are usually solitary, unilocular, large, round, and smoothly marginated. Most often supratentorial, in the middle cerebral artery territory.
• Congenital CNS toxoplasmosis Atrophy, dilated ventricles, and calcifications. Periventricular white matter, basal ganglia and cerebral hemisphere calcifications. In CMV, calcifications are usually periventricular only.
• Amebic meningoencephalitis Amebae enter nasal cavity of patients swimming in infested water. Direct extension through cribriform plate to the brain. Severe meningoencephalitis results and is usually fatal. Early in infection, meninges and gray matter may enhance. Later, diffuse cerebral edema ensues.
• Neurosyphilis Symptomatic patients may have aseptic meningitis, tabes dorsalis, general paresis, or meningovascular disease. Imaging is usually normal in tabes dorsalis, rarely gummas are found: small enhancing nodules on brain surface with adjacent meningeal enhancement. Meningovascular syphilis thickening of meninges and medium to large vessel arteritis.
• CNS Lyme disease 2 Forms. Cranial neuritis: Thick, enhancing nerves. CNs III to VIII may be involved (CN VII most common). Parenchymal form: Multiple small white matter lesions. Similar to multiple sclerosis. Lesions may have nodular or ring enhancement. Meninges may enhance.
• Cytomegalovirus, congenital CNS infection Most common CT findings: Periventricular calcification. No calcifications of basal ganglia or cortices as seen congenital toxoplasmosis.
• Neonatal herpes simplex encephalitis Early in course: Diffuse brain swelling or bilateral patchy areas of decreased density (hypoechoic, too) in cerebral white matter and cortex. Sparing of basal ganglia, thalami, and posterior fossa structures. Multicystic encephalomalacia is the end result.
• Adult herpes simplex CNS infection May cause encephalitis or cranial neuritis. 70% mortality rate in untreated patients. Ill-defined hypodensities within one or both temporal lobes. Virus is usually latent within gasserian ganglion. Frontal lobes may be involved. Insular cortex is often involved, but adjacent putamen is spared. Usually swelling with mass effect. Streaky enhancement is variable. The CT findings are not usually seen before the fifth day of symptoms. Increased FLAIR and T2 signal within temporal and/or frontal lobe(s) with sparing of putamen. Middle cerebral artery infarct (often involves putamen, unlike herpes).
• Ramsay Hunt syndrome Herpes zoster facial neuritis. Ear pain, facial paralysis, vesicular eruption about the ear. MR may reveal increased enhancement of facial nerve.
• Acute disseminated encephalomyelitis (ADEM) May occur after viral infection, following a vaccination, or spontaneously. When treated early with steroids, most patients make a full recovery. Increased T2 and FLAIR signal within white matter of brainstem, cerebellum, and basal ganglia. Optic neuritis is also common.
• Subacute sclerosing panencephalitis caused by variant of measles virus. Occurs in children and young adults who had measles before age 2, after a 6- to 10-year asymptomatic period. Causes progressive dementia, seizures, and paralysis, leading to death. Initially may have focal lesions in gray matter and subcortical white matter. Later, periventricular white matter lesions may enhance. Late stages usually is profound cortical atrophy.
• Progressive multifocal leukoencephalopathy (PML) Demyelinating disease caused by a papova virus. Occurs only in immunosuppressed patients, especially in AIDS.
• Creutzfeldt-Jakob disease Caused by a prion. Rapidly progressive dementia, ataxia, and myoclonus, leading to death. Early stage, high DWI signal within cerebral cortex and basal ganglia. Later stage, atrophy and increased T2 and FLAIR signal within cortex and basal ganglia.
• Meningitis forms causing thick meningeal enhancement (pachymeningeal) Tuberculous meningitis. Fungal meningitis. Racemose cysticercosis. Sarcoidosis.
• Most common AIDS CNS infections HIV encephalopathy. Toxoplasmosis. Cryptococcosis. Other fungal infections. CMV and Herpes meningoencephalitis. Mycobacterial infection. PML. Meningovascular syphilis.

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