Newly Described Anatomic Signs Reliably Define Temporal Lobe Anatomy in Multiple Planes on MRI Vance...

Newly Described Anatomic Signs Reliably Define Temporal Lobe Anatomy in Multiple Planes on MRI

Vance T. Lehman, MDKirk M. Welker, MDDavid F. Black, MD

Mathew A. Bernstein, PhD

Department of RadiologyMayo 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

• 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

• 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:

STSSTG

MTSITSITG

OTS

LOTG

RS

PHG

STGSTS

MTG

ITGITG

OTS

LOTG

CS

STG

HG

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 IdentifiedMales: n=24Mean age: 19 years (range 1-79)Right-handedLeft-handedAmbidextrous

Results

Frequency of Temporal Lobe Anatomic Signs

Sign Right

Hemisphere

Left

Hemisphere

Total

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 regionsWhile 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 regionsWhile 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 resolutionValidate signs in other patient populationsDemonstrate fMRI activation of various tasks in relationship to these signs