HOW I DO IT - NEUROSURGICALTECHNIQUES

How I do it – selective amygdalohippocampectomy viasubtemporal approach

Tomislav Sajko & Ivan Škoro & Krešimir Rotim

Received: 2 April 2013 /Accepted: 10 August 2013 /Published online: 29 August 2013# Springer-Verlag Wien 2013

AbstractBackground Surgery is superior over medicamentous treat-ment of pharmacoresistant mesial temporal lobe epilepsy causedby hippocampal sclerosis. The armamentarium of surgical pro-cedures comprises standard temporal lobectomy and more se-lective procedures. Selective amygdalohippocampectomy canbe performed via transcortical, transsylvian or subtemporalapproach.Method Describe the selective amygdalohippocampectomythrough the subtemporal approachConclusion After the detailed preoperative epilepsy evalua-tion, surgery can be offered to pharmacoresistant epilepsypatient with hippocampal sclerosis. Selective amygdalo-hippocampectomy can be safely performed through thesubtemporal approach. The good knowledge of the mesialtemporal lobe anatomy is necessary when performing thisprocedure.Key points• Perform the subtemporal craniotomy with additional boneremoval up to temporal petrous part to minimize retractionof the brain.

• Release the CSF from the subarachnoid sulcal space in orderto relax the temporal lobe. Dissect the arachnoid aroundbasal temporal veins and protect them with hemostatic ma-terial in order to avoid vein rupture.

• After gyrus fusiformis corticotomy, always follow the whitematter in order to enter the temporal horn.

• Place the self-retraining retractor gently to secure anunobstructed view of the intraventricular mesial temporal lobestructures.

• Visualize the choroid plexus and the inferior choroidal point.They represent the two most important landmarks.

• While performing the anterior disconnection the goal is toreach the arachnoid of the interpeduncular and crural cisternmedially and the tentorial edge laterally.

• Follow the tentorial edge and the arachnoid of the temporalbase to securely perform the lateral disconnection.

• Perform the posterior disconnection at the level of themesencephalon superior colliculi.

• During the medial disconnection the dissection of the arach-noid of the hippocampal sulcus must be done as close to thehippocampus as possible in order to avoid damage to thebrain stem perforators or the loop of the anterior choroidalartery.

• Knowledge of mesial temporal lobe anatomy is crucial.

Keywords Pharmacoresistant epilepsy . Hippocampalsclerosis . Selective amygdalohippocampectomy .

Subtemporal approach

Introduction

About one third of temporal lobe epilepsy (TLE) patients donot become seizure-free, despite optimized drug treatment.Hippocampal sclerosis is found in approximately 50–75 %of temporal lobe resections made for medically intractabletemporal lobe epilepsy [3]. Satisfactory surgical results interms of seizure control and cognitive improvement has clear-ly shown that mesial temporal lobe epilepsy (MTLE) can betreated surgically [7].

This article reviews the subtemporal approach in performingthe selective amygdalohippocampectomy (SelAH).

Electronic supplementary material The online version of this article(doi:10.1007/s00701-013-1846-2) contains supplementary material,which is available to authorized users.

T. Sajko : I. Škoro (*) :K. RotimDepartment of Neurosurgery, “Sestre milosrdnice” UniversityHospital Center, Vinogradska cesta 29, 10000 Zagreb, Croatiae-mail: iskoro@gmail.com

Acta Neurochir (2013) 155:2381–2387DOI 10.1007/s00701-013-1846-2

Relevant anatomy

The neural structures constituting the mesial temporal lobe arethe parahippocampal gyrus, uncus, hippocampus, fimbria,dentate gyrus and amygdala [10]. These structures can beclearly identified in the temporal horn of the lateral ventricle.Inside the temporal horn the choroid plexus and the choroidfissure are the best landmarks. Choroid fissure lies betweenthe tenia fimbriae and tenia thalami. Inferior chodoidal point(ICP) marks the beginning of the choroid fissure (Fig. 1). Allstructures located laterally (hippocampus, parahippocampus)and anteriorly (amygdala, uncus) from the ICP can be safelyremoved. Beneath the medial wall of the anterior aspect of thetemporal horn formed by uncus and head of the hippocampusis the crural cistern containing the P2 segment of the posteriorcerebral artery (PCA), and the oculomotor nerve. Opening thechoroid fissure uncovers the ambient cistern with the posteriorcerebral artery and basal vein of Rosenthal. Perpendicular tothe ambient cistern is the hippocampal sulcus, an arachnoidmembrane containing the hippocampal arteries and veins. Itrepresents another landmark separating the dentate gyrus su-periorly from the parahippocampal gyrus inferiorly [9].

Indications

Patients suffering from pharmacoresistant mesial temporallobe epilepsy (MTLE) caused by hippocampal sclerosis.

Preoperative workup

A thorough preoperative evaluation of a pharmacoresistantMTLE patient is performed including history taking, semiologyanalysis, videoEEG monitoring, epilepsy protocol magnetic

resonance (MR) of the brain (1,5 or 3 T), PET/CT scan of thebrain, neuropsychological testing and visual field examination.A T1-weighted MR of the brain according to the neurona-vigation protocol is done.

Specific information to give to the patient about surgeryand potential risks

It should bemade clear to the patient that the surgical goal is toachieve seizure freedom while preserving the patients’ preop-erative neurologic condition. Patients should be informedabout the possibility of potential complications and measuresnecessary to deal with them. Complications include: intrace-rebral hemorrhage due to possible lesion of the basal temporalvein and temporal lobe retraction, anterior choroidal artery(AChA) syndrome due to lesion of the AChA or its loop,cerebrospinal fluid (CSF) leak and meningitis.

Selective amygdalohippocampectomyusing the subtemporal approach

The operative procedure is done under general anesthesia. Thepatient is placed supine with a role under the ipsilateral shoul-der or in lateral position in order to achieve the position of thepatient’s head almost parallel to the floor. The head is placedin aMayfield three pin holder (Mayfield ®). A curvilinear skinincision is made from the tragus of the ear curving superiorlyabout 3 cm above the pinna of the ear and ending posteriorly atthe level of the mastoid. The temporalis muscle is elevated tothe level of the external auditory canal and temporal end of thezygomatic process. A subtemporal craniotomy is performed.To reach the temporal base, more of the temporal bone is takenaway to the level of the temporal petrous part using the high-

Fig. 1 Schematic drawing ofmesial temporal structures as seenby a neurosurgeon upon enteringthe temporal horn of the leftventricle. Note the position ofinferior choroidal point as itrepresents the most importantsurgical landmark

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speed drill. Any pneumatized cells that are opened are beingwaxed. The dura is opened in a semicircular fashion andreflected toward the temporal base. The operative microscopeis brought into field. A portion of the temporal lobe includingthe middle and inferior temporal gyri is visualized. Using a

sharp dissector the arachnoid around the sulci is opened torelease the CSF in order to achieve relaxation of the temporallobe.

A self-retraining retractor is placed about 2 cm on thebrain surface toward the temporal base. By retraction carehas to be taken in order not to damage the veins runningfrom the temporal surface toward the petrous sinus. Withthe neuronavigation the collateral sulcus is identified. Acorticotomy on the gyrus fusiformis (gyrus occipitotempo-ralis lateralis), measuring 2–3 cm in an anteroposteriordirection is performed. Following the white matter andheading medially and superiorly, the temporal horn ofthe lateral ventricle is entered at the depth of approximate-ly 1,5 cm (Fig. 2). Using the cavitron ultrasound aspirator(CUSA) the ependyma of the roof of the temporal horn isopened in the anteroposterior direction to visualize theamygdala and the tip of the temporal horn anteriorly, thehead and body of the hippocampus in the middle and thehippocampal tail posteriorly. The beginning of the choroidplexus and choroid fissure (inferior choroidal point) isvisualized (Fig. 3). The ventricular portion of the amyg-dala is removed first together with the uncus and anteriorextension of the parahippocampal gyrus i.e. entorhinalcortex, to reach the interpeduncular cistern and the edge ofthe tentorium laterally. The head of the hippocampus is alsoremoved, reaching laterally the arachnoid of the temporal baseand medially the crural cistern above the crura cerebri.

The CUSA is set at the low values in order to preserve thearachnoid and the structures passing through the interpeduncularcistern (oculomotor nerve, P1 segment of the posterior cerebriartery) and crural cistern ( P2A segment of the posterior cerebralartery).

Fig. 3 Intra-operative photoshowing the most importantintraventricular landmarks:choroid plexus and inferiorchoroidal point. Laterally are theleft-sided hippocampus andanteriorly the left-sided amygdala

Fig. 2 Schematic drawing of the temporal lobe (coronal section). Theinterrupted red line marks the trajectory toward the temporal horn takenduring the subtemporal approach. STG-superior temporal gyrus; MTG-medial temporal gyrus; ITG-inferior temporal gyrus; FG-fusiform gyrus;PHG-parahippocampal gyrus; TH-temporal horn; HC-hippocampus;OTS-occipitotemporal sulcus; CS-collateral sulcus; PCA-posterior cere-bral artery

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By removing the intraventricular portion of the amygdala,the uncus, entorhinal cortex and the head of the hippocampusthe anterior disconnection is completed (Fig. 4).

Lateral disconnection follows including the resectionof the lateral part of the parahippocampal gyrus throughthe ventricular sulcus between the hippocampus andemminentia collateralis. Once the arachnoid of the temporalbase is reached it is followed posteriorly toward the pointwhere the parahippocampal gyrus curves around the brainstem (Fig. 5).

Posterior disconnection is performed on the tail of thehippocampus at the level of the superior colliculi of themesencephalon (Fig. 6).

Finally medial disconnection, i.e. the en bloc removal ofthe hippocampal body together with the medial part of theparahippocampal gyrus and fimbria hippocampi is performed.The inferior choroidal point is shown together with the cho-roid fissure and the above lying choroid plexus. The choroidplexus is moved superiorly and fimbria hippocampi is visual-ized (Fig. 7). Using the dissector fimbria hippocampi is gently

Fig. 5 Intra-operative photohighlighting the hippocampalbody after the lateraldisconnection is done. Mark theeminentia collateralis and theventricular sulcus between thehippocampus andparahippocampus

Fig. 4 Intra-operative photo aftercompleting the anteriordisconnection. Note the preservedarachnoid over the crural cistern

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lifted from the arachnoid of the choroid fissure. Careful dis-section and coagulation of the hippocampal vessels in thehippocampal sulcus is performed. Following the arachnoidof the hippocampal sulcus the hippocampus and the medialpart of the parahippocampal gyrus are lifted leaving the arach-noid and the structures (P2P segment of the posterior cerebralartery, basal vein of Rosenthal, brain stem) intact (Fig. 8). Theen bloc specimen is sent for the patho-histologic analysis.

Careful hemostasis, mainly of minor venous bleeding, isdone using hemostatic material (Surgicel ®) in order not to

damage small perforating arteries with coagulation. The durais closed in a watertight fashion. Bone flap is returned and fixedwith sutures. The rest of the wound is closed in a standardfashion.

Instructions for the postoperative care

In the postoperative period care consideration include airwayclearance, pain control and deep venous thrombosis prophylaxis.

Fig. 7 Intra-operative photo ofthe beginning of medialdisconnection revealing thehippocampal body, choroidplexus and fimbriae hippocampi.Elevating the fimbriaehippocampi the choroid fissurecomes into sight together with theambient cistern and brainstemunderneath

Fig. 6 Intra-operative photo ofthe posterior disconnection of thehippocampal tail. Choroid plexuscontinues posteriorly toward theatrium

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Patients are usually discharged on day 5–9 post-operatively andare followed by a neurologist and neurosurgeon at 6–12 weeks.Of the uttermost importance is not to discontinue the antiepileptictherapy. To determine the extent of resection a control postoper-ative MRI is done three months after surgery (Fig. 9a and b).

Advantages, limitations and complication avoidance

Advantages of the subtemporal approach include sparing thetemporal neocortex, the temporal stem and the optic Mayerloop. Disadvantages include temporal lobe retraction, injuryof the basal temporal veins, lack of landmarks to enter thetemporal horn and possibility of damaging basal temporallanguage areas, especially on the dominant side [1].

To avoid complication care must be taken not to excessive-ly retract temporal lobe in order to preserve basal temporalveins. To avoid damage of small perforating arteries aroundthe brain stem, careful dissection and coagulation of thehippocampal vessels in the hippocampal sulcus should bedone as close to hippocampus as possible.

Conclusion

The selective amygdalohipocampectomy has been described byNiemeyer [4]. Several modifications of amygdalohippo-campectomy were developed and are named after the approachused. Transylvian SelAH was described by Wieser and Yasargil[10]. Transcortical (trans-middle temporal gyrus) approach was

Fig. 9 MR of the brain threemonths after left-sided selectiveAH via subtemporal approach. a .T2-weighted axial image showingthe extent of the resection in theanterior-posterior (A-P) line.Resection cavity expends fromthe posterior clinoid process to thelevel of the mesencephalonsuperior colliculi. b . T2-weightedcoronal image showing thetrajectory toward the temporalhorn and the cavity after resectionof the hippocampus

Fig. 8 Intra-operative photo atthe end of the procedure. Note theintact interpeduncular cistern withthe oculomotor nerve, the cruralcistern and the ambient cistern.Perpendicular to the ambientcistern is the hippocampal sulcus,arachnoid membrane thatseparates the gyrus dentatus andthe parahippocampal gyrus

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popularized by Olivier [5]. Subtemporal approach was describedby Hori [2].

Transylvian approach has the advantage of reaching thetemporal horn more comfortable [9]. Disadvantages includedamage to the temporal stem, increased risk of vasospasmworking around the middle cerebral artery branches and dam-age to the Mayer loop [8].

The transcortical approach through the superior or middletemporal gyrus offers a route to the temporal horn that isstraightforward. Disadvantages include the damage to thetemporal neocortex and Mayer loop [6].

The subtemporal approach with its advantages and disad-vantages represents a safe and functionally sparing techniquein performing selective amygdalohippocampectomy.

Acknowledgments Authors would like to express their gratitude toMrs. Maja Mravec for her help in illustrating Figs. 1 and 2.

Conflicts of interest None.

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