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 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: STS STG MTS ITS ITG OTS LOTG RS PHG STG STS MTG ITG 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 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 Hemisphere Left Hemisphere Total Pointed STG49/50 (98%) 98/100 (98%) Posterior Insular Corner50/50 (100%) 100/100 (100%) Fork Prong38/50 (76%)44/50 (88%)82/100 (82%) Collateral Sulcus Bracket47/50 (94%)45/50 (90%)92/100 (92%) Collateral Sulcus Arc45/50 (90%)42/50 (84%)87/100 (87%) Occipitotemporal Sulcus Plateau47/50 (94%) 94/100 (94%) Rabbit Ear41/50 (82%)43 (86%)84/100 (84%) Parahippocampal Y49/50 (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