Clinical Correlation
THE RELATIONSHIP BETWEEN NEUROANATOMY AND NEUROLOGY: PRINCIPLES OF
LESION LOCALIZING
Dr. Bruce Giffin
Monday, April 9, 2007 11:00 am
Objectives: The student should
 Appreciate the close link between basic and clinical neurosciences
 Describe how in localizing a lesion, the topography of the lesion(s) in the CNS is determined
in terms of the level of involvement and the systems affected
 Discuss how type localization involves identifying whether the lesion is unifocal, multifocal,
diffuse, or confined to a system
 List the typical signs and symptoms of lesions of the nervous system involving various levels
and systems and use these in anatomical localization
The foundations of clinical neurology include anatomy and physiology, the patient history, the
neurologic examination, and the intellectual exercise of identifying where in the nervous system
is the site, and what is the nature of the pathology.
THE INTERPRETATION OF PHYSICAL SIGNS FOUND UPON CLINICAL EXAMINATION OF
A PATIENT WITH NEUROLOGICAL PROBLEMS DEPENDS HEAVILY UPON YOUR
PRACTICAL KNOWLEDGE OF NEUROANATOMY!
In order to for the physician to come up with a differential diagnosis, a correct diagnosis, and a
prognosis for pathology and diseases affecting the nervous system, two questions need to be
answered: Where is the lesion? and What is the lesion? The information in this handout is
intended as an introduction to clinical thinking to help you in the CASE-BASED PROBLEM
SOLVING exercises which are a scheduled activity of the Brain and Behavior I course.
SOME DEFINITIONS
Lesion-a zone of localized dysfunction within the CNS or PNS and may be anatomic (structural
damage) or physiologic (absence of demonstrable anatomic abnormalities).
Differential diagnosis-the process of making a diagnosis by comparing and analyzing the
similarities and differences between the signs, symptoms, and other findings associated
particularly with two or more diseases sharing certain characteristics; similar conditions are
systematically eliminated from consideration
SOME GENERALIZATIONS
Manifestations of neurologic disease by be negative (loss of function) or positive
(abnormalities resulting from inappropriate excitation). Some neurological disorders affect
primarily gray matter, others affect primarily white matter, and some disorders affect both gray
and white matter. Neurologic disease can result in syndromes (a constellation of signs and
symptoms frequently associated with each other and suggest a common origin). Many
pathologic processes result in lesions that are larger than any single nucleus or tract. In these
cases neighborhood signs (combinations of signs and symptoms) may help to localize the
lesion. Dysfunction of the nervous system can be due to destruction or compression of neural
tissue, or compromise of the cerebrovascular system.
PROCESSES CAUSING NEUROLOGIC DISEASE
Focal pathology causes signs and symptoms on the basis of a single, geographically
contiguous lesion.
Multi-focal pathology results in damage to the nervous system at multiple, separate sites.
Diffuse dysfunction of the nervous system can result from toxins or metabolic abnormalities.
WHERE IS THE LESION?
The location of a lesion needs to be determined by (1) rostral-caudal localization (examine
the constellation of neurologic signs and symptoms and relating them to appropriate tracts and
nuclei; it is often possible to place the lesion at the appropriate level along the rostro-caudal
axis) and (2) transverse localization (place the lesion within the cross section of the brain or
spinal cord). There are four major anatomical levels at which the lesion can be localized. These
levels are defined by the meninges and the bony structures to which they are related.




Medial (A) and lateral (B) views of
sections though brain and spinal cord
illustrating major levels: supratentorial
(dark shading), posterior fossa with
brainstem (lines) and cerebellum (dots),
and spinal (clear area). Peripheral level is
not shown.
Supratentorial level: the portion of
the nervous system located above
the tentorium cerebelli (cerebral
hemispheres, basal ganglia,
thalamus, hypothalamus, cranial
nerves I and II)
Posterior fossa level: contains
structures located within the skull,
below the tentorium cerebelli but
above the foramen magnum
(midbrain, pons, medulla,
cerebellum, cranial nerves III-XII)
Spinal level: the portion of the
nervous system located below the
foramen magnum but contained
within the vertebral column (spinal
cord and nerves contained in the
body vertebral column and in the
intervertebral foramina)
Peripheral level: includes all
neuromuscular structures located
outside the skull and vertebral
column (cranial and peripheral
nerves, their branches, and
structures innervated by them,
autonomic ganglia and nerves)
WHAT IS THE LESION?
After anatomical localization it is necessary to determine the pathologic features of the
lesion. This requires knowledge of the cellular elements of the nervous system and their
pathological reactions.
Information from the examination and the history such as age, gender, and the general
medical context (smoking, hypertension, etc.) is important.
The time-course of the illness in many cases can provide invaluable information about
the nature of the illness.
 Transient ischemic attacks: (brief, reversible neurologic dysfunction resulting from
reversible ischemia which resolves in about 24 hours) can be predictive of an
upcoming stroke.
TIME

Relapsing-remitting: patient experiences bouts of dysfunction lasting days to weeks
followed by functional recovery (e.g. multiple sclerosis)

Sudden onset: a fixed deficit comes on suddenly; characteristic of cerebrovascular
disease

Slowly progressive dysfunction: evolves over years and suggests a
neurodegenerative disease (Alzheimer's, Parkinson's)

Subacutely progressive dysfunction: advances over weeks to months (e.g. brain
tumors)
CLINICAL CORRELATIONS
Think of the nervous system as you
would an electrical circuit (later we
will call these wires “line segments”).
The longitudinal systems (motor and
sensory) lead to and from the cerebral
hemispheres and conduct impulses
from one segment to another.
Segmental “wires” (nerves) come
off of these intersegmental “cables”.
If there is damage to an intersegmental
cable, there will be a loss of function
beyond that point. Damage to a
segmental wire will result in a
loss of function confined to that
individual segment.
Major nervous system connections. (A), cranial
nerves; (B), spinal nerves. Note the long
intersegmental pathways leading to and from
higher centers and multiple, short segmental
pathways (cranial and spinal nerves) to the
peripheral level.
SEGMENTAL PATHWAYS
INTERSEGMENTAL PATHWAYS
LOCALIZATION is determined by the level of the nervous system in which the pathway
function is interrupted. To aid in localization, the functions of each of the major
anatomical levels are summarized below:
LEVEL
SUPRATENTORIAL
POSTERIOR
FOSSA
SPINAL
PERIPHERAL
CLINICAL FINDING
SIDE OF LESION
Loss of sensation and/or weakness
on the SAME side of the body and face
Contralateral to the deficit
Loss of sensation and/or weakness on
ONE side of the face and OPPOSITE side of body
Ipsilateral to side of the face
Cranial nerve deficit
Cerebellar deficit
Loss of pain and temperature on ONE side and
weakness and loss of position sense on
OPPOSITE side of the body
Loss of sensation to all modalities in distribution of
nerve or sensory loss in glove-and-stocking
distribution
Muscle weakness in distribution of nerve
Ipsilateral to cranial nerve
Ipsilateral to cerebellar deficit,
cerebellar signs (incoordination)
Ipsilateral to loss of position
sense and weakness
Ipsilateral to sensory loss
COMMON
SEGMENTAL SIGNS
OF THE LEVEL
Vision
Olfaction
Cognition
Memory
Intelligence
Behavior
Seizures
Hearing
Tinnitus
Vertigo
Diplopia
Dysarthria
Dysphagia
Neck/back pain;
findings related to
specific spinal level
Limb pain without back
pain; loss of sensation
and muscle weakness
in distribution of a
nerve
SOME EXAMPLES OF HOW TO GO ABOUT THE LESION LOCALIZING PROCESS
Think of each symptom or abnormal physical finding as a line segment that connects the
CNS to a muscle or sensory receptors out in the periphery. If all these line segments
intersect at a single point, that point will be where the lesion is localized. In the event
that there are two or more points where all the line segments intersect, each potential
localization site will need to be evaluated further by determining whether the patient has
other symptoms or signs that would be expected with a lesion in that location.
EXAMPLE 1:
A patient is found to have the following: (1) weakness of abduction of the little
finger on the right hand and (2) reduced pinprick sensation on the palmar surface
of the little finger of the right hand. Where is the lesion?
EXAMPLE 2:
A patient is found to have the following: (1) reduced pinprick sensation on the left
forehead and (2) reduced pinprick sensation on the palmar surface of the little
finger of the right hand. Where is the lesion?
EXAMPLE 3:
A patient is found to have reduced vibration sense in the left foot and reduced
pinprick sensation on the palmar surface of the little finger of the right hand.
Where is the lesion?
EXAMPLE 4:
A patient is found to have reduced vibration sense in the left and right foot and
the left and right hand. Where is the lesion?
This page and the following page are to help you begin developing a
vocabulary for lesion localizing as you work through case-based problems.
THE LOCATION OF LESIONS
The following is a systematic survey of the nervous system with examples of lesions that
can be located in the following anatomic sites. It is by no means all-inclusive.

Muscles: weakness, atrophy, depressed deep tendon reflexes (dystrophies,
polymyositis)

Motor end-plates: weakness, abnormal fatigabililty; may involves limbs or trunk, or
muscles involved in chewing, swallowing, eye movement (LEMS, myasthenia gravis)

Peripheral nerves: motor and sensory deficits together or separately (peripheral
neuropathies)

Roots: segmental motor deficit (may be mediated through several nerves if a plexus
lesion); sensory difficult due to dermatomal overlap

Spinal cord: decussation pattern is staggered for fine touch and pain and
temperature-permits localization within the cord; LMN signs and symptoms at the
level of injury with UMN signs and symptoms below the level of injury

Brainstem: functional deficits of the long tracts and cranial nerve signs and
symptoms can localize the lesion to the medulla, pons, or midbrain

Cerebellum or its peduncles: impaired motor coordination, decreased muscle tone
ipsilateral to the lesion site

Diencephalon: hypothalamus-endocrinologic and visual abnormalities; thalamussensory and motor dysfunction; subthalamus-dyskinesias (hemiballism);
epithalamus- compression of the cerebral aqueduct (hydroencephalus)

Subcortical white matter: abnormal myelin (leukodystrophy); destruction of normal
myelin (multiple sclerosis) with abnormal axonal conduction; pathology-diffuse, focal,
or multi-focal

The basal ganglia (subcortical gray): movement disorders (Parkinson's disease,
Huntington's disease)

Cerebral cortex: focal lesions (disorders of language, neglect syndromes, UMN
weakness of contralateral limbs); irritative lesions (focal or generalized seizures)

Meninges: hemorrhages into spaces in and around the meninges (subarachnoid,
subdural, epidural); infection (meningitis)

Skull, vertebral column, and associated structures: intervertebral disks,
ligaments, joints
THE NEUROPATHOLOGIC CLASSIFICATION OF VARIOUS DISORDERS
AFFECTING THE NERVOUS SYSTEM

Vascular disorders: usually sudden onset; cerebrovascular disease secondary to
hypertension; stenosis or occlusion; embolism from ulcerated plaques; subarachnoid
hemorrhage and intraparenchymal hemorrhage; subdural and epidural hemorrhages
as a result of trauma

Trauma: head injuries; penetrating injuries destroying brain tissue

Tumors: primary tumors of brain and spinal cord directly invade and destroy brain
tissue; hydroencephalus from compression of the ventricular system; progresses
over weeks, months, or years

Infections and inflammation: meningitis, abscess, encephalitis, and granulomas;
may be accompanied by fever

Toxic, deficiency, and metabolic disorders: toxic substances, vitamin
deficiencies, enzyme defects

Demyelinating diseases: can produce multiple lesions in the CNS white matter

Degenerative diseases: spinal, cerebellar, subcortical, and cortical degenerative
disorders often characterized by specific functional deficits

Congenital malformations and perinatal disorders: exogenous factors, genetic
and chromosomal factors that produce abnormalities of the brain and spinal cord

Neuromuscular disorders: muscular dystrophies, congenital myopathies, NMJ
disorders, nerve lesions or neuropathies
SELECTED REFERENCES
Adams, R.D., Victor, M., and Ropper, A.H. Principles of Neurology. (6th edition). New
York: McGraw-Hill. 1997.
Brazin, P.W., Masdeu, J.C., and Biller, J. Localization in Clinical Neurology. (3rd edition).
Boston: Little, Brown and Company (Inc), 1996.
DeMeyer, W.E. Technique of the Neurologic Examination. (4th edition). New York:
McGraw-Hill, Inc. 1994.
Fitzgerald, M.J.T. Neuroanatomy: Basic and Clinical. (3rd edition). Philadelphia:
Saunders and Company. 1996.
Plum, F., and Posner, J.B. The Diagnosis of Stupor and Coma. (3rd edition).
Philadelphia: F.A. Davis Company. 1982.
Ross, R.T. How to Examine the Nervous System. (3rd edition). Connecticut: Appleton
and Lange. 1999.
Wilkinson, I.M.S. Essential Neurology. (3rd edition). Oxford: Blackwell Science. 1999.
Patten, J. Neurological Differential Diagnosis. (2nd edition). New York: Springer-Verlag,
1996.