Transcript Newly Described Anatomic Signs Reliably Define

Newly Described Anatomic Signs
Reliably Define Temporal Lobe
Anatomy in Multiple Planes on MRI
Vance T. Lehman, MD
Kirk M. Welker, MD
David F. Black, MD
Mathew A. Bernstein, PhD
Department of Radiology
Mayo Clinic, Rochester MN
Background
• The temporal lobe is anatomically and
functionally complex
• Types of functional cortex include:
– Primary auditory
– Wernicke’s language
– Limbic
– Unimodal auditory association
– Unimodal visual association
Background
• The importance of anatomic details of
temporal lobe anatomy is increasing with
increased knowledge/use of fMRI
• We devised 8 new anatomic signs to facilitate
recognition of temporal lobe anatomy by
visual inspection in clinical practice
Hypothesis
• The hypothesis of this study was that these 8
signs are routinely present in patients with
normal temporal lobe anatomy
Methods
• IRB approval obtained
• 50 consecutive patients with high resolution
MPRAGE series performed for evaluation of
seizures with normal or near-normal exams
included
Methods
• Exclusion criteria = malformation of cortical
development, intracranial mass,
hydrocephalus, delayed myelination, temporal
lobe encephalomalacia, MTS, hippocampal
malrotation, prior temporal lobe surgery,
excessive motion, lacunar infarcts in the
temporal lobe, patients less than 3 years of
age
Methods
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Abbreviations of Gyri:
HG = Heschl’s Gyrus/Gyri
STG = Superior Temporal Gyrus
MTG = Middle Temporal Gyrus
ITG = Inferior Temporal Gyrus
LOTG = Lateral Occipital Temporal (fusiform)
Gyrus
• PHG = Parahippocampal Gyrus
Methods
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Abbreviations of Sulci:
STS = Superior Temporal Sulcus
ITS = Inferior Temporal Sulcus
OTS = Occipitotemporal Sulcus
RS = Rhinal Sulcus
CS = Collateral Sulcus
Methods
• Definitions of evaluated sulci and gyri:
STG
MTS
PHG
LOTG ITG
RS
OTS
STS
HG STG
STS
ITS
STG
MTG
LOTG ITG
ITG
CS
OTS
Methods
• Pointed STG sign: The STG has an anteriorly
‘pointed’ appearance with a broader base
posteriorly and narrower tip anterior (can be
rounded). The posterior medial base is
contiguous with the posterior insula; however
it is broad and extends laterally unlike Heschl’s
gyri.
Methods
• Posterior Insular Corner Sign: In the axial
plane, the transverse gyrus of Heschl, or HG, is
a finger-like gyrus that arises from the
posterior insula, projected anterolaterally. This
can consist of one or multiple gyri.
Methods
• Fork Prong Sign: The anterior most extent of
anteroposteriorly directed basal temporal
sulci (rhinal sulcus and OTS) are assessed. An
anteriorly directed RS extends inferior to the
temporal horn of the lateral ventricle, forming
the medial prong. The lateral prong is formed
by an anteriorly projected OTS sulcus is
located lateral to the temporal horn of the
lateral ventricle.
Methods
• CS Arc Sign: The CS is seen as a temporal lobe
sulcus on sagittal images with a discrete upward
convex curved line (sulcus), consisting of an
anterior slope, a single apex, and a posterior
slope. Posterior to the apex, the sulcus continues
as the occipital extension of the CS. The arc apex
is at the anteroposterior level of the atrium of the
lateral ventricle. The PHG is located superior to
the upward convex line anteriorly and the LOTG is
located inferior to it.
Methods
• CS Bracket Sign: On axial images, the collateral
sulcus proper extends nearly to or to the
medial temporal lobe surface, bracketing the
posterior border of the PHG. The lateral tip of
this sulcus at the levels of the bracket sign is
angled anteriorly or straight laterally, but not
posteriorly.
Methods
• OTS Plateau Sign: Upward convex plateau of
grey matter within the temporal lobe with a
broad base along the inferior temporal lobe,
located medial to the superior and inferior
temporal sulci. A second plateau may be seen
posteriorly, representing a separate segment
of this often discontinuous sulcus.
Methods
• PHG Y sign: Posteriorly, the parahippocampal
gyrus is continuous with both the isthmus of
the cingulate gyrus superiorly and the lingual
gyrus inferiorly on at least one sagittal image,
with the anterior extent of the calcarine sulcus
interposed. The white matter of these gyri
creates a roughly horizontal ‘Y’ appearance
that splits posteriorly.
Methods
Rabbit Ear Sign: The RS anteriorly and CS proper
posteriorly arc upward from the inferior surface
of the temporal lobe on at least one common
sagittal image. This sign was recorded as
absent or present.
Results
50 patients Identified
Males: n=24
Mean age: 19 years (range 1-79)
Right-handed
Left-handed
Ambidextrous
Results
Frequency of Temporal Lobe Anatomic Signs
Sign
Right
Left
Total
Hemisphere
Hemisphere
Pointed STG
49/50 (98%)
49/50 (98%)
98/100 (98%)
Posterior Insular Corner
50/50 (100%)
50/50 (100%)
100/100 (100%)
Fork Prong
38/50 (76%)
44/50 (88%)
82/100 (82%)
Collateral Sulcus Bracket
47/50 (94%)
45/50 (90%)
92/100 (92%)
Collateral Sulcus Arc
45/50 (90%)
42/50 (84%)
87/100 (87%)
Occipitotemporal Sulcus Plateau
47/50 (94%)
47/50 (94%)
94/100 (94%)
Rabbit Ear
41/50 (82%)
43 (86%)
84/100 (84%)
Parahippocampal Y
49/50 (98%)
49/50 (98%)
98/100 (98%)
Results
• Pointed STG sign:
– Coned-in axial image
– STG is outlined in yellow
Results
• Posterior Insular Corner Sign:
– Coned in axial image
– HG are outlined in red
Results
• Fork Prong Sign:
– Coned-in axial image
– Medial prong = rhinal sulcus
– Lateral prong = OTS
Results
• CS Arc Sign:
– Coned-in Sagittal image
– CS = light green
Results
• CS Bracket Sign:
– Coned-in axial view
– CS = dark blue
Results
• OTS Plateau Sign:
– Coned-in sagittal image
– OTS is outlined in yellow
– Note the double-plateau in this case
Results
• PHG Y sign:
– Coned-in sagittal image
– PHG is outlined in blue
– Cingulate isthmus is outlined in red
– Lingula is outlined in green
Methods
Rabbit Ear Sign:
Discussion
This study confirms the hypothesis that 8 newly
described anatomic signs to delineate temporal
lobe anatomy in the axial and sagittal planes are
frequently present
Discussion
This topic is particularly relevant with increased
use of fMRI and need for anatomic correlation
to functional regions
While these functional regions cannot be
completely delineated with anatomic imaging,
many are sharply demarcated by sulci since
subjacent gyri frequently have very different
function, cytoarchitecture, and clinical relevance
Discussion
This topic is particularly relevant with increased
use of fMRI and need for anatomic correlation
to functional regions
While these functional regions cannot be
completely delineated with anatomic imaging,
many are sharply demarcated by sulci since
subjacent gyri frequently have very different
function, cytoarchitecture, and clinical relevance
Discussion
The major temporal lobe sulci and gyri can be
identified in multiple imaging planes
Some clinically relevant examples:
Discussion
HG
-contains primary auditory cortex
-bilateral lesions typically needed for
cortical deafness
LOTG
-contains unimodal visual association cortex
-contains object/face identification centers
- bilateral lesions posteriorly may result in
prosopagnosia
Discussion
PHG
-immediately adjacent to LOTG
-but, different function (limbic cortex)
Future Study
Validate at lower spatial resolution
Validate signs in other patient populations
Demonstrate fMRI activation of various tasks in
relationship to these signs