J Neurosurg Pediatrics 14:563–572, 2014 ©AANS, 2014

Endoscopic disconnection of hypothalamic hamartomas: safety and feasibility of robot-assisted, thulium laser–based procedures Technical note Amedeo Calisto, M.D.,1 Georg Dorfmüller, M.D.,1 Martine Fohlen, M.D.,1 Christine Bulteau, M.D., Ph.D.,1 Alfredo Conti, M.D., Ph.D., 2 and Olivier Delalande, M.D.1 Division of Pediatric Neurosurgery, Fondation Adolphe de Rothschild, Paris, France; and 2Department of Neurosurgery, University of Messina, Italy

1

Object. Hypothalamic hamartomas (HH) may induce drug-resistant epilepsy (DRE), thereby requiring surgical treatment. Conventionally, treatment is aimed at removing the lesion, but a disconnection procedure has been shown to be safer and at least as effective. The thulium laser (Revolix) has been recently introduced in urological endoscopy because of its ability to deliver a smooth cut with good control of the extent of tissue damage. The authors sought to analyze the safety and efficacy of the thulium 2-mm laser applied through navigated, robot-assisted endoscopy in disconnection surgery for HHs. Methods. Twenty patients with HH who were drug resistant were treated during a 12-month period. Conventional disconnection by monopolar coagulation (endoscopic electrode) was performed in 13 patients, and thulium laser disconnection was performed in the remaining 7 patients. The endoscope was inserted into the ventricle contralateral to the attachment of the HH on the third ventricular wall. Results in terms of safety, efficacy, and ease of use of the instrument were analyzed. Results. All 20 patients achieved a satisfactory postoperative Engel score (Classes I–III). At 12 months, the Engel class was I or II in 8 of 13 patients (61.5%) who underwent monopolar coagulation and in 6 of 7 patients (85.7%) who underwent laser disconnection (p = 0.04). Seven of 13 patients (53.8%) who underwent monopolar coagulator disconnection and 2 of 7 patients (28.6%) who underwent laser disconnection had immediate postoperative complications. At the 3-month follow-up, only 2 patients (15.4%) treated by coagulation still experienced mild surgery-related recent memory deficits. No complications persisted at the 12-month follow-up. Conclusions. The disconnection procedure is a safe and effective treatment strategy to treat drug-resistant epilepsy in patients with HHs. With the limitations of initial experience and a short-term follow-up, it appears that the thulium 2-mm laser has the technical features to replace the standard coagulation in this procedure. (http://thejns.org/doi/abs/10.3171/2014.8.PEDS13586)

Key Words      •      hypothalamic hamartoma      •      disconnection      •      gelastic seizures      •      thulium laser      •      epilepsy surgery      •      neuroendoscopy

H

hamartomas (HHs) are rare developmental malformations consisting of glial cells intermingled with neurons. They originate from nodules of heterotopic and hyperplastic neurons dispersed in the wall and/or floor of the third ventricle, attached to the tuber cinereum or mammillary bodies (Fig. 1). These lesions often cause epilepsy, typically gelastic seizures refractory to medical therapy. Seizures may evolve into a generalized epileptic encephalopathy characterized by different types of seizures (both generalized and partial) ypothalamic

Abbreviation used in this paper: HH = hypothalamic hamartoma.

J Neurosurg: Pediatrics / Volume 14 / December 2014

that eventually affect behavior and cognition. Central precocious puberty is often associated with these lesions. The relationship of HHs with the mammillo-thalamic circuit seems to explain the diffusion of the chaotic electrical activity generated inside the hamartoma.7,18 These lesions can be sessile or pedunculated, depending on the extent of their attachment to the adjacent structures and on the pattern of growth within the hypothalamic parenchyma or in the ventricular and interpeduncular space. This article contains some figures that are displayed in color on­line but in black-and-white in the print edition.

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Fig. 1.  Coronal MR image of a Type II HH. According to Delalande’s classification, a Type I HH has a horizontal implantation plane, while a Type II HH has a vertical insertion plane and resides in an intraventricular location (intrahypothalamic). Type III is a combination of Types I and II, and Type IV includes all giant hamartomas.

Resection of such benign lesions has been associated with a significant risk of neurological sequelae,13,25 including memory deficits, visual defects, and damage to the capsular region, which typically results in major motor deficits. Furthermore, iatrogenic hypothalamic injuries may cause life-threatening complications, including serum electrolyte alterations, syndrome of inappropriate antidiuretic hormone release, diabetes insipidus, hyperthermia, hyperphagia, hypothyroidism, and poikilothermia. The disconnection of the hamartomas from the surrounding neural structures is increasingly considered a safe and effective procedure. Either transcranial or endoscopic, disconnection has proved to be as effective as resection (49%–60% of patients will become seizure free), with a lower incidence of surgery-related complications.5,15,21,29 Since 1997, patients with HHs and refractory epilepsy, defined as seizures not controlled by up to 3 different medications for at least 6 months, have been treated at our institution by means of a disconnection procedure because these procedures cause less damage than resection in certain situations. A robot and navigation system (ROSA, Medtech S.A.S.) is used to control the endoscope, allowing restricted movement along a predetermined trajectory or a “safe” space. The unipolar coagulator tip, usually introduced through the operative channel 564

of the endoscope, is used to carry out the disconnection. Nevertheless, we consider the use of unipolar coagulation not fully satisfactory because its effect on the neural tissue often results in a “micro-explosion” that is not always localized and under control, even when used at minimal intensity. The use of a laser is an attractive alternative to maximize the control of the microdisconnection procedure, but until recently available lasers were not suitable for this procedure. A new type of laser has been recently introduced whose characteristics make it suitable for HH endoscopic disconnection. The Revolix (LISA Laser Products OHG) is a thulium laser instrument with a wavelength of 2.0 mm. Because of the wavelength’s great absorption in water, the destructive vaporization effect is highly limited around the tip of the silica fiber. This allows for gentle cutting of the white matter combined with coagulation, without deep penetration and uncontrolled tissue necrosis. The laser operates in a continuous or pulsated wave mode, with a variable intensity according to the desired result. The effect is restricted to less than 2 mm in front of the tip of the fiber. The tissue penetration is approximately 500 mm. Here, we report a preliminary analysis of results of a group of 20 patients, treated during a period of 12 months, who harbored an HH (Delalande Types II, III, and IV) that protruded inside the third ventricle, causing drug-resistant epilepsy. Patients were treated using an endoscopic, navigated, and robot-assisted disconnection procedure performed using either thulium laser or unipolar microcoagulation. Population

Methods

The present series includes patients undergoing surgery performed by O.D. or G.D. at the Fondation Ophtalmologique Adolphe de Rothschild, Paris, during a 12-month period (June 2011–May 2012). Twenty patients were included in this series, and analysis was retrospectively conducted. The inclusion criteria were drug-resistant epilepsy; presence of Type II, III, or IV HH according to Delalande’s classification; and indication for endoscopic disconnection. Details concerning patients’ demographics, hamartoma and seizure characteristics, and previous interventions are reported in Table 1. All patients underwent preoperative, long-term video-electroencephalography, with evidence of multiple daily epileptic seizures; preoperative MRI showed or confirmed a hypothalamic lesion in all patients, which was interpreted to be an HH. Lesions were classified based on their implantation on the third ventricle wall as horizontal or vertical, with a doublesided insertion, or mixed. Two days after surgery the following variables were assessed: occurrence of motor deficits, immediate persistence of seizures, percentage of hemoglobin decrease at 48 hours (< 10%, between 10% and 20%, and > 20%), electrolyte levels (correction necessary or not), and urinary density variation respective to the preoperative value (< 10%, between 10% and 20%, and > 20%). J Neurosurg: Pediatrics / Volume 14 / December 2014

Age (yrs), Sex

6, F

4, M

17, F

6, F

15, M

1.3, M

18, M

5, F

11, M

24, M

6, M

7, M

37, F 12, F

12, F

16, F

1, M 0.8, F 3, M

Case No.

1

2

3

4

5

6

7

8

J Neurosurg: Pediatrics / Volume 14 / December 2014

9

10

11

12

13 14

15

16

17 18 19

rt lt rt

lt

rt

lt lt

lt

rt

lt

lt

rt

lt

rt

lt

lt

rt

rt+lt

rt

Side of Disconnection

Revolix Revolix Revolix

Revolix

Revolix

monopolar   coagulation monopolar   coagulation monopolar   coagulation Revolix Revolix

monopolar   coagulation monopolar   coagulation monopolar   coagulation monopolar   coagulation monopolar   coagulation monopolar   coagulation monopolar   coagulation monopolar   coagulation monopolar   coagulation

Instrument

generalized tonic-clonic drop   attack, gelastic/dacrystic generalized (absent since first op)  gelastic gelastic, lt facial spasm gelastic seizures partial complex, clonic, gelastic

generalized tonic-clonic tonic seizures, gelastic, dacrystic

partial seizures

spasms, gelastic

generalized tonic-clonic, gelastic

spasms, gelastic, status epilep  ticus

generalized tonic-clonic partial  complex absence, gelastic

generalized tonic-clonic, partial   complex, gelastic gelastic seizures

generalized tonic-clonic, drop at  tacks, partial complex, gelastic gelastic, tonic, visual hallucination

absence, partial complex, gelas  tic, face blush generalized tonic-clonic, gelastic

Type of Epilepsy

1 0.6 3

15

11

19 12

5

4

23

11

5

8

1.5

7

6

6

1

6

140 315 35

14

5

2 0.2

28

21

21

42

14

0.3

42

1

31

66

21

84

Epilepsy Mean No. Duration of Seizures (yrs) per Wk Additional Symptoms

no early puberty concentration deficit, mild retardation, early   puberty

mild retardation mild retardation, behavioral disorder, aggres  siveness, early puberty, obesity hyperphagia epileptic encephalopathy, precocious puberty,   memory deficits early puberty (iatrogenic)

behavioral disorder, mild retardation, anxiety

polymicrogyria, mild retardation

peripheric hypothyroidism, concentration deficit

hypopituitarism, obesity, retardation, aggres  siveness

aggressiveness

none

slight retardation, attention deficit, memory   impairment, CN VII lt deficit none

difficulties in reading/writing

rt hemiparesis

mild retardation

aggressiveness

TABLE 1: Demographic and clinical characteristics of the patients with hypothalamic hamartomas at surgery*

III III IV

II

II

II IV

III

IV

II

IV

II

II

II

III

II

II

III

II

Delalande HH Type

(continued)

GKS twice transcranial debulking   twice GKS, transcranial   debulking twice previous amygdalohip pocampectomy no no no

contralateral endo  scopic disconnec  tion (coagulation) endoscopic disconnec  tion (coagulation) endoscopic disconnec  tion (coagulation) no

endoscopic disconnec  tion (coagulation) none

none

endoscopic disconnec  tion (coagulation) endoscopic disconnec  tion (coagulation) none

endoscopic disconnec  tion (coagulation) none

Previous Op

Thulium laser in hypothalamic hamartoma endoscopic disconnection

565

566

transcranial debulking   & endoscopic dis connection IV 48.3

Endoscopy. We used a 30° Storz rigid endoscope (Karl Storz GmbH&C), with a Stryker Quantum 4000 fiber optic light source (Xe light source), a Stryker Endoscopic 814 Medical video camera (Stryker Instruments), and a Sony HR Trinitron screen (Sony).

Laser. The Revolix Junior 15-W thulium:YAG surgical laser unit with a 2.0-mm wavelength (LISA Laser Products OHG) was used with a reusable or 550-mm laser bare fiber (RigiFib) through an operative channel of the endoscope.

7.8

monopolar generalized tonic-clonic, gelastic   coagulation

Coagulation. A Lamiday Medical Surgilec MC4 monopolar electric coagulator was used to achieve the disconnection in some of the patients. In the second group, where the Revolix laser was used for the disconnection, the coagulator was also subsequently used for the inner part of the hamartoma aiming at the greatest destruction of the mass.

12, M

10.7

20

mean

*  CN = cranial nerve; GKS = Gamma Knife surgery.

11

84

mild intellectual retardation, language deficit

Robotic Neuronavigation. ROSA is a robotic surgical assistant that integrates the functions of a neuronavigational frameless stereotactic system, a robotic arm for preplanned movements, and a surgical movement assistant by means of an haptic sensor that receives the input by the surgeon, under the surveillance of the preset parameters provided. ROSA acts in cooperated mode to permit the ventriculostomy with millimetric precision, thereby allowing the “double cone” movement that results from the surgeon’s intraventricular maneuvers while acting in isocentric mode with the entry point on the cortex surface used as a mechanical constraint. A specially provided instrument warranted compatibility between the robot’s arm and the endoscope.

rt

Additional Symptoms Instrument

Type of Epilepsy

Epilepsy Mean No. Duration of Seizures (yrs) per Wk

Equipment

Age (yrs), Sex

Side of Disconnection

At 3 and 12 months of follow-up, the Engel epilepsy class was determined,12 and a neuropsychological outcome analysis assessing behavior, attention, and IQ was performed. The endocrinological tests evaluated a possible pituitary hormonal imbalance. Hyperphagia and weight gain were also assessed. The statistical analysis was conducted using the chisquare test with Yates correction or the Fisher exact test.

Case No.

TABLE 1: Demographic and clinical characteristics of the patients with hypothalamic hamartomas at surgery* (continued)

Delalande HH Type

Previous Op

A. Calisto et al.

Surgical Technique

The day before surgery, the surgical planning was performed based on a volumetric MRI uploaded on the ROSA remote planning system. The site for the disconnection, which is the attachment of the hamartoma to the wall of the third ventricle, was chosen as the final target of the stereotactic plan. The entry point on the cortical surface was adjusted to ensure avoidance of any major vessel along the trajectory. This entry point was initially set at a distance of 2 cm from the midline, contralateral to the side of the hamartoma insertion on the third ventricle’s wall, just anterior to the coronal suture. The day of the intervention, the patient was positioned supine. The Mayfield headrest was applied and was firmly connected to the ROSA robot by means of a special arm. The surgical plan was transferred to the robot, J Neurosurg: Pediatrics / Volume 14 / December 2014

Thulium laser in hypothalamic hamartoma endoscopic disconnection and the preliminary setup started with the identification of the cranial points necessary for the exact localization of the target. Once the plan was definitively verified, a laser pointer on the arm of the robot was used to localize an exact point for a 15-mm linear skin incision. After performing the bur hole, according to the size of the endoscope, the height of the instrument’s reference was set at 165 mm on the ROSA, corresponding to the known distance between the special holder/adapter and the tip of the endoscope’s introducer fastened to it. The entry of the endoscope’s introducer into the ventricle through the brain parenchyma was accomplished in cooperative mode and in real time followed on ROSA’s display. The cooperative modality in the ROSA device allows a special interaction between the robot and the surgeon. The surgeon determines in advance which movement direction and speed will be allowed by the robotic arm holding the scope at the moment his or her hand will apply a force to move the complex holder-endoscope. The resulting restricted movement has the precision of a frame-based stereotactic procedure. Once in the ventricle, the endoscope was inserted into the introducer and the navigation was started. The safety of the procedure was further enhanced by the ROSA security zone feature replacing the cooperative mode. This tool limits all endoscope motions within a preoperatively planned virtual double cone along the surgical trajectory. The fulcrum of the cone can be preset at any point along the trajectory; it corresponds to the only part of the endoscope not moving during the intraventricular navigation. A point in the cortical-subcortical matter or the foramen of Monro, for example, can be set as the fulcrum to avoid stretching. After entering the foramen of Monro, the hamartoma was usually immediately visualized with its insertion plane. Sometimes the insertion plane was partially or totally hidden by the mass. The choice of the cutting line was determined by accurately inspecting the anatomy of the third ventricle, supported by the MR appearance; however, the third ventricle was usually distorted by the hamartoma itself. Once the disconnection point had been chosen, the flexible fiber of the laser was introduced and then advanced through the endoscope’s working channel. Contact with the lesion was established and the laser was activated, at first, in the pulsating mode (frequency 5–10 Hz), from 5 to 15 W for 100 msec to carry out the precise cut under constant visual control (Fig. 2). Due to the simultaneous cutting and vaporizing effects of the fiber tip, a groove was made, produced by multiple adjacent cuts. Then, the fiber was slightly deepened and the endoscope was gently and continuously moved back and forth along the cut, gently changing the inclination of the trajectory according to the envisaged profile of the wall of the third ventricle, until the lesion was satisfactorily separated from normal hypothalamus without any traction. The different pulsation of the structures helped in understanding the extent of the disconnection achieved. Since the risk for injury to the diencephalic structures increases with the depth of the cut, we preferred to perform multiple surgeries instead of performing a more extensive cut during a single procedure (Video 1). J Neurosurg: Pediatrics / Volume 14 / December 2014

Video 1. Video clip showing endoscopic, robot-assisted laser disconnection of an HH. Copyright Amedeo Calisto. Published with permission. Click here to view with Media Player. Click here to view with Quicktime.

In the cases in which only simple coagulation was used, the cut was made in a similar fashion by progressive deepening of the unipolar coagulator tip. Coagulation of the inner part of the hamartoma was attempted at the end of the disconnection to destroy as much “electrically active” tissue as possible, avoiding any damage to the surrounding structures. As soon as the disconnection was satisfactorily achieved and full hemostasis was achieved, the tip of the endoscope was retracted up to the body of the lateral ventricle and the instrument was retracted in the axial direction in cooperative mode. The bur hole was then commonly filled using SURGICEL sheets and bone dust before closing the skin with a resorbable suture. No external ventricular drainage was left inside at any time.

Results

Twenty patients who underwent surgery between June 2011 and May 2012 (10 males and 10 females, age range 6 months to 44 years [mean 11.8 years]) with at least 12 months of follow-up were included in this study. Thirteen patients underwent disconnection using monopolar coagulation; thulium laser disconnection was performed in the remaining 7 patients. Patients were consecutively treated using monopolar coagulation up to February 2012; after this point the laser-based disconnection was performed. The 2 groups were similar in terms of mean patient age (10.1 vs 11.7 years), mean epilepsy duration (6.9 vs 4.9 years), mean number of weekly seizures (24.5 vs 24.5), previous surgery (53% vs 42%), and incidence of Type IV lesions (23% vs 29%). Further demographic and clinical characteristics of the 2 groups are summarized in Table 1. Surgical results are summarized in Table 2. All 20 patients (100%) achieved a satisfactory postoperative Engel score (Classes I–III). At 12 months, the Engel score was still satisfactory. In the monopolar coagulation group (n = 13) at 12 months, 4 patients (30.7%) achieved Engel Class III and 8 patients (61.5%) achieved Class I or II. In the laser disconnection group (n = 7), 6 patients (85.7%) achieved Engel Class I or II (p = 0.04), and 1 patient (14.3%) achieved Class III. In the coagulation group, 1 patient’s Engel class decreased to Class IV (7.7%). Seven of 13 patients (53.8%) who underwent monopolar coagulator disconnection had immediate postoperative complications including oculomotor deficits, memory deficits, hydroelectrolyte alterations, and mutism. Among those who underwent laser disconnection, 1 patient reported drowsiness that required a prolonged hospital stay (5 additional days). An early CT scan showed a grossly round area of hypodensity in the anterior ventromedial part of the ipsilateral thalamus of approximately 1 cm in diameter. A second patient had recent memory deficits for some weeks. At the 3-month follow-up, only 2 patients (15.4%) both treated by monopolar coagulation, still had surgeryrelated recent memory deterioration (Table 2). No complication persisted at the 12-month follow-up. 567

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Fig. 2.  Endoscopic view of the thulium laser tip. The flexible fiber of the laser was advanced through the endoscope’s working channel (A). The contact with the lesion was established and the laser activated, at first, in the pulsating mode (B). Disconnection was accomplished by multiple adjacent cuts (C).

No significant difference in terms of duration of the surgical procedures for laser versus simple monopolar coagulation was found (127 vs 116 minutes). No postsurgical modification of hemoglobin levels or non–preexisting endocrinological disturbance was noted.

Discussion

Our results suggest that the disconnection of the HH is a safe procedure that may achieve meaningful improvement (Engel Classes I–III) of seizures in up to 90% of patients with a risk of temporary mild new neurological deficits in about 10% of cases. Furthermore, data from the small group of patients who underwent laser disconnection suggest that the results could be even more satisfactory, with almost 86% of patients achieving Engel Class I or II after 12 months and no patient suffering long-term surgical complications. The relationship between epilepsy and HH was first reported by Munari and colleagues who recorded a low voltage fast activity inside the hamartoma using depth electrodes.18 Furthermore, the electrode stimulation reproduced the typical laughing attack. This experience has been confirmed by SPECT analysis,14 showing an ictal hyperactivation in a region corresponding to the hamartoma location in the absence of any area of cortical hyperperfusion, which is what usually happens in focal cortical dysplasia–generating seizures. A growing number of resections of HH confirmed the etiology of the seizures, suggesting a benefit for early surgery. Nevertheless, resective surgery carries the risk of severe complications including memory deficits, endocrinological disturbances, electrolyte disorders, motor deficits, and oculomotor impairment.13,24–26 Furthermore, total HH removal could be attained in approximately 50% of the procedures, but postoperative seizure control largely depends on the extent of the resection.1 Finally, the resection is often complicated by the macroscopic appearance of the hamartoma that does not easily allow the surgeon to discriminate the limits of the lesion from the hypothalamus, which is frequently distorted by the lesion. For these reasons, alternative treatment strategies to 568

resection have been attempted. Radiofrequency stereotactic lesioning has been performed in a few cases with various results.1 Stereotactic radiosurgery has shown promising results.22–24,26 In some series in which stereotactic radiosurgery was used, satisfactory outcomes were obtained with a low incidence of adverse effects. Nevertheless, long-term effects of the irradiation of the hypothalamic area surrounding the lesion still need to be assessed. Furthermore, stereotactic radiosurgery requires several months to be effective,22,24,29 while early seizure control is often necessary to avoid secondary epileptic encephalopathy. Nonetheless, stereotactic radiosurgery may play an important role in adult patients, who are less susceptible to radio-induced complications.25 Curry et al. recently reported 2 cases of HHs treated by stereotactic laser cooled thermoablation under MRI control and thermal monitoring. Interestingly, the 980-nm laser and the integrated cooling system allowed a sharp fall off in temperature at the edge of the ablation zone, with a clear cut at the lesional zone and preservation of the surrounding important structures. The results are encouraging and there are no side effects, but the follow-up is short and the series is limited.6 Based on the concept of an intrinsic epileptogenic role of hamartomas with propagation through a thalamic activation, mediated by the mammillo-thalamic tracts, Delalande and colleagues developed the idea of a simple disconnection of the hamartoma from the surrounding hypothalamus7,8,13 (Fig. 3). In selected cases, this technique proved to achieve minimal surgical morbidity, a dramatic improvement in terms of seizures, and a striking improvement in attention, behavior, and cognitive development of pediatric patients.5,10,19,21,29 To guide treatment modality, Delalande et al. also proposed a classification based on the attachment characteristics of the HH at the hypothalamus.1,3,30 Stereoendoscopic disconnection of HHs has proven to be not only safe and effective, but also a minimally invasive surgical approach to a functional disease. We advocate performing multiple procedures, in which less aggressive cuts are made rather than a single operation with a more aggressive and risky approach. Four of our 7 patients who underwent laser treatment had previously J Neurosurg: Pediatrics / Volume 14 / December 2014

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coagulation coagulation coagulation coagulation coagulation coagulation

coagulation coagulation coagulation coagulation

coagulation coagulation

Revolix Revolix Revolix Revolix Revolix Revolix Revolix coagulation

1 2 3 4 5 6

7 8 9 10

11 12

13 14 15 16 17 18 19 20

37 12 12 16 1 0.8 3 12

6 7

18 5 11 24

6 4 17 6 15 1.3

Age (yrs)

II II II II Ib Ib Ib Ib

Ib Ib

II I III II

I III I III I II

Early Postop

II II II II Ib II II Ib

Ib Ib

III II III II

III III III III III II

3-Mo

Engel Class

Ia II III II Ia I II II

Ia Ib

III Ia III II

II I IV III III Ia

12-Mo

*  No complications were present at the 12-month follow-up.

Instrument

Case No. Immediate Complications

no drowsiness no recent memory deficit no no fever no

no no dyplopia no no drowsiness, seizures, respiratory failure, hypo  natriemia, hypocortisolemia no ipsilateral CN III deficit polyuria recent memory deficit, lumbar pain, proteinuria,   hematuria, elevated blood pressure mutism lt CN III deficit (ipsilateral)

TABLE 2: Surgical results at the 3- and the 12-month follow-up*

no no no recent memory impair ment no memory impairment, CN   III deficit improved no no no no no no no no

no no no no no no

3-Mo Complications

O.D. O.D. O.D. O.D. O.D. O.D. O.D. G.D.

G.D. G.D.

O.D. O.D. G.D. O.D.

G.D. G.D. G.D. G.D. O.D. O.D.

Surgeon

behavior & attention improvement

thalamic hypodensity detected on CT

thrombotic microangiopathy renal   failure suspected behavior & attention ameliorated

behavior improvement

cerebral venous thrombosis sus  pected on imaging

behavior & attention improvement

Remarks

Thulium laser in hypothalamic hamartoma endoscopic disconnection

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Fig. 3.  Coronal MR image of an HH after disconnection was performed using a thulium laser. The arrow indicates the cut along the HH adherence to the hypothalamus.

undergone multiple treatments. This could have affected results and complications, but to what extent it is difficult to conclude. In this approach, the use of the sharpest instrument to perform the disconnection is of paramount importance. The ideal instrument should interrupt the continuity between the HH and hypothalamus with minimal impact on the neural tissue. The endoscopic microcoagulation unipolar probe does not have such capability, frequently producing a microexplosion with gas bubbles and an effect that can become hard to handle. Microendoscopic scissors are equally inadequate, because they cannot perform coagulation. The Fogarty balloon exerts pressure in any direction with risk to the hypothalamus, which is often already defected. The ultrasonic aspirator has been elsewhere used for open resections27 but not for endoscopic disconnections. Similarly, a new model of “resector” was designed and was used by the Phoenix group to endoscopically resect the HH with a greater safety.15 The solid-state continuous-wave laser seems to be an ideal instrument, but distinctive features make the device substantially different and suitable for some uses, but not for others. The use of a laser in neurosurgery has had various outcomes in recent history.4,9,16 The initial enthusiasm because of the laser’s photo-vaporization and photocoagulation capabilities at the same time has been tempered by some practical problems. The explosive effect of the first pulsed-wave lasers, the excessive wavelength that caused a remarkable edema surrounding the target zone, the lack of flexible fibers, and the need for protective glasses has prevented, so far, extensive use of lasers in neurosurgery.28 Nevertheless, the technical advances in this field, especially with regard to urological surgery, ensureds lasers a new possible role in neurosurgery, and specifically in neuroendoscopy.11,17,20 What characterize lasers are the wavelength (depending on the element, e.g., CO2), power output, beam density (spot size), and time of exposure. The energy density, being expressed in W/cm2*time, is determined by these factors. Other issues to be considered are 1) the absorption coefficient related to the tissue itself, meaning that the light, once adsorbed, produces heat; 2) the extinction 570

length (the depth that light will penetrate); and 3) the presence of light-absorbing chromophores, such as water, hemoglobin, or melanin. All of these factors contribute to the final effect, that is, the type of lesion created in the set target.28 For a smooth cut and good control over the extent of tissue damage so as to avoid unintentional surrounding tissue necrosis, sufficient penetration and good hemostasis are required. Provided that the medium and the target are predetermined, as well as that the power output can be varied, the effect largely depends on the wavelength, and hence on the laser emitting element.2 The neodymium:YAG laser was initially used in neurosurgery. It had a wavelength of 0.13 cm-1, meaning that in a water medium the laser beam travels 7.7 cm before being attenuated by 63%. It has a theoretical damage zone of 2000–3000 mm. Considering the extent of the hypothalamus, this means unintentional damage to the diencephalic structures is certain when the YAG laser is used in that region. To overcome this limitation, Vandertop and colleagues in 199831 designed a special laser catheter for endoscopic use, fitted with an atraumatic ball-shaped fiber tip pretreated with a layer of carbon particles to limit the amount of energy delivered, thereby increasing safety even near critical structures.31 The thulium laser has a wavelength of 2013 nm. At this wavelength the chromophore is water and the absorption length is 180 mm. The effect is independent of tissue vascularization or color since the laser energy is absorbed by the cerebrospinal fluid, reducing thermal damage to the brain and obtaining an unparalleled precision cut. The continuous mode allows a vaporization effect during movement. The power sufficient to have a smooth cut and an efficient coagulation was found to be 6–8 W with a frequency of 10–15 Hz. The fiber properly fit the operative channel of the endoscope and was not subjected to uncontrolled displacement, and it constantly remained under direct visualization. Personnel were not required to wear protective glasses. It was seldom necessary to slip off the fiber to clean its tip. The vaporizing effect allowed the surgeon to regularly see the groove that he was making while moving along the desired ideal line of disconnection. This is of paramount importance to understand when to stop carving, avoiding violating the pia of the interpeduncular cistern. Our preliminary experience with laser-assisted disconnection suggests the feasibility and safety of the procedure. We recorded transient postoperative deficits in 2 patients, which are worthy of analysis. Among those who underwent laser disconnection, 1 patient reported drowsiness due to a minor stroke. The finding of a limited thalamic hypodensity was considered consistent with a laser cut extending too far posteriorly on retrospective review of the video recording. A second patient had temporary memory disturbances. These were considered to be related to fornix stretching, but the previous amygdalohippocampectomy could have played a role. We found no difference in the duration of the surgeries between laser and unipolar coagulation; the initial setup of the robot was the longest part of the procedure. The coagulator was also used after laser disconnection to deJ Neurosurg: Pediatrics / Volume 14 / December 2014

Thulium laser in hypothalamic hamartoma endoscopic disconnection stroy as much hamartoma as possible, within ideal safety boundaries, to further reduce the chaotic electric activity in the case of an incomplete disconnection.1 Another relevant question is the correlation of the disconnection lines, as visualized on postoperative neuroimages, with the clinical outcome. However, we have the clear feeling that the aspect of the cut on the postoperative MRI did not correlate with the intraoperative finding. In some cases it was barely appreciable by the radiologist despite the fact that the procedure was effective. As a consequence the postoperative radiographic appearance was not included among the factors considered in the study. The absence of many exploding bubbles during the cut allows an uninterrupted disconnection constantly visualizing the profile of the hypothalamus.

Conclusions

The present study was primarily aimed at verifying the feasibility of using the laser to improve a wellacquired technique in terms of safety, ease of use, and surgical duration. With the limitations of a learning curve still in its initial stage, a limited number of patients, and a short-term follow-up, it can be suggested that the thulium 2-mm laser has the technical features to replace the standard monopolar coagulation in disconnecting HHs in patients with drug-resistant epilepsy. In our opinion it is not possible to provide an objective measurement of the extent of tissue that is simultaneously resected and vaporized, but we got the impression that, using the laser, we can obtain a finer cut with margins remaining clean and regular. A histopathological analysis comparing the 2 techniques appears advisable for a more objective comparison. Disclosure The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Author contributions to the study and manuscript preparation include the following. Conception and design: Calisto, Fohlen, Delalande. Acquisition of data: Calisto, Dorfmüller, Fohlen. Analysis and interpretation of data: Calisto, Fohlen, Conti. Drafting the article: Calisto. Critically revising the article: Dorfmüller, Fohlen, Bulteau, Delalande. Reviewed submitted version of manuscript: Calisto, Dorfmüller, Fohlen, Delalande. Approved the final version of the manuscript on behalf of all authors: Calisto. Statistical analysis: Conti. Administrative/technical/material support: Calisto, Dorfmüller, Fohlen, Conti, Delalande. Study supervision: Dorfmüller, Fohlen, Bulteau, Delalande. References   1.  Arita K, Kurisu K, Kiura Y, Iida K, Otsubo H: Hypothalamic hamartoma. Neurol Med Chir (Tokyo) 45:221–231, 2005   2.  Bach T, Herrmann TR, Cellarius C, Gross AJ: Bladder neck incision using a 70 W 2 micron continuous wave laser (RevoLix). World J Urol 25:263–267, 2007   3.  Boyko OB, Curnes JT, Oakes WJ, Burger PC: Hamartomas of the tuber cinereum: CT, MR, and pathologic findings. AJNR Am J Neuroradiol 12:309–314, 1991   4.  Cerullo LJ, Burke LP: Use of the laser in neurosurgery. Surg Clin North Am 64:995–1000, 1984

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Manuscript submitted November 4, 2013. Accepted August 22, 2014. Please include this information when citing this paper: published online October 17, 2014; DOI: 10.3171/2014.8.PEDS13586. Supplemental online information: Video 1: http://mfile.akamai.com/21490/wmv/digitalwbc.download. akamai.com/21492/wm.digitalsource-na-regional/peds13-586_ video_1.asx (Media Player). http://mfile.akamai.com/21488/mov/digitalwbc.download.akamai. com/21492/qt.digitalsource-global/peds13-586_video_1.mov (Quicktime). Address correspondence to: Amedeo Calisto, M.D., Division of Paediatric Neurosurgery, Fondation Adolphe de Rothschild, 25 Rue Manin, 75019 Paris, France. email: [email protected].

J Neurosurg: Pediatrics / Volume 14 / December 2014