Thalamic approaches

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Anterosuperior-medial thalamus (Lat Vent. & 3rd Vent. surfaces)

Supine, Head flexed, Head rotated (aid retraction)

2/3 anteriorly and 1/3 posteriorly to the coronal suture and crosses the midline SSS

Interhemispheric fissure, corpus callosum, Lat Vent., 3rd Vent. (access to 3rd Vent.: transforaminal, transchoroidal, interforniceal)

Corpus callosum (perform a callosotomy of < 1.5 cm in between pericallosal a. and 2.5 cm posterior to the genu) / anterior body (& choroidal fissure)

Cortical veins, SSS, pericallosal & callosomarginal arteries, corpus callosum, thalamostriate vein, fornix, caudate nucleus

- Low incidence of cortical damage
- Good for tumors protruding into the Lat Vent. or 3rd Vent. & w/ minimal lat extension

Narrow corridor & long distance, limited lat exposure, disconnection syndrome

Right ventricle is entered when the vein is on the right side of the foramen of Monro.
extended into the 3rd vent. Via transchoroidal, transforaminal, or interforniceal variations

Posterosuperior - medial thalamus (cisternal & 3rd Vent. surfaces)

Lateral or supine with
the head rotated to the ipsilateral side (for gravity retraction) and the neck slightly flexed to the contralateral side.

Craniotomy is centered on the pathology, extends 4 cm above the inion and mostly stays inferior to the lambdoid suture to avoid the complex arrangements
of parasagittal veins between the coronal and lambdoid sutures

Interhemispheric fissure, splenium, quadrigeminal cistern

Corpus callosum/ splenium

Corpus callosum, forceps major, deep cerebral veins, visual cortex

- Low incidence of cortical damage
- Access to posterior & medial surfaces of thalamus

Callosotomy (disconnection syndrome), risk of injury to deep cerebral veins, visual deficits

The corpus callosum is then exposed through the interhemispheric fissure and the splenial branches of the posterior cerebral arteries and the distal branches of the anterior cerebral arteries are identified and protected. The galenic venous complex is identified under the splenium
For an intervenous approach, the callosotomy is made midline, and the thin translucent tela
choroidea is exposed. The tela is sharply dissected, and the internal cerebral veins (ICVs) are separated. In this region,
the crura of the fornices are lateral to the ICVs. The choroidal fissure and cisternal surface of the pulvinar are visible along the lateral edges of the ICVs.
For paramedian tumors, the corpus callosum should be opened off midline, creating a corridor to work between the ICVs medially and the ipsilateral crus of the fornix laterally. This approach can be extended to better access the pineal region and quadrigeminal plate by cutting the tentorium

Posteroinferior, posteromedial thalamus (cisternal & 3rd Vent. surfaces)

Prone, semisitting, or lateral decubitus (if paramedian approach)

Vertical incision from the subocciput to a few cm above inion. In the midline or off to the side of the pathology. Craniotomy
exposes the confluence of the dural venous sinuses or torcular Herophili

Supracerebellar infratentorial space, quadrigeminal cistern

N/A

Deep cerebral veins

Low incidence of cortical damage

Only medial puLat Vent.inar lesions, risk of injury to deep cerebral veins, long working distance

Craniotomy exposes torcular. A wider craniotomy including the torcula provides a wider angle of attack, and a potential backup plan for a contralateral approach in case difficulty is encountered in exposing the pathology with the ipsilateral approach.
superior cerebellar and tentorial veins are skeletonized and mobilized or otherwise bipolar coagulated and divided if small and having collateralization with tributaries.
arachnoid is widely dissected, and the superior surface of the cerebellum is untethered from the tentorium
tributaries to the vein of Galen (VoG) are identified and protected. The pineal gland, VoG, and ICVs are located medially, while the thalamus, basal vein of Rosenthal, and medial posterior choroidal and posterior cerebral arteries are located more laterally
paramedian approach in the lateral decubitus position exposing the transverse sinus can bedesigned to develop a supracerebellar infratentorial corridor to the posterior thalamus and can be advantageous for reaching the posterolateral surface of the thalamus (especially of the contralateral side).

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Posterosuperior, posteromedial, and posterolateral thalamus especially in the setting of hydrocephalus

Supine with a large shoulder bump or lateral, making the parietal prominence the highest point of the field

Incision and craniotomy are performed centered at the superior parietal lobule

Superior parietal lobule—atrium of Lat Vent.

Superior parietal lobule or intraparietal sulcus

Visuospatial pathways, SLF I and II , tapetum

- Avoids optic radiation & language area
- Short distance to atrium

- Cortical damage may lead to Gerstmann syndrome, spatial hemineglect
- Needs dissectible sulcus

A deep sulcus is carefully selected with navigation guidance, and the arachnoid here is widely dissected for developing a transsulcal approach to the roof of the atrium of the ipsilateral ventricle. transsulcal approach because it minimizes injury to white matter tracts and decreases the operating distance. Also, a transsulcal approach only transgresses the “U” white association fibers. To safely reach the bottom of the sulcus, meticulous sharp dissections under high magnification should be performed. We only recommend a transgyral approach if there is an unexpected venous network that precludes a safe transsulcal approach.
Entering the roof of the atrium avoids the optic radiations on the ventricle’s lateral walls

Inferolateral thalamus

Supine

Expose the middle fossa floor and the inferior and middle temporal gyri

Middle temporal gyrus & temporal horn of Lat Vent.

Temporal gyri/ sulci

Optic radiation (Meyer's loop), Wernicke's area, LF

Short access to tumors protruding to temporal region

Visual & speech disorder

Protect Labbe. enter the temporal horn located 3–4 cm posterior to the temporal pole.
Avoid
- Superior temporal gyrus (optic radiations)
- Inferior temporal gyrus (collateral sulcus/ILF)
the choroid fissure is opened superior to the hippocampus and all the way posterior to the lateral geniculate body, exposing the
inferolateral thalamus. The anterior choroidal artery and hippocampal arteries are identified and protected.

Lateral surface of the thalamus, more superiorly
and posteriorly than the TTGA

Supine

Pterional craniotomy → exposing the whole length of the sylvian fissure. → detaching the frontal and temporal operculi → M3 are followed proximally to the M2 segments, and each branch is circumferentially skeletonized → goal is to reach the thalamus while avoiding the posterior limb of the internal capsule, which is located deep in the cerebral central core in line with the anterior transverse temporal gyrus (Heschl’s gyrus) in the planum temporale of the fissure

Sylvian fissure, insula

Insular cortex

Insula, MCA branches, arcuate fascicle, MLF, corona radiata, internal capsule, putamen

Short access to tumors invoLat Vent.ing posterior limb of internal capsule

Risk of vascular & insular damage, speech & motor disturbances

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