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OPERATIVE NUANCES STEP BY STEP (VIDEO SECTION)
Year : 2020  |  Volume : 68  |  Issue : 8  |  Page : 322--324

Pallidotomy for Dystonia

Kanwaljeet Garg1, Raghu Samala1, Mohit Agrawal1, Roopa Rajan2, Manmohan Singh1,  
1 Department of Neurosurgery, AIIMS, New Delhi, India
2 Department of Neurology, AIIMS, New Delhi, India

Correspondence Address:
Prof. Manmohan Singh
Department of Neurosurgery, AIIMS, New Delhi
India

Abstract

Background: Deep brain stimulation (DBS) is currently the preferred surgical treatment for various movement disorders. Pallidotomy is an effective procedure for patients with dystonia and Parkinson's disease and was the surgical treatment of choice before the advent of DBS. However, it can be the preferred modality in immunocompromised patients and those patients who cannot afford DBS due to financial constraints. Hypophonia, dysarthria and dysphagia are the most significant complications of bilateral pallidotomy. Objective: The aim of this study was to present the surgical technique and nuances involved in bilateral simultaneous pallidotomy in a patient with generalized dystonia. Procedure: A 30-year male with primary generalized dystonia presented to us with preoperative Burke–Fahn–Marsden (BFM) Dystonia Rating Scale of 24. After acquiring preoperative volumetric 3T MRI and stereotactic CT, bilateral pallidotomy was done under general anesthesia. There were no procedure related complications. Results: At two months of follow-up, his BFM dystonia score improved from 24 to 4.5. Conclusion: Appropriately acquired volumetric MRI, meticulous planning and meticulously performed surgical procedure can help in achieving good outcome and minimize the complications.



How to cite this article:
Garg K, Samala R, Agrawal M, Rajan R, Singh M. Pallidotomy for Dystonia.Neurol India 2020;68:322-324


How to cite this URL:
Garg K, Samala R, Agrawal M, Rajan R, Singh M. Pallidotomy for Dystonia. Neurol India [serial online] 2020 [cited 2021 Apr 15 ];68:322-324
Available from: https://www.neurologyindia.com/text.asp?2020/68/8/322/302460


Full Text

The surgical management of movement disorders started in the late part of the twentieth century. Initially, the target of interest in movement disorders like dystonia was ventrolateral thalamic nuclei. Good results with up to 70% reduction in the dystonia symptoms were reported by Cooper using thalamus as the target.[1] However, these results were not reproduced in other studies, and the risk of developing dysphagia and dysarthria after bilateral thalamotomy was high.[2],[3] This led to search for new targets, and globus pallidus interna was found to be a promising target.[3]

Pallidotomy was first used in treatment refractory dyskinesias in advanced Parkinson's disease. Soon it became the favoured target for lesioning in dystonia. However, the trends changed after the introduction of Deep brain stimulation (DBS) in 1996.[4] Subsequently, the popularity of DBS increased and the charm of pallidotomy decreased. Although DBS is preferred over pallidotomy, the disadvantages of DBS over pallidotomy include the risk of infection of the implants, especially in patients who are immunocompromised.[5],[6] Although DBS is preferred over pallidotomy, requirement for change of implantable pulse generator (IPG) is higher in dystonia due to the requirement of higher currents.[7] Moreover, the patients need to be under close follow due to the frequent need of programming. Hence, pallidotomy is a potential option to consider when the patient cannot be adequately followed up or have financial constraints or in patients who are at high risk of infection.

Primary generalised dystonia, presence of DYT 1 gene mutation and normal preoperative MRI are associated with good response following pallidotomy.[6],[8] Various controversies exist in relation to management of dystonia such as unilateral versus bilateral lesioning, and the use of microelectrode recording or microstimulation intraoperatively. Simultaneous bilateral pallidotomy has been reported to be associated with high complication rate. However, we have not found this to be true in our practice.[9] The role of microelectrode recording and microstimulation in pallidotomy is controversial. One meta-analysis showed that the use of microstimulation did not add to the therapeutic advantage. However, its use was found to be associated with higher rate of symptomatic intracranial hematoma formation.[10]

Objective: We present a step by step technique and nuances of pallidotomy for primary generalized dystonia.

Workflow in a pallidotomy

Preoperative work up

The procedure of pallidotomy starts with preoperative work up to assess the severity and distribution of dystonia. The Burke-Fhan-Marsden dystonia rating scale is often used to quantify the severity of dystonia. Visual field charting is obtained pre-operatively as the pallidal target lies near to the optic tract. Preoperative work up also includes metabolic and genetic work up to find out the etiology of dystonia.

Frame fixation

Frame fixation is usually done in general anaesthesia in case of generalized dystonia to create a stereotactic space around head.

Stereotactic CT scan acquisition

Stereotactic CT acquisition is done after the stereotactic frame fixation.

Planning

Stereotactic CT scan is then transferred to the planning station and fused with the MRI images. Anterior and posterior commissures are defined on MRI images. Target can be defined by two methods: indirect (atlas based) and direct (based on direct visualization of the target).

Lesioning

The patient is positioned supine with the head end elevated by 30 degrees. The X-Y-Z coordinates and the arc and the ring values are set on the stereotactic frame and confirmed by at least two other members of the team. A burr hole is made, and dura is coagulated before the insertion of the radiofrequency (RF) electrode. Stimulation is useful in patients to rule out adverse events. Six lesions are created on each side.

Post-operative care

We routinely get volumetric non contrast CT and fuse it with the preoperative MRI to confirm the site of lesioning and to rule out an intracranial hematoma formation.

Video Link: https://youtu.be/ANcGXdhs8_s

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Video timeline with audio transcript:

Preop Clinical status

00-00.22 - We present the step by step planning and operative technique for bilateral pallidotomy via radiofrequency ablation. A 30-year-old male patient presented to us with generalized primary dystonia with BFM dystonia score of 24. He had no other neurological deficits. Patient was given the option of DBS or bilateral pallidotomy and he opted for pallidotomy.

Image acquisition and Frame application

00.23- 00.39 min - A 3D volumetric MRI is acquired prior to surgery, preferably on a 3T machine, with a slice thickness of 1 mm. There should be no gaps or overlap of slices. T2, inversion recovery and T1 double contrast sequences are essential00.40-00.48 - The components of the Leksell stereotactic frame include the base, 2 long anterior and 2 short posterior fixation posts00.49- 01.04 - Ear plugs are used at the time of frame fixation to prevent movement in the axial and coronal plane. Frame fixation in patients with generalized dystonia is usually done under general anesthesia to facilitate frame fixation01.05 – 01.16 –The orbito meatal line is marked as it is corresponds to the AC-PC line. The base of the frame is aligned along the orbitomeatal line and the head is placed in the centre of the stereotactic frame01.17 – 01.32 - The patient is shifted to the CT gantry and a fiducial indicator box is attached on the stereotactic frame. The markings on the side plates and the midline of the indicator box are aligned with the CT gantry laser lights to ensure that there is no tilt01.33 – 01.43 - CT scan is acquired with 1 mm slice thickness with no tilt on the gantry. All nine fiducials should appear in acquired CT01.44- 01.55 - CT images are then transferred to the planning system. Ct is the registered and it is ensured that the error is less than 0.30 mm01.56 – 02.10 - The CT images are then fused with the preoperative MRI. On a split screen view, it is confirmed that the intracranial landmarks like sulci, ventricles, and major vessels overlap perfectly on CT and MRI02.11- 02.28 - The anterior and posterior commissure are then marked on axial images and checked on sagittal and coronal views. Midline is confirmed using the structures like aqueduct and septum pellucidum. It can be tilted in the coronal view to get proper alignment02.29 – 02.52 - GPi is best visualized on the IR sequence. This slide shows all the structures relevant for the planning of target. The optic tract is identified passing beneath the GPi. On T2W MRI image, the optic tract can be traced from anterior to posterior02.53 – 03.11 - Within the GPi the target lies 2 mm anterior to the mid commissural plane, 2 mm above the supero lateral edge of the optic tract. The target lies at the junction of the anterior 2/3 and posterior 1/3rd of the GPi, which is also the plane traversing the anterior most part of the mammillary bodies03.12 – 03.27 - The trajectory is planned once the target is defined. The trajectory is planned to avoid passing through any sulcus or ventricle. The trajectory should have a mediolateral angulation between 0 to 5 degrees and anterior angle of approximately 60 degrees03.28 – 03.35 - The trajectory is then checked on the contrast enhanced image to ensure that no blood vessel is traversed in the sulci or basal ganglia03.36 – 03.58 - We have described the direct targeting of the Gpi. Indirect targeting can be done using Schaltenbrand-Wahren stereotactic atlas. One can also confirm the target chosen by direct targeting using the atlas. Once the plan is finalized, the orientation of the frame is selected03.59 – 04.10 - The final co-ordinates for the right and left GPi are provided by the workstation as X, Y, Z values along with values for the stereotactic ring and arc.

Surgical procedure

04.11 – 04.27 - The patient is positioned supine on the operating table with the stereotactic frame fixed to Mayfield fixation clamp. The head end is raised by 30 degrees. The head and stereotactic frame are prepped and draped04.28 – 04.40 - The X, Y, Z co-ordinates are set on the stereotactic frame. The arc and ring values are set to localize the entry point. All the settings must be checked by two team members04.41- 04.52 - The entry point is marked and a 3 cm linear incision is given and held open by a self-retaining retractor. A burr hole is made at the entry point04.53 – 05.04 - The orientation of the guide should be set at 150 degrees on the left side and 30 degrees on the right side05.05 – 05.23 - The monopolar lesioning probe is of 190 mm length with an active tip 2 mm long and 1 mm wide. It is gradually inserted towards the target with rolling movements. The impedance is checked while the probe is being inserted05.24 -0.5.44 - The lesioning is performed at a temperature of 74 degrees for 60 seconds. The probe is passed in 2 pre-decided trajectories on each side. 3 lesions are created in each trajectory, thus creating a cylindrical lesion of minimum of 4 mm in diameter and 6 mm in length05.45 – 05.55- Postoperative CT scan is acquired and fused with the planned trajectories to check for the lesion accuracy and the presence of intraparenchymal hematoma

Postoperative Clinical Status

05.56 – 06.17 - On postoperative evaluation at 2 months, patient's BFM dystonia score improved to 4.5 from 24. He was able to carry out his activities of daily living without any help, with no postoperative motor deficits or dysphagia.

 Conclusion



Despite widespread acceptance of the procedure, several aspects of pallidotomy remain poorly defined such as the size of the lesion, the long-term benefits of the procedure, and the necessity of obtaining microelectrode recordings. However, appropriately acquired volumetric MRI and meticulous planning can help in accurate targeting and minimize the complications.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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