Original Article The transylvian trans-insular approach to lateral thalamic lesions

Shashwat Mishra, Ramesh C. Mishra

Department of Neurosurgery, Neurosurgical Clinics, Kamayani Hospital, Agra, India

Abstract

Background: Thalamic tumors are rare intracranial tumors. The most common approaches to the have been directed through the , which surrounds it. The transsylvian trans-insular approach to the lateral thalamus has been infrequently described probably because of the vulnerability of the internal capsule, which skirts this part of the thalamus. Aims: To describe the approach emphasizing its anatomical basis and also to evaluate its safety and efficacy. Settings and Design: Retrospective study conducted at a tertiary hospital. Materials and Methods: Patient population included all the patients who underwent surgery for the lesions in lateral thalamus using the transylvian trans-insular approach between 2005 and 2011. A trephine craniotomy was made, centered over posterior sylvian fissure and the surgical corridor was developed through the insular cortex. Results: During the study period Address for correspondence: 10 patients (7 tumors and inflammatory lesions and 3 hypertensive bleeds) were treated using Dr. Shashwat Mishra, this approach. One peri-operative mortality was noted. In patients with lesions other than A-31, Gyandeep Apartments, hypertensive thalamic hemorrhage, there was no postoperative worsening of neurological Mayur Vihar Phase-1, deficit as comparative to preoperative deficits. Total excision/evacuation of the lesion could New Delhi-91, India. be accomplished in all the patients. Conclusions: The transylvian trans-insular approach is E-mail: [email protected]. safe, effective, anatomical procedure, and can be performed at a peripheral center without Received : 07-05-2012 the need for navigation and intra-operative monitoring. Review completed : 28-06-2012 Accepted : 17-07-2012 Key words: Surgical approach, thalamus, trans-insular, transylvian

Introduction of surgical corridors have been utilized for approaching thalamic lesions with transventricular approaches being The thalamus (Gk: “meeting place”/“bridal chamber”), the most frequent and popular among neurosurgeons. as the name suggests, is a secluded part of the brain and The extra-axial approaches to the thalamus through the is the largest component of the diencephalon. Thalamic subarachnoid space are advantageous in not violating the lesions are rare and thalamic tumors account for 4% of cortex but often employ a long corridor and sometimes all intracranial tumors.[1] Surgical treatment of thalamic require special positioning of the patient. Though, lesions has generally been associated with significant the posterior transylvian trans-insular approach for morbidity, necessitating a careful evaluation of the risks thalamic lesions has been described long ago, but is and benefits before making a decision to operate. A variety only infrequently mentioned in published literature. We describe our experience with this approach in treating a Access this article online spectrum of thalamic lesions at a small peripheral center, Quick Response Code: emphasizing the efficacy and safety of this approach. Website: www.neurologyindia.com Materials and Methods PMID: *** Surgical anatomy of the thalamus DOI: A brief discussion of relevant surgical anatomy of 10.4103/0028-3886.100725 the thalamus is pertinent to the discussion of our

Neurology India | Jul-Aug 2012 | Vol 60 | Issue 4 385 Mishra and Mishra: Trans-insular approach to thalamic lesions technique and results. Thalamus is often represented fissure was opened. Sometimes, a minor bridging vein as a tetrahedron with three free surfaces exposed to was sacrificed to widen the operating space. An effort was ventricular system and one surface in contact with critical made to open the sylvian fissure along its entire visible neural structures. The posterior, dorsal, and medial length to allow atraumatic separation of the operacula. faces of this tetrahedron are open to the atrium, body We adopt an “inside-out” technique for opening the of lateral ventricle, and , respectively. sylvian fissure, separating the opercular arachnoid bands Anteriorly, thalamus is bounded by foramen of Monro; in the depth before slitting the superficial arachnoid. dorsally, by the roof of third ventricle and posteriorly it Attention was directed toward the temporal operculum is delimited by the . Inferiorly, the and transverse temporal gyri were identified by their hypothalamic sulcus distinguishes it from sub-thalamic oblique orientation and undulating appearance on an structures. The enlarged lateral and caudal parts of the otherwise flat opercular surface. Normally, the postero- thalamus overlie the brain stem. Thalamic radiations, medial ends of these gyri converge toward the posterior emanating from the lateral surface of the thalamus, half of the superior limiting sulcus of the insula, which is are the reciprocal connections of thalamic nuclei with superficial to the posterior thalamus, the retro-lentiform cerebral cortex. Upon the dorsal surface of the thalamus, internal capsule and the anterior limit of the atrium.[2,3] thalamostriate vein delineates it from caudate nucleus Though the transverse temporal gyri still remain anterolaterally. Ventrolaterally, the thalamus is in contact identifiable when the tumor distorts posterior insula, with posterior limb of internal capsule, a structure of their medial ends are often rendered obscure. Mechanical critical importance in approaches directed towards the retraction of the opercula was conscientiously avoided lateral surface. From the insular segment of sylvian as initial tumor decompression provided the required fissure, the insular cortex, extreme capsule, external working space. For the initial approach, the opercula capsule and the retrolentiform limb of internal capsule were held apart with cottonoids wedged into the fissure. are sequentially traversed to reach the lateral aspect of However, keeping the normal relationship in mind, the the thalamus [Figure 1]. posterior insular cortex (the long insular gyri posterior to the central sulcus) was entered and the lesion was Materials and Methods found beneath a thin cortical layer. The lesion was then removed using routine microsurgical techniques. Care We analyzed case records of patients with thalamic was taken to remain within the substance of the tumor. lesions treated by transylvian trans-insular approach at Lesion excision was followed by hemostasis and routine Kamayani Hospital, Agra, India, between 2005 and 2011. closure. Transylvian trans-insular approach was employed for patients with laterally projecting thalamic lesions Results approaching the posterior sylvian fissure on imaging. Following the surgery, these patients were closely The clinical data of the patients who underwent this followed up and outcome information was collected. The surgical approach are presented in Table 1. Seven clinical presentation, imaging studies and the outcome tumors and three hypertensive thalamic hematomas data for eligible patients were analyzed. were treated using this approach. We had one death in the peri-operative period. One patient remains in Surgical technique chronic vegetative state following evacuation of thalamic Patients were positioned supine and the head was hematoma. In patients with thalamic lesions other rotated to the contralateral side with an aim to bring than hypertensive thalamic hematoma, there was no sagittal suture parallel to the floor. Ipsilateral shoulder postoperative worsening of the preoperative deficits. was propped up with padding to check excessive Total excision of the lesion could be achieved in all the neck rotation. The head was held in this position with cases [Figure 3]. Sugita head holder and a linear incision was marked, centered at a point along the surface projection of the Discussion posterior sylvian fissure about 2–3 cm anterior to the parietal eminence [Figure 2]. The incision was deepened Thalamic lesions, historically, have been considered through fascia and temporalis muscle and bone exposed. to be inoperable due to the complex architectural A trephine craniotomy was made as shown in the figure. organization of vital thalamic nuclei and the proximity After opening the dura, posterior sylvian fissure was to critically important structures such as the internal identified by the presence of prominent superficial capsule, subthalamus, and basal ganglia. However, middle cerebral vein and the M4 branches entering the with the evolution of microsurgical techniques and fissure along both operculae. Arachnoid over the veins improved understanding of microsurgical anatomy, was sharply divided on the frontal side and the sylvian these lesions no longer remain unassailable. Recent

386 Neurology India | Jul-Aug 2012 | Vol 60 | Issue 4 Mishra and Mishra: Trans-insular approach to thalamic lesions studies have demonstrated improved outcomes with Tumors arising in one of the thalamic nuclei remain aggressive surgical resection of thalamic lesions.[4] confined to the segment of the origin and distort as Complete excision of benign tumors can be curative well as displace the surrounding structures as they while the resection of high grade tumors confers a expand. Alternatively, when arising from the thalamus survival advantage.[1,5-7] in proximity to the ventricular surface, an exophytic tumor growth beneath the intact ventricular ependyma Three distinguishable patterns of expansion and growth is often observed. The third group of tumors may expand for thalamic tumors have been described by Yasargil.[8] laterally and superiorly into the white matter of an adjoining gyrus. This is the group, which in our opinion grows toward the sylvian fissure and posterior insula. Thus tumor expansion frequently entails a separation rather than infiltration of critical white fiber bundles and vascular structures.

A variety of surgical approaches have been described for thalamic tumors depending upon the part of thalamus that is predominantly involved. Transventricular approaches are the most frequent because of the intimate relationship of the thalamus with the . Access to the ventricles and subsequently to the thalamus may be gained either by transcortical or interhemispheric routes. The interhemispheric approaches may jeopardize the bridging cortical veins and may even sometimes be precluded by anomalous Figure 1: A diagram displaying the relationship between the structures venous anatomy. Transcortical approaches, do not deal traversed in the trans-sylvian trans-insular approach (blue arrow) to the thalamic lesions [TO-temporal lobe, PIC-posterior insular cortex, with veins, but necessitate a potentially epileptogenic ExC- external capsule and claustrum,RLIC- retrolentiform limb of internal cortical incision. The trans-parietal, trans-atrial approach capsule, Pu-putamen, Gp-globus pallidus, ALIC-anterior limb of internal capsule, PLIC-posterior limb of internal capsule, TV-third ventricle, may also affect the superior loop of the optic radiations. Th-thalamus, HC-head of caudate nucleus] Further, in the absence of , these

a b

c d Figure 2: (a) The relationship between the thalamus, overlying cortex, and the pinna, (b-a). CT scout film exhibiting the trephine craniotomy, (c) showing the operative incision (case 4) and (d) Complete neurological recovery. [STg - superior temporal gyrus, MTG - Middle temporal gyrus, PCG -Precentral gyrus, PoCG - Postcentral gyrus, IFG - Inferior frontal gyrus, SMG - Supramarginal gyrus]

Neurology India | Jul-Aug 2012 | Vol 60 | Issue 4 387 Mishra and Mishra: Trans-insular approach to thalamic lesions

a c

b d Figure 3: Respective preoperative (a and c) and postoperative (b and d) images of a pilocytic astrocytoma (Case 6) and Fungal granuloma (Case 7) operated upon using the discussed approach

Table 1: Clinical characteristics, pathology and outcome of studied patients. Age/ Pathological Clinical presentation Neurological status Follow-up Final outcome sex diagnosis (post-operative) duration 65/m Hypertensive (lt.) Sudden LOC with Rt. Neurological status 10 days expired POD 10 thalamic bleed hemiplegia, E1VetM4 unchanged 25/f Inflammatory cyst Headache and right Hemiparesis improved 4 years Mild residual hemiparesis, (Neurocysticercosis) hemiparesis partially asymptomatic 58/f Hypertensive (lt.) Sudden LOC with Rt. E4V4M6 on POD2, 3 years Hemiplegic, needs assistance thalamic bleed Hemiplegia, E2V2M5 Hemiplegia persistent for daily activities 5/m (Rt.) Thalamic anaplastic E3V2M5 with left Power recovered to 3/5 at 2.5 years No recurrence, No deficits ependymoma hemiplegia discharge on POD4 7/f (Rt.) Thalamic Headache, vomiting, left Deficits resolved completely 3 years Fatal disseminated recurrence Glioblastoma Multiforme hemiparesis 3 years following surgery 14/f (Rt.) thalamic pilocytic Headache, vomiting, left Power improved to 4/5 at 2 years No recurrence, No deficits astrocytoma hemiplegia discharge on POD3 20/m Fungal granuloma Progressive left Deficit stable at discharge 1.5 years Improvement in deficit, (species unidentified) hemiparesis, headache (POD3) remains asymptomatic 69/m Hypertensive (lt.) Sudden LOC and left Discharged in E1VtrM3 1 year Remains in chronic vegetative thalamic bleed hemiplegia, E1VetM3 status. Hemiplegia persistent state 13/m (Rt.) thalamic pilocytic Progressive left Mild hemiparesis (power-4/5) 0.5 years Asymptomatic, complete astrocytoma hemiparesis and tremors at discharge on POD3 recovery of neurological deficit 6/f (Rt.) thalamic pilocytic Headache, blurring of Deficit resolved completely 0.5 years Asymptomatic, no deficit. astrocytoma vision, and left hemiparesis LOC = Loss of consciousness, Lt = Left, Rt = Right, POD = Postoperative day approaches may penetrate a substantial depth of approach and its variations and hence are not preferable the cortex to reach the target. The extra-axial trans- for lesions in lateral thalamus. arachnoidal approaches such as the infratentorial, supracerebellar approach (Krause’s), and the posterior Direct transcortical approaches to the lesions in interhemispheric approach, aim to circumvent the ventrolateral thalamus are directed through the disadvantages of the transventricular approaches. The temporal cortex. Besides, the general disadvantages of posterior interhemispheric approach takes advantage the cortical incision, they also place the Meyer’s loop of the fact that the midline bridging veins are scarce and Wernicke’s area (in dominant hemisphere) at risk. posterior to the lambdoid suture. Approach to the atrium In contrast, the transylvian trans-insular approach to and posterior thalamus necessitates a small incision in lateral thalamic lesions offers a natural corridor and the precuneus, which is inconsequential. However, these avoids an incision in eloquent cortex. The main criticism approaches are applicable mainly to pulvinar lesions of this approach is that it apparently traverses the retro- and necessitate a long operative corridor. Moreover, the lenticular portion of the internal capsule. However, as basal veins often limit the lateral reach of the Krause’s our experience has borne out, the white matter tracts

388 Neurology India | Jul-Aug 2012 | Vol 60 | Issue 4 Mishra and Mishra: Trans-insular approach to thalamic lesions are separated and splayed by the expanding tumor corridor and avoidance of incision over the eloquent and can safely be preserved by confining the surgical cortex. dissection to the lesion. Further, the extension of the tumor beneath the insular cortex provides an avenue References for atraumatic dissection. This approach was initially described by Yasargil, and has been attempted by 1. Cuccia V, Monges J. Thalamic tumors in children. Childs Nerv Syst others.[5,6,9] These authors have affirmed the feasibility 1997;13:514-21. 2. Wen HT, Rhoton AL Jr, de Oliveira E, Castro LHM, Figueiredo EG, of this approach in selected thalamic lesions. However, Teixeira MJ. Microsurgical anatomy of the temporal lobe: Part it must be remembered that the configuration of the 2-sylvian fissure region and its clinical application. Neurosurgery thalamic lesion suitable for this approach is usually 2009;65(6 Suppl):1-36. encountered when the lesion arises from the posterior 3. Türe U, Yaşargil DC, Al-Mefty O, Yaşargil MG. Topographic anatomy of the insular region. J Neurosurg 1999;90:720-33. ventrolateral thalamus, as this part of the thalamus 4. Albright AL. Feasibility and advisability of resections of thalamic tumors is closest to the retro-lenticular white matter and the in pediatric patients. J Neurosurg 2004;100(5 Suppl Pediatrics):468-72. posterior insular gyri. Expectedly, the site of origin 5. Kelly PJ. Stereotactic biopsy and resection of thalamic astrocytomas. within the thalamus is difficult to determine when the Neurosurgery 1989;25:185-95. 6. Ozek MM, Türe U. Surgical approach to thalamic tumors. Childs Nerv lesion is sizeable, which is quite frequently seen. In these Syst 2002;18:450-6. cases, extension of lesion toward posterior insular cortex 7. Yasargil MG. In: Microneurosurgery: In 4 volumes Vol. 4B. Microsurgery and anterior displacement of the lenticular complex of CNS tumors. Stuttgart. New York: G. Thieme; Thieme-Stratton; renders it suitable for the trans-insular approach.[7] We 1996. p. 29-91, 291-342. 8. Yasargil MG. In: Microneurosurgery: In 4 volumes Vol. 4A, CNS Tumors: have also explored hypertensive thalamic bleeds using Surgical Anatomy, Neuropathology, Neuroradiology, Neurophysiology, the same operative corridor. However, we did not see Clinical Considerations, Operabilty, Treatment Options. Stuttgart. New encouraging results or significant neurological recovery York: G. Thieme; Thieme-Stratton; 1994. p. 115-53. in these cases. This observation is consistent with the 9. Villarejo F, Amaya C, Pérez Díaz C, Pascual A, Alvarez Sastre C, Goyenechea F. Radical surgery of thalamic tumors in children. Childs view that hypertensive bleeds often destroy the affected Nerv Syst 1994;10:111-4. white matter, thus reducing the chances for neurological 10. Adeoye O, Broderick JP. Advances in the management of intracerebral recovery. Hence a more conservative strategy, as hemorrhage. Nat Rev Neurol 2010;6:593-601. advocated in cases of other ganglion bleeds,[10-12] is also 11. Qureshi AI, Mendelow AD, Hanley DF. Intracerebral haemorrhage. Lancet 2009;373:1632-44. applicable here. 12. Fewel ME, Thompson BG Jr, Hoff JT. Spontaneous intracerebral hemorrhage: A review. Neurosurg Focus 2003;15:E1. To conclude, in our view the transylvian trans-insular approach is a safe and effective operative plan for lesions How to cite this article: Mishra S, Mishra RC. The transylvian arising in the ventrolateral thalamus and extending trans-insular approach to lateral thalamic lesions. Neurol India toward the insular cortex. For these lesions, the chief 2012;60:385-9. advantages of this approach are a short operative Source of Support: Nill, Conflict of Interest: None declared.

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