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Top 3 Differentials in
Neuroradiology
A Case Review
William T. O'Brien Sr.

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Top 3 Differentials in Neuroradiology
A Case Review

William T. O'Brien Sr., DO
Program Director, Diagnostic Radiology Residency
David Grant USAF Medical Center
Travis Air Force Base, California
Former Chairman, Department of Radiology
Wilford Hall USAF Ambulatory Surgical Center
Joint Base San Antonio-Lackland, Texas
Associate Clinical Professor
Department of Radiology
University of california, Davis School of Medicine
Sacramento, California

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Dedicated in memory of

Robert L Meals, DO
12 March 1928-9 June 2005

© Susan Schary 2005

For decades, Dr. Meals inspired thousands of students while serving as Academic Chairman of the
Department of Radiology, Philadelphia College of Osteopathic Medicine, Philadelphia, Pennsylvania.
Dr. Meals was more than an instructor; he was a mentor and a true friend.
To those who chose to pursue a career in radiology, he will always be a legend.
He is sorely missed but will never be forgotten.


Contents
Foreworcl by Richard E. Latchaw

Preface
Aclmowledgments

vii
viii

ix

Section 1. Brain
Subsection la. Congenital and Developmental
Subsection lb. Attenuation and Signal Abnormality

2
44

Subsection le. Masses and Masslike Lesions

110

Subsection Id. Vasculature and Cerebrospinal Fluid Spaces

186

Section IL Head and Neck

vi

Subsection Ha. calvarium and Skull Base

260

Subsection IIb. Temporal Bone

296

Subsection IIe. Sinonasal

330

Subsection IId. Maxillofacial

362

Subsection IIe. Neck (induding spaces)

382

Subsection Hf. Orbits

444

Section ID. Spine

484

Index of Differential Diagnoses, by Case

607

Index of Key Findi�

612


Foreword
Unique/

derive from multiple diagnostic categories. For some appear­
ances, he even indudes some uncommon but potentially

lbat is the best word to describe Top 3 DijJerentials in

important considerations ("Additional Diagnostic Considera­

Neuroradiology by William T. O'Brien-unique in its approach

tions"), thus providing more than just three possibilities for

to the clinical practiœ of neuro-imaging, and unique in its

cases with more nonspecific findings. He finishes each case

approach to education in this rapidly expanding subspecialty.

with dinical and imaging "Pearls," which provide quick dif­

The traditional clinical practiœ of a neurologist, neuro­

ferentiating features. He also provides some selected refer -

surgeon, orthopedic surgeon-any physician ordering a

ences for more in-depth reading on the topic.

neuro-imaging examination-is to evaluate the patient's his­

Sorne imaging appearances within each section are unique,

tory in conjunction with signs and symptoms, corne ta a

without differential diagnoses and not having a Top 3; they

probable conclusion, and then request an imaging study to

are called "Aunt Minnies." Dr. O'Brien considers a number of

confirm or deny that clinical conclusion.
The clinical practice of a radiologist initially requires the

these to be fundamental to the knowledge base of the student,
sa they are presented at the end of each section. Each has an

recognition of a combination of findings on an imaging study

extensive discussion regarding pathophysiology and charac­

within the stated clinical context This is followed by the

teristic imaging appearances, along with selected referenœs,

iterative comparison of these findings to examples from

similar to that found with the cases having Top 3 differential

diagnostic categories, including masses, demyelinating dis­

possibilities.

eases, ischemia, infection, degenerative disease, etc. This

How did Dr. O'Brien validate his Top 3 choices with so

iterative proœss may be mental or actually require compari­

many varied appearances in diverse clinical contexts? By

son with published examples. The result is a differential

doing extensive research as to the most common diagnoses

diagnosis that may vary in specificity and depth. One might

for a given finding; by consulting with many radiologists who

list the top three possible diagnoses, or one could list the most

subspecialize in neuroradiology, head and neck radiology,

likelywith that which is the most dangerous and thus must be

and

excluded, along with one that would be easy to exclude with

that tend to be favorites in general and subspecialty board

more studies.

examinations.

spinal

radiology;

and

by incorporating

entities

How dowe traditionally educate a reader of neuro-imaging

How will this book change how we practice and teach

studies7 We usually ensure that the novice reader has seen

neuro-imaging? lt is vital that neuro-imagers have ingrained

examples from the various diagnostic categories with which

in their brain the basic categories of neuropathology, so that

we deal, and has leamed how diseases within each category

they can be sure that they caver ail potential disease catego­

differ from those in other categories. The organization of our

ries when confronted with an unknown case. However,

books and our teaching sessions is typically based upon such

O'Brien's approach can easily be superimposed on that basic

categories: Neoplasms, Congenital Disease, Infections, etc.

knowledge of disease organization. lt is fast, accurate, and

However, what happens when the imager is confronted

removes the potential that the reader will be slowed down,

with an "unknown," a finding that does not fit easily into

trying to ensure that ail categories are covered. This approach

one of the categories to which he or she has become so

provides a way to be "complete" in developing differential

accustomed? Unfortunately, even though the imager has

diagnoses rapidly and accurately.

leamed the appearances of the majority of entities within

1 found reading this book to be a joy. One can approach it by

a given category of disease, the finding does not tell the

playing the student, viewing each image as an unknown,

imager to which category it belongs! So, the imager must

determining what the most prominent finding is, and then

now search the categorically based textbooks for a "look

giving one's own Top 3. Frankly, this is a book not just for the

alike," which is very time-consuming and may not even be

resident or fellow, but one that will give any academic faculty

successful.

member a positive learning experienœ, just like the one that

Dr. O'Brien's approach ta both the clinical practice and the

1 hadl

education of neuro-imaging is quite unique amongst the
textbooks 1 have seen over many years as a neuroradiologist
He has divided this book into three sections: Brain, Head and

Richard E. Latchaw, MD

Neck, and Spine. Within each section, he conœntrates on the

Professor of Radiology

most apparent imaging finding(s) within the presenting clin­

Neuroradiology Section

ical context, and gives the "Top 3" potential diagnoses for that

University of California, Davis Medical Center

appearance (that "gamut"), including entities that may well

Sacramento, California

vii


Preface
It is a distinct pleasure to present Top 3 Differentials in

would not be considered in the Top 3 for the particular

version of the original "Top 3" book, Top 3 Differentials in

gamut. Instead, the primary aim of the book is to generate

Radiology, had been an aspiration of mine since its publica­

and have an understanding of a reasonable list of gamut­

tion in 201O. This subspedalty version is primarily designed

based differentials rather than to obtain the "correct"

for senior radiology residents, neuroradiology fellows, and

answer.

staff radiologists preparing for the neuroradiology portion

As with the earlier Top 3 Differentials in Radiology, it is

of initial and recertification board examinations; however, it

important to realize that the differentials and discussions are

may also prove useful for dinicians and surgeons who

based on the key finding or gamut and not necessarily the

routinely utilize neuroimaging.

illustrative cases that are shown This is by design, because 1

This book is organized into three main sections: brain,

felt it would be more high-yield to base the differentials and

head and neck, and spine imaging; and further divided into

discussions on the overall gamut/key finding rather than the

subsections based upon anatomie region or pattern of imag­

illustrative case presented. Having an understanding of

ing abnormality. Each section begins with a series of

gamut-based differentials will allow one to subsequently

unknown differential-based cases and ends with "Roentgen

tailor the Iist of differentials for any case that is shown within

dassics," which are cases with imaging findings character­

the gamut, whereas basing the differentials on the selected

istic of a single diagnosis.

images would be more limited in terms of future utility.

On the first page of each case, readers are presented with

Given the vast, evolving field of neuroimaging, this book is

images from an unknown case, along with a clinicat history

not meant to be a comprehensive reference book; rather, it is

and an image legend. The images are meant to illustrate a

meant to serve as a high-yield review for board preparation,

key imaging finding, which is the basis for the subsequent

as well as a quick reference for clinical practice. With these

case discussion. The second page Iists the key imaging

intentions in mind, the selection and ordering of differentials

finding, from which a list of differentials is broken down

for each gamut were based upon a combination of the most

into the Top 3, along with "additional diagnostic considera­

likely diagnoses to be enrountered in a board setting, as well

tions." The discussion section of each case provides a brief

as clinical practice. Sorne "additional diagnostic considera­

review of important imaging and clinical manifestations for

tions" were selected over others (which may actually be more

all entities on the list of differentials, making this a high­

rommon) in order to provide the opportunity to discuss as

yield reference for board preparation. lmaging pearls are

many diagnostic entities as possible throughout the book.

provided at the end of each case to allow for a quick review

viii

fact, many illustrative cases have a final diagnosis that

Neuroradiology: A Case Review. Developing a neuroradiology

1 sinœrely hope that you find this Top

3 case-based

of key points. The final diagnosis is provided for each case;

approach enjoyable and useful, and I wish you all the best

however, it is by no means the focus of this review book. In

in your future endeavors.

Acknowledgments
This book would not have been possible without the contri­

image legend for each case in which they were involved. 1

butions of numerous colleagues and mentors. First and

cannot possibly thank them enough for their significant

foremost, 1 am forever indebted ta the faculty of David Grant

contributions ta this book. Although there are far tao

USAFMedicalCenter, the UniversityofCalifornia-Davis, and

many ta name individually, 1 would like to espedally thank

Oakland Children's Hospital, where 1 completed my radiol­

Paul M. Sherman, MD, who not only authored portions of

ogy residency training, as well as the University of Cincin­

the neuroimaging sections in the original "Top 3" book, but

nati and Cincinnati Children's Hospital Medical Center,

also served as my neuroradiology mentor during residency

where 1 completed my neuroradiology fellowships. The

and bas been one of my neuroradiology partners in San

dedicated staff at these institutions afforded me their

Antonio for the past 4 years.

time and expertise during my years of training and have

Lastly, 1 would like to thank my family for their continu­

had a profound impact on my career. Their influence is what

ous love and support, as well as the sacrifices they

inspires me to remain in academics in the hopes of having a

made during completion of this project. 1 have been

similar impact on the next generation of radiologists.
Severa! colleagues contributed to the content of this book

blessed with a wonderful wife, Annie; two sons, Patrick
and Liam; and a daughter, Shannon. Annie and 1 have been

through images and case material, some of which was

together for nearly two decades, and we could not be more

induded in the original "Top 3" book, Top 3 Di.fferentials

proud of our three incredible children. I am grateful

in Radiology. Their contributions have greatly enhanced the

beyond words for the joy that they bring into my life

final manu script. The contributors are listed at the end of the

each and every day.

ix




Brain

Case 1

Fig. 1 .1 Axial T2 (a) and Tl (b) images demonstrate a "figure 8" appearance of the brain with a thickened cortex and absence of the normal gyral and
sulcal pattern. The inner surface of the cortex has an irregular "cobblestone" appearance. Diffuse abnormal signal intensity is identified throughout
the brain parenchyma. Susceptibility artifact from a shunt catheter is noted overlying the right occipital and posterior temporal lobes.

•

Clinical Presentation

An infant boy with seizures, weakness, and failure to meet developmental milestones ( � Fig. 1.1 )

2


Case 1

•

Key lmaging Finding

Agyria

•

Top 3 Differential Diagnoses

• JYpe 1 lissencephaly. Type

1

or dassic lissencephaly is a con­

syndrome, Fukuyama congenital muscular dystrophy, and to

genital neuronal migration disorder that results in a smooth

a lesser degree, musde-eye-brain disease. Patients present

appearance of the brain secondary to absence of the normal

early in Iife with severe muscular weakness, eye abnormali­

gyral and sulcal pattern. There may be diffuse involvement

ties, developmental delay or mental retardation, and compli­

(agyria) or focal involvement (pachygyria) of the cerebral cor­

cations of assodated brain malformations. Patients with

tex. Diffuse involvement results in a "figure 8" appearance of

Walker-Warburg often have characteristic findings, includ­

the brain with vertically oriented Sylvian fissures and absence

ing occipital cephaloceles, cerebellar and brain stem hypo­

of the normal gyral and sulcal pattern. On pathologie evalua­

plasia, and kinking of the brain stem with a dassic "striking

tion, there is a thickened, smooth four-layer cortex with a thin

cobra" appearance on sagittal sequences. Hydrocephalus is

ribbon of subcortical band heterotopia, rather than a normal

present in the vast majority of cases.

1 lissencephaly may be associated with
cytomegalovirus (CMV) infection, Miller-Dieker syndrome,
and cerebellar hypoplasia. With CMV infection, periventricu­

• Band heterotopia. Gray matter heterotopia refers ta collec­

lar and intraparenchymal calcifications are noted. Patients

rons migrate from the ependymal surface of the lateral ventri­

six-layer cortex. Type

tions of disorganized neurons in abnormal locations. It results
from premature arrest of normal neuronal migration. Neu­

with Miller-Dieker syndrome demonstrate midline septal

des to the peripheral cortex, and then undergo organization

calcifications, microcephaly, and characteristic dysmorphie

into a normal six-layer cortex. If arrest occurs at any point
during migration, heterotopias occur. Heterotopia may be

facial features.
• JYpe 2 lissencephaly. Type 2 or cobblestone lissencephaly is

dassified as nodular (most common), which most often

characterized by overmigration of neurons, severe dis­

occurs along the margins of the lateral ventricles, or band,

organization of the gray matter, underdevelopment of gyri

which is located within the subcortical or deep white matter.

and sulci, and diffuse white matter hypomyelination. The

When diffuse and subcortical in location, band heterotopia

disorganized gray matter results in an irregular, "cobble­

may mimic lissencephaly. Patients typically present with

stone" appearance of the cortex. There is an association with

seizures, developmental delay, and spasticity.

congenital muscular dystrophies, induding Walker-Warburg

•

Additional Differential Diagnoses

• Prematurity. Prier ta -26 weeks gestation, the fetal brain nor­

•

appearance at term. Therefore, lissencephaly should not be

mally appears Iissencephalic due ta Jack of gyral and sulcal

diagnosed until after 26 weeks gestation. When uncertain, a

development. After 26 weeks gestation, the gyral and sulcal

follow-up examination may be helpful to evaluate for interval

pattern gradually

gyral and sulcal formation.

progresses until its relatively normal

Diagnosis

1}'pe 2 cobblestone lissencephaly in a patient with Walker­
Warburg syndrome

y' Pearls
• The premature infant brain normally appears lissencephalic
prier ta 26 weeks gestation.
• Llssencephaly is a neuronal migration disorder with absence
of normal gyri/sulci and a thickened cortex.

1 lissencephaly is smooth and may be associated
CMV, Miller-Dieker, and cerebellar hypoplasia.

• Type

with

• Type 2 lissencephaly has a "cobblestone" appearance and is
associated with congenital muscular dystrophies.

Suggested Readings
Barlmvich AJ, Chuang SH, Norman D. MR of neuronal migration anomalies. AmJ
Roentgenol 1988; 150: 179-187

Ghai S, Fong KW, Thi A, Chitayat D, Pantazi S, Blaser S. Prenatal US and MR imaging
findings of lissenœphaly: review offetal œrebral sulcal devclopment Radio­
graphies 2006; 26; 389-405

3


Brain

Case 2

Fig. 2.1 Axial Tl image demonstrates abnormal cortical thickening and
absence of the normal gyri and sulci within the right occipital lobe.
Abnormal cortical and subcortical signal intensity is noted involving the
right occipital and temporal lobes.

•

Clinical Presentation

A 2-day-old boy with seizures and spasms (� Fig. 2.1 )

4


Case 2

•

Key lmaging Finding

Cortical malformation
•

Top 3 Differential Diagnoses

• Pachygyria. Pachygyria is an incomplete or focal form of

lissenœphaly. As with lissencephaly, there is both abnormal
neuronal migration and failure to form the normal six-layer
cortex. Instead, a four-layer cortex is most commonly seen
pathologicaliy. Imaging findings are characterized by short,
broad gyri with a lack of sulcation in the involved segments.
Symptoms depend upon the extent and location of parenchy­
mal involvement. Patients may present with seizures, devel­
opmental delay, mental retardation, and/or spasticity.
• Polymicrogyria. Polymicrogyria is a neuronal migration
abnormality characterized by abnormal distribution of neu­
rons along the cortical surface. Multiple, small gyri replace
the normal organized gyral and sulcal pattern. It is thought to

result from laminar necrosis of neurons after they reach the
cortical surface. It is commonly seen in association with cyto­
megalovirus (CMV) infection. Para-Sylvian locations are com­
monly involved. The polymicrogyria pattern is best depicted
on magnetic resonanœ imaging (MRI). Abnormal signal is
commonly seen in the subjacent white matter. dinically,
patients present with seizures, developmental delay, mental
•

atous overgrowth of ail or a portion of one cerebral hemi­
sphere with associated neuronal migration abnormalities of
varying severity. It is thought to occur as a result of an insult
during neuronal migration. The ipsilateral hemisphere and
ventricle are enlarged. Affected gyri are thickened and may
show a primitive lissenœpahlic appearanœ with shallow or
absent sulci. There is often abnormal attenuation (computed
tomography) and signal intensity (MRI) within the subjacent
white matter. Calcifications are not uncommon. dinically, the
patient may present with seizures, developmental delay,
mental retardation, and/or hemiplegia. Syndromes associated
with hemimegalencephaly include neurofibromatosis type 1,
Klippel-Trenaunay-Weber syndrome, tuberous sderosis, and
Proteus syndrome.

Additional Differential Diagnoses

• Subcortical band heterotopia. Gray

matter heterotopia
refers to collections of disorganized neurons in abnormal

locations due to premature arrest of normal migration.
Neurons migrate from the ependymal surface of the lateral
ventricles to the peripheral cortex, and then undergo orga­

pial surface to the ventricle. The defts are typically para­
Sylvian in location and lined by polymicrogyric gray matter.
In Type I (dosed-lip) schizenœphaiy, the gray matter Iinings
are apposed with a small ventricular dimple of cerebrospinal
fluid (CSF) extending into the deft. Type II (open-lip) schizen­

nization into a normal six-layer cortex. If arrest occurs at
any point during migration, heterotopias occur. Heteroto­

œphaly consists of a large CSF-filled space between the
gray matter linings. Schizenœphaly may be bilateral and asso­
dated with septooptic dysplasia. dinical manifestations
depend upon the severity of the lesion. Patients with type I
are often almost normal in terms of development, but may
have seizures and hemiparesis. Type II patients usually dem­

pia may be classified as nodular, which most often occurs
along the margins of the lateral ventricles, or band-type,
which occurs within the subcortical or deep white matter.
Patients typically present with seizures, developmental
delay, and spasticity.
• Schizencephaly. Schizencephaly is a congenital malformation
characterized by gray matter-lined clefts extending from the
•

retardation, and, occasionally, hemiparesis. Polymicrogyria

may be associated with various syndromes, including Aicardi
(callosal anomalies, infantile spasms, and retinal lesions) and
Zellweger (cerebrohepatorenal) syndromes.
• Hemimegalencephaly. Hemimegalencephaly is a hamartom­

onstrate mental retardation, seizures, hypotonia, spasticity,
inability to walk or speak, and blindness.

Diagnosis

Pachygyria

� Pearls
• Pachygyria is a form of focal lissencephaly with a thickened,

four-layer cortex (instead of the normal six layers).
• With polymicrogyria, small gyri replace the normal, orga­
nized gyral pattern; it is associated with CMV.

• Heterotopia (nodular or band) refers to collections of disor­

ganized neurons in abnormal locations.

Suggested Readings
Barlwvich AJ, Clmang SH, Norman D. MR of neuIOllill migration anomalies. AmJ
Roentgenol 1988; 150: 179-187
Broumandi DD. Haywanl UM, Benzian]M, Gonzalez 1, Nelson MD. Best cases from
the AFIP: hemimegalenœphaly. Radiographies 2004; 24: 843-848

Hayashi N, Tsutswrù Y, Barlcvvich AJ. Morphological features and associated anoma­

lies of schizencephaly in the dinkal population: detailed analysis of MR images.
Neuroradiology 2002; 44: 418-427

5


Brain

Case 3

Fig. 3.1 Axial fluid-attenuated inversion recovery (FLAIR) MR image
demonstrates asymmetry of the cerebral hemispheres with the right
smaller than the left and associated prominence of the sulci on the
right. An enlarged medullary vein is seen along the anterior margin of
the right lateral ventride. Hazy, periatrial white matter signal intensity
corresponds to regions of terminal myelination.

•

Clinical Presentation

A 2-year-old girl with developmental delay (� Fig. 3.1 )

6


Case 3

•

Key lmaging Finding

Asymmetry of cerebral hemispheres

•

Top 3 Differential Diagnoses

• Nonnal variant. Slight variation in size of an entire cerebral

hemisphere, one or more lobes, or individual sulci is not
uncommon, occurring in -10% of normal cases. Parenchymal
morphology, attenuation, and signal intensity should other­
wise be normal and are useful discriminators from pathologie
causes of parenchymal volume Joss. Patients are oft:en neuro­
logically and developmentally intact for age.
volume Joss as a result of some form of insult Hypoxic-ischemic
injury is the most common cause of enœphalomalacia, followed
by trauma and infectious or inflammatory processes. Ischemic
injury typically follows a vascular distribution. During the acute
phase of injury, there is often focal edema and swelling. In the
chronic stage, there is volume Joss with surrounding gliosis. In

Iateral œrebral hemisphere. Venous drainage is diverted through
enlarged medullary and subependymal veins. Hemiatrophy
results, likely from venous hypertension. Magnetic resonanœ
imaging (MRI) shows œrebral atrophy, abnormal leptomenin­
geal enhanœment, and increased enhanœment within a hyper­
trophied ipsilateral choroid plexus. The involved hemisphere
may demonstrate abnormal signal, cortical enhanœment, and

the setting of an asymmetric small œrebral hemisphere, a large

cortical calcifications in a "tram trad<" configuration.

• Encephalomalacia. Enœphalomalacia refers to parenchymal

•
•

Additional Differential Diagnoses
Dyke-Davidolf-Mason syndrome (DDMS). DDMS refers to
compensatory enlargement of the ipsilateral calvarium, para­
nasal sinuses, and mastoid air cells secondary to underdevel­
opment or atrophy of the underlying œrebral hemisphere.
The most common causes of ipsilateral cerebral atrophy

include a large-territory ischemic insult at a young age or
SWS. Symptoms are related to the causative process.
• Hemimegalencephaly. Hemimegalencephaly is a hamartom­
atous overgrowth of all or a portion of one œrebral hemi­
sphere with associated neuronal migration abnormalities. lt is
thought to result from an insult during neuronal migration.
The ipsilateral hemisphere and ventride are enlarged.
Affected gyri are thickened and may show a lissenœpahlic
appearance with shallow or absent suld. There is oft:en abnor­
mal attenuation {computed tomography) and signal intensity
(MRI) within the white matter of the ipsilateral hemisphere.

•

territory infarct (middle œrebral artery) is the most likely cause
of enœphalomalacia.
• Sturge-Weber syndrome (SWS; encephalotrigeminal angioma­
tosis). SWS is a sporadic phakomatosis thought to result from
abnormal development of venous drainage. lt is characterized
by a cutaneous port-wine stain (usually in the Vl distribution of
the trigeminal nerve) and pial angiomatosis overlying the ipsi­

calcifications are not uncommon. Œnically, patients may
present with seizures, developmental delay, mental retarda­
tion, and hemiplegia. Associated syndromes indude neuro­
fibromatosis type 1, Klippel-Trenaunay-Weber syndrome,
tuberous sderosis, and Proteus syndrome.
• Rasmussen encephalitis. Rasmussen enœphalitis is a rare,
progressive, inflammatory neurological disorder of unknown
origin. A viral or postviral autoimmune etiology bas been
postulated. Patients present in childhood with persistent,
relentless, focal motor seizures (epilepsia partialis continua),
hemiplegia, and cognitive deficits. Early on, MRI demon­
strates abnormal edema and increased T2 signal within the
involved hemisphere. Chronically, findings are more charac­
teristic with abnormal signal, asymmetric atrophy, and
decreased perfusion and metabolism on the affected side.
Treatment consists of functional hemispherectomy.

Diagnosis

Sturge-Weber syndrome

� Pearls
• Enœphalomalacia refers to parenchymal volume Joss from

some form of insult; ischemia is most common.

• Hemimegalencephaly is a hamartomatous overgrowth of all

or part of one cerebral hemisphere.

• SWS is characterized by seizures, cutaneous port-wine stain,

and pial angiomatosis of the ipsilateral hemisphere.

Suggested Readings
Shapiro R, Galloway SJ, Shapiro MD. Minimal asyrnrnetryof the brain: a normal variant ArnJ RDentgenol 1986; 147: 753-756

Sener RN, Jinkins JR. MR of cranioœrebral herniatrophy. Œn Irnaging 1992; 16:
93-97

7


Brain

Case 4
Fig. 4.1 Axial T2 (a) and
fluid-attenuated inver­
sion recovery (FLAIR)
(b) images of the brain
demonstrate a hypoin­

tense subependymal
nodular lesion within the
frontal horn of the right
lateral ventricle. The
lesion is isointense to
white matter on Tl
sequences (c) and dem­
onstrates homogeneous
enhancement (d).
Wedge-shaped regions
of cortical and sub­
cortical signal abnormal­
ity are also noted on the
T2/FLAIR sequences (left
hemisphere). (Courtesy
of Paul M. Sherman, MD.)

•

Clinical Presentation

An adolescent with seizures (� Fig. 4.1 )

8


Case 4

•

Key lmaging Finding

Subependymal nodules
•
•

•
•

•

Top 3 Differential Diagnoses
Tuberous sclerosis (TS). TS is a neurocutaneous syndrome
that results from gene mutations affecting chromosomes
9q34.3 {hamartin) and 16p13.3 {tuberin). Two-thirds of cases
occur sporadically, whereas the remaining occur in an auto­
somal dominant fashion with variable penetrance. The classic
triad consists of fadai angiofibromas, mental retardation, and
seizures, but it is only seen in approximately one-third of
cases. Central nervous system (CNS) manifestations include
cortical/subcortical tubers, white matter lesions that occur in
a radial pattern along paths of neuronal migration, subepen­
dymal nodules, and subependymal giant œll astrocytomas
(SEGAs). The cortical/subcortical tubers are composed of dis­
organized glial tissue and heterotopic neuronal elements.
They present as triangular regions of cortical and subcortical
signal abnormality that may calcify and occasionally demon­
strate enhancement Subependymal nodules have variable Tl
and T2 signal intensity and commonly enhance. They demon­
strate gradient echo susœptibility (hypointensity) when cald­

fied; the majority are caldfied by 20 years of age. SEGAs are
low-grade tumors that occur in -1 O to 15% of cases. They are
located at the foramen of Monro, enlarge over time, and
enhance. Interval growth is the best sign to distinguish
SEGAs from dominant subependymal nodules. Treattnent is
typically geared toward œrebrospinal fluid diversion. Com­
mon abnormalities associated with TS include retinal hamar-

tomas, cardiac rhabdomyomas, renal cysts and angiomyolipo­
mas, pulmonary lymphangioleiomyomatosis, subungual
fibromas, and skin lesions, such as "ash-leaf spots" and sha­
green patches.
• Heterotopic gray matter. Heterotopic gray matter results
from arrest or disruption of normal neuronal migration
from the subependymal region to the overlying cortex. lt is
thought to occur secondary to some form of fetal insult during
development. Heterotopia may be nodular or bandlike. Sube­
pendymal heterotopic gray matter is isointense to gray
matter on ail magnetic resonanœ (MR) sequences, does not
enhance, and does not caldfy. Patients often present with
seizures and developmental delay. Mild cases, however, may
be asymptomatic.
• TORCH infection. The TORCH infections consist of toxoplas­
mosis, rubella, cytomegalovirus (CMV), and herpes simplex
virus. CMV is the most common TORCH infection to result in
subependymal and periventricular calcifications, mimicking
tuberous sclerosis on computed tomography {CT). Toxoplas­
mosis also causes intracranial calcifications; however, the
distribution is more random with Jess propensity for the peri­
ventricular region. Common associated findings indude

microcephaly and neuronal migration abnormalities, includ­
ing polymicrogyria and pachygyria. Patients commonly suffer
from mental retardation, seizures, and hearing Joss.

Additional Differential Diagnoses
Metastatic disease. Subependymal metastatic disease may
result from primary CNS neoplasms or hematogenous spread
from extracranial malignandes. Primary CNS neoplasms
prone to subependymal spread include glioblastoma multi­
forme, medulloblastoma, ependymoma, primary CNS lym-

phoma, germ cell neoplasms, pineal cell neoplasms, and cho­
roid plexus tumors. Extracranial metastases from multiple
primary sites may involve the subependymal surfaces and
choroid plexus, particularly breast carcinoma.

Diagnosis

Tuberous sclerosis

� Pearts
TS results in subependymal nodules, which caldfy and dem­
onstrate enhancement.
• Heterotopic gray matter is due to an insult in utero and fol­
lows gray matter signal on all MR sequenœs.

•

CMV is the most common TORCH infection to cause sub­
ependymal/periventricular calcifications.

• Metastases from primary CNS or extracranial malignandes
may present as subependymal nodules.

•

Suggested Readings
Barlmvich AJ, Chuang SH, Norman D. MR of neuronal migration anomalies. AmJ

Roentgenol 1988; 150; 179-187
Braffman BH, Bilaniuk IJ', Naidich TP et al. MR imaging oftuberous sderosis: patho­
genesis of tlùs phalclllnatosis, use of gadopentetate dimeglumine, and literatuœ
review. Radiology 1992; 183; 227-238

Pink KR, Thapa MM, Ishak GE, Prutlù S. Neuroimaging ofpediatric central nervou5
systrm cytmnegalovirus infection. Radiographics 2010; 30: 1779-1796

9


Brain

Case 5
Fig. 5.1 Sagittal Tl magnetic resonance image
shows a defect involving the anterior body of the
corpus callosum with adjacent porencephaly that
communicates with the lateral ventride. The
genu, posterior body, splenium, and rostrum are
present. Additional findings indude signal
abnormality in the region of the hypothalamus,
enlargement of the posterior third ventride, and

a small posterior fossa with mild tonsillar ectopia.

•

Clinical Presentation

A 1 6-year-old boy with difficulties in school (� Fig. 5.1 )

10


Cases

•

Key lmaging Finding

Callosal abnormality
•
•

•
•

•

Top 3 Differential Diagnoses
Agenesis/hypogenesis of the corpus callosum (ACC). Normal
development of the corpus callosum occurs from anterior to
posterior with formation of the genu first, followed by the

body and splenium. The rostrurn is located along the inferior
margin of the genu and is the last portion to form. lmaging
findings with complete agenesis include absence of the cor­
pus callosum and Jack of visualization of the cingulate gyrus
due to failure of rotation. As a result, the third ventride is ele­
vated between the lateral ventrides, which are parallel in
configuration on axial images. There is colpocephaly with dil­
atation of the atria and occipital homs of the lateral ventricles.
The white matter tracts that would cross through the corpus
callosum instead align along the media! margin of the lateral
ventricles and run in an anterior-posterior direction. These
tracts are referred to as Probst bundles. On coronal sequences,
the frontal horns of the lateral ventricles demonstrate a "long­
horn" configuration secondary ta indentation medially by
the Probst bundles and absence of the genu. The gyri of the
media) cerebral hemispheres extend to the margin of the
third ventride with a radial configuration. ACC is nearly
always associated with additional anomalies. With hypogene­
sis of the corpus callosum, portions of the body, splenium,
and rostrum are absent. Absence of the rostrum is a key fea­
ture in distinguishing hypogenesis (rostrum absent) from an
enœphaloclastic process in which the rostrum is typically
present Pericallosal lipomas are often seen in the setting of
abnormal callosal development.

Callosal injury/encephaloclastic process. The majority of
encephalodastic injuries are from surgical interventions, usu­
ally associated with resection of a mass within the third
ventricle or suprasellar region. Trauma and hemorrhage are
Jess common causes of callosal destruction. Imaging findings

include absence of the callosum in the region of injury,
whereas the remaining portions of the callosum are intact
Presenœ of the rostrum exdudes hypogenesis.
• Holoprosenœphaly. Holoprosencephaly is a spectrum of
anomalies characterized by failure of the forebrain to separate
into two distinct hemispheres. There are three variants: alo­
bar, semilobar, and lobar, all of which have complete or partial
absence of the faix and septum pellucidum. In the alobar form
(most severe), there is a large dorsal interhemispheric cyst
(monoventride), and the remaining cerebral parenchyma is
fused and flattened anteriorly. Thalami are also fused. The
corpus callosum, anterior faix, interhemispheric fissure, and
Sylvian fissures are absent Associated craniofacial abnormali­
ties include hypotelorism and cleft patate. In the semilobar
variant, the posterior portions of the callosum are usually
present, whereas anterior portions, induding the rostrum,
are absent. In the least severe lobar variant, the corpus callo­
sum may appear normal or demonstrate partial absence of
the genu. Holoprosencephaly is the one congenital anomaly
in which the genu may be absent whereas the body and sple­
nium are present.

•

Additional Differential Diagnoses
Volume loss. The volume of the corpus callosum is related to
the volume of white matter within the supratentorial brain.
Prior to myelination, the corpus callosum normally appears
thin. As myelination progresses, it obtains its more typical
volume and appearanœ. With severe supratentorial paren­

chymal injury, al! or portions of the corpus callosum demon-

strate atrophy, because the callosal volume is dependent
upon the white matter fibers forming the tracts. Severe
hydrocephalus may produce similar findings secondary to
pressure-related changes or encephalomalacia of the corpus
callosum.

Diagnosis

Callosal injury/encephaloclastic process (postsurgical)

� Pearls
•
•

With ACC or hypogenesis, al! or a portion of the corpus callo­
sum is absent, including the rostrum, which is last to form.
Callosal injury is most often postsurgical, followed by trauma
and hemorrhage.

•

Holoprosencephaly is the one congenital anomaly where the
genu may be absent and the splenium present.

Suggested Readings
Batul B, Kocaoglu M, AkgunV, Bulakbasi N, Tayfun C. Corpus callosum; normal
imaging appearanœ, variants and pathologie conditions. j Med lmaging Radiat
Oncol 2010; 54: 541-549

Sztriha I. Spectrum ofcorpus callosum agenesis. Pediatr Neurol 2005; 32; 94-101

11


Brain

Case 6
Fig. 6.1 Sagittal T2 image demonstrates
significantly decreased volume of the cerebellar
vermis with prominence of the sulci. The brain
stem appears normal in size and morphology.

•

Clinical Presentation

A 20-year-old man with chronic ataxia and progressive neurological decline (� Fig. 6.1)

12


Case 6

•

Key lmaging Finding

Cerebellar atrophy/volume Joss

•

Top 3 Acquired Differential Diagnoses

Alcohol abuse. Alcohol abuse results in progressive cerebel­
lar degeneration. Alcohol is neurotoxic, causing cerebellar
and cortical {frontal lobe predominant) degeneration, as well
as peripheral polyneuropathies. There is disproportionate
involvement of the superior vermis and cerebellum com­
pared with the cerebral hemispheres. Associated findings
may include Wemicke enœphalopathy, which presents as
abnormal T2 hyperintensity within the periaqueductal gray
matter, mammillary bodies, medial thalamus, and hypo­
thalamus: and Jess commonly Marchiafava-Bignami disease,
which results in abnormal signal intensity within the corpus
callosum.
• Anticonvulsant therapy. Both seizures and long-term anti­
convulsant therapy may produce irreversible cerebellar

•

•

Top 3 Sporadic or lnherited Differential Diagnoses

Sporadic olivopontocerebellar atrophy (sOPCA). sOPCA,
also referred to as multisystem atrophy, is a neuro­
degenerative disorder of unknown etiology that typically
presents in adulthood. Cross-sectional imaging demon­
strates atrophy of the ventral pons and midbrain with

enlargement of the fourth ventride and widening of the
superior and middle œrebellar peduncles. There is hemi­
spheric greater than vermian cerebellar atrophy, as well as
less pronounced cerebral atrophy, which most preferentially
involves the frontal and parietal lobes. Crudform-Iike T2
hyperintensity in the base of the pons gives the characteris­
tic "hot cross bun" sign. Abnormal signal intensity is also
seen in the middle cerebellar peduncles and dorsolateral
putamen. Patients present with parkinsonian features,
ataxia, dysarthria, and autonomie dysfunction.
• Ataxia telangiectasia (AT). AT is an autosomal reœssive com­
plex that results in spinoœrebellar degeneration. ocular and
cutaneous telangiectases, radiation sensitivity, immunodefi-

•

•

degeneration with disproportionate œrebellar atrophy.
Patients present with ataxia, nystagmus, and peripheral
neuropathies. Phenytoin is the most common drug therapy,
and its use may also result in diffuse calvarial thickening.
• Paraneoplastic syndrome. Cerebellar degeneration may
occur as a result of a paraneoplastic syndrome. Breast and
Jung cancer are by far the most common primary neoplasms.
Less common associated malignancies indude gastro­
intestinal and genitourinary neoplasms, Hodgkin lym­
phoma, and neuroblastoma. The œrebellar degeneration is
thought to result from autoantibodies to Purkinje fibers or a
cytotoxic process associated with T cells. The paraneoplastic

cerebellar degeneration often precedes the diagnosis of a
primary tumor.

ciendes, and increased risk of neoplasms. Patients often
present as toddlers with signs of ataxia. The neurological
decline is progressive. Cross-sectional imaging demonstrates
œrebellar atrophy with enlargement of the cerebellar suld
and compensatory enlargement of the fourth ventricle. There
is also atrophy of the dentate nuclei. lntracranial telangiec­
tases may result in scattered foci of gradient echo susceptibil­
ity secondary to microhemorrhages. Occasionally, associated
supratentorial white matter demyelination or dysmyelination
may be seen.
• Friedreich ataxia. Also known as spinocerebellar ataxia, Frie­
dreich ataxia typically presents in the second decade of life and
has bath autosomal dominant and recessive forms. Cross­
sectional imaging demonstrates mild atrophy of the vermis
and paravermian structures, a small medulla, and significant
atrophy of the spinal cord. The dorsal cord has a flattened
appearance. Oinically, patients often present with Iawer
extremity ataxia, upper extremity tremors, and kyphoscoliosis.

Diagnosis

Ataxia telangiectasia

� Pearts
Alcohol, anticonvulsant therapy, and paraneoplastic syn­
dromes are secondary causes of œrebellar atrophy.
• sOPCA results in cerebellar and brain stem atrophy; pontine

hyperintensity is referred to as "hot cross bun" sign.

•

• AT

presents with spinocerebellar degeneration, telangiec­
tases, immunodeficiendes, and risk ofneoplasms.

Suggested Readings
Fisdtbein NJ, DillonWP, Barkovidl. AJ. TeachingAtlas of Brain Imaging. NewYork,
NY: Thieme. 1999

Huang YP, Tuason MY, Wu T, Plaitaki5 A MRI and CTfeature5 ofcerebeUar degenera­
tion j Formes Med Assoc 1993; 92: 494-508

13