Anatomy and Physiology of the Basal Ganglia and Thalami

(29-1) Graphic depicts basal ganglia, caudate nucleus , putamen , globus pallidus (GP) . Thalami form borders of the third ventricle.

(29-2) Axial T1WI shows basal ganglia, thalami as isointense with gray matter. GP are slightly hyperintense to the caudate and putamen.

(29-3) On T2WI, the GP are more hypointense than putamen, caudate. Putamen reaches same hypointensity in 7th or 8th decade.

Two areas of the brain are especially susceptible to toxic and metabolic damage: the deep gray nuclei and the cerebral white matter (WM). The basal ganglia (BG) are highly vascular, rich in mitochondria, and loaded with neurotransmitters. The BG—especially the putamen and globus pallidus (GP)—are particularly susceptible to hypoxia or anoxia and are also commonly affected by toxins and metabolic derangements. The cerebral WM is particularly vulnerable to lipophilic toxic substances.

Dopaminergic Striatonigral System

The substantia nigra pars compacta (SNPc) contains most of the dopaminergic neuron population of the midbrain. Mesencephalic dopaminergic neurons help regulate voluntary movement. Degeneration of dopaminergic neurons in the SNPc reduces dopaminergic input to the striatum and results in movement disorders such as Parkinson disease. The dopaminergic striatonigral system is discussed in greater detail in Chapter 33.

Normal Gross Anatomy

The BG are symmetric paired subcortical (deep gray matter) nuclei that form the core of the extrapyramidal system and control motor activity. The BG consist of (1) the caudate nucleus (CNuc), (2) the putamen, and (3) the GP.

The caudate nucleus and putamen form the corpus striatum. Two other structures—the substantia nigra and subthalamic nuclei—are functionally related to the striatum. Together these structures form the striatonigral system.

Because of their triangular or lens shape, the putamen and GP together are also called the lentiform nuclei (29-1).

The lentiform nuclei lie just deep to the insular cortex and are separated from it (from medial to lateral) by the WM of the external capsule, the gray matter of the claustrum, and the thin WM layer of the extreme capsule. Medially, the lentiform nuclei are separated from the caudate nucleus and thalamus by the anterior and posterior limbs of the internal capsule (29-4).

The substantia nigra and subthalamic nuclei are considered next, as they are an integral part of the striatonigral system.

The thalami are the largest and most prominent of the deep gray matter nuclei but are generally not included in the term "basal ganglia." The thalami are also considered separately below.

Caudate Nucleus

The CNuc is a C-shaped structure with a large head, tapered body, and downcurving tail. The CNuc parallels the lateral ventricle body, forming part of its floor and lateral wall. The tail follows the curve of the temporal horn, lying along its roof. Anteriorly, the tail expands and becomes continuous with the posteroinferior aspect of the putamen. The most anterior aspect of the tail abuts—but remains separate from—the amygdala.

A deep groove called the sulcus terminalis separates the CNuc from the thalamus and covers a band of fibers called the stria terminalis. The ST runs all the way around the lateral ventricle from the amygdala to the hypothalamus.

The CNuc together with the putamen receives input from the cerebral cortex and is connected to the substantia nigra and GP.

Putamen

The putamen is the outermost part of the BG. Medially, the putamen is separated from the GP by a thin layer of WM fibers, the lateral (external) medullary lamina.

Globus Pallidus

The GP consists of two segments. The lateral (external) segment is separated from the medial segment by a thin layer of myelinated axons, the internal medullary lamina.

Thalamus

The thalami are symmetric, obliquely oriented ovoid masses of gray matter that lie posteromedial to the lentiform nuclei. The two thalami form the lateral walls of the third ventricle (29-7). The anterior aspect of each thalamus abuts the foramen of Monro. The posterior thalamus bulges into the lateral ventricle atrium, whereas the dorsal surface forms part of the lateral ventricle floor. The stria terminalis demarcates the border between the thalamus and the body of the CNuc. The fornix curves above the thalamus and is separated from it by the choroid fissure.

Laterally, the thalami are separated from the GP by the posterior limb of the internal capsule. The thalami act as sensory and motor relay stations to the cortex.

Each thalamus is subdivided into several groups of nuclei (anterior, medial, and lateral thalamic). The lateral geniculate nuclei (part of the visual system) and medial geniculate nuclei (part of the auditory system) are also considered part of the thalamus. The pulvinar is the most posterior aspect of the thalamus and is nestled within the curve of the lateral ventricle, just in front of the atrium.

Substantia Nigra

The substantia nigra is located in the midbrain (mesencephalon). The substantia nigra appears black on gross anatomical sections because of high melanin levels in dopaminergic neurons. The substantia nigra is composed of two parts, a deep cell-rich pars compacta (SNPc) and a larger but less cellular segment, the pars reticulata.

Subthalamic Nucleus

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(29-4) Coronal graphic through frontal horns shows caudate nucleus , putamen , GP , external capsule , and internal capsule .

(29-5) On coronal T1WI, the GP are slightly hyperintense to the putamina except for punctate hypointensities caused by Ca++ .

The subthalamic nucleus (STN) is a small lens-shaped nucleus that lies in the upper midbrain, inferomedial to the thalamus and internal capsule and

(29-6) Coronal T2WI shows that medial GP are the most hypointense of the basal ganglia. Putamina are isointense with cortex.

(29-7) Coronal graphic depicts the major thalamic subnuclei and their relationship to the third ventricle and internal capsules .

(29-8) Coronal T2WI through the posterior third ventricle shows that thalami are mostly isointense with the cortex.

superolateral to the red nucleus. The STN is wrapped by fibers of the substantia nigra but receives its main input from the GP.

Normal Imaging Anatomy

Although the lentiform nuclei, CNuc, thalami, and internal/external capsules can be identified on CT scans, their anatomy is best detailed on MR.

T1WI

The CNuc, putamina, and thalami are isointense with cortex on T1 scans. The globi pallidi are less cell-rich than either the putamen or caudate (29-2). As the site of both physiologic calcification and age-related iron deposition, the GP segments vary in signal intensity (29-5).

Calcification may cause T1 shortening and mild hyperintensity in the medial segment. The fully myelinated, compact WM in the internal and external capsules appears hyperintense relative to the BG.

T2WI

The CNuc, putamina, and thalami are isointense with cortical gray matter on T2 scans (29-8). The myelin content in the GP is higher relative to the putamen (29-3) (29-6), so it appears relatively more hypointense on T2WI. Increasing iron deposition occurs with aging, and the putamen becomes progressively more hypointense. A "dark" putamen is normal by the seventh or eighth decade of life.

T2*

The GP is hypointense relative to cortex on GRE or SWI imaging. By the seventh or eighth decade of life, iron deposition in the putamen "blooms," and the lateral putamen appears hypointense relative to the thalami but not as intensely hypointense as the GP. The age-associated changes of brain iron deposition are discussed in greater detail in Chapter 33.

Quantitative susceptibility mapping (QSM) is a new advanced MR technique that depicts and quantifies sources of magnetic susceptibility. Mapping iron—the dominant susceptibility source in the brain—has many important clinical applications, and QSM may assist in the early diagnosis of disorders such as amyotrophic lateral sclerosis and Parkinson disease.

Toxic and Metabolic

Disorders

Many toxic, metabolic, systemic, and degenerative diseases affect the basal ganglia (BG) and thalami in a strikingly symmetric fashion.

When imaging discloses bilateral lesions that involve all the deep gray nuclei, the lesions are most often secondary to diffuse systemic or metabolic derangements.

Patchy, discrete, focal, and asymmetric lesions are more commonly infectious, postinfectious, traumatic, or neoplastic in origin.

Bilateral BG lesions have many potential causes. Diseases that specifically affect the putamen or globi pallidi in a bilaterally symmetric pattern have a somewhat different pathoetiologic spectrum.

Additional information such as patient age and specific imaging characteristics can also help establish a reasonable differential diagnosis.

In the subsequent chapters in this part, we consider toxic and metabolic disorders by diagnosis (e.g., chronic hepatic disease, acute hepatic encephalopathy, and hypoxic-ischemic encephalopathy).

Here we address the differential diagnosis of BG lesions first by general location (i.e., bilateral BG lesions) and then by sublocation. Entities within each differential diagnosis are categorized as common, less common, and rare but important.

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Differential Diagnoses of Bilateral Basal Ganglia Lesions

The most common bilateral BG lesions are normal variants, such as physiologic calcification and prominent perivascular spaces. Vascular disease, hypoxic-ischemic insults, and common metabolic disorders, such as chronic liver failure, are the most frequent causes of abnormality.

Infection, toxins and drug abuse, or metabolic disorders, such as osmotic demyelination and Wernicke encephalopathy, are less common causes of bilateral BG lesions.

Careful evaluation of imaging findings outside the BG such as cortical or white matter (WM) involvement—together with clinical correlation and laboratory data—is essential to differentiate among the many disorders that cause bilateral BG abnormalities (29-9) (29-10) (29-11) (29-12) (29-13) (29-14) (29-15) (29-16) (29-17) (29-18).

(29-9) Axial NECT scan in a 34y woman with headaches and normal neurologic examination shows normal bilateral symmetric physiologic calcifications in the medial GP . (29-10) Autopsy case of hypoxia with acute striatal necrosis shows bilateral caudate nuclei and putamina lesions. The GP and thalami are spared. (Courtesy R. Hewlett, MD.)

(29-11) Axial T2WI in a patient with anoxia, basal ganglia necrosis shows bilateral hyperintensity in caudate nuclei , putamina, GP , cortex. The thalamus is relatively spared. (29-12) Axial T2WI shows innumerable variably sized CSF-like cysts in the caudate nuclei, putamina, and GP with relative sparing of the thalamus. These are unusually prominent enlarged perivascular spaces (sometimes called "état criblé" or "cribriform state").

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(29-13) FLAIR shows bilateral CNuc , putamina, thalamic hyperintensity ; West Nile encephalitis. (Courtesy M. Colombo, MD.)

(29-14) Axial FLAIR shows CNuc , putamina , thalamic symmetric hyperintensity. This is extrapontine osmotic myelinolysis.

(29-15) Axial FLAIR shows bilateral but asymmetric CNuc , putamen , thalamic hyperintensity. This is deep vein occlusion.

COMMON BILATERAL BASAL GANGLIA LESIONS

Normal Variants

•Physiologic mineralization

○Medial globus pallidus (GP) > > caudate, putamen

•Prominent perivascular spaces

○Follow CSF, suppress on FLAIR

Vascular Disease

•Lacunar infarcts

○Multiple bilateral, scattered, asymmetric

•Diffuse axonal/vascular injury

○Hemorrhage, other lesions

Hypoxic-Ischemic Injury

•Hypoxic-ischemic encephalopathy (HIE)

○BG ± cortex/watershed, hippocampi, thalami

Metabolic Disorders

•Chronic liver disease

○GP, substantia nigra hyperintensity

LESS COMMON BILATERAL BASAL GANGLIA LESIONS

Infection/Postinfection

•Viral

○Especially flaviviral encephalitides (West Nile virus, Japanese encephalitis, etc.)

•Postvirus, postvaccination

○Acute disseminated encephalomyelitis (ADEM): patchy > confluent; WM, thalami, cord often involved

○Acute striatal necrosis

Toxic Poisoning and Drug Abuse

•Carbon monoxide

○GP (WM may show delayed involvement)

•Heroin

○BG, WM ("chasing the dragon")

•Methanol

○Putamen, WM

•Cyanide

○Putamen (often hemorrhagic)

•Nitroimidazole

○Dentate nuclei, inferior colliculi, splenium, BG

Metabolic Disorders

•Osmotic ("extrapontine") demyelination

○BG, ± pons, WM

•Wernicke encephalopathy

○Medial thalami, midbrain (periaqueductal), mammillary bodies

Vascular Disease

•Internal cerebral vein/vein of Galen/straight sinus thrombosis

○BG, deep WM

•Artery of Percheron infarct

○Bilateral thalami, midbrain ("V" sign)

Neoplasm

•Primary CNS lymphoma

○Periventricular (WM, BG)

•Astrocytoma

○Bithalamic "glioma"

RARE BUT IMPORTANT BILATERAL BASAL GANGLIA LESIONS

Metabolic Disorders

•Acute diabetic uremia

○GP, putamen, caudate

•Acute hyperammonemia

○Acute liver failure

○Ornithine transcarbamylase deficiency, etc.

•Acute hyperglycemia

○GP, caudate

•Severe hypoglycemia

○Occipital cortex, hippocampi, ± WM

Infection and Inflammation

•Toxoplasmosis

○Often HIV-positive, other ring-enhancing lesions

•Behçet disease

○Midbrain often involved

○Orogenital aphthous ulcers

•Chronic longstanding multiple sclerosis (MS)

○BG become very hypointense

○Putamina, thalami > GP, caudate nucleus (CNuc)

○Extensive WM disease, volume loss

•Creutzfeldt-Jakob disease (CJD)

○Anterior BG (caudate, putamen)

○Posteromedial thalami (T2/FLAIR hyperintense "hockey stick" sign)

○Variable cortical (occipital = Heidenhain variant)

Inherited Disorders

•Neurofibromatosis type 1 (NF1)

○GP T1 hyperintensity, T2 hyperintense foci

•Mitochondrial encephalopathies

○Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS), myoclonic epilepsy with ragged red fibers (MERRF)

○Leigh disease (putamen, periaqueductal region, cerebral peduncles)

•Wilson disease

○Putamina, CNuc, ventrolateral thalami

•Pantothenate kinase-associated neurodegeneration (PKAN)

○GP ("eye of the tiger")

•Huntington disease

○Atrophic CNuc, putamina

•Fahr disease

○Dense symmetric BG, thalami, dentate nuclei, subcortical WM Ca++

•Iron storage disorders

○Symmetric BG "blooming" hypointensity

Putamen Lesions

In general, the putamina are less commonly affected than either the globi pallidi or thalami. The most common lesion to affect the putamen is hypertensive hemorrhage. Acute hypertensive bleeds are usually unilateral although T2* scans often disclose evidence of prior hemorrhages.

Bilateral symmetric putamen lesions usually occur with more generalized BG involvement. However, there are some lesions that predominantly or almost exclusively involve the putamina.

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(29-16) Axial T1WI in a patient with NF1 shows multifocal basal ganglia (BG) hyperintensities , large hypointensity from myelin vacuolization.

(29-17) Axial T1WI in a patient with mitochondrial encephalopathy (MERRF) shows multifocal hypointensities in the BG .

(29-18) T2* GRE in a patient with aceruloplasminemia shows symmetric "blooming" hypointensities in BG , thalami , cortex .

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(29-19A) FLAIR scan in a patient with anoxia shows bilateral putamina , caudate nuclei , and cortical hyperintensity.

(29-19B) FLAIR shows symmetric hyperintensity in the CNuc , putamina , cortex . This is severe hypoglycemia. (Courtesy M. Castillo, MD.)

Toxic, metabolic, and hypoxic-ischemic events and degenerative disorders account for the vast majority of symmetric putamen lesions (29-19A) (2919B) (29-20).

COMMON PUTAMEN LESIONS

Metabolic Disorders

•Hypertensive hemorrhage

○Lateral putamen/external capsule

Hypoxic-Ischemic Encephalopathy

•HIE in term infants

•Hypotensive infarction

LESS COMMON PUTAMEN LESIONS

Toxic Disorders

•Methanol toxicity*

○Often hemorrhagic

○± Subcortical WM

•Osmotic demyelination

○Extrapontine myelinolysis

Inherited Disorders

•Leigh disease

•Neuroferritinopathy

○Putamina, GP, dentate

*Predominantly or almost exclusively involves the putamina

RARE BUT IMPORTANT PUTAMEN LESIONS

Degenerative Diseases

•Huntington disease

○CNuc, putamina

•Parkinson disease

○Putamen hypointensity

•Multiple system atrophy

○Parkinsonian type* (hyperintense putaminal rim)

Miscellaneous

•Creutzfeldt-Jakob disease*

○Anterior putamina, CNuc

○Posteromedial thalami

○Variable cortex (± predominant or exclusive involvement)

*Predominantly or almost exclusively involves the putamina

Globus Pallidus Lesions

The globus pallidus (GP) is the part of the BG that is most sensitive to hypoxia. The vast majority of symmetric GP lesions are secondary to hypoxic, toxic, or metabolic processes. Most cause bilateral symmetric abnormalities on imaging studies (29-21) (29-22) (29-23).

The differential diagnosis of GP lesions can be approached by prevalence (common, less common, rare but important), etiology, age, imaging appearance, or a combination of these factors.

COMMON GLOBUS PALLIDUS LESIONS

Normal Variant

•Physiologic calcification

○Medial GP

Hypoxic-Ischemic Encephalopathy

•Anoxia, hypoxia (near-drowning, cerebral hypoperfusion)

•Neonatal HIE (profound acute)

Toxic/Metabolic Disorders

•Chronic liver disease

○T1 hyperintensity, T2* hypointensity

•Carbon monoxide

○T2 hyperintense medial GP

LESS COMMON GLOBUS PALLIDUS LESIONS

Toxic/Metabolic Disorders

•Postopioid toxic encephalopathy

○Often combined with HIE

•Hyperalimentation

○Manganese deposition, short T1

•Chronic hypothyroidism

○Punctate calcification

○T1 hyperintensity, T2 hypointensity

Inherited Disorders

•NF1

•Leigh disease

RARE BUT IMPORTANT GLOBUS PALLIDUS LESIONS

Toxic/Metabolic Disorders

•Kernicterus

○T1 shortening

•Cyanide poisoning

○Hemorrhagic GP, laminar cortical necrosis

Inherited Disorders

•Fahr disease

○Dense symmetric confluent calcification

•Wilson disease

○T2 hyperintensity in GP, putamen

○"Face of giant panda" sign in midbrain

•PKAN

○"Eye of the tiger" (central T2 hyperintensity, peripheral hypointensity)

○Not always present!

•Neurodegeneration with brain iron accumulation (NBIA)

○GP, substantia nigra hypointensity ± putamen

•Maple syrup urine disease (MSUD)

○Edema (GP, brainstem, thalami, cerebellar WM)

•Methylmalonic acidemia (MMA)

○Symmetric GP T2 hyperintensity ± WM

Degenerative Diseases

•Hepatocerebral degeneration

○1% of patients with cirrhosis, portosystemic shunts

○T1 shortening

•Progressive supranuclear palsy

○Also affects subthalamic nucleus, substantia nigra

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(29-21) T2WI in a patient with hypotensive infarct following narcotic overdose shows bilateral GP hyperintensities .

(29-22) T2WI shows bilateral medial GP hyperintensities , confluent WM hyperintensity; this is carbon monoxide poisoning.

(29-23) T2WI shows classic "eye of the tiger" with medial GP hyperintensities surrounded by well-defined hypointensity . This is PKAN.

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(29-24) Axial T2WI shows bilateral medial thalamic infarcts caused by artery of Percheron occlusion.

(29-25) Axial FLAIR shows bithalamic lesions with less extensive involvement of putamina and GP. This is internal cerebral vein occlusion.

Globus Pallidus Lesions by Age

Some GP lesions are common in adults but rare in children; others are seen primarily in the pediatric age group.

GLOBUS PALLIDUS LESIONS BY AGE

GP Lesions of Adulthood

•Hypoxia/anoxia

•Drug abuse

•Carbon monoxide poisoning

•Hepatic encephalopathy

•Hyperalimentation

•Hypothyroidism

•Wilson disease

•NBIA

GP Lesions of Childhood

•HIE

•NF1

•Leigh disease

•Wilson disease

•Kernicterus

•NBIA, PKAN

•MSUD

•MMA

Globus Pallidus Lesions by Appearance

Some GP lesions can be distinguished by their typical attenuation on CT or signal intensity on MR.

GLOBUS PALLIDUS LESIONS BY CHARACTERISTIC APPEARANCE

NECT Hypodensity

•HIE

•Carbon monoxide poisoning

NECT Hyperdensity

•Physiologic Ca++

•Hypothyroidism

•Fahr disease

T1 Hyperintensity

•Chronic hepatic encephalopathy

•Hyperalimentation (manganese deposition)

•NF1

•Hypothyroidism

•Kernicterus (acute)

•Wilson disease

T2 Hyperintensity

•HIE

•Drug abuse

•Carbon monoxide poisoning

•NF1

•Leigh disease

•Kernicterus (chronic)

•Wilson disease

•PKAN, MSUD, MMA

Thalamic Lesions

Because lacunar infarcts and hypertensive bleeds are so common, unilateral thalamic lesions are much more common than bilateral symmetric abnormalities.

UNILATERAL THALAMIC LESIONS

Common

•Lacunar infarction

•Hypertensive intracranial hemorrhage

Less Common

•NF1

•Diffuse astrocytoma (low-grade fibrillary)

•Glioblastoma multiforme

•Anaplastic astrocytoma

•ADEM

Rare But Important

•MS

•Unilateral internal cerebral vein thrombosis

•Germinoma

In contrast, bilateral symmetric thalamic lesions are relatively uncommon and have a somewhat limited differential diagnosis. As with the symmetric basal ganglia lesions discussed previously, bilateral thalamic lesions tend to be toxic, metabolic, vascular, infectious, or hypoxic-ischemic (29-24) (29-25) (29-26) (29-27) (29-28) (29-29).

Bithalamic Lesions by Age

As with GP lesions, some symmetric bithalamic lesions—such as those caused by inherited metabolic disorders—are more common in infants and children. Others are seen primarily in adults. Some (e.g., acquired metabolic disorders, deep venous occlusion, ADEM) occur in all ages.

The most common and rare but important causes of bithalamic lesions in children and adults are shown in the boxes on the next page.

BITHALAMIC LESIONS BY AGE

Childhood Bithalamic Lesions

•Hypoxic-ischemic encephalopathy

•ADEM

•Bithalamic astrocytoma

•Inherited metabolic disorder

•Acquired metabolic disorders

•Toxic encephalopathy

•Deep venous occlusion

•Acute necrotizing encephalitis

Adult Bithalamic Lesions

•Deep venous occlusion

•Artery of Percheron, "top of the basilar" occlusion

•Profound hypoperfusion

•ADEM

•Wernicke encephalopathy

•Osmotic demyelination

•Vasculitis

•CJD

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(29-27) FLAIR in a patient with Wernicke encephalopathy shows symmetric lesions in both medial thalami .

(29-28) FLAIR scan in a patient with CJD shows classic "hockey stick" sign as well as anterior caudate and putamen hyperintensity.

(29-29) T2WI shows bithalamic and right insular hyperintensity in a patient with gliomatosis cerebri, WHO grade II astrocytoma.

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(29-30) Autopsy of severe obstructive hydrocephalus shows symmetrically enlarged lateral ventricles. (Courtesy R. Hewlett, MD.)

(29-31) T2WI in longstanding compensated shunted hydrocephalus shows symmetrical enlargement of both lateral ventricles.

COMMON BITHALAMIC LESIONS

Vascular Lesions

•Deep venous occlusion

○Thalami > GP, putamina

○CNuc ± deep WM

•Arterial ischemia

○Artery of Percheron infarct

○"Top of the basilar" thrombosis

•Vasculitis

Hypoxic-Ischemic Encephalopathy

•Profound hypoperfusion

○BG, hippocampi, cortex

•Usually occurs in full-term neonates

LESS COMMON BITHALAMIC LESIONS

Infection/Postinfection/Inflammatory Disorders

•ADEM

○Usually with WM lesions

•Viral encephalitis

○Many agents affect thalami

○Epstein-Barr virus, West Nile virus, Japanese encephalitis, etc.

•CJD

○"Hockey stick" sign

○Pulvinar, medial thalami

Toxic/Metabolic Disorders

•Osmotic myelinolysis

○Extrapontine involvement variable

○Thalami

○External capsules, putamina, CNuc

•Wernicke encephalopathy

○Medial thalami (around 3rd ventricle)

○Pulvinar

○Midbrain (periaqueductal)

○Mammillary bodies

○Cortex variable

•Solvent inhalation

○Toluene

○Glue

○Ethylene glycol

•Acute hypertensive encephalopathy (PRES)

○Occipital lobes, watershed zones

○"Atypical" PRES may involve BG, thalami

•Status epilepticus

○Pulvinar

○Corpus callosum splenium (usually transient excitotoxic)

○Often hippocampi ± cortex

Neoplasms

•Bithalamic low-grade astrocytoma

•Germinoma

•Lymphoma

RARE BUT IMPORTANT BITHALAMIC LESIONS

Infection/Postinfection/Inflammatory Disorders

•MS (severe, chronic)

○Hypointense BG on T2*

•Acute necrotizing encephalopathy of childhood

•Flavivirus encephalitis

•Neuro-Behçet

Inherited Disorders

•Mitochondrial disorders

•Krabbe disease

○Hyperdense on CT, hypointense on T2

•Wilson disease

○Putamina, CNuc > thalami

•Fahr disease

○GP > thalami

•Fabry disease

○T1 hyperintense posterior thalamus ("pulvinar")

○M > > F

○Strokes (territorial, lacunar)

○Renal, cardiac disease

Neoplasm

•Glioblastoma

•Anaplastic astrocytoma

Paraneoplastic Syndromes

•Paraneoplastic can mimic prion disease (variant Creutzfeldt-Jakob disease)

•Limbic involvement not always present

Degenerative and CSF

Disorders

Age-Related Changes

Normal age-related changes in the brain occur throughout life. Understanding the different stages of brain formation and normal progression of myelination is essential to diagnosing inherited metabolic disorders.

At the opposite end of the age spectrum, volume is normally lost in some parts of the brain, while other areas remain relatively intact. Abnormal mineral deposition in the basal ganglia can be a clue to degenerative and metabolic disorders. Understanding what is normal heavy metal deposition in different decades is a prerequisite to diagnosing these abnormalities on imaging studies.

Dementia and Brain Degeneration

Once an understanding of the normal aging brain is established, we discuss the pathology and imaging manifestations of dementia. Although identifying a "lobar predominant" pattern of volume loss on CT and standard MR can be accomplished in many cases, these are usually latestage manifestations. The early diagnosis of dementing disorders increasingly relies on functional MR and PET studies.

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CNS degenerations from Parkinson disease to wallerian and hypertrophic olivary degeneration are considered. The anatomy and physiology of the brain dopaminergic system are briefly reviewed, as is the anatomy essential to evaluating preand postoperative deep brain stimulation.

Hydrocephalus and CSF Disorders

Because abnormalities of the brain CSF spaces are a common manifestation of brain degeneration in the elderly as well as a potentially treatable cause of encephalopathy, we devote the last chapter in this part to hydrocephalus and CSF disorders.

We first address the normal anatomy of the ventricles and CSF spaces as well as imaging variants that can be mistaken for disease.

Hydrocephalus, disorders of CSF production/circulation/absorption, and the newly described syndrome of inappropriately low-pressure acute hydrocephalus are then discussed. Lastly, we consider CSF leaks and sequelae including intracranial hypotension—conditions in which imaging plays an essential role in both diagnosis and patient management.

ABNORMALITIES OF VENTRICULAR SIZE

Large Ventricles

•Common

○Aging brain (brain parenchyma volume loss)

○Generalized encephalomalacia (posttrauma/infection, etc.)

○Extraventricular obstructive hydrocephalus (meningitis, subarachnoid hemorrhage, etc.)

○Dementias (Alzheimer, frontotemporal dementia, etc.)

•Less common

○Intraventricular obstructive hydrocephalus

○Colpocephaly (occipital horns)

○Normal pressure hydrocephalus

○Shunt failure

•Rare but important

○Choroid plexus papilloma (CSF overproduction)

○Megalencephaly syndromes

○Huntington disease (frontal horns)

Small Ventricles

•Common

○Normal (children, young adults)

○Shunt failure ("slit ventricle" syndrome)

○Increased intracranial pressure

•Less common

○Diffuse cerebral edema

○Intracranial hypotension

○Idiopathic intracranial hypertension

•Rare but important

○Brain death