KEY FACTS Terminology Nonneoplastic cyst arising from remnants of embryonic Rathke cleft Benign sellar region endodermal cyst lined by ciliated, mucus-producing epithelium Imaging Nonenhancing, noncalcified, intrasellar &/or suprasellar cyst with intracystic nodule Completely intrasellar (40%), suprasellar extension (60%) Density/signal intensity varies with cyst content (serous vs. mucoid) Most symptomatic Rathke cleft cysts (RCCs): 5-15 mm in diameter Occasionally, RCCs can become very large Claw sign =…

KEY FACTS Terminology Acute clinical syndrome with headache, visual defects/ophthalmoplegia, altered mental status, variable endocrine deficiencies Caused by either hemorrhage or infarction of pituitary gland Preexisting pituitary macroadenoma common Imaging CT Sellar/suprasellar mass with patchy or confluent hyperdensity Peripheral enhancement, ± hemorrhage May be associated with subarachnoid hemorrhage MR Enlarged, hypointense (hemorrhagic), or hyperintense (nonhemorrhagic) pituitary on T2WI T2* (SWI/GRE) “blooming” (best sequence if blood products…

KEY FACTS Terminology Benign neoplasm of adenohypophysis Imaging Upward extension of macroadenoma = most common suprasellar mass in adults Best imaging technique MR with sagittal/coronal thin-section imaging through sella + T1 C+ with FS Sellar mass without separate identifiable pituitary gland = macroadenoma Mass is pituitary gland Usually isointense with gray matter Enhance strongly, often heterogeneously Cavernous sinus invasion difficult to determine Top Differential Diagnoses Pituitary…

KEY FACTS Terminology Microadenoma: ≤ 10 mm in diameter Imaging Intrasellar mass is typical location Rare: Ectopic origin outside pituitary fossa Best technique = dynamic contrast-enhanced thin-section T1-weighted MR Generally enhance more slowly than adjacent normal pituitary Beware: 10-30% can be seen only on dynamic contrast-enhanced scans Occasionally, adenoma may be cystic or hemorrhagic Intrapituitary “filling defect” may be benign nonneoplastic cyst, as well as incidental…

KEY FACTS Terminology Congenital anomalies of pituitary stalk → potential hypothalamic/pituitary axis malfunction Imaging Posterior pituitary ectopia (PPE) Duplicated pituitary gland/stalk (DP) PPE: No (or tiny) pituitary stalk, ectopic posterior pituitary on midline sagittal T1WI MR Look for associated anomalies: Heterotopia, optic nerve hypoplasia, corpus callosum anomalies DP: 2 pituitary stalks on coronal view, thick tuber cinereum on midline sagittal view Top Differential Diagnoses PPE Surgical…

Gross Anatomy Sella Bony anatomy : The sella turcica (“Turkish saddle”) is a concave, midline depression in the basisphenoid that contains the pituitary gland (also called the hypophysis). The anterior borders of the sella are formed by the anterior clinoid processes of the lesser sphenoid wing and the tuberculum sellae, whereas the posterior border is formed by the dorsum sellae. The top of the dorsum sellae…

KEY FACTS Terminology Hydrocephalus Enlargement of cerebral ventricles secondary to abnormal cerebrospinal fluid (CSF) formation, flow, or absorption resulting in ↑ CSF volume Imaging Shunt failure → dilated ventricles + edema around ventricles, along catheter and reservoir Use CT or MR to evaluate ventricle size, plain radiograph shunt series to identify mechanical shunt failure Baseline CT/MR following shunt insertion, follow-up at 1 year and as clinically…

KEY FACTS Terminology Normal pressure hydrocephalus (NPH) Ventriculomegaly with normal cerebrospinal fluid (CSF) pressure, altered CSF dynamics Imaging Enlarged lateral & 3rd ventricles, 4th ventricle relatively normal Disproportionately large ventricles compared with subarachnoid spaces (particularly sylvian fissures and basal cisterns) Subarachnoid spaces over convexity may appear effaced Periventricular T2/FLAIR hyperintensity ↓ regional cerebral metabolism on F-18 FDG PET In-111 DTPA cisternography Prominent ventricular reflux, with no…

KEY FACTS Terminology Focal reduction of cerebral aqueduct diameter Imaging Ventriculomegaly of lateral and 3rd ventricles with normal-sized 4th ventricle ± periventricular interstitial edema (uncompensated hydrocephalus) Multiplanar MR with sagittal 3D-heavy T2WI sequences and sagittal cardiac-gated cine MR Top Differential Diagnoses Obstructing extraventricular pathology Neoplasm Vein of Galen malformation Quadrigeminal cistern arachnoid cyst Obstructing intraventricular (aqueductal) pathology Postinflammatory gliosis (aqueductal gliosis) Rhombencephalosynapsis Pathology Congenital aqueductal stenosis…

KEY FACTS Terminology Extraventricular obstructive hydrocephalus (EVOH): Enlarged ventricles due to mismatch between cerebrospinal fluid (CSF) formation, absorption Synonym: “Communicating” hydrocephalus Imaging Impaired absorption of CSF distal to 4th ventricle outlet foramina Ventricular size varies with duration of obstruction All ventricles enlarged with no intraventricular obstructive cause Lateral, 3rd, and 4th ventricles dilated ± periventricular white matter interstitial edema ± abnormal density/intensity of cisternal CSF ±…

KEY FACTS Terminology Intraventricular obstructive hydrocephalus (IVOH) = obstruction proximal to foramina of Luschka, Magendie Acute (aIVOH) Chronic “compensated” (cIVOH) Imaging aIVOH = “ballooned” ventricles plus indistinct (“blurred”) margins “Fingers” of CSF extend into periventricular white matter Most striking around ventricular horns (periventricular “halos”) After decompression, corpus callosum may show hyperintensity cIVOH = “ballooned” ventricles without periventricular “halo” Top Differential Diagnoses Ventricular enlargement secondary to parenchymal…

KEY FACTS Terminology Cystic CSF cavity of septum pellucidum (SP) Occurs ± cavum vergae (CV) Imaging Elongated finger-shaped CSF collection between lateral ventricles Cavum septi pellucidi (CSP): Between frontal horns of lateral ventricles CV: Posterior extension between fornices CV is posterior extension of CSP Size varies from slit-like to several mm, occasionally > 1 cm SP invariably cystic in fetus Width of fetal CSP increases between…

Gross and Imaging Anatomy Ventricles and Choroid Plexus Basic embryology : Early in embryonic development, the forebrain cavity divides into 2 lateral ventricles, which develop as outpouchings from the rostral 3rd ventricle and are connected to it by the interventricular foramen (a.k.a. foramen of Monro). In the coronal plane, these form a central H-shaped “monoventricle.” The cerebral aqueduct develops from the midbrain vesicle. The 4th ventricle…

KEY FACTS Terminology Inferior olivary nucleus (ION) degeneration Unique type of transsynaptic neuronal degeneration Olivary deafferentation thought to be source of ensuing hypertrophic olivary degeneration (HOD) Usually caused by primary lesions in dento-rubro-olivary pathway (anatomical triangle of Guillain-Mollaret) Triangle of Guillain-Mollaret defined by 3 anatomic structures Dentate nucleus (DN) of cerebellum Ipsilateral red nucleus (RN) ION ipsilateral to RN Imaging ION initially hypertrophies rather than atrophies…

KEY FACTS Terminology Diaschisis = sudden loss of function in brain connected to (but at distance from) damaged area Crossed cerebellar diaschisis (CCD) = decreased blood flow/metabolism in cerebellar hemisphere contralateral to supratentorial infarct Imaging Acute: CT/MR perfusion shows ↓ cerebral blood flow (CBF) in cerebellar hemisphere opposite acute hemispheric infarct ↑ Time to peak, ↓ CBF in cerebellum contralateral to infarct Add DTI as subtle…

KEY FACTS Terminology Spinocerebellar ataxias (SCAs) Spinocerebellar atrophy; spinocerebellar degeneration Previously known as Marie ataxia, inherited olivopontocerebellar atrophy, spinocerebellar degeneration Inherited progressive neurodegenerative disorders Clinically, genetically very heterogeneous (> 60 types) – SCA 3 most frequent subtypes 2 groups: Autosomal dominant, autosomal recessive Imaging General features Atrophy of cerebellum, brainstem with normal cerebral hemispheres Cerebellar atrophy = hallmark of cerebellar ataxias but can be mild or…

KEY FACTS Terminology Wallerian degeneration (WaD) Secondary anterograde degeneration of axons and their myelin sheaths caused by interruption of the axonal integrity or damage to neuron Imaging Primary lesion is cortical or subcortical with WaD in descending white matter tracts ipsilateral to neuronal injury WaD can be seen in fibers crossing the corpus callosum, fibers of optic radiations, fornices, and cerebellar peduncles CT is not sensitive…

KEY FACTS Terminology Amyotrophic lateral sclerosis (ALS) Selective degeneration of somatic motor neurons of brainstem/spinal cord and large pyramidal neurons of motor cortex Eventual loss of corticospinal tract (CST) fibers Imaging Small percentage demonstrate CST hyperintensity As CST is normally slightly hyperintense, especially at 3.0 T, this finding lacks sensitivity & specificity T2 hyperintense CST may be specific for ALS when seen on corresponding proton density…

KEY FACTS Terminology Neurodegenerative disease characterized by supranuclear palsy, postural instability, mild dementia Imaging Midbrain atrophy (penguin or hummingbird sign) Sagittal T1WI shows concave/flat upper border of midbrain (normally convex) Axial T1WIs show abnormal concavity of lateral margins of midbrain tegmentum (morning glory or Mickey Mouse sign) Thinning of superior colliculus Midsagittal 3D-MP-RAGE or FS-PGR images Voxel-based morphometry used to calculate ratio of midbrain to pons…

KEY FACTS Terminology Corticobasal degeneration Progressive neurodegenerative disease Presents with cognitive dysfunction, “asymmetrical” parkinsonism Imaging Severe focal asymmetric cortical atrophy Perirolandic (posterior frontal, parietal cortex) Relative sparing of temporal, occipital regions ↑ signal intensity in frontal &/or parietal subcortical white matter Marked T2 hypointensity Putamen, globi pallidi FDG-18 PET decreased uptake in cortical and subcortical regions (frontal, temporal, sensorimotor, and parietal association cortices), caudate, lentiform nucleus,…