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Bailey & Love's Surgery, 27th Edition Surgery Essence by Pritesh Singh (PGMEE) Sabiston's Textbook of Surgery
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Microsurgical Anatomy of Medial Temporal Lobe

Here is one of my recent presentation on Microsurgical anatomy of Medial Temporal Lobe, hope you find it informative.

Synopsis

Introduction


  • Temporal Lobe is unique as neocortex, paleocortex and archicortex coexist  
  • This makes it preferred site for certain tumors and epilepsy
  • Most common target for resections to treat convulsive disorders 

Histology

Three-layered archicortex (allocortex)
  • hippocampus 
  • semilunar gyrus of the uncus
  • prepiriform area
Six-layered paleocortex (mesocortex)
  • parahippocampal gyrus

Six-layered neocortex (isocortex)
  • Superior temporal gyrus
  • Middle temporal gyrus
  • Inferior temporal gyrus
  • Transverse temporal  gyri 
  • Fusiform gyrus.

Boundaries of Temporal Lobe

  • Located below sylvian fissure
  • Anterior and inferior limits are natural bone structures
  • posteriorly separated from the occipital lobe by the lateral parietotemporal line  
  • separated from the parietal lobe by the occipitotemporal line

Surfaces of Temporal Lobe
4 Surfaces
  • Lateral 
  • Superior  (aka Temporal Operculum)
  • Inferior
  • Medial

Relationship of the temporal lobe with bony structures

  • Sylvian fissure - Squamosal suture 
  • Temporal pole - Greater wing of the sphenoid bone. 
  • Lateral surface - Squamous part of the temporal bone
  • Basal surface - sits on the floor of the middle fossa

Lateral Surface of Temporal Lobe

Three gyri: 
  • Superior
  • Middle
  • Inferior

Separated by two parallel sulci: 
  • Superior sulcus
  • Inferior Sulcus

Superior Surface  of Temporal Lobe

It presents three morphologically distinct parts 
  • Planum polare 
  • Heschl’s gyrus- contains the primary auditory cortex (Brodmann area 41)
  • Planum temporale

Basal Surface of Temporal Lobe

The basal surface is composed laterally to medially

  • part of the inferior temporal gyrus
  • occipitotemporal sulcus
  • fusiform gyrus
  • collateral sulcus
  • parahippocampal gyrus 

Medial Surface of Temporal Lobe

  • Hippocampus 
  • Uncus
  • Parahippocampal gyrus
  • Fimbria
  • Dentate gyrus
  • Amygdala 

Hippocampus


  • Club-shaped structure divided into three parts: head, body, and tail.
  • Curved shape which resembles a shape of a seahorse 
  • Appears ‘ S’ shaped on coronal section
  • Consists of two interlocking C shaped gray matter structures
                  – Hippocampus proper
                  – Dentate gyrus
  • CA stands for cornu ammonis, from its ram's horn shape 
  • Gray matter of the hippocampus is an extension of the subiculum
Parahippocampal Gyrus

  • Occupies transitional area between the basal and the mesial surfaces of the temporal lobe
  • grey matter cortical region surrounding the hippocampus 
  • part of the limbic system 
  • role in memory encoding and retrieval.
  • Components of the Parahippocampal gyrus
               -Subiculum: medial round edge of the parahippocampal gyrus. 
               -Presubiculum
               -Parasubiculum
               -Entorhinal area 

Uncus: Clinical Significance
  • Seizures preceded by hallucinations of disagreeable odours originate here
  • ICP-  uncal herniation -> III nerve compression -> ipsilateral fixed, dilated pupil and an eye with a characteristic "down and out" gaze
Amygdala

Temporal or principal amygdala: located in the temporal lobe
Extratemporal or extended amygdala: located in the primordial floor of the lateral ventricle

Relations

Temporal amygdala -located within anterior segment of uncus 
Superiorly- blends into the globus pallidus without any clear demarcation 
Inferiorly- bulges inferiorly from the most anterior portion of the roof of the temporal horn

Arteries encountered in Medial Temporal Lobe surgical interventions

  • Middle Cerebral Artery 
  • Posterior Cerebral Artery 
  • Anterior Choroidal Artery 
  • Internal Carotid Artery 

Middle Cerebral Artery and Medial Temporal Lobe


Posterior Cerebral Artery and Medial Temporal Lobe

  • Main role of supplying the Medial Temporal Region and the inferior surface of the temporal lobe. 
  • 4 segments: P1, P2, P3, and P4 

Anterior Choroidal Artery 
  • Arises from the posterior wall of the ICA 
  • Supplies the anterior MTR 
Internal Carotid Artery 

Branches of the ICA supplying the MTR
  • present in 45% of hemispheres. 
  • If present, these arteries always arose from choroidal segment of the ICA 
Venous Drainage of Medial Temporal Region
  • Superficial group 
  • Deep group 
Superficial group: Venous Drainage of Medial Temporal Region




Deep Group: Venous Drainage of Medial Temporal Region

Drainage of anterior MTR (2 variants)
  • posterior peduncular segment via the anterior basal anastomotic vein 
  • cavernous sinus or into the sphenoparietal sinus via a large preuncal vein 

Drainage of middle MTR 
  • amygdalar vein drains to basal vein
  • anterior longitudinal hippocampal vein drains to basal vein

Drainage of posterior MTR
  • posterior longitudinal hippocampal vein
  • medial temporal vein
  • lateral and medial atrial veins. 
  • all drain to mesencephalic segment of the basal vein 

Surgical techniques for temporal lobe epilepsy (TLE)

Non Selective

  • Anterior temporal lobectomy (ATL)


Selective

  • Transcortical selective amygdalohippocampectomy (TCAH):
  • Transsylvian selective amygdalohippocampectomy (TSAH): 


Anterior Temporal Lobectomy


  • Two-step resection of
                 -anterior temporal neocortex
                 -anterior hippocampus and lateral amygdala
  • 4 cm of anterior neocortex removed

Transcortical selective amygdalohippocampectomy (TCAH)


  • access is obtained through middle temporal gyrus
  • selective amygdalohippocampectomy
  • lateral temporal neocortex is not resected


Transsylvian selective amygdalohippocampectomy (TSAH)

  • Less distance to reach to the temporal horn
  • Need for the retraction of the sylvian lips 
  • Presence of vascular structures 
  • Damage to the lenticulostriate artery or MCA branches - > Ischemic injury - > causes surgical morbidity
  • Finding the temporal horn is difficult, because a blind dissection in the white matter

Landmarks to achieve a safe resection in Medial Temporal Lobe Surgery

Collateral eminence (at floor of temporal horn): Neural tissue lateral to the collateral eminence can be removed safely without any risk of damaging midbrain structures 

Tentorial edge: Resection is aimed lateral to the free edge of the tentorium, the damage to the inferior limiting sulcus, the sylvian fissure, and midbrain structures will be avoided 

Choroidal fissure: Never extend the resection superior to the choroidal fissure

Avoiding Optic Radiation in Temporal Lobe Surgery

Optic radiations lies
  • roof of the temporal horn 
  • cover its lateral wall except its anterior part 
  • At the level of the atrium -> cover only lateral wall
  • medial wall of the atrium -> free from the optic radiation
  • Exceed the anterior wall by a few millimeters -> Meyer Loop
  • 5mm +/- 3.9mm
  • Optic radiation courses in the superior aspect of the temporal horn
  • Transcortical transtemporal approach-> lateral wall is opened 
  • Transcortical approach is less likely to threaten the optic radiation
Memory Deficit in Temporal Lobe Surgery

Neocortical removal can also lead to negative neurocognitive sequelae 
Two structures having memory function  have important role 
  • Uncinate fasciculus (UF)
  • Inferior Longitudinal fasciculus  (IOFF )
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