The temporal stem is a bridge of white matter in the brain connecting the temporal lobe to other regions. It contains several important tracts, including the uncinate fasciculus, inferior fronto-occipital fasciculus, and Meyer's loop. The temporal stem plays a role in functions like learning, memory, and language processing. It can also be a pathway for tumor or seizure spread. Precise knowledge of the temporal stem and its connections is important for surgical planning and understanding cognitive disorders.

1. TEMPORAL STEM ANATOMY
Dr. Sandeep Mishra

2. INTRODUCTION
• The term temporal stem seems to have derived from the pictorial
appearance of the structure on coronal sections of the brain and was
initiated by Horel.
• White matter tract connecting
temporal lobe with other parts of
brain.

3. definition
• The ambiguity of the temporal stem is due to lack of obvious
anatomical structures to clarify the temporal stem and the posterior
continuation of inferior limiting sulcus of insula.
• Yasargil insisted that the temporal stem is ambiguous anatomical
term.
• It can be defined as a bridge of white matter between the temporal
lobe and the basal ganglia, extending from the amygdala anteriorly to
the level of the lateral geniculate body posteriorly.

4. • Cirillo stated the temporal stem as white matter representing connections
between temporal cortex/amygdala and orbital frontal cortex, striatum,
and thalamus.
• Ebeling and von Cramon described the temporal stem as narrow gate
between roof of the temporal horn and lower circular sulcus in the white
matter of the temporal lobe and that it included the anterior commissure,
uncinate fasciculus, inferior occipito-frontal fasciculus, Meyer’s loop of
optic radiations, and inferior thalamic fibers.
• Duvernoy described it in a slightly different way as the narrow lamina of
white matter between the temporal horn and superior temporal sulcus,
extending from the level of the amygdala to the level of the lateral
geniculate body.

5. • Wang insisted that the temporal stem begins at the limen insulae and
ends at the postero-inferior insular point on the inferior limiting
sulcus.
• In the study of Peuskens, it is described that the temporal stem forms
the junction of the anterior temporal lobe and thalamus, brain stem,
and the frontal lobe and connects the polymodal association areas in
the anterior temporal lobe with the frontal lobe, basal forebrain,
thalamus, and contralateral temporal lobe.

6. importance
• It has been considered to have an important role as a reciprocal route
of tumor, infection, seizure spread, and a number of disorders
including amnesia, traumatic brain injury, Alzheimer disease (because
of a bridge between the temporal lobe and other regions of the brain)

7. boundaries
• The temporal stem corresponds to the superior limit of the temporal
horn and it is also related to the inferior limiting sulcus of insula
superiorly.
• The length of the TS can be calculated from the limen insula
anteriorly to the posterior insular point (intersection point of the
Heschl gyrus with the inferior limiting sulcus of insula) posteriorly,
and it measures about 33mm.

8. The temporal stem can be arbitrarily divided in three portions

9. • The human adult temporal stem is completely enclosed and
concealed under the lateral orbital and superior temporal gyri in the
depths of the lateral fissure.

10. Tracts making the temporal stem
• Several tracts including the Meyer loop of the optic radiation, the
uncinate fasciculus, the occipitofrontal fasciculus, the anterior
commissure, the inferior thalamic peduncle, the posterior thalamic
peduncle, the extreme capsule, the temporopontine fibers, the
corticotectal fibers, the corticotegmental fibers, and the
occipitopontine fibers are embedded in a dense network within the
temporal stem.

11. The three main accepted components of the temporal stem are:
• 1. The Uncinate Fasciculus (UF)
• 2. The Inferior Fronto-occipital Fasciculus (IFOF)
• 3. The Meyer’s Loop (ML)

12. • Unciate fasciculus (UF)- recognizing faces, actions, objects and
emotions
• IFOF- picture and sound naming, language processing

14. • The temporal stem composed of several white matter tracts has been
known to have an intimate relation with learning spatial, visual, and
verbal functions.
• It can be a route for tumor, infection, and seizure spread.
• The temporal stem used to be a direct surgical route in the trans-
sylvian approach. This approach can minimize the temporal
neocortical damages, retraction injuries, and the injuries of the
Meyer’s loop.

16. Temporal Stem, Epilepsy, and Brain Tumors
• Epilepsy: The uncinate fasciculus, the stria terminalis, the fornix and
the amydgdalofugal fibers - preferred pathway for seizure spread. The
main sites of seizure origin are the hippocampal formation more than
the amygdala. In addition, the IFOF seems to produce the visual
hallucinations that can accompany epilepsy.
• Tumors: represent 13% of tumors of the limbic and paralimbic
system. Tumors in this region average > 5 cm in diameter.
• Gliomatosis cerebri- a well-myelinated structure so constitutes a
pathway of glioma dissemination and multicentricity.
• Infiltrating insular glioma and LGG in children

17. Temporal Stem and Surgical Approaches
• Anterior transsylvian and subtemporal transfusiform approaches to
avoid retraction of the temporal lobe and damage to the temporal
stem, especially the optic radiations
• Transsylvian, transcisternal, mesial en bloc resection for hippocampal
sclerosis. preserves the lateral and laterobasal temporal lobe.
• The subtemporal transfusiform gyrus approach to the
parahippocampal gyrus spares the lateral temporal
neocortex with its higher cortical functions.

18. Temporal Stem, Functional Significance, and
Cognitive Pathology
• The temporal stem plays an important role in numerous of disorders,
including amnesia, Klüver-Bucy syndrome, traumatic brain injury,
autism and Alzheimer disease.
• TS involved in 6-8% of DAI.

19. role of DTI in temporal stem
• Tumor- can push the fibers medially, laterally or can go through it
• Seizures- TS can be damaged by surgical treatment of TLE like TPR or
SAH (SAH>TRP)- damage to the UF
• Cognitive pathology- reduction in white matter tract fibers

20. conclusion
• Bridge between the temporal lobe and other regions of the brain
• The three main accepted components of the temporal stem are:
1. The Uncinate Fasciculus (UF)
2. The Inferior Fronto-occipital Fasciculus (IFOF)
3. The Meyer’s Loop (ML)
• The temporal stem can be a route for tumor, infection, and seizure
spread and can be used to be a direct surgical route.

21. references
• Ebeling U, Cramon DV: Topography of the uncinate fascicle and adjacent temporal fiber tracts. Acta
Neurochir (Wien) 115:143–148, 1992
• Peltier J, Verclytte S, Delmaire C, Pruvo JP, Godefroy O, Le Gars DL : Microsurgical anatomy of the temporal
stem : clinical relevance and correlations with diffusion tensor imaging fiber tracking. JNeurosurg 112 : 1033-
1038, 2009
• Rhoton AL Jr : The Cerebrum. Neurosurgery 51 : S1-S51, 2002
• Peuskens D, Van Loon J, Van Calenberg F, Van den Bergh R, Goffin J, Plets C: Anatomy of the anterior
temporal lobe and the frontotemporal region demonstated by fiber dissection. Neurosurgery 55:1174–1184,
2004
• Kier EL, Staib LH, Davis LM, Bronen RA: MR Imaging of the temporal stem: anatomic dissection tractography
of the uncinate fasciculus, inferior occipitofrontal fasciculus, and Meyer’s loop of the optic radiation. AJNR
Am J Neuroradiol 25:677–691, 2004
• Yaşargil MG, Yaşargil DCH: Impact of temporal lobe surgery. J Neurosurg 101:725–738, 2004