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OPERATIVE NUANCES: STEP BY STEP (VIDEO SECTION)
Year : 2023 | Volume
: 71
| Issue : 4 | Page : 662-666
A Combined Trans-Cerebelomedullary Fissure and Sub Tonsillar Approach to Foramen of Luschka
BC Anil Kumar, Kuntal Kanti Das, Pooja Tataskar, Awadhesh Kumar Jaiswal, Priyadarshi Dikshit, Raj Kumar
Department of Neurosurgery, Sanjay Gandhi Post-Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
Correspondence Address:
Kuntal Kanti Das
Department of Neurosurgery, Sanjay Gandhi Post-Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh - 226 014
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/0028-3886.383810
How to cite this article:Key Message: This video article shows the steps of performing the telo-velar approach with additional sub tonsillar corridor to access the foramen of Luschka. This approach is an extremely versatile approach and needs to be learnt. Here the author describe a case of foramen of Luschka ependymoma to demonstrate the successful application of this approach.
Ependymomas are one of the most common intracranial neoplasms in the pediatric age group[1] and frequently arise infratentorially.[1] Their diagnosis is often delayed as the symptoms progress slowly and are often nonspecific. Despite the slow pace of growth, prognosis remains guarded due to close proximity to other vital neurologic structures.
The two most commonly employed surgical approaches to the fourth ventricle are the transvermian and the telovelar approaches.[2] The lateral recess of the fourth ventricle and foramen of Luschka (FOL) can be a difficult region to reach surgically. A variety of lesions can originate in this area, requiring a neurosurgical intervention.[3] Traditional transvermian approach is a medial to lateral approach and has demerits secondary to vermian division.[4] On the other hand, lateral to medial access requires a skull base approach like a retrosigmoid or a far lateral approach.[4] An approach through Cerebello-Medullary Fissure (CMF), also called the telo-velar approach, is a direct approach to this location and avoids neurologic injury to the surrounding structures.
We demonstrate the use of the latter approach in our patient. We demonstrate the additional utility of a sub-tonsillar window to this classical approach to remove lesions located even at the upper part of the FOL from a caudal aspect.
Case Details
A 2-year-old boy was brought to our center with a tendency to sway toward the right side for the last 3 months and headache accompanied with vomiting for 15 days. The child's growth had been satisfactory until then and all the milestones had been achieved on time. Clinical examination was unremarkable.
Further magnetic resonance (MR) neuroimaging revealed a well-defined lobulated lesion at the left lateral recess of the fourth ventricle and adjoining FOL. The lesion was compressing the brainstem and distorted the fourth ventricle toward the right side. It was heterogeneously hyperintense on T2/FLAIR (Fluid Attenuation and Inversion Recovery) with foci of blooming on SWI (Susceptibility Weighted Imaging). It showed patchy enhancement [Figure 1].
Figure 1: Well-defined lobulated lesion at the left lateral recess of the fourth ventricle and the Fora- men of Luschka. The lesion was found to be compressing the brainstem and distort the 4th ventricle towards the right side. It was heterogeneously hyperintense on T2/FLAIR with foci of blooming on SWI. It showed patchy enhancement Surgical Treatment The patient was taken up for a midline suboccipital craniotomy in a prone position with maximum allowable neck flexion. Using an approach through CMF and beneath the left cerebellar tonsil, the tumor was near totally resected, leaving behind small specks of tumor attached to the lateral aspect of medulla oblongata.
Postoperative period: The patient recovered without any added neurologic deficits and discharged uneventfully. A repeat magnetic resonance imaging (MRI) after 3 months showed no residual tumor [Figure 2]. As we did not perform a spinal screening MRI in the preoperative period, a postoperative spine screening was done with 3 months postoperative cranial MRI, which showed no evidence of spinal drop metastasis [Figure 3]. Histology was reported as ependymoma, a World Health Organization (WHO) grade 1 tumor.
The salient operative steps in our case were as follows:
Patient positioningThe patient was placed in a prone position, with the head fixed using a three-pin fixation in Mayfield head holder. Head was flexed to a maximum allowable limit.Midline suboccpital craniotomy (MLSO) craniotomy and removal of C1 posterior archA standard midline scalp incision from inion to C2 vertebra was used. Multilayered dissection was continued all the way to the bone.Subperiosteal elevation of the soft tissues exposed the suboccipital region and C1 posterior arch.MSLO craniotomy and C1 laminectomy were performed. The dura was opened with a Y-shaped incision.Exposure of CMF and tela choroideaUsing the microscope, the arachnoid was opened sharply over the cisterna magna.This step revealed the fourth ventricle.The left CMF was opened sharply, freeing the arachnoid from PICA (Posterior Inferior Cerebellar Artery).The tela choroidea was thinly stretched over the tumor. An incision was made in the superior part toward the choroid plexus.Tonsil was elevated superiorly allowing a simultaneous sub-tonsillar window.A plane was developed between the tumor and the brainstem by spreading gently using a micro-forceps.Resection of tumorFirst, the center was debulked using an ultrasonic aspirator.Micro-bayonet forceps were used to perform extracapsular dissection.Microsurgical techniques were used to remove the tumor, preserve lower cranial nerves, vertebral artery and medullary perforators.Small capsular attachments were left over the lateral aspect of the medulla.ClosureAfter achieving hemostasis, the dura was closed with a graft.A cranioplasty was performed with a titanium plate.Finally, we closed the wound in a standard multilayered fashion.Postoperative courseThe postoperative course remained uneventful.Postoperative imaging revealed gross total resection of the tumor. Spine screening showed no evidence of drop metastasis.The histopathologic examination confirmed the diagnosis of a WHO grade I ependymoma.Video link
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Video timeline with audio transcript
0:02–0:10- In this video, the authors present the surgical steps of a combined trans-cerebellomedullary fissure and sub-tonsillar approach to FOL.
0:11–0:27- A 2-year-old male child presented with a tendency to sway toward the right side for the last 3 months with headache for 15 days. The child's growth had been satisfactory until that point and all the milestones were achieved on time. The cerebellar signs could not be assessed; however, the other clinical examinations were unremarkable.
0:28–0:39- On neuroimaging, we could see a mass which was T2 hyperintense located on the left side in relation to the brainstem and it was occupying the cerebellomedullary fissure, showing contrast enhancement on coronal scans as well.
0:40–0:58- This patient was taken up for a midline posterior fossa approach with the neck in maximum allowable flexion. This figure shows the location of the Frazier's point for emergency CSF drainage during craniotomy. The incision was a midline incision and it led to exposure of the subcutaneous tissue and the galea aponeurotica, and a layered opening was created.
0:59–1:45- We started with opening of the dura at the craniocervical junction. Hitches were applied at the dural edges and some amount of CSF egress at this point made the brain further lax. The dura was opened in a Y-shaped fashion, taking care of the occipital sinus as well as the marginal sinus, which can be very prominent in children of this age and can be a source of substantial bleeding if not attended to. Here, we could see the occipital sinus was being thoroughly coagulated before division. This point is crucial because some amount of significant bleeding can happen sometimes.
1:46–6:07- After exposure, the arachnoid over this cerebellomedullary fissure and tonsils was opened, and as soon as it was done, a pale-colored tumor came into our view. It was located in the sub-tonsillar area. The arachnoid over the tonsils was opened in the midline to allow mobilization of the left-sided cerebellar tonsil. The tumor was exposed in this area. Coagulation of the tumor surface was performed before it was entered. It was moderately vascular. The tumor was sucked with the help of Cavitron Ultra Sonic Aspirator (CUSA) and once the mass effect reduced, it allowed us to go around the tumor. We could see the lower cranial nerves, which were located deep and inferior to the tumor. Sharp dissection was performed here to preserve these nerves, and we could see the lateral aspect of the medulla here. The tonsillomedullary segment of PICA was seen to be very closely applied on the tumor and it was running through the tumor here, and therefore, it was decided to further debulk the tumor, so that we could preserve this artery. The tumor had calcific areas in between, and after decompression, it was possible for us to go to the upper pole of the tumor. Further debulking of the tumor was deemed necessary at this point to avoid traction injuries. Here, we can see egress of CSF, indicating that we had reached the upper pole of the tumor. Here, the microscope orientation was changed and we could see the left cerebellomedullary fissure area. We could see the lower cranial nerves, which were very badly stuck to the tumor and required careful decompression of the tumor as well as dissection. With utmost care, this part of the tumor was delivered. We could see the part of the tumor going into the area of FOL. The tumor was gritty at places, not easy to suck, and here we could see that the lateral end of the tumor has been reached. The tumor was resected with a small rim of cerebellar tissue to ensure that the tumor had been completely resected there. Small feeders coming from the cerebellum going into the tumor were divided to free the tumor as well as devascularize it. We could very clearly see the vertebral artery, the PICA branch, and the tumor which was growing in between this arterial arcade. Here, we could see the fourth ventricle, the middle and inferior cerebellar peduncle, and the brainstem. The tumor which was stuck to the pia here was very gently separated and removed. So, the tumor was stuck to the lateral surface of the medulla here, we are working around the PICA to remove the small bit of tumor which was stuck to the area of the inferior cerebellar peduncle. Now, the lateral surface of the brainstem was very clearly seen. The vertebral artery was going towards the midline to meet its counterpart in front of the brainstem. These were the lower cranial nerves which were going to the jugular foramen. They were located deep and inferior to the tumor. The lower cranial nerves were seen here and this is the vertebral artery and the arachnoid deep to the tumor. At the end of the resection, small bits of tumor stuck to the lateral surface of the brainstem were left, and further the infiltrated part of the cerebellar peduncle was carefully freed of the tumor and hemostasis was achieved with topical hemostatic agent. We can see the intact cerebellar tonsil overlying the tumor, Now the orientation of the microscope has been changed again. Now the surgeon is standing on the left side, this is the area of the caudal part of the fourth ventricle, the area of the obex and the tumor was located lateral to the brainstem and it was arising from the lateral surface of the brainstem, whereas the 4th ventricle was completely free.
6:08- 6:35 - In the post-operative period the child recovered well. In the initial few days the child required nasogastric feeding, she was however conscious, oriented without any gross neurological deficits, except for the transient impaired deglutition. The child was discharged and at 3 months follow up she is doing well. We can see that the tumor has been completely removed. Post-operative spinal screening did not show any residual tumor. These are the references and thank you for watching this video.
Pearls and pitfalls
A concorde position or maximum allowable neck flexion is crucial which allows inferior to a superior view unlike a pure prone position.If present, hydrocephalus should be utilized surgically by doing an external ventricular drainage before opening the dura. Frazier's point is the most feasible location in a prone position.The craniotomy should be in the midline but more on the side of the tumor. We have seen that tonsilar retraction cranio-laterally is facilitated by this additional bone removal.During dural opening, care must be taken to avoid excessive blood loss from often prominent occipital and marginal sinuses in children. Adequate bipolar coagulation is advised before cutting across these structures. If needed, metallic vascular clips are excellent tools to manage bleeding in these situation. However, postoperative imaging may suffer from artefacts due to these clips.It is important to open the arachnoid of the CMF widely. This reduces traction and injuries secondary to that subsequently. It is also important to visualise the caudal fourth ventricular floor and lateral edge of the brainstem before ensuing tumor decompression.Sub-pial hemorrhages may occur secondary to severing of the pial veins during retraction needed to remove tumor.It is important to deliver the cranial pole of the tumor after some internal debulking. It allows egress of CSF making the brain further lax and allowing the surgeon to determine resection limits.The pial and arachnoid planes leading to the cerebellopontine angles must be respected to avoid cranial nerve deficits.Sufficient care must be exercised to avoid damage to the brainstem, either directly or indirectly from perforator damage, particularly when trying to remove tumor stuck to the lateral surface of the brainstem. DiscussionThe CMF (telovelar) is a natural plane between the cerebellar tonsil and the inferior edge of the vermis. This approach is variously known as sub-tonsillar approach, a TCMF and telovelar approach. Generally, this approach is advocated for caudal fourth ventricular lesions when one can spare ver- mian division and its attendent effects. For lesions of the FOL, it additionally avoids excessive re- traction of the vermis and severe injuries. Matsushima et al.[5] described this approach in 1992. Since then a number of studies have established the efficacy of this elegant surgical approach.
Apart from tumors, other pathologies like arteriovenous malformations, or aneurysms of the PICA[6],[7] have been reported to be addressed by this approach. Complications are rarely due to damage to the isolated opening of the tela and velum. Most complications are secondary to manipulation of struc- tures of the 4TH-ventricular areas like cranial nerve nuclei and cerebellum (dentate nuclei and cere- bellar peduncles.[2],[5],[6],[7]
With minor modifications of the technique described in those and subsequent reports,[2],[6],[7],[8],[9],[10],[11] we used the sub- tonsillar approach for adult patients with tumors at the FOL. These tumors differ from most described in previous reports of similar surgical techniques because they are in the most lateral part of the CMF and not in 4th-ventricle. By mobilizing the tonsil and incising the tela-choroidea, we established direct path to the lesion and minimized the required retraction on the tonsil, rather than being truly retracted or pushed aside, the tonsil is actually rotated rostrolaterally, out of the operative field. The tela-choroidea and telovelar junction contain no neural elements; therefore, preservation of the cerebellar tissue reduces the risk of complications.[5]
Furthermore, the surgical exposure is panoramic, because of extension of the bony opening laterally toward the sigmoid sinus, expansion of the opening of the foramen magnum with resection of a small medial portion of the occipital condyle, and wide opening of the CMF. In the mediolateral direction, the view extends from the midline to the cranial nerves of the cerebellomedullary and cerebellopon- tine angles. In the rostrocaudal direction, it extends from the foramen magnum to the middle cerebel- lar peduncle. Therefore, the subtonsillar approach to the FOL simultaneously maximizes neural preservation and surgical exposure.
As we saw, the vertebral artery, PICA and lower cranial nerves may be interwined and get injured during tumor removal. Also, small perforators arising from PICA and supplying the medulla remain at risk. Although rare, postoperative dyskinesia and dystonia secondary to the manipulation of the dentate nucleus just rostral to the superior pole of the tonsil, may still occur. Small flecks of tumor may have to be left adherent to the lateral part of the medulla, the perforating vessels to avoid post- operative direct or an indirect injury to the brainstem.
This approach has been described well. But, in this video, we additionally demonstrate the utility of superior tonsillar mobilization to visualize the upper pole of such tumors for a better inferior to superior viewing angle. Secondly, this video demonstrates safe, step by step resection of foramen of Luschka ependymoma which are rare compared to those which are located inside the fourth ventricle and extend to foramen of Luschka secondarily. While the latter can be dealt with the classical telovelar approach, pure foramen of Luschka lesions like the one we present here require more improvisation as shown in this technical video.
ConclusionThis video article describes the steps of sub-tonsilar TCMF approach to FOL. This approach spares tedious lateral approach and vermis splitting midline approach. It is an extremely versatile approach and needs to be learnt. Subtle nuances are explained in details in this video which will be an excellent learning material for the young neurosurgeons.
Patient consent
A full and detailed consent from the patient/guardian has been taken. The patient's identity has been adequately anonymized. If anything related to patient's identity is shown, adequate consent has been taken from the parent/relative/guardian. The journal will not be responsible for any medico-legal issues arising out of the issue related to patient's identity or any other issues arising from the public display of the video.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
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