Neuronavigation in Skull Base Tumors

A. Kurtsoy A. Menku B. Tucer I. S. Oktem H. Akdemir

Objective: Computer-assisted neuronavigation was used in 87 cases of skull base lesions (SBLs). Preoperative planning and intraoperative identification of anatomic landmarks is especially important in SBLs since it helps to avoid or minimize surgical morbidity and mortality. In this study, we assessed the accuracy and the clinical usefulness of a frameless system based on the optical digitizer in SBLs. Patients and Methods: Between April 2000 and March 2003, eighty-seven patients with SBLs were operated on in our department using cranial neuronavigation. A passive-marker-based neuronavigation system was used for intraoperative image guidance. There were 56 women and 31 men. The patient's ages ranged from 4 to 76 years (average: 45.7 year). The locations of the tumors reported in this series were as follows: frontobasal, 24 cases; sellar/parasellar, 32 cases; petroclival, 16 cases; tentorial/subtemporal, 15 cases. Results: The computer-calculated registration accuracy ranged between 0.3 and 1.7 mm (mean, 1.1 mm). Gross total removal of the SBLs was accomplished in 82 out of 87 patients as was confirmed on postoperative CT and MRI scans. The follow-up period ranged from 1 month to 48 months (average: 20.1 months). Overall mortality and severe morbidity (meningitis, permanent cranial nerve deficits, and cerebrospinal fluid fistulae) rates were 4.6 % and 33.3 %, respectively. Conclusion: The image-guided surgery is a valuable aid for safe, helpful and complete removal of SBLs of the brain where accurate localization of the lesion is critical. Although our preliminary series is not large, interactive image guidance provides a constant display of surgical instrument position during surgery and its relationship with the SBLs components, surrounding normal brain, and vascular structures, providing valu-

able guidance to the surgeon during an operation. Our experience with the neuronavigation suggests that image guidance is helpful in this type of lesions, providing better anatomic orientation during skull base surgery, delineating tumor margins and their relation to critical neurovascular structures.

Original Article

Abstract

Neuronavigation in Skull Base Tumors

Key words Skull base tumors ´ frameless stereotaxy ´ neuronavigation

Introduction Tumors of the skull base frequently encase or extend into normal neural and vascular structures. Recently, with the development of stereotactic techniques, stereotactic neurosurgery is increasingly used in the treatment of different brain lesions [1 ± 8]. With the recent developments in computer technology and the improvements in modern neuroimaging, frame-based stereotactic guidance for open microsurgical procedures has been increasingly replaced by neuronavigation, also called frameless stereotaxy [9 ± 11]. It allows the transfer of individual patient images onto the operative field to assist the neurosurgeon intraoperatively in defining the tumor margins or identifying functionally important brain areas [9,12]. Evolving experience with image guidance over the past few years indicates the potential value of neuronavigation in skull base lesions [10,13 ± 15]. Surgical navigation can reduce the incidence of complications, increase the extent of resections, and shorten the duration of procedures. The greatest value and versatility of surgical navigation in the

Affiliation Department of Neurosurgery, Erciyes University, Medical School, Kayseri, Turkey Correspondence Ali Kurtsoy, M. D. ´ Department of Neurosurgery ´ Erciyes University ´ Medical School ´ 38039 Kayseri ´ Turkey ´ Phone: +90-352-437-4574 ´ Fax: +90-352-437-2934 ´ E-mail: [email protected] Bibliography Minim Invas Neurosurg 2005; 48: 7±12 Georg Thieme Verlag KG Stuttgart ´ New York DOI 10.1055/s-2004-830151 ISSN 0946-7211

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skull base surgery is the fact that it provides guidance in planning the incision, determining the size of the craniotomy flap, and assessing the extent of bone resection at the skull base. With appropriate preoperative image preparation, CT and MRI image fusion can be performed, thus leading to enhanced visualization [16] and helping to avoid or minimize surgical morbidity, particularly in skull base surgery. Lesions within and attached to the bone of the skull base are ideal for surgical navigation because the bone remains fixed in relation to the fiducial landmarks which are used to calibrate the equipment.

Original Article 8

In this study, our preliminary experience with 87 consecutive patients operated on skull base lesions using an advanced image guidance system is reported.

Patients and Methods Five hundred and forty-five consecutive patients with brain tumors have been operated with the assistance of interactive image guidance, as well as the development of new software applications and hardware tools. Among the 545 cases in our series, 87 were skull base lesions. The senior authors AK and HA between April 2000 and March 2003 operated each of the 87 patients. We performed mainly four approaches: an extended frontobasal approach for anterior skull base tumors (Fig. 1), a cranioorbitozygomatic approach for sellar and parasellar tumors (Fig. 2), a subtemporal approach for tentorial and subtemporal tumors (Fig. 3), and a presigmoid transpetrosal approach for petroclival and giant cerebellopontine angle (CPA) tumors (Fig. 4). There were 56 women and 31 men. The patients' ages ranged from 4 to 76 years (mean 45.7 years). The locations of the tumors reported in this study were as follows: frontobasal, 24 cases; sellar/parasellar, 32 cases; petroclival/CPA, 16 cases; tentorial/subtemporal, 15 cases. For navigational planning, either computed tomography scans or T1-weight magnetic resonance images with 2-mm thick axial slices with contrast injection were chosen. The navigation system (BrainLab VectorVision2, Munich, Germany) used for this study operates with Windows NT 4.0-based software. Preoperatively, CT or MR scans were performed after 5 ± 6 adhesive fiducial markers were placed in a non-colinear fashion on the patient's

head according to the surgical position. The CT or MR imaging data sets were transferred to the computer workstation at the planning room via a network. The computer reformatted the axial images into coronal and sagittal views and three-dimensional images. For the manual adjustment of the image fusion, a variety of options can be used. When the bone-window CT images are fused with the MR images, the visibility of structures may improve. In skull base surgery, such information is essential during surgery, particularly if bone structures are invaded by the tumor. On these images, pathological lesions and different structures can be assigned different colors. Surgical planning was conducted to the operating room via a zip disc while the patient was undergoing anesthesia. Intraoperative data for localization are acquired as two infrared cameras activate and receive the signal emitted from reflective markers placed on a reference star array attached to a Mayfield clamp fixed to the patient's head. After patient positioning and application of the Mayfield head clamp, patient to image registration was performed using a non-sterile handheld pointer. Various reflective marker arrays were applied to surgical instruments so that they could be used as active pointers during the operation.

Results Registration using the adhesive markers did not substantially prolong the length of the surgical procedures. This procedure was performed in approximately 10 minutes or less in each procedure. The computer-calculated registration accuracy ranged between 0.3 and 1.7 mm (mean: 1.1 mm). The system was technically usable in all cases in this series. We had no technical difficulties using our neuronavigation system. Because of the relative immobility of the bone structures and/or the tumor, no significant deviation from the preoperative registration accuracy was noted at the end of the procedures, in contrast to intra- or extraaxial tumors located out of skull base. Intraoperatively, a Toshiba sonography unit (Tosbee, SSA-240A) was used with a 7 MHz probe. A reference coordinate system with reflecting spheres was attached to the ultrasound probe. The infrared cameras registered movement of the probe in space. Ultrasound images and CT-MR images overlay the two-dimensional reconstructions. Ultrasound visualized changes of anatomy and helped especially to assess the degree of tumor resection and residual tumor.

Fig. 1 Homogeneous intensity in the lesion on T1-weighted axial MRI scan (left). A large olfactory grove meningioma was removed totally (right) using the neuronavigation (center) via an extended frontobasal approach. Kurtsoy A et al. Neuronavigation in Skull Base Tumors

Minim Invas Neurosurg 2005; 48: 7 ± 12

Fig. 2 An axial MRI scan with contrast injection shows a left trigeminal schwannoma (left). It was removed totally (right) using the neuronavigation via a cranioorbitozygomatic approach.

Original Article Fig. 3 A coronal MRI scan with contrast injection shows a left tentorial meningioma located on the petrous apex (left). It was approached subtemporally and removed totally (right). Neuronavigation guided the surgeon to incise the tentorium according to the tumor margins (center).

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Fig. 4 An axial MRI scan with contrast injection shows a glomus jugulare involving the mastoid air cells, the right petrosal bone, and jugular foramen (left). The invasive tumor was removed under surgical navigation guidance (center) via a presigmoid transpetrosal approach. The postoperative axial MR images revealed no residual tumor (right).

In the present study, gross total removal of the SBLs was accomplished in 82 out of 87 patients who were confirmed with postoperative CT and MRI scans (Figs. 1 ± 3). All tumors were removed completely as judged by intraoperative inspection in all patient except for five; in the first patient with a frontobasal metastatic tumor, an adherent piece of tumor that had infiltrated the cavernous sinus was left at the medial surface of the cavernous sinus. A second patient had a craniopharyngioma adherent to the hypothalamus. In the third patient, chondrosarcoma had invaded the petrous apex and middle clivus. Another two patients had meta-

static lesions extending extradurally into the sphenoethmoidal and maxillary sinuses. Table 1 lists the pathologic diagnosis for these 87 patients. The morbidity rates (33.3 %) were different depending on the performed surgical approaches. We noted more than one complication in our few patients. The overall complications related to different surgical approaches are summarized in Table 2. The overall mortality rate was 4.6 %. The follow-up period ranged from 1 month to 48 months (average: 20.1 months).

Kurtsoy A et al. Neuronavigation in Skull Base Tumors


Table 1

Tumor characteristics

Tumor

No.

Approach

Frontobasal

24

Extended frontobasal

Meningioma

10

Rhinorre/duraplasty

5

Extradural malign tumors

8

Osteoma

Original Article 10

in one patient on a CT scan obtained on the first postoperative day, but this morbidity resolved spontaneously on CT at the 4th day. Anosmia was observed in 19 (79 %) patients. Reduced vision was observed in one patient but the patient was normal in the postoperative first month.

1

Sellar/parasellar

32

Meningioma

14

Pituitary adenoma

4

Epidermoid tumor

3

Trigeminal schwannoma

3

Craniopharyngioma

2

Other

6

Petroclival

16

Meningioma

4

Schwannoma

4

Glomus jugulare tumor

2

Metastasis

2

Chondrosarcoma

1

Epidermoid tumor

1

Medulloblastoma

1

Tentorial/subtemporal

15

Meningioma

11

Trigeminal schwannoma

2

Astrocytoma

1

Arachnoid cyst

1

Table 2

Cranioorbitozygomatic

Presigmoid transpetrosal

Subtemporal

Complications according to the approach

Type

No.

Extended frontobasal

24

Anosmia

19

%

100

CSF leakage

1

4.1

Optic nerve injury

1

4.1

Cranioorbitozygomatic

32

Oculomotor nerve injury

3

9.4

Trochlear nerve injury

3

9.4

Sixth cranial nerve palsy

3

9.4

Severe periorbital edema

1

3.1

CSF leakage

1

3.1

Presigmoid transpetrosal

16

CSF leakage

7

43.7

Facial nerve palsy

4

25

2

12.5

Lower cranial nerve palsy Subtemporal

15

Oculomotor nerve palsy

1

6.6

Brain edema/contusion

1

6.6

Extended frontobasal approach A CSF leakage occurred in one patient and was managed with bed rest for three days. However, pneumocephalus was detected on the control CT, the drainage procedure was terminated and dural leak was surgically closed. Moderate pneumocephalus was noted Kurtsoy A et al. Neuronavigation in Skull Base Tumors

Cranioorbitozygomatic approach Severe periorbital edema was noted in one patient and was managed with cold application for 3 days. Temporary third, fourth and sixth cranial nerve palsy was noted in three patients for whom we employed the extradural cavernous sinus approach. These complications resolved spontaneously and completely in three months. Subtemporal approach Oculomotor nerve palsy occurred in one patient (6.6 %) but an improvement of the oculomotor function was observed during the first 2 postoperative months. Mild brain edema and contusion not requiring surgical decompression were detected in one patient (6.6 %). Steroid and mannitol were sufficient in resolving this problem. Presigmoid transpetrosal approach CSF leakage developed in seven patients (43.7 %) who underwent the presigmoid transpetrosal approach, and was managed with continuous spinal drainage, and bed rest for three to five days. Temporary seventh nerve palsies were the next most common in this approach, occurring in 18.7 % of cases. However, permanent facial palsy occurred in one patient (6.2 %). In this young patient, there was an extensive involvement of the facial nerve by a glomus jugulare tumor that could not be removed without sacrificing the nerve. We decided to sacrifice the nerve in order to achieve a gross total tumor resection. Although the facial nerve was anastomosed with the hypoglossal nerve, the postoperative facial nerve paresis has not recovered in the tenth month. However, we believe that in most cases the facial nerve should be left in continuity due to a probable risk of tumor recurrence, especially in the elderly patients. Pneumocephalus was found in 3 patients (18.7 %) but resolved totally without developing clinical signs of increased intracranial pressure on the control CT obtained during the postoperative seventh day.

Discussion Tumors of the skull base regions represent a real surgical challenge. Because of fact that they are critical and deeply located, access and total removal have always been the main problems in the surgical management of such cases. Over the past 30 years, many surgeons have designed and promoted their approach to the skull base in order to prevent or decrease the complications associated with the surgical interventions [17 ± 31]. An excellent knowledge and understanding of anatomy and its possible variations are especially important in skull base surgery. For these lesions, precise planning, intraoperative orientation, localization of anatomical landmarks, and avoidance of vital structures are important issues in surgery. Invasion of bone and critical neurovascular structures often impedes complete resection of skull


base neoplasms, and these lesions tend to recur unless all tumors are complete removed [17,18, 32]. It may be that new technological developments relating to three-dimensional imaging and image-directed surgery will assist the surgeon in the exact intraoperative localization.

The major disadvantage is the use of preoperative data for navigation, leading to inaccuracies when anatomical structures are altered during the operation by resection of tumors or shift of intracranial soft tissue [33]. A major limitation of the conventional frameless neuronavigation systems has been that navigation is based on preoperative CT-MR imaging. Peroperative changes with tumor resection, loss of CSF and patient position can limit the surgeon's access to the operative field [5, 33]. Intraoperative ultrasonography is a useful alternative for obtaining feedback about intraoperative shift and tumor resection. Intraoperative ultrasound system also delineates the degree of tumor resection [33]. However, we did not use intraoperative ultrasonography for determining intraoperative shift. As brain shift is not important in skull base tumor [33], we used intraoperative ultrasonography only for delineating the degree of tumor resection or determining residual tumor. The advantages of intraoperative ultrasonography include its low cost, ease of use, and minimal interference with the operative procedure. By the method of intraoperative ultrasonography used in our department it has already been possible to update neuronavigation with images reflecting intraoperative changes anatomy (Fig. 1, center). The tremendous advantage of neuronavigation becomes obvious during the treatment of skull base lesions more than in any other type of neurosurgery, because the osseous and neurovascular structures do not move during the surgical manipulation [2,13 ± 16].

Our preliminary experience with the computer-assisted neuronavigation suggests that image guidance is helpful for this type of lesion, providing better anatomical orientation during surgery and delineating tumor margins and their relation to critical neurovascular structures. The system facilitates resection by volumetric contour information, allowing a more aggressive and complete resection. Sanna et al. [26] reported lesions of the petroclival region and their removal totally in 17 patients (74 %) out of 23 cases who were surgically treated by using the skull base approach. Lang et al. [23] removed totally in 11 cases (61 %) out of 18 patients with lesions located in the central skull base region by the extended transbasal approach. In the present study, by using the neuronavigation guidance, total tumor removal was accomplished in all cases except for five patients (94.2 %). We believe that the use of neuronavigation as presented in our series might additionally help to keep the total surgical removal rates high in patients suffering from skull base lesions. The early identification of distorted and/or eroded vital neurovascular structures during the transtumoral dissection without anatomic landmarks is the most important benefit that is offered by neuronavigation. In the present study, although overall mortality (4.6 %) and severe morbidity (33.3 %) related to different surgical approaches were similar to published large series [17, 23 ± 27, 32, 34], no postoperative intracerebral hematomas or brain edema occurred requiring reexploration. In conclusion, image guidance facilitates complex approaches to various pathologies and enables mapping of skull base anatomy, especially during the translesional dissection of complex tumors distorting and invading neurovascular and osseous structures. Owing to the fact that the neuronavigation system can be widely applied to neurosurgical procedures, we consider that skull base surgery is the best target for it because of the minimum possible brain shift. On the other hand, the utilization of any computer-assisted technology is not a substitute for profound anatomic knowledge. An individually tailored strategy and skilful microsurgical technique still remain the most important factors in order to reduce the surgical mortality and morbidity and computer-assisted technology equipped with interactive features may convert the aggressive skull base approaches to less invasive surgical procedures. We hope that by using a neuronavigation system, more accurate and less invasive surgery will contribute to a better outcome for a patient having a skull base lesion.



Original Article

Operative neurosurgery has recently entered an exciting area of image-guided surgery or neuronavigation and application of this novel technology is beginning to have a significant impact in many ways on a variety of intracranial procedures [1, 3, 4, 6, 9 ± 11]. In order to fully assess the advantages of imageguided techniques over conventional planning and surgery in selected cases, detailed prospective evaluation has been carried out during the advanced development of an optically tracked neuronavigation system. Neuronavigation was the most helpful for operations on deeply seated lesions, skull base tumors and lesions in brain areas with high functionality [2, 4,10,14]. Imageguided surgery provides truely useful feedback to the surgeon in planning and simulation of the surgical approach, intraoperative orientation, avoidance of vital neurovascular structures, and assessing the extent of resection. It ensures warning of the proximity of the important anatomical structures and identifies the possible location of residual tumors. Skull base lesions benefit from computer-assisted neuronavigation, particularly while planning a critical approach. This technology can also help to identify prominent vascular and neural structures associated with skull base, in an effect to providing a visual warning that these structures are in the vicinity during an aggressive tumor resection. Skull base approaches widely remove bone structures; again, frameless stereotaxy can help guide the degree of resection needed for skull base tumors.

By creating a surgical plan, the image guidance software offers assistance in the establishment of a surgical approach [7]. During surgery, the neuronavigation system directly shows the location of anatomic landmarks of the skull base regardless of any erosion or displacement. Since osseous structures do not shift due to CSF loss, these landmarks are easily and safely identified using the CT- or MR-based image guidance.

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References 1

Original Article 12

Barnett GH. Surgical management of convexity and falcine meningiomas using interactive image-guided surgery systems. Neurosurg Clin North Am 1996; 7: 279 ± 284 2 Eisenberg MB. The application of modern skull base techniques to routine neurosurgical problems. Contemp Neurosurg 2000; 22: 1 ± 7 3 Elias WJ, Chadduck JB, Alden TD, Laws ED. Frameless stereotaxy for transsphenoidal surgery. Neurosurgery 1999; 45: 271 ± 277 4 Germano IM, Villalobos H, Silvers A. Postclinical use of the optical digitizer for intracranial neuronavigation. Neurosurgery 1999; 45: 261 ± 270 5 Gumprecht HK, Widenka DC, Lumenta CB. BrainLab VectorVision neuronavigation system: technology and clinical experience in 131 cases. Neurosurgery 1999; 44: 97 ± 105 6 Muacevic A, Steiger HJ. Computer-assisted resection of cerebral arteriovenous malformations. Neurosurgery 1999; 45: 1161 ± 1171 7 Schul C, Wassmann H, Skopp GB, Marinov M, Wolfer J, Schuierer G, Joos U, Willich N. Surgical management of intraosseous skull base tumors with aid of Operating Arm System. Comput Aided Surg 1998; 3: 312 ± 319 8 Wagner W, Gaab MR, Schroeder HWS, Tschiltschke W. Cranial neuronavigation in neurosurgery: Assessment of usefulness in relation to type and site of pathology. Minim Invas Neurosurg 2000; 43: 124 ± 131 9 Ostertag CB, Warnke PC. Neuronavigation. Computer-assisted neurosurgery. Nervenarzt 1999; 70: 517 ± 521 10 Wadley J, Dorward N, Kitchen N, Thomas D. Pre-operative planning and intra-operative guidance in modern neurosurgery: a review of 300 cases. Ann R Coll Surg Engl 1999; 81: 217 ± 225 11 Watanabe E, Watanabe T, Manaka S, Mayanagi Y, Takakura K. Threedimensional digitizer (neuronavigator): new equipment for computed tomography-guided stereotaxic surgery. Surg Neurol 1987; 27: 543 ± 547 12 Nimsky C, Ganslandt O, Kober H, Möller M, Ulmer S, Tomandl B, Fahlbusch R. Integration of functional magnetic resonance imaging supported by magnetoencephalography in functional neuronavigation. Neurosurgery 1999; 44: 1249 ± 1256 13 Klimek L, Mösges R, Laborde G, Korves B. Computer-assisted imageguided surgery in pediatric skull-base procedures. J Pediatric Surg 1995; 30: 1673 ± 1676 14 Mehdorn HM, Schrader B, Nabavi A, Hempelmann R. Neuronavigation in the region of the skull base. Laryngorhinootologie 2000; 79: 404 ± 411 15 Sure U, Alberti O, Petermeyer M, Becker R, Bertalanffy H. Advanced image-guided skull base surgery. Surg Neurol 2000; 53: 563 ± 572 16 Hill DLG, Hawkes DJ, Crossman JE, Gleeson MJ, Cox TCS, Bracey EEC, Strong AJ, Graves P. Registration of MR and CT images for skull base surgery using point-like anatomical features. Br J Radiol 1991; 64: 1030 ± 1035


Al-Mefty O, Ayoubi S, Smith RR. The petrosal approach: indication, technique, and results. Acta Neurochir 1991 (suppl); 53: 166 ± 170 18 Al-Mefty O, Fox JL, Smith RR. Petrosal approach for petroclival meningiomas. Neurosurgery 1988; 22: 510 ± 517 19 Al-Mefty O. Supraorbital-pterional approach to skull base lesions. Neurosurgery 1987; 21: 474 ± 477 20 Al-Mefty O. The cranio-orbital zygomatic approach for intracranial lesions. Contemp Neurosurg 1992; 14: 1 ± 8 21 Cass SP, Sekhar LN, Pomeranz S, Hirsch BE, Synderman CH. Excision of petroclival tumors by a total petrosectomy approach. Am J Otology 1994; 15: 474 ± 484 22 Delashaw Jr JB, Tedeschi H, Rhoton AL. Modified supraorbital craniotomy: Technical note. Neurosurgery 1992; 30: 954 ± 956 23 Lang DA, Honeybul S, Neil-Dwyer N, Evans BT, Weller RO, Gill J. The extended transbasal approach: Clinical application and complication. Acta Neurochir 1999; 141: 579 ± 585 24 Raveh J, Laedrach K, Speiser M, Chen J, Vuillemin T, Seiler R, Ebeling U, Leibinger K. The subcranial approach for fronto-orbital and anteroposterior skull-base tumors. Arch Otolaryngol Head Neck Surg 1992; 119: 385 ± 393 25 Roux FX, Moussa R, Devaux B, Nataf F, Page P, Laccourreye O, Schwaab G, Brasnu D, Lacau Saint-Guily J. Subcranial fronto-orbito-nasal approach for ethmoidal cancers: Surgical techniques and results. Surg Neurol 1999; 52: 501 ± 510 26 Sanna M, Mazzoni A, Saleh EA, Taibah AK, Russo A. Lateral approaches to the median skull base through the petrous bone: The system of the modified transcochlear approach. J Laryngol Otol 1994; 108: 1036 ± 1044 27 Sekhar LN, Janecka IP, Jones NF. Subtemporal-infratemporal and basal subfrontal approach to the extensive cranial base tumor. Acta Neurochir 1998; 92: 83 ± 92 28 Sekhar LN, Schessel DA, Bucur SD, Raso JL, Wright DC. Partial labyrinthectomy petrous apicectomy approach to neoplastic and vascular lesions of the petroclival area. Neurosurgery 1999; 44: 537 ± 552 29 Shah JP, Kraus DH, Arbit E, Galicich JH. Craniofacial resection for tumors involving the anterior skull base. Otolaryngol Head Neck Surg 1992; 106: 387 ± 393 30 Dijk JMC Van, Thomeer RTWM. Control of complication in the midfrontobasal approach. Acta Neurochir 1997; 139: 355 ± 358 31 Zabramski JM, Talat K, Sankhia SK, Cabiol J, Spetzler RF. Orbitozygomatic craniotomy. J Neurosurg 1998; 89: 336 ± 341 32 Deschler DG, Gutin PH, Mamelak AN, McDermott MW, Kaplan MJ. Complication of anterior skull base surgery. Skull Base Surgery 1996; 6: 113 ± 118 33 Dorward NL, Alberti O, Velani B, Gerritsen FA, Harkness WF, Kitchen ND, Thomas DG. Postimaging brain distortion: magnitude, correlates, and impact on neuronavigation. J Neurosurg 1998; 88: 656 ± 662 34 Catalano PJ, Hecht CS, Biller HF, Lawson W, Post KD, Sachdev V, Sen C, Urken ML. Craniofacial resection: An analysis of 73 cases. Arch Otolaryngol Head Neck Surg 1994; 120: 1203 ± 1208
