Interhemispheric Transcallosal Resection of Thalamic Glioma- Preserving Function While Maximizing Resection

Key Message: Preserving function is of utmost importance, especially in patients with deep-seated lesions. Tractography can be helpful while selecting an approach to avoid damaging corticospinal tracts. Thalamic gliomas are rare and constitute 1% of all intracranial tumors. Their deep location and proximity of critical neuro-vascular structures make them challenging to remove. Because of the inherent risks of many of the approaches taken for these lesions, the majority of surgeons favor a conservative strategy for such lesions. There have been only a few case series on successful management of these challenging lesions with surgical resection, rather many of these patients will undergo stereotactic biopsy followed by adjuvant chemo- and radiotherapy. Objective This video article demonstrates the step-by-step resection of a thalamic glioma through an interhemispheric transcallosal route. Case description A 35-year-old male presented with altered mental status for 2 days and underwent ventriculoperitoneal shunting because of a thalamic lesion causing obstructive hydrocephalus. Detailed imaging conducted later revealed a contrast-enhancing solid-cystic 3.5 × 2.7 × 3.3 cm lesion involving the posteromedial part of the left thalamus. Tractography revealed displacement of corticospinal tracts laterally with the tumor. Procedure The surgery was conducted under general anesthesia with navigation guidance. A right-side parasagittal craniotomy was made crossing the midline, 1/3rd anterior, and 2/3rd posterior to the coronal suture. The details of the procedure are mentioned in the video. Video timeline with audio transcript 00:00-00:10- Microsurgical resection of a thalamic glioma through interhemispheric transcallosal route. 00:12-01:14- A gentleman aged 35 years presented to our emergency department with altered mental status following a history of headache and vomiting for 15 days. He underwent emergency VP shunting for a thalamic lesion causing obstructive hydrocephalus. A contrast-enhanced MRI conducted 3 days later revealed a T1 and T2 hyperintense lesion, which was showing homogenous contrast enhancement, involving the left thalamus and abutting the left lateral ventricle. This lesion was showing a choline peak on spectroscopy and tractography revealing lateral displacement of the corticospinal tracts with the tumor. Considering a preoperative diagnosis of a high-grade glial tumor, surgery was planned through the interhemispheric transcallosal route, as any other transcortical route would have led to a violation of corticospinal tracts. 01:15-01:54- He was positioned supine, with head on 4-pin rigid head frame fixation, and navigation was registered. On the right side, a horseshoe-shaped skin incision was marked, crossing the midline, 1/3rd anterior, and 2/3rd posterior to the coronal suture. Three burrhole were then made in the midline and a right side fronto-parietal craniotomy was made. Dural tack-up sutures were taken, and the dura was opened in C-shaped manner and reflected toward the superior sagittal sinus. 01:55-03:16- The arachnoid overlying the veins and the medial posterior frontal lobe was dissected sharply from the dura. This step is important, and care must be taken to avoid injuring any of the veins. Meticulous dissection is needed at this step to avoid any cortical or venous injury. Once this step was conducted, then a retractor was gently placed in the depth of the interhemispheric fissure. In addition, paired pericallosal arteries were identified. The whitish corpus callosum can be appreciated between these two arteries seen in between these two vessels and the site of callosotomy was localized using neuronavigation. 03:17-03:38- Callosotomy was made using a sharp knife, and it was widened using bipolar forceps. After entering the ventricle, navigation was again used to identify the tumor location. 03:39-03:55- An endoscope was then brought into the field and endoscopic inspection of the ventricle cavity revealed the frontal horn, the thalamostriate, and the anterior septal vein. 03:56-05:48 The choroidal fissure was then opened on the fornicial side, and the tumor was encountered at a depth of only a few millimeters. Approximately, 5–10 ml of yellowish fluid was removed initially, representing the contents of the cystic part of the tumor. Biopsy was then taken from the solid part of the tumor. In this study, we can see the greyish solid part of the tumor, which was resected using a combination of bipolar and suction. While resecting thalamic tumors, bipolar must be used at low settings and its use should be minimized as much as possible to avoid injury to surrounding critical areas such as the hypothalamus. A tumor was moderately vascular and resected till normal gliotic tissue was encountered on all sides. A hemostatic agent (SurgicelTM) was then applied on the walls of the tumor cavity once the resection was deemed complete. 05:55-06:27-Endoscope was inserted once again to look for any blood clot inside the ventricular cavity. In this study, normal choroid plexus can be appreciated, and my dissector is at the level of the foramen of monro. An external ventricular drain was left in the operative cavity and closure was done in layers. 06:29-06:44- A CT head conducted on postoperative day 3 after removal of the external ventricular drain showed good resection with no evidence of bleeding or ventriculomegaly. 06:45-07:25- He was discharged to home on postoperative day 6, with subtle right-side weakness, which resolved partially at 3 weeks follow-up. Histopathology was WHO grade 4 astrocytoma, isocitrate dehydrogenase (IDH) wildtype, and these are our references, thank you. Video link https://youtu.be/2rsMXTrQk7o QR Code: Outcome- The patient had delayed awakening after surgery and was extubated on postoperative day 2. He had subtle right hemiparesis and developed transient aphasia, which resolved over 3 days. At 1 month follow-up, he was ambulating without any support. Pathological examination suggested WHO grade 4 astrocytoma (1p/19q deletion negative, IDH wildtype), and he was started on concomitant chemotherapy and radiation therapy. Pearls and pitfalls The following points need specific attention while planning to operate on thalamic gliomas: Detailed radiological evaluation to look for the surface of the tumor, which can be accessed without disturbing normal brain parenchyma as much as possible. Use of tractography to look for the displacement of corticospinal tracts and plan a trajectory that does not violate them. Navigation guidance is of utmost importance, especially while planning craniotomy and second while doing corpus callosotomy. Meticulous and sharp dissection of draining veins is important, and every effort should be made to preserve them to avoid venous infarction. For large tumors causing obstructive hydrocephalus, use of a shunt or intraoperative external ventricular drainage is helpful, especially before dural opening. Once inside the ventricle, anatomical landmarks need to be defined and followed (navigation accuracy gets questionable after cerebrospinal fluid (CSF) drainage) Endoscope can be very helpful in understanding the normal anatomy particularly when the operative corridor is a narrow and deep one. Bipolar coagulation should be used at minimal settings Hemostasis at each step is important to avoid transgressing into normal surrounding brain tissue. Discussion The thalamus is a complex of nuclei situated in the diencephalon, which forms a part of the central core of the brain. It acts as an important relay station for sensory and motor pathways, apart from its role in higher cortical functions such as language and memory.[1] Multiple classification schemes have been suggested by neurosurgeons with the main focus being how to reach a particular area of the thalamus.[2,3] Thalamic gliomas are rare and constitute 1%–5% of all intracranial gliomas. They present with distinct symptomatology in the form of motor deficits because of the involvement of motor pathways and raised intracranial pressure due to obstruction of the cerebrospinal fluid (CSF) pathway. Other common symptoms described in these patients include speech apraxia, naming deficits, poor recall, oculomotor incoordination, and comprehension difficulties.[4] Owing to their rarity, the natural history of thalamic gliomas is not fully understood. Because of their proximity to critical neurovascular structures and deep location, extensive surgical resection is not being conducted in the majority of these patients. Rather most of these patients would undergo biopsy followed by chemo- and radiotherapy. Esquenazi et al.[4] their analysis of 57 patients with thalamic glioblastomas (the largest series published to date) has shown that most of these patients have a uniformly dismal prognosis and the survival outcomes are similar to that of subtotal resection conducted for other supratentorial lobar glioblastomas. However, surgical resection conducted confers a survival advantage to these patients as shown by Zhang et al.[5] and Ferroli et al.[6] As the overall number of series on surgical resection of thalamic gliomas is limited, the true potential of surgery is yet to be unfurled. The main factors governing the approach to a thalamic tumor include- tumor origin, direction of its growth, and displacement of corticospinal tracts with the tumor.[7,8] Although many approaches have been described, the most commonly employed are 1) Interhemispheric-transcallosal for tumors in the medial part of the thalamus; 2) Middle frontal gyrus approach- for tumors involving anteromedial thalamus; 3) Middle temporal gyrus approach – for tumors involving posterior part of thalamus and thalamopeduncular tumors; 4) Occipital- transtentorial approach- for tumors extending medially to the posterior third ventricular region; and 5) Trans-sylvian approach for tumors arising from the posterolateral part of the thalamus and growing laterally. In cases with tumors displacing corticospinal tracts laterally, any approach from the lateral side would lead to their violation. However, the transcallosal route will give direct access to the tumor in such cases, thus ensuring safe resection in this particular group of patients. The side of the surgical approach in interhemispheric transcallosal is based upon following factors: 1) Lateral extension of tumor; 2) Use of intraoperative adjuncts such as navigation; and 3) Surgeon’s dexterity and preference. We have chosen the right side for this case because of the following reasons: 1) Being a right-handed surgeon, it is easier for us to operate from right side; 2) In a narrow and deep operative corridor, the contralateral approach has provided us with a panoramic view of the entire extent of the tumor with a minimal retraction; and 3) Because of the availability of intraoperative navigation, we could precisely make callosotomy at the desired site and enter the ventricular cavity on the side of the tumor, which would have been a bit tricky in the absence of navigation. Surgical resection of thalamic gliomas involves deep and narrow operative corridors because of their location in the center of brain. Various adjuncts have been utilized in modern surgical theaters including the use of neuronavigation, intraoperative electrical stimulation to look for the proximity of corticospinal tracts, evoked potential monitoring including MEPs and SSEPs, and the use of intraoperative imaging to look for the extent of resection.[8] The length of callosotomy is another important consideration in interhemispheric transcallosal approaches. We have made a callosotomy of 12 mm in this case (just enough to accommodate a Leyla retractor blade with a width of 10 mm at the tip). Although the safe limit is debatable, most authors agree that up to 2 cm of callosotomy is safe and is usually associated with minimum deficits. Owing to their diffuse and infiltrative nature, gross total resection of thalamic glioblastomas is seldom possible, and one should aim for maximal safe resection without compromising functional integrity of the patient. Another important consideration is to avoid excessive electrocoagulation at tumor brain interface, as it can have devastating effect on surrounding normal nuclei of the thalamus and hypothalamus. Surgical resection of thalamic glioblastomas can lead to potential complications ranging from subtle speech disturbances to mortality. In a series of 111 patients with unilateral thalamic tumors, Cao et al.[9] have a mortality of 4.5% (5/111), while new-onset motor deficits were seen in 21.7% of their patients. Other complications which can be seen in patients undergoing surgical resection of thalamic gliomas include new onset sensory deficits, raised intracranial pressure, hemianopia, memory disorders, involuntary movements, spasticity, speech disorders, behavioral problems, and seizures. Despite the advances in microneurosurgery, the overall outcomes of thalamic gliomas remain dismal with a median progression-free survival of 9 months and an overall, 2-year survival rate of 19.7%.[4,6,10] Total or subtotal resection is associated with significantly longer survival compared to partial resection or biopsy.[9] Maximal safe resection should be the goal if possible, but it needs careful evaluation of individual tumor and patient characteristics along with meticulous microsurgical dissection. Conclusion Thalamic gliomas in selected cases are amenable for surgical resection without causing new-onset motor or sensory deficits. A careful preoperative evaluation of motor pathways along with navigation guidance is imperative, while embarking on these challenging tumors. Declaration of patient consent Full and detailed consent from the patient and his guardian has been taken. The patient’s identity has been adequately anonymized. If anything related to the patient’s identity is shown, adequate consent has been taken from the patient/relative/guardian. The journal will not be responsible for any medico-legal issues arising out of issues related to the 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.