Craniofacial osteotomies to facilitate resection of large tumours of the anterior skull base

Journal of Cranio-Maxillofacial Surgery (1996) 24, 224 229 © 1996 Em-opean Association for Cranio-Maxillofacial Surgery

Craniofacial osteotomies to facilitate resection of large tumours of the anterior skull base F. Tzortzidis 1, G. Bejjani4, T. Papadas 2, P. Triantafyllou3, M. Partheni ~, P. Goumas 2, N. Papadakis 1

1Department of Neurological Surgery (Head."Prof N. Papadakis), 2Department of Ear, Nose and Throat Surgery (Head." Prof. P. Goumas), 3Department of Maxillofacial Surgery (Director: P. Triantafylloy), University of Patras, Patras, Greece. 4Department of Neurosurgery (Head."Laligam N. Sekhar), George Washington University, Washington, DC, USA S U M M A R Y . Large tumours of the anterior cranial fossa can be a major challenge to the neurosurgeon or the maxiliofacial surgeon. However, skull base approaches facilitate their resection. We describe our experience with the extended subfrontal approach in treating tumours of the anterior cranial base. This approach was performed on 29 patients with large tumours of the anterior skull base. The final outcome in all 29 patients was favourable in terms of total resection of the tumour with minimal subsequent neurological deficit. Two patients developed transient oedema of the frontal lobes without persistent neurological sequelae. Another patient developed a postoperative cerebrospinal fluid fistula that was successfully repaired. The patients were followed for a period ranging from 6 to 28 months. There was no recurrence. The operative technique is described. En bloc removal of the roofs of the orbits and part of the anterior cranial fossa permits wide exposure of the lesion with minimal brain retraction. Reconstruction of the anterior cranial base should be meticulous to avoid cerebrospinal fluid leaks and subsequent meningitis. Loss of smell is a sequel to this approach. The possible risks and some important technical details are highlighted.

INTRODUCTION

meningiomas had undergone previous surgery with subtotal resection. All patients had preoperative computer tomography (CT) scans and 19 patients had preoperative magnetic resonance imaging (MRI) scans.

The extended subfrontal approach is a modification of the transbasal approach described by Derome in 1972. Large tumours of the anterior skull base are approached after a bilateral frontal craniotomy followed by an en bloc osteotomy of the orbital roofs and frontal sinus. This technique has certain advantages. It allows the surgeon access to midline structures of the anterior skull base with minimal retraction and a wider exposure. It also allows multidirectional viewing of the lesion and meticulous reconstruction of the anterior cranial base. This approach has permitted the total or near-total excision of large tumours with acceptable morbidity.

Operative technique

Approach The patient is placed in the supine position. After induction of general anaesthesia, the head is placed in the Mayfield head rest in three point fixation. A coronal skin incision is made, starting immediately anterior to the tragus. The incision is extended in a curvilinear fashion and ends anterior to the opposite tragus. This is cosmetically acceptable and spares the frontalis branch of the facial nerve. The scalp is reflected anteriorly to the supraorbital rims. The temporalis muscle is freed from its insertion over the zygomatic arch and retracted posteriorly to expose the junction of the frontal, sphenoidal and zygomatic bones. The pericranium is separated carefully and preserved for later use during reconstruction of the anterior skull base. The supraorbital vessels and nerve are released from their foramina anteriorly and preserved. This is done by utilizing a small chisel to break away the outer aspect of the supraorbital foramen, thus transforming it into a groove. A bifrontal craniotomy is then performed. The

MATERIALS AND METHODS This is a retrospective study of patients who underwent an extended subfrontal approach for tumour resection during a 3 year period, between April 1990 and April 1993. There were 29 patients: 18 males and 11 females. Their ages ranged between 12 and 55 years with a mean of 44 years. The histological diagnosis was as follows: twelve olfactory groove meningiomas, ten tuberculum sella meningiomas, three pituitary adenomas, one clival chordoma, two parasellar dermoid cysts and one sellar choriocarcinoma. Two of the patients with tuberculum sellae 224

Craniofacial osteotomies

lateral bur holes are made, first over the pterion (key hole), then they are united by a transverse cut. This cut violates the frontal sinus above the orbital rim. The mucosa is removed from the sinus and the latter is filled with fat at the end of the procedure. This is done to obliterate the dead space and prevent cerebrospinal fluid (CSF) leakage. Another cut is made more posteriorly and the bifrontal craniotomy removed (Fig. 1). The periorbita is then carefully stripped from the orbital roofs and the medial and lateral orbital walls. It is important to keep the periorbita intact to prevent herniation of the orbital fat into the operative field. The dura of the anterior cranial fossa is stripped back to the planum sphenoidale. The crista galli is exposed and removed with a small rongeur. The olfactory nerves are cut and the openings in the dura hermetically sewn. This is followed by an en bloc osteotomy of both orbital roofs and a variable segment of the ethmoidal sinus using an air drill with a fine cutting bit (Fig. 2). A brain spatula is used to protect the periorbita when the orbital cuts are made for the osteotomy. The lateral cuts start usually at the lateral third of the orbital rim, but they can be more medial, depending on the size and location of the lesion. The posterior cut location is also variable, depending on the particular tumour location. If the tumour is purely extradural, it can be removed without opening the dura. If the tumour is intradural, then the dura is opened in a transverse fashion, 3-4 cm posterior to the frontal poles. The superior saggital sinus is ligated and transected along

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Fig. 2 - Intra cranial view with the indicated osteotomies in the anterior cranial fossa.

with the falx cerebri. The interhemispheric fissure is opened to separate the medial surface of the frontal lobes from each other. The subsequent steps depend on the nature and texture of the tumour and its relationship and adherence to the carotid arteries, optic nerves, hypothalamus or cavernous sinus. Cerebral retraction should be kept to a minimum to avoid postoperative oedema and intracerebral contusions.

RECONSTRUCTION Reconstruction is a crucial part of the procedure, because of the potential CSF leak. A fascia lata graft is harvested and laid intradurally over the basal dura. The dura is then closed in a water tight fashion. The pericranium is placed under the frontal lobes and over the open ethmoidal and frontal sinuses. The osteotomized fragments are put back in place and secured with miniplates or wires. The bifrontal bone flap is then attached to the skull and the skin closed. An epidural drain is used. Cerebrospinal fluid drainage for 2 or 3 days, with a lumbar drain, will reduce the intracranial pressure, speed up dural healing and reduce the risk of a CSF leak. This is done if extensive drilling of the anterior skull base was performed, or if there was extensive dural resection. The patient is nursed in the semisitting position for 3-5 days to decrease the intracranial pressure and prevent CSF leak also.

RESULTS

Fig. 1 - . ~ r o p o s t e r i o r photograph of the bifrontal craniotomy. The black stripes indicate the cuts.

Total resection was accomplished in all cases, as documented by postoperative CT and MRI scans. No patient required a combined transfacial-intracranial approach. The patient with the J giant pituitary adenoma

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received postoperative radiation therapy to prevent recurrence. The patient with choriocarcinoma received postoperative chemotherapy. The follow-up period ranged from 6 to 28 months. No evidence of recurrence was seen at the latest follow-up (as documented by radiological imaging). Complications

In a patient with an intradural tumour, excessive drilling of the bone of the anterior cranial base was performed. This patient had a postoperative CSF leak despite postoperative lumbar drain placement. This required reoperation and closure of the dural tear. Two patients developed postoperative frontal oedema. Corticosteroids and elevation of the head of the bed led to resolution of the oedema without major sequelae.

and confirmed the total resection (Fig. 4). Her postoperative course was uneventful and she was discharged home 7 days later. Illustrative Case 2

A 60-year-old male presented with a 6 month history of headaches and a recent onset seizure. Radiological investigations revealed a tuberculum sellae mass (Fig. 5). The patient was taken to the operating room and the mass was completely removed via the subfrontal approach. The pathology was consistent with a meningioma. Postoperatively the patient had transient bilateral frontal lobe swelling (Fig. 6) that resolved with Dexamethasone and Mannitol. He was discharged home 2 weeks later, in good condition. Illustrative Case 3

ILLUSTRATIVE CASES Illustrative Case 1

A 62-year-old woman presented with headaches and a frontal lobe syndrome. Neurological examination was unremarkable except for anosmia. An M R I of the brain was done and revealed a large olfactory groove meningioma (Fig. 3). The patient was taken to the operating room, where the tumour was totally resected via an extended subfrontal approach. A C T scan was done on the first postoperative day

Fig. 3 - Preoperativecoronal Tl-weighted MRI with guadolinium

shows a large mass in the olfactory groove (arrows).

A 69-year-old man started complaining of decreased visual acuity. He was seen by an ophthalmologist who discovered a bitemporal hemianopsia. A brain M R I revealed a sellar and suprasellar mass (Fig. 7). No evidence of hormonal hypersecretion was found on blood examination. The patient was taken to the operating room where he underwent an extended subfrontal approach for resection of his pituitary tumour. The pathology confirmed the diagnosis of a non-secreting pituitary adenoma. He was discharged home 9 days later in good condition.

Fig. 4 - Postoperativeaxial CT scan shows the osteotomycuts and the space in the region of the olfactorygroove.

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Preoperativeaxial CT scan revealsa large enhancing tumour in the tuberculum sellae area.

Fig. 5 -

Postoperativeaxial CT scan shows oedemain the frontal lobes bilaterally.

Fig. 6 -

DISCUSSION Skull base tumours are challenging tumours because of their location in areas that were once considered to be inaccessible. Surgery for tumours in this area had elevated morbidity and mortality rates in the past, thus leading to more conservative approaches.

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Over the past two decades there has been a revival in the interest in approaches to the skull base. These approaches are a combination of cranial and facial approaches. In a combined effort by neurosurgeons and maxillofacial surgeons or E N T surgeons, craniofacial osteotomies are added to more conventional craniotomies to improve exposure of these lesions that are located under the basal aspect of the brain. Adding an orbital osteotomy to a pterional craniotomy improves the angle of the field of view by 75% from 11 to 19 degrees as shown by Alaywan and Sindou (1990). These osteotomies are not a new concept. McArthur in 1912 and Frazier in 1913 advocated removal of part of the orbital rim to improve exposure of the pituitary gland and sellar area. The use of orbital osteotomies was further developed by Jane et al. (1982) and Jackson et al. (1984). Derorne et al. (1972) described the transbasal approach in which a bifrontal craniotomy is made down to the orbital rim and the lesion is approached extradurally. This technique allows approach to the anterior cranial fossa, to the sphenoid sinus and to the clivus also. Cophingnon et al. (1983) described the addition of an orbital osteotomy to the bifrontal craniotomy, thus the denomination extended transbasal approach. The orbital osteotomies were used for a variety of vascular and tumoural lesions by Jackson et al. (1984) and several other authors (Hakuba et al., 1986; AlMefty, 1987; Lesoin et al., 1986; Sekhar et al., 1988, Sekhar et al., 1989). Some authors advocate the use of two separate bone flaps for the bifrontal craniotomy (Sekhar et al., 1992). We raise a simple bone flap that crosses the superior sagittal sinus and have not had any problems with bleeding. The use of this approach improves the exposure of the tumours of the anterior cranial base with minimal frontal lobe retraction. This allows complete resection to be achieved with less difficulty, as seen from our results. There are a few complications that are seen with this route. Extensive drilling of the frontal base and wide excision of involved segments of the dura increase the risk of CSF leakage. The proximity of the nasal sinuses and nasal cavity makes the presence of cerebrospinal fluid leakage a very dangerous situation. Subsequent meningitis can be fatal, thus the obvious need for meticulous reconstruction. In our series, we did not have any problems with the reconstruction of the anterior cranial base in all but one case who suffered from a postoperative CSF leak and required reintervention. Infection of the osteotomy site and osteomyelitis is another serious complication that necessitates removal of the osteotomized bone and delayed reconstruction of the orbital rim. We have not had any incidence of osteomyelitis in our series. Anosmia is a consequence of this approach also. Its impact varies depending on the occupation of the

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Fig. 7 - Preoperative sagittal T-1 weighted MRI shows a large sellar and suprasellar mass (arrows). patient. S p e t z l e r et al., (1993) have described a technical variation that allows, theoretically, preservation of the sense of smell. Circumferential osteotomy cuts are made around the cribriform plate, and the nasal mucosa is left attached to the bone. The ethmoid trabeculae are cut individually with scissors. The cribriform plate is elevated with the frontal dura superiorly. The olfactory nerves are not severed in this technical variation. However, the orbital osteotomy must extend posteriorly to allow the posterior cut of the ethmoidal osteotomy to be made through the planum sphenoidale. Another possible complication of this approach is injury to the supraorbital nerves. This is avoided by releasing the supraorbital nerves anteriorly from their foramina. The cerebral oedema is not a particular consequence of this approach; in fact its incidence and severity should be reduced by the wider exposure allowed by the orbital osteotomy. We do not think that transient postoperative frontal lobe oedema in two out of 29 patients harbouring large lesions of the anterior cranial base is an excessive number.

CONCLUSION Tumours in the region of the anterior cranial fossa, if large enough, raise problems of exposure and m a y require excessive retraction of the frontal lobes, with the risk of subsequent frontal oedema and serious neurological sequellae. Close cooperation between the maxillofacial surgeon and the neurosurgeon is essential in treating these particularly difficult cases via the extended frontal approach. The exposure is

obtained by removing bone rather than by retraction of the brain. The additional time spent in performing this approach is fully justified, since it provides a wider exposure with less brain retraction as compared with more conventional approaches. The important technical details to watch for are the following: careful separation of the periorbita and basal dura, precise osteotomy, decreased brain retraction and meticulous reconstruction. References Alaywan, M., M. Sindou: Frontotemporal approach with

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