HE temporal stem overlying the inferior limiting sul-cus of the insula and the lateral superior margin of thetemporal horn3–5,10,11,16,18,22,38 is the white matter bridge

between the anterior temporal lobe and thalamus and thebrainstem and frontal lobe. Dysfunction of the temporalstem, resulting from congenital, traumatic, surgical, or de-generative disconnection of the temporal and frontal lobes,is involved in a number of cerebral disorders. This structureis also a critical landmark for the transinsular surgical tra-jectory to the temporal horn. A cortical incision in the infe-rior limiting sulcus is required for the surgical approach, butin this process the temporal stem can be injured. This injurymay result in various cognitive deficits and/or visual fielddefects.5,9,12,18,21,30

The temporal stem contains several white matter tracts.The anterior limit of the temporal stem is the amygdaloidbody, and the posterior limit is the lateral geniculate body.4,

22,40 However, it is difficult to identify these fiber tracts andlandmarks on MR studies and in the surgical fields.2,16 Inthis study, after briefly reviewing the anatomy of the insu-la and the temporal horn,23,28,31 we apply the DTT techniqueto define the anatomical landmarks of the white mattertracts, and we then introduce a simple, yet effective, meth-od for locating the fiber tracts of the temporal stem on MRimaging and intraoperatively.

Additionally, the term “temporal stem” is confusing be-cause it reduces the multidimensional, multidirectional, andmultimodular activities of the temporal lobe in the neo-,archi-, and paleopallial cortices and the amygdala nucleusto merely anterior connections.37 Nevertheless, there is cur-rently no suitable term to describe the region. Therefore, wewish to develop a more accurate term.

Materials and Methods

Anatomical Study

The topographical anatomy was studied in 10 adult human brainspecimens (20 hemispheres). Each specimen was later dissected and

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J Neurosurg 108:775–781, 2008

Diffusion tensor tractography of the temporal stem on theinferior limiting sulcus

Laboratory investigation

FENG WANG, M.D.,1,2 TAO SUN, M.D.,2 XING-GANG LI, M.D.,1 AND NA-JIA LIU, M.D.3

1Department of Neurosurgery, Qilu Hospital of the Shandong University, Jinan, Shandong; andDepartments of 2Neurosurgery and 3Radiology, The Affiliated Hospital, Ningxia Medical College,Yinchuan, Ningxia, China

Object. The aim of this study was to use diffusion tensor tractography (DTT) to define the 3D relationships of theuncinate fasciculus, anterior commissure, inferior occipitofrontal fasciculus, inferior thalamic peduncle, and optic radi-ation and to determine the positioning landmarks of these white matter tracts.

Methods. The anatomy was studied in 10 adult human brain specimens. Brain DTT was performed in 10 healthy vol-unteers. Diffusion tensor tractography images of the white matter tracts in the temporal stem were obtained using thesimple single region of interest (ROI) and multi-ROIs based on the anatomical knowledge.

Results. The posteroinferior insular point is the anterior extremity of intersection of the Heschl gyrus and the inferi-or limiting sulcus. On the inferior limiting sulcus, this point is the posterior limit of the optic radiation, and the tempo-ral stem begins at the limen insulae and ends at the posteroinferior insular point. The distance from the limen insulae tothe tip of the temporal horn is just one third the length of the temporal stem. The uncinate fasciculus comprises the coreof the anterior temporal stem, behind which the anterior commissure and the inferior thalamic peduncle are located, andthey occupy the anterior third of the temporal stem. The inferior occipitofrontal fasciculus passes through the entire tem-poral stem. The most anterior extent of the Meyer loop is located between the anterior tip of the temporal horn and thelimen insulae. Most of the optic radiation crosses the postmedian two thirds of the temporal stem.

Conclusions. On the inferior limiting sulcus, the posteroinferior insular point is a reliable landmark of the posteriorlimit of the optic radiations. The limen insulae, anterior tip of the temporal horn, and posteroinferior insular point maybe used to localize the white matter fibers of the temporal stem in analyzing magnetic resonance imaging or during sur-gery. (DOI: 10.3171/JNS/2008/108/4/0775)

KEY WORDS • anatomical study • diffusion tensor tractography • inferior limiting sulcus •optic radiation • temporal stem

T

775

Abbreviations used in this paper: DT = diffusion tensor; DTT =DT tractography; MR = magnetic resonance; ROI = region of in-terest.

found to be normal. The goal of the anatomical study was to deter-mine the morphological landmarks corresponding to the white mat-ter tracts of the temporal stem on the DT images. Particular attentionwas given to the observation and measurement of the followingstructures: the insula, limen insulae, inferior limiting sulcus, Heschlgyrus, temporal horn, and lateral geniculate body. The anatomicalstructure in our study is described in accordance with standard no-menclature. The term “posteroinferior insular point” is introduced toindicate the most anterior junction of the Heschl gyrus and the infe-rior limiting sulcus.

Acquisition of DT MR Images and Directional Maps

Diffusion tensor imaging was performed in 10 healthy volunteersby using a 1.5-T MR imager (Signa Horizon LX, version 8.3;General Electric Medical Systems) with a single-shot, spin echo–echo planar, diffusion-weighted pulse sequence (15 different mo-tion-probing gradient directions; TR 6000 msec, TE 78 msec, b value0 and 1000 seconds/mm2, matrix 128 3 128, field of view 24 cm,slice thickness 5 mm [no gap], number of excitations 2). Visualiza-tion of the DTT images was performed using dTV II and VOLUME-ONE DT imaging software. We visualized the fiber tracts of the tem-poral stem ROIs based on anatomical knowledge and conventionalMR imaging. The fractional anisotropy threshold for tracking wasset at 0.18, and stop length was set at 160 steps. First, we used a sim-ple single ROI by stepwise decreases to reconstruct the entire tem-poral stem. Second, we used a multiple-ROI approach to reconstructthe individual fiber tracts of the temporal stem. When multiple ROIswere used for a tract reconstruction, we used 3 types of operations:seed, target, and avoidance. The choice of operation depended on thecharacteristic trajectory of the tract. The convention we used for di-rectional red-green-blue color mapping is red for left–right, green foranterior–posterior, and blue for superior–inferior.

To reconstruct tracts of the optic radiation,35 the first ROI wasplaced in the occipital lobe on a reconstructed coronal image with aseed operation, and after we placed the first ROI, the fibers penetrat-ing this region were identified. The second ROI was manually placedin the lateral geniculate body on a reconstructed sagittal image witha target operation. When we placed the second ROI, the fibers pen-etrating the first ROI were already shown on a reconstructed sagittalimage, and thus we could see a bundle of fibers penetrating the firstROI and the lateral geniculate body.

Similarly, tractographic reconstructions of the uncinate fascicu-lus29 were obtained with the seed area in the white matter of the fron-tal lobe on coronal images at the tip of the frontal horn of the lateralventricle and also with the target area in the white matter on coronalplanes at the tip of the temporal horn of the lateral ventricle in theipsilateral temporal tip. Tractographic reconstructions of the inferioroccipitofrontal fasciculus29 were obtained with the same seed area asthe uncinate fasciculus and with the target area in the ipsilateral sag-ittal stratum on coronal images at the level of the trigone. Tracto-graphic reconstructions of the bilateral anterior commissures wereobtained with the seed area in the anterior wall of the third ventricleon the median sagittal images and with the target area in the whitematter of the bilateral temporal lobe on coronal planes at the level ofthe anterior wall of the third ventricle. Tractographic reconstructionsof the unilateral anterior commissure were obtained with the sameseed area as the bilateral anterior commissures and with the targetarea in the white matter of the unilateral temporal lobe on the sagit-tal images lateral to the tip of the temporal horn. In addition, we ob-tained reconstructions of the auditory radiation, with the seed in themedial geniculate body and with the target area in the white matterof the Heschl gyrus.

Results

Anatomical Study

The opercula covered and enclosed the insula. The ante-rior, superior, and inferior limiting sulci clearly demarcatedthe insula and distinguished it from the surrounding corti-cal areas. The inferior limiting sulcus was located below

the long gyrus of the insula, it separated the insula from thesylvian surface of the temporal lobe, and it averaged 46.15mm (range 42–52 mm) in length. The limen insulae (thresh-old to the insula) was a slightly raised, arched ridge locatedat the inflection point of the sylvian stem and extendingfrom the anterior end of the long gyrus, where it fused withthe temporal pole and extended further to the posterior or-bital gyrus. The temporal stem was positioned above thelateral and anterior edge of the temporal horn (Fig. 1). Theshortest distances from the inferior limiting sulcus to thesuperior floor of the temporal horn averaged 6.5 mm (range4–9 mm).

The Heschl gyrus, the most anterior of the transversetemporal gyri, and the adjoining part of the superior tem-poral gyrus served as the primary auditory receiving area.23

They extended obliquely backward and medially towardthe posterosuperior angle of the insula. We found that theproximal posterior portion of the Heschl gyrus alwayscurved around and “hugged” the inferior aspect of the pos-terior long gyrus. An obtuse angle was formed at the mostanterior point of intersection where the Heschl gyrus passedthrough the inferior limiting sulcus. This angle averaged138° (range 130–145°) in our specimens (Fig. 1B). On thebasis of the anatomical characteristics and reference to themethod of the nomenclature of Türe et al.,31 we named thecurve point the “posteroinferior insular point,” which is theterm used to describe the most anterior intersection of theHeschl gyrus and the inferior limiting sulcus. The curvedpoint corresponded to the lateral geniculate body. The dis-tance from the limen insulae to the posteroinferior insularpoint averaged 32.95 mm (range 30–40 mm). The distancefrom the limen insulae to the tip of the temporal horn aver-aged 10.9 mm (range 9–14 mm) and was just one third ofthe distance from the limen insulae to the posteroinferior in-sular point. In fact, the presence of the posteroinferior insu-lar point divided the inferior limiting sulcus into anteriorand posterior portions, which made the shape of the insulaan approximation of a quadrilateral structure rather than atriangle.

Diffusion Tensor Imaging Study of the Temporal Stem

The temporal stem was composed of the white matterconnecting the anterior temporal lobe and the basal ganglia,the brainstem, and the frontal lobe. It contained severalidentifiable structures in close apposition. Based on our an-atomical study, MR imaging findings (Fig. 2), and the nu-merous published investigations,2–5,13,16,22–24,26–32 we describethe white matter tracts as follows (Fig. 3).

The uncinate fasciculus made up the core of the anteriortemporal stem, which can be divided into temporal, insular,and frontal segments5 (Fig. 3D). It coursed from the tem-poral lobe and hooked around the stem of the sylvian fis-sure. It then curved upward through the anterior temporalstem into the extreme and external capsules medial to theinsular cortex and fanned out into the frontal lobe to con-nect the orbital and inferior frontal gyri of the frontal lobeto the anterior temporal lobe. Its midportion actually ad-joined the middle part of the inferior occipitofrontal fasci-culus before heading inferolaterally into the anterior tem-poral lobe (Fig. 3C, D, J, and K).

The inferior occipitofrontal fasciculus connected the oc-cipital and frontal lobes via the temporal lobe. It had a long,

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anteroposterior course in the temporal lobe below the in-sula. The middle portion of the inferior occipitofrontal fas-ciculus was bundled together with the middle portion of theuncinate fasciculus. Posteriorly, it joined the inferior lon-gitudinal fasciculus, and portions of the optic radiations toform most of the sagittal stratum (Fig. 3C, E, J, and K).

The optic radiation is one of the most complex fiber sys-tems. It mingles with many kinds of white matter tracts.32

We observed that the optic radiation passed laterally fromthe lateral geniculate body and coursed in the roof of thetemporal horn along the temporal stem and lateral to theatrium to reach the calcarine sulcus on the medial aspect ofthe occipital lobe (Fig. 3C, J, and K). The optic radiationswere located deeply on the inferior occipitofrontal fascicu-lus throughout most of its course and covered the superi-or and lateral wall of the temporal horn (Fig. 3J). It was di-vided into 3 main bundles (Fig. 3F). The anterior bundlepassed forward in the roof of the temporal horn, turnedbackward forming the Meyer loop, and proceeded posteri-orly along the roof and lateral surface of the temporal horn.The anterior bundle consistently reached the anterior tipof the temporal horn. At the level of the atrium of the later-al ventricle, the fibers left the sagittal stratum, crossed thefloor of the ventricle, and reached the lower lip of the cal-carine sulcus. The middle bundle crossed the roof of thetemporal horn without a significant anterior bend. Thisbundle also joined the sagittal stratum and detached fromit to reach the occipital pole. The posterior bundles ranstraight posteriorly from the lateral geniculate body in thelateral wall of the atrium of the ventricle.

The anterior commissure interconnected the olfactorystructures and anterior part of the temporal lobes on bothsides. It formed a compact and ropelike structure at themidline and extended to the temporal stem, fanned out pos-teriorly to the uncinate fascicle, anterior and superior to thetemporal horn of the lateral ventricle into the temporal gy-

ri. The anterior commissure was shaped somewhat like thehandlebars of a bicycle (Fig. 3G). Its anterior fibers con-nected the olfactory structures, and its posterior fibers con-nected middle and inferior temporal gyri. Some fibers of theanterior commissure merged with the uncinate fasciculus atthe temporal pole, but most fibers were directed posteriorlyto form the sagittal stratum (Fig. 3A, C, G, H, and J).

The inferior thalamic peduncle (also known as the extra-capsular thalamic peduncle)22 connected the temporal lobeto the thalamus. Together with the ventral amygdalofugaltract and ansa lenticularis, it formed the ansa peduncularis,which curved around the medial edge of the internal cap-sule, inferior and parallel to the anterior commissure. Me-dially, its fibers reached the medial thalamic nucleus andthe hypothalamus (Fig. 3H–J).

Diffusion Tensor Imaging Study of the Auditory Radiation

Tractographic reconstructions demonstrated the auditoryradiations of the Heschl gyrus through the posterior limbof the internal capsule, superior to the optic radiations andmedial geniculate body (Fig. 3B, J, K, and L). The pos-teroinferior insular point was the anterior extremity of theintersection of the Heschl gyrus and the inferior limitingsulcus. The optic radiations coursed below the auditory ra-diations and were absent from the posterior part of the infe-rior limiting sulcus. Thus, this point can be regarded as theposterior limit of the optic radiations. The distance from thelimen insulae to the posteroinferior insular point was thelength of the temporal stem on the inferior limiting sulcus.In addition, the distance from the inferior limiting sulcus tothe superior floor of the temporal horn can be regarded asthe thickness of the temporal stem.

Discussion

Dysfunction of the temporal stem plays an important role

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FIG. 1. Photographs of brain specimens. A: Anterior view of the coronal plane showing the temporal stem and its rela-tion to the anterior temporal lobe, thalamus, brainstem, and frontal lobe. B: An obtuse angle is formed at the most ante-rior point of intersection where the Heschl gyrus passes through the inferior limiting sulcus. The curved line is the pos-teroinferior insular point, which makes the shape of the insula seem to approximate a quadrilateral shape rather than atriangle. AcG = accessory insular gyrus; ALG = anterior long gyrus; ASG = anterior short gyrus; Cent. = central; Gen. =geniculate; Gyr. = gyrus; Hippo. = hippocampus; Inf. = inferior; Ins. = insulae or insular; Lat. = lateral; Lim. = limiting;MSG = middle short gyrus; Parahippo. = parahippocampus; PI. = posteroinferior; PLG = posterior long gyrus; PSG = pos-terior short gyrus; Sul. = sulcus or sulci; Temp. = temporal; TG = transverse insular gyrus.

in a number of disorders, including amnesia,8,9,40 Klüver–Bucy syndrome,10,18 traumatic brain injury,1 temporal lobeepilepsy,15 and Alzheimer disease.7,14,29 It is also a reciprocalroute for tumor, infection, and seizure spread.16 Surgical le-sions of the temporal stem may result in abnormalities oflearning and spatial, visual, and verbal functions.5,6,11,12,16,18,21,

23,24,30,36,39

The transinsular approach has been used for selectiveamygdalohippocampectomy.27,36,39 In this approach, resec-tion of the temporal neocortex is avoided and brain retrac-tion is kept to a minimum.27,36 The transinsular approach isalso used for hippocampal transection,25 which could be aneffective procedure for seizure control and preservation ofverbal memory in patients with left mesial temporal lobeepilepsy. In addition, after entering the temporal horn via atransinsular approach, by opening the temporal portion ofthe choroidal fissure one can reach the posterior crural, am-bient, and proximal quadrigeminal cisterns.28 The transin-sular–transchoroidal approach can be expanded for largelesions extending to the perimesencephalic cisterns, by re-secting the anterior two thirds of the hippocampus and ad-jacent parahippocampal gyrus.38 This approach may alsobe combined with the pretemporal approach for a moreextended exposure of the crural, interpeduncular, and pre-pontine cisterns.28 Compared with the lateral subtemporalapproach, the transinsular approach could not only avoidexcessive temporal lobe retraction and corticectomy of thetemporal lobe27,39 but also the anterior drainage of the veinof Labbé and other bridging veins of temporal lobe.33 Thetransinsular approach, however, requires an incision of theinferior limiting sulcus. In this procedure, the uncinate fas-cicle, inferior occipitofrontal fasciculus, anterior commis-sure, and a part of the optic radiations can be interrupted tovarious degrees.

For the transinsular approach, passing through a trian-gular area located between the Meyer loop and the optictract with the apex at the lateral geniculate body is proposedas a relatively safe route for preserving optic pathways tothe anteromesial temporal lobe structures.2 However, it isdifficult to define the optic radiations and lateral genicu-

late body during surgery. Computer-assisted neuronaviga-tion increases the accuracy of the transsylvian exposure foramygdalohippocampectomy and minimizes cortical dam-age and vessel trauma.34 However, it does not directly showthe thin optic radiations.

Diffusion tensor imaging is a quantitative form of diffu-sion-weighted imaging and is created based on similaritiesbetween neighboring voxels in the shape and orientation ofthe diffusion ellipsoid. However, it shows only major tra-jectories and allows the delineation of large white mattertracts.17,19 Diffusion tensor tractography, based on line prop-agation, is a promising and widely used modality. It canprovide detailed delineation of in vivo white matter path-ways in a 3D space based on rates of microscopic waterdiffusion.13,20 When using DT imaging during neurosurgi-cal procedures, it is of critical importance to construct andinterpret the normal white matter tract maps based on thedetailed knowledge of anatomy. The temporal stem is acomplex and compact white matter structure. However, al-though its main fiber tracts are larger, their origin, course,and termination are significantly different and only com-pact in the temporal stem. Thus, these fiber tracts can be re-constructed by using the origin and termination areas. Inthe present study, we used a multiple-ROI approach to ex-ploit existing anatomical knowledge of tract trajectories.This method has low sensitivity to the ROI size and loca-tion and is highlybeneficial for reproducible reconstructionof prominent white matter tracts with known trajectories.35

This 2-ROI method is relatively easy, and there is no vari-ability that will bias the fiber tracking results.35 In addition,we visualized the entire temporal stem by using a singleROI. The temporal stem is adjacent to the sylvian fissureand lateral ventricle and because it has a clear demarcationfrom surrounding structures, it can be easily depicted. Themethod of combining a simple 1-ROI and multiple-ROIapproach could increase the validity of DT imaging–basedtractography over any simple method.35

Diffusion tensor imaging offers a more controlled wayof examining brain structures than studying cadaveric brainspecimens. On the workstation, we can repeatedly recon-

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FIG. 2. Cerebral MR images. A: Coronal T1-weighted image showing the relationship between the temporal stem andthe surrounding structures. B: Sagittal T1-weighted image demonstrating the relationship between the Heschl gyrus andthe posteroinferior insular point (asterisk). The dashed line demarcates posterior portions of the inferior limiting sulcus,and the double arrow indicates the temporal stem.

struct and observe the 3D anatomy of the temporal stemfrom various angles and directions. Diffusion tensor im-aging provided a supplementary modality for the studyof neuroanatomy. One of the most important limitations ofthe DTT technique is that specificity may be lost for tractsthat run parallel to (or are merged with) one another. Ana-

tomical features of the optic radiation fibers may have hadsome effect on the results of DT fiber tractography in thisstudy. In addition, space limitations preclude a comprehen-sive review of all tracts potentially visualized with DT im-aging—some tracts are occasionally, but not consistently,identified on directional DT imaging color maps. If the de-

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Fig. 3. Tractographic images of the temporal stem obtained using a simple 1-ROI approach (A–C and K) and a multiple-ROI approach (D–Jand L). A: The temporal stem is the white matter bridge between the anterior temporal lobe, the thalamus, the brainstem, and the frontal lobe.B: The white matter tracts of the lateral aspect of the cerebral hemisphere are shown. The insular region is surrounded by the arcuate fascicu-lus, external capsule, and internal capsule, and the corona radiata fans out into the insular region. A bunch of fibers on the anterior extremityof the Heschl gyrus pass through the internal capsule. The intersection is the posteroinferior insular point. The double arrow represents the tem-poral stem on the inferior limiting sulcus. C: The main white matter tracts of the temporal stem are shown. The temporal stem begins at thelimen insulae and ends at the posteroinferior insular point. D: The uncinate fasciculus courses from the temporal lobe, curves upward throughthe anterior temporal stem, and fans out into the frontal lobe. It can be divided into temporal, insular, and frontal segments. E: The inferioroccipitofrontal fasciculus connects the occipital and frontal lobes via the temporal lobe. F: Three bundles of the optic radiation are seen. Theanterior bundle passes forward in the roof of the temporal horn, turns backward forming the Meyer loop, and proceeds posteriorly along theroof and lateral surface of the temporal horn; the middle fibers course laterally above the roof of the temporal horn and turn posteriorly; andthe posterior fibers course directly backward. G: The anterior commissure forms a compact and ropelike structure at the midline and extend-ing to the temporal stem, which is shaped somewhat like the handlebars of a bicycle. Its anterior fibers connect the olfactory structures; its pos-terior fibers connect the middle and inferior temporal gyri. H: The inferior thalamic peduncle curves around the medial edge of the internalcapsule, inferior and parallel to the anterior commissure. Medially, its fibers turn sharply to reach the medial thalamic nucleus and the hy-pothalamus. I: The optic tract passes laterally to reach the lateral geniculate body. The optic radiation passes laterally from the lateral gen-iculate body, courses in the roof of the temporal horn along the temporal stem, and wraps around the lateral ventricle to reach the calcarinesulcus on the medial aspect of the occipital lobe. The Meyer loop follows a curved anterior course to the tip of the temporal horn and turnsbackward along the roof of the temporal horn. J: The white matter tracts of the lateral aspect of the cerebral hemisphere show the relationshipbetween the auditory radiation and the temporal stem. The auditory radiation turns at the posteroinferior insular point into the Heschl gyrus.The optic radiation is located below the posteroinferior insular point, which does not again participate in the posterior part of the inferior lim-iting sulcus. Some fibers of the anterior commissure merge with the uncinate fasciculus at the temporal pole. The inferior occipitofrontal fas-ciculus is bundled together with the middle portion of the uncinate fasciculus and then joins the anterior commissure, the inferior longitudinalfasciculus, and portions of the optic radiation to form the stratum sagittal. K: The anterior margin of the limen insulae is the anterior limit ofthe temporal stem, and the posteroinferior insular point is its posterior limit. L: The auditory radiation, generated from the medial geniculatebody, turns at the posteroinferior insular point into the Heschl gyrus. White indicates the uncinate fasciculus; blue, the inferior occipitofrontalfasciculus; red, the anterior commissure and inferior thalamic peduncle; green, the optic radiation; and purple, the auditory radiation. Ant. =anterior; Arc. = arcuate; Aud. = auditory; Call. = callosum; Cap. = capsule; Comm. = commissure; Cor. = corona; Corp. = corpus; Ext. = ex-ternal; Fas. = fascicle or fasciculus; Fibs. = fibers; Inf. = inferior; Int. = internal; Long. = longitudinal; Mid. = middle; OF. = occipitofrontal;Ped. = peduncle; Post. = posterior; Pyram. = pyramidal; Rad. = radiation or radiata; Sag. = sagittal; Thal. = thalamic; Tr. = tract. Uncin. = unci-nate. (See previous figure legends for additional abbreviations.)

lineated ROI is smaller than the actual range, it may resultin incomplete reconstruction of the fiber tract.

The auditory radiation fibers are directed from the medi-al geniculate body through the posterior limb of the inter-nal capsule to the auditory area in the Heschl gyrus and theadjacent parts of the superior temporal gyri.23 The auditoryand optic radiations intersect at the “posteroinferior insularpoint,” which may be regarded as the posterior limit of theoptic radiations on the inferior limiting sulcus. This pointalso divides the inferior limiting sulcus into anterior andposterior portions. In fact, the anterior part is the temporalstem. The distance from the limen insulae to the anterior tipof the temporal horn is just one third of the distance fromthe limen insulae to the posteroinferior insular point. Be-cause the limen insulae is the inherent anterior extremity ofthe inferior limiting sulcus, the temporal stem begins at thelimen insulae and ends at the posteroinferior insular pointon the inferior limiting sulcus. These landmarks can bemuch more easily identified on conventional MR imagingand during surgery.

The temporal stem is a thin band of white matter thatforms a bridge between the inferior limiting sulcus of theinsula and the roof of the temporal horn. It is commonlybelieved that the temporal stem contains the anterior com-missure, uncinate fasciculus, inferior occipitofrontal fasci-culus, Meyer loop of the optic radiations, and inferior tha-lamic fibers. The lateral geniculate body posteriorly is theposterior limit of the temporal stem.5,16 In fact, the 3 bun-dles of the optic radiation pass laterally from the lateralgeniculate body and course in the deep white matter of theinferior limiting sulcus to cover the superior and lateralwall of the temporal horn to reach the calcarine sulcus.26 Onthe inferior limiting sulcus, the posterior limit of the opticradiation is the posteroinferior insular point. We suggestthat the temporal stem should contain the entire optic radi-ation and not merely the Meyer loop, so as to easily identi-fy the posterior limit of the optic radiation.

Obvious interindividual differences in the size and shapeof the temporal stem have been noted in our study, but theessential configuration of the temporal stem is similar be-tween individuals. On the inferior limiting sulcus, the dis-tance from the limen insulae to the posteroinferior insularpoint is the length of the temporal stem. The distance fromthe inferior limiting sulcus to the temporal horn approxi-mates the thickness of the temporal stem. The uncinate fas-ciculus comprises the core of the anterior temporal stem,behind which the anterior commissure and the inferior thal-amic peduncle are located, and they occupy the anteriorone third of the temporal stem. The inferior occipitofron-tal fasciculus passes through the entire temporal stem. Themost anterior extent of the Meyer loop is located behind theanterior commissure and between the anterior tip of thetemporal horn and the limen insulae. Most of the optic ra-diations cross the postmedian two thirds of the temporalstem. In addition, the fiber tracts of the temporal stem werefound to merge extensively with each other.

The shorter the incision, the better one can preserve thetemporal stems.21,36,39 The size and shape of the temporalstem are considerably different from individual to individ-ual. In cases in which the temporal stem is the longest andthinnest, access to the temporal horn will be the easiest anddamage to the temporal stem will be the most minimal.Therefore, the preoperative MR imaging, DT imaging, and

intraoperative neuronavigation will be helpful to adjust thedifferences in individual cases.

Conclusions

The method that combines a simple 1-ROI and multiple-ROI approach can identify the fiber tracts of the temporalstem. On the inferior limiting sulcus, the posteroinferior in-sular point is a reliable landmark of the posterior limit ofthe optic radiations. The limen insulae, anterior tip of thetemporal horn, and posteroinferior insular point may beused to localize the temporal stem on MR imaging or dur-ing surgery.

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Manuscript submitted November 27, 2006.Accepted May 24, 2007.This work was supported by the National Natural Science Found-

ation of China (Grant No. 30750014).Address correspondence to: Tao Sun, M.D., 692 Shengli Street,

Yinchuan, Ningxia 750004, China. email: nxwwang@163.com.

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