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|SPECIAL NI FEATURE - OPERATIVE NUANCES: STEP BY STEP
|Year : 2020 | Volume
| Issue : 2 | Page : 270-273
Posterior Quadrant Disconnection for Sub-Hemispheric Drug Refractory Epilepsy
Ramesh S Doddamani1, Manjari Tripathi2, Raghu Samala1, Mohit Agarwal1, Bhargavi Ramanujan2, Sarat P Chandra1
1 Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
2 Department of Neurology, All India Institute of Medical Sciences, New Delhi, India
|Date of Web Publication||15-May-2020|
Sarat P Chandra
Professor and Head of Unit 1, PI and Team Leader, COE Epilepsy and MEG center, In Charge, Core Faculty, Epilepsy and Functional Neurosurgery, Room 7, 6th Floor, CN Center, Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
The posterior quadratic epilepsy (PQE) is a form of a multilobar epilepsy, involving the temporal-parietal and occipital lobes. Basically, epilepsies with localized networks to the posterior temporal, posterior parietal, and occipital lobes can benefit from this type of surgery. Gliosis due to perinatal insult and cortical dysplasis and angiomas in Sturge Weber syndrome involving the PQ have often been cited in the literature as the etiology for PQE. However, before considering surgery, it is important to localize the epileptogenic focus through a complete pre operative work up involving; EEG (Electro-Encephalo-Graphy), video EEG, single photon emission computed tomography (SPECT), positron emission tomography (PET), and magneto encephalography (MEG). Historically, these pathologies were dealt with multi-lobar resections, which were associated with high morbidity and mortality, owing to blood loss, especially in young children, hydrocephalus, and hemosiderosis. Based on the theory of networks involved in epileptogenesis, the concept of disconnection in epilepsy surgery was introduced. Delalande and colleagues, described the technique of hemispheric disconnection (functional hemispherectomy) for pathologies like: hemimegalencephaly, rasmussens encephalitis involving the entire hemisphere. The technique has evolved with time, moving towards minimally invasive endoscopic vertical hemispherotomy, described by Chandra and colleagues., The posterior quadrant disconnection (PQD) evolved as a tailored disconnection on similar lines as hemispherotomy, for managing refractory epilepsy arising from the posterior quadrant. The technique and principles involved in the PQD surgery are similar to the those of peri-insular hemispherotomy and has been described in the literature by few authors.,,, The technique of performing PQD will be described here in a step-wise fashion with illustrations supplemented by a surgical video.
Keywords: Multilobar epilepsy, peri insular, splenial disconnection, temporo-parieto-occipital disconnectionKey Message: Sub-hemispheric disconnections like the PQD, offers a minimally invasive solution to the previously practiced extensive anatomical resection, with equal seizure freedom and minimal morbidity in appropriately selected patients. However, image guidance and intraoperative neuro monitoring are extremely useful in enhancing the seizure outcome and maintaining a minimal complicat
|How to cite this article:|
Doddamani RS, Tripathi M, Samala R, Agarwal M, Ramanujan B, Chandra SP. Posterior Quadrant Disconnection for Sub-Hemispheric Drug Refractory Epilepsy. Neurol India 2020;68:270-3
|How to cite this URL:|
Doddamani RS, Tripathi M, Samala R, Agarwal M, Ramanujan B, Chandra SP. Posterior Quadrant Disconnection for Sub-Hemispheric Drug Refractory Epilepsy. Neurol India [serial online] 2020 [cited 2022 May 26];68:270-3. Available from: https://www.neurologyindia.com/text.asp?2020/68/2/270/284358
A 15-year-old, right handed female child, presented with a 5 year long history of seizures with a frequency of 1–2 seizures/day, even with 4 adequately dosed antiepileptic drugs. The patient exhibited multiple seizure semiology localized to the temporal and parietal lobes. Birth history was significant in that, it was a breech presentation and the baby was delivered in the hospital normally. There was delayed cry following birth and neonatal jaundice requiring neonatal intensive care. The patient had an evidence of left homonymous hemianopia and severely impaired attention along with moderately impaired visual memory on neuropsychological testing. There were no focal sensory motor deficits on examination.
Video electro-encephalography (VEEG) was localized to the right parieto-occipital lobe. MRI showed the features suggestive of gliosis involving right superior temporal gyrus, left posterior perisylvian region, and parietal and occipital cortex with exvacuo dilatation of right lateral ventricle. Arterial spin labeling (ASL) sequence suggests hypoperfusion at gliotic areas. Functional MRI (fMRI), visual stimulation task showed bilateral visual fields represented predominantly on the left visual cortex. Other ancillary investigations like; PET, SPECT, and MEG were suggestive of posterior quadrant origin of the seizures [Figure 1]. Based on the evaluation findings, a plan of posterior quadrant disconnection was formulated for this patient at the epilepsy surgery meeting by our epilepsy team.
|Figure 1: (a) Preoperative MRI Fluid-attenuated inversion recovery (FLAIR) sequence showing right sided parieto-occipital gliosis with temporal extension and ex-vacuo dilatation of right occipital horn. (b) fMRI showing predominantly left visual cortical lighting up following on left sided visual task. (c) PET CT –Hypo metabolism in right parietal lobe. (d and e) MEG (S-LORETA) right parieto temporal localization|
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| » Operative Steps for Performing Pqd|| |
The most important requirements prior to performing the PQD are:
- Concrete hypothesis following comprehensive epilepsy workup
- Intra operative neuro monitoring (IONM).
The use of neuro-navigation is extremely useful for a precise pre operative marking of the skin incision, centered along the Rolandic sulcus and the sylvian fissure. Hence, the use of navigation aids in planning the incision and thereby tailoring the craniotomy. In cases with small ventricles, it can guide the surgeon in locating the ventricles.,,,,
Similarly, IONM plays a significant role in the success of this complex surgery. Intra operative monitoring of motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs) assists the surgeon to accurately localize the primary motor and sensory areas, respectively.,,
The patient is placed supine with head end elevated by 30 degrees and turned to side contralateral to the craniotomy by approximately 60–70 degrees and fixed with mayfield clamp. A shoulder role can be placed underneath the ipsilateral shoulder to avoid the excessive twisting of the neck, thereby avoiding venous engorgement [Figure 1].
A linear incision of 10 cm is fashioned beginning 2-3 cm across the midline just behind and parallel to the rolandic sulcus (localized with image guidance) [Figure 2]. The incision is continued laterally and anteriorly in an oblique manner along the sylvian fissure, up till the front of the ear pinna.
|Figure 2: (a) Patient positioned supine with head rotated to the opposite side and fixed with mayfield clamp. Linear hairline skin incision extnding from the midline to the front of the pinna. (b) After strip craniotomy and dural opening, the anatomical landmarks are defined|
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A rectangular strip craniotomy of approximately 8 × 4 cm is created using image guidance, beginning just off midline and extending laterally, so as to expose the parietal and temporal operculae and the sylvian fissure. After opening the dura, the landmarks, specifically the sylvian fissure and the central sulcus (CS) are confirmed with the help of image guidance.[Figure 2].
In the cases of cortical dysplasia/gliosis/angiomas visual interpretation and sometimes navigation may be misleading. Hence, at this stage MEPs and SSEPs assist in accurately localizing the CS.
| » Temporal Disconnection|| |
Lateral cortical disconnection
Once, the landmarks are localized, the temporal disconnection is started by coagulating the arachnoid over the superior temporal gyrus (STG/T1) just below the sylvian fissure [Figure 3] and [Figure 4]. Subpial aspiration of the T1 is performed all along the length, till the insular arachnoid is reached [Figure 4]. The inferior limiting sulcus (ILS) of the insula is traced in entirety. The white matter along the ILS is aspirated by traversing in an oblique direction to reach the temporal horn [Figure 4] and [Figure 5]. This step effectively disconnects all the tracts traversing in the temporal stem. The TH is opened up from atrium till the tip, so that the hippocampal head and the choroid plexus of the temporal horn are exposed [Figure 5].
|Figure 3: (a) The cortical incision (red dotted line) beginning along the post-central sulcus and extending along the superior temporal gyrus. The area colored dark pink represents the affected posterior quadrant. (b) The central vein is visible and the dotted black line represents the cortical incision posterior to the sensory cortex.|
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|Figure 4: (a) After the removal of T1 gyrus, insula is exposed (b) Defining the inferior limiting sulcus (ILS) (c) The schematic illustration depicting incision along the inferior limiting sulcus (ILS) of the insula (1) to enter into the temporal horn (interrupted black line). The hippocampus (broken blue line) lies deep to the ILS|
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|Figure 5: (a) Temporal horn is exposed along the entire length by slicing through the ILS. The head of the hippocampus (H) and the choroid plexus (CP) seen. (b) The free tentorial edge (broken white line) and the 3rd nerve (Arrow head) visible after removing the hippocampal head|
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The pre choriodal portion of the head of the hippocampus is resected using the standard technique. The temporal amygdala also known as the ventral amygdala, which forms the anterosuperior part of the roof of the TH is resected. Extreme caution should be exhibited during this step by avoiding transgression into the roof of the TH [Figure 5]. This can be accomplished by staying below the imaginary wens line.
| » Parieto-Occipital Disconnection|| |
The incision along the ILS is continued in a posterior and superior direction, extended onto the parietal operculum continued to the parietal convexity towards the midline [Figure 3].
The parietal cortical disconnection is commenced behind the postcentral gyrus extending from the lateral cortex to the falx medially. Effectively, the cortex is disconnected spanning from superior sagittal sinus, superiorly to the splenium inferiorly. Utmost precaution must be exhibited in preserving the arteries and veins [Figure 6] and [Figure 7].
|Figure 6: (a) Following the removal of hippocampal head (H) the temporal horn and the atrium are connected, the splenium (Sp) can be seen. (b) The parietal lobe is disconnected posterior to the post-central gyrus medially till the falx cerebri. Splenium is sectioned. The fornix (F) is disconnected (solid black band) finally, the choroid plexus (CP) is a constant landmark guiding through the surgery and the pulvinar of the thalamus (T) is seen. (c) Completed temporal parietal occipital (TPO) disconnection|
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|Figure 7: Schematic illustration depicting complete TPO disconnection. The exposed temporal horn showing the entire hippocampus from head (2) to the fornix. The parietal lobe disconnected just posterior to the sensory cortex extending from superior sagittal sinus superiorly till the splenium (4) inferiorly and falx (5) medially. This is connected laterally to the line of temporal disconnection. Intraventricularly the splenium is disconnected (broken black line). The 2 white bands on the hippocampus depicting disconnected hippocampal head (2) anteriorly and Fornix posteriorly. The hippocampal head is resected out completely. The pulvinar of the thalamus (3) is seen|
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| » Splenial Disconnection|| |
The atrium of the ventricle and the choroid plexus, as landmarks are vital in ensuring successful disconnection of the splenium. The atrium of the lateral ventricle, choroid plexus, and falx are the most important landmarks. Intraventricularly, the splenium is sectioned along the junction of superior and medial wall of the atrium of the lateral ventricle [Figure 6] and [Figure 7].
| » Fornicial Disconnection|| |
The hippocampal tail curves anteriorly to enter into the atrium of the lateral ventricle posterior and superior to the pulvinar of the thalamus as fornix. The disconnection of thefornix is performed at this level, thereby isolating the posterior quadrant completely from the frontal lobe sparing the primary sensory cortex [Figure 6] and [Figure 7].
| » Pearls and Pitfalls|| |
The PQD is a technically challenging procedure, requires a thorough knowledge of the ventricular anatomy. The experience of the surgeon is immensely imperative for the safe and effective performance of this procedure.,,,,
As already detailed in the technique, the following points needs to be focused:
- The regular use of image guidance aids in performing this procedure in a minimally invasive fashion, right from placing a linear incision to strip craniotomy. It also assists the surgeon to accurately identify the Rolanic sulcus and also localize the ventricles, especially when the ventricles are small. Image guidance becomes essential to avoid disorientation, and thereby avoiding major complications.
- IONM is another vital tool, providing confidence to the surgeon all throughout the surgery. It not only helps in precisely localizing the motor (MEP) and sensor (SSEP) cortices, but also the deep corticospinal tracts, with the help of the suction probe. This helps in preventing the catastrophic complications.
- Preservation of the cortical arteries and the major veins should be attempted in all cases.
- Respecting the arachnoid and confining the resection in the subpial plane, especially during the resection of mesial temporal structures, avoids injury to the major vessels, and thus minimizes the complications.
The seizure freedom following PQD depends upon the completeness of the disconnection. Compared to the anatomical PQ resection, the PQD leaves behind the whole of the temporo-parieto-occipital lobes insitu, by severing the connections. Hence, there is a chance of recurrent seizures following surgery, owing to residual connections/incomplete disconnection if missed.,
| » Conclusion|| |
The posterior quadrant disconnection surgery is a tailored multi-lobar disconnection and equivalent in efficacy with lesser complications compared to the resective surgery. This is a technically demanding procedure and one needs to be cognizant of the anatomy prior to performing this operation effectively. Image guidance and intra operative neuro-monitoring adds to the success of the surgery and minimizes morbidity.
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Conflicts of interest
There are no conflicts of interest.
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Chandra SP, Tripathi M. Endoscopic epilepsy surgery: Emergence of a new procedure. Neurol India 2015;63:571-82.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]