Extended frontobasal approach to the skull base.
The extended frontobasal approach provides an adequate midline exposure from the anterior cranial fossa to the sphenoclival region. Between November 1991 and August 1999, 13 patients with extensive anterior and anterolateral skull base tumours extending to supra and parasellar regions, cavernous sinus and sphenoclival regions were operated upon using this approach alone (7 patients) or in combination with subtemporal -infratemporal (4 patients) or transfacial (2 patients) approaches. Gross total excision was performed in 8 patients while in 4 patients with malignant tumours and in a patient with extensive skull base fungal granuloma, only partial excision was possible. Basal repair was performed using pedicled pericranium, temporalis muscle or fascia lata. The complications included increase in the cranial nerve paresis, endophthalmitis, facial oedema, CSF leak, frontal haematoma and internal carotid artery injury. This study reviews the operative technique, the indications and the complications of extended frontobasal approach.
The extended frontobasal (EFB) approach described by Sekhar et al is a modification of the transbasal approach described by Derome et al. The procedure includes a bilateral orbito-frontal or orbito-fronto-ethmoidal osteotomy, to gain a wide exposure of the midline skull base, upto the sphenoclival region with minimal retraction of the orbitofrontal lobes. In the present series, the EFB approach alone or in combination with the subtemporal - infratemporal (ST-IT),, or facial approaches,,, has been utilised to resect lesions of the anterior and anterolateral skull base with extensions to the supra and parasellar regions, cavernous sinus and the sphenoclival region.
Thirteen patients with tumours of the anterior, middle and posterior skull base were operated between November 1991 and August 1999, using the EFB approach [Table I]. The age range of the patients was from 24 to 61 years and the M:F ratio was 8:5.
Radiology : Plain and contrast CT scans with bone windows were used to assess the extent of the lesion. Multiplanar MRI with MR angiography was extremely useful in 4 patients to delineate the
anatomical structures involved including the encasement of the internal carotid artery (ICA). Selective middle meningeal artery embolisation was performed in case of frontal and orbital osseous haemangioma. The patients with giant cell tumour of the sphenoid and adenoid cystic carcinoma did not tolerate balloon occlusion test (BOT) of ICA prior to surgery.
Combined approaches : The EFB approach was combined with the sublabial midline degloving approach and with lateral rhinotomy (one case each respectively) in patients in whom the tumour extended into the nasopharynx and maxillary sinus; with orbitozygomatic osteotomy (one case) in the patient with frontal and orbital osseous haemangioma; and, with orbitozygomatic osteotomy and ST-IT approach (4 cases) in patients in whom the tumour extended laterally along the lesser wing of the sphenoid, temporal base and cavernous sinus.
A brief outline of the operative technique of EFB approach used in the present series, the various modifications of which have been previously described,,,,,,, is as follows: Patient position : The patient is placed supine with the head elevated and slightly extended and fixed with pins to Sugita's head frame. The endotracheal tube requires secure fixation to facilitate repositioning of the patient's head during surgery. Proximal control of ICA is taken in the neck especially in cases with ST-IT or cavernous sinus extension.
Incision and flap reflection : A bicoronal incision is placed, far enough posteriorly, to ensure an adequate galeal and pericranial flap length for reconstruction. The incision extends from the ipsilateral zygomatic arch, just anterior to the tragus and reaches the opposite tragus. The scalp flap including the pericranium is separated from the skull and temporalis fascia and reflected anteriorly exposing the orbital rims and the frontonasal suture. The frontal and zygomatic branches of the facial nerve are preserved by reflecting anterolaterally with the scalp flap, both the superficial temporal fascia as well as the fat layer (containing the nerves) present between the superficial and deep temporal fascia., Bony cuts are made around the supraorbital nerves and vessels to release and retract them along with the scalp flap. In case of the EFB approach combined with the ST-IT approach, the temporalis muscle and its fascia are separated from the temporal fossa and reflected postero-inferiorly (leaving a cuff of the muscle attached to the bone flap for later resuturing) exposing the lateral orbital rim. The periorbita is separated from the bony orbit superiorly, laterally and medially on the ipsilateral side and superiorly and medially on the contralateral side.
Bifrontal craniotomy and orbitofrontal osteotomy :A low bifrontal craniotomy is performed and the bone elevated by gently separating the superior sagittal sinus from it. The mucosa of the frontal sinus is curetted out. The brain is adequately relaxed using intravenous mannitol and/or frusemide or lumbar cerebrospinal fluid drainage. The subfrontal dura is separated from crista galli and the latter removed. Dura is then gently separated from the cribriform plates of the ethmoid, bilateral orbital roofs and planum sphenoidale [Figure - 1]. The basal dura over the cribriform plate is sutured to close small perforations that occur during the dural separation. The frontal basal dura and the periorbita are protected by retractors. Using a reciprocating saw or a chisel and a mallet, the orbital roofs are cut from the anterior cranial fossa to the orbit. A horizontal cut is also made at the frontonasal suture, angling the saw upwards so that it enters the anterior cranial fossa anterior to the region of crista galli. Additional bone cuts are made obliquely on the ipsilateral and contralateral zygomatic process of frontal bone (or in case of a more restricted exposure, vertically on the orbital rim medial to the supraorbital foramina on the contralateral side). The orbitofrontal osteotomy piece is loosened using osteotomies and removed. For orbito-fronto-ethmoidal osteotomy, the orbital cuts are made 2-3 mm deeper in the ethmoid bone and the horizontal osteotomy is performed through the nasal and ethmoidal bones to pass through the foramen of anterior ethmoidal artery. The fragment is then loosened out in a single piece [Figure - 2] and [Figure - 3].
Tumour excision : In cases of tumours confined to the anterior cranial base, a wide exposure for tumour excision without brain retraction is achieved by removing the posterior part of the orbital roof and the medial wall of the orbit [Figure. 4] and [Figure - 5]. The optic nerve canals may also require deroofing from the medial aspect. However, drilling of the anterior clinoids is safer from the intradural aspect. In cases of the midline tumours of the middle skull base and the clivus, a part of the ethmoidal bone may be included in the orbitofrontal osteotomy. The middle and the posterior ethmoidal cells as well as the superior and the lateral walls of the sphenoid are drilled. Thus, the medial aspect of the cavernous sinus and the intracavernous ICA as well as the clivus becomes accessible without brain retraction. While removing the clival tumour, the VI nerve entering the cavernous sinus through the Dorello's canal laterally, the hypoglossal nerves at the inferolateral limit and the basilar artery and the brainstem posteriorly must be adequately protected. However, a tumour involving a high dorsum sellae remains inaccessible due to inferior obliquity of the approach as one moves from anterior to posterior direction.
Combination of approaches : In case the tumour extends laterally along the middle fossa base, the infratemporal fossa or the greater wing of sphenoid, the EFB approach is combined with orbito-zygomatic osteotomy and ST-IT approach.,, The skin incision is extended below the zygomatic arch, which is exposed by incising the attachment of the temporal fascia to it, separating the temporalis muscle that is passing underneath the arch and then reflecting the muscle anteroinferiorly, thus exposing the lateral orbital rim, temporal and subtemporal regions. A bifrontal and ipsilateral temporal craniotomy is performed. Bony cuts are made similar to that made for orbito-frontal craniotomy. Additional cuts made for the orbito-zygomatic osteotomy include the division of the zygomatic process of temporal bone anterior to the temporo-mandibular joint and the oblique cut through the zygomatic bone lateral to the inferior orbital issure.,, The orbito-zygomatic piece is loosened and removed. The greater wing of sphenoid is drilled and the superior orbital fissure unroofed. The temporal basal dura is stripped from the middle fossa base exposing the arcuate eminence, greater superficial petrosal nerve, middle meningeal artery, the dural sleeves of the maxillary and mandibular nerves passing through their exit foramina and the inferior aspect of the superior orbital fissure. The sphenoid bone is drilled to open the space between mandibular and maxillary nerves and between maxillary nerve and the lower border of superior orbital fissure. This gives access to the subtemporal region, petrous apex, pterygoid fossa and sphenoid sinus. Since carotid control is taken in the neck, exposure of the petrous part of the carotid is not Banerji et al required. The greater superficial petrosal nerve and the middle meningeal artery are divided. The tumour is removed from between the branches of the trigeminal nerve., The sphenoid sinus is accessed from the midline as well as lateral aspect by drilling of the sphenoid bone at the base of the pterygoid process., For tumours extending inferiorly from the anterior skull base into the ethmoids and nasopharynx, the transfacial approaches such as lateral rhinotomy and facial degloving are useful.
Reconstruction : The frontal, ethmoidal and sphenoidal sinus mucosa is curetted out and the sinus cavity is packed with fat. The dural defects are closed primarily with sutures or with a facial graft. A pedicled flap consisting of pericranium, galea aponeurotica and frontalis muscle and vascularised by the supraorbital and supratrochlear vessels [Figure. 6] are placed along the base.,,, In order to obliterate the residual cavity, occasionally, an additional temporalis muscle rotational flap or vascularised free flap may be required. The orbitofrontal/orbito-fronto-zygomatic as well as the bifrontal/bifronto-temporal segments are secured in their respective anatomical positions using silk sutures. Bony reconstruction of the skull base was performed in one patient in the series.
Gross total excision was performed in 8 patients in the series [Figures. 7] and [Figures. 8]. In 4 patients with malignant tumours and in a patient with skull base fungal granuloma, only partial excision was possible. Basal repair using pedicled frontal pericranial sheath occasionally supplemented by fascia lata or temporalis muscle was performed in all patients. Two out of the five patients with preoperative unilateral ophthalmoplegia showed postoperative recovery in extraocular functions. Of the three patients with preoperative IX-X nerve paresis, two required a tracheostomy for tracheal toilet. The postoperative complications included XI nerve paresis (1), significant orbitofacial oedema (2), injury to the left ICA controlled by bipolar coagulation and wrapping of the vessel wall (1), and CSF rhinorrhoea (4). There was no perioperative mortality.
The follow up in the series ranged from 22 months to 5 years. The patients operated for benign tumours had significant clinical improvement at follow up. A repeat computed tomographic study performed after 1 to 5 years showed no recurrence of the tumour. However, the patient with fungal granuloma showed residual lesion and was administered amphotericin.
The patients with malignant lesions received radiotherapy and had maintained their preoperative status at the first follow up after 2 to 4 months except two patients. The patient with aesthesioneuroblastoma developed subgaleal metastasis below the frontal flap at 4 months and required boost radiotherapy; and the patient with chondrosarcoma expired due to extensive regrowth of the lesion at 3 months.
Evolution of technique : The approach to the midline skull base has advanced from an isolated exposure of the anterior skull base to extensive visualisation of the sphenoclival region upto the foramen magnum. The combined craniofacial approach was pioneered by Ray and McLean in 1943 for resection of a retinoblastoma and by Smith et al in 1954 for resection of paranasal sinus tumours. Since then, the technique of frontal craniotomy and en-bloc resection of the paranasal sinuses in continuity with the cribriform plate area of the anterior cranial fossa with,,,, or without, transfacial approaches has frequently been utilised. Frazier in 1913 first removed the orbital rims to gain additional exposure of the skull base with minimal brain retraction. Since the utilisation of orbital osteotomy in the transbasal approach by Derome in 1972, the procedure has gained wide acceptance.,,,[26-31] Sekhar and Spetzler, added an ethmoidectomy to the orbitofrontal osteotomy to extend the exposure to the sphenoclival region and the foramen magnum. In the present series, this EFB approach has been used in 7 patients, in combination with orbitozygomatic osteotomy and ST-IT approach in 4 and with transfacial approaches in 2 cases. However, the subtemporal-infratemporal dissection has been less extensive than proposed by Sekhar et al. Only a restricted orbital rim osteotomy was performed on the contralateral side. The temporomandibular joint was not dislocated, the parotid and submandibular regions were not exposed and the petrous ICA was not deroofed. The exposure was sufficient for a piecemeal resection of the tumour and an en-bloc resection of malignant tumours was not attempted. Ketchum et al stated that despite the delivery of the tumour in a single piece, the anatomy of the paranasal sinuses and the nasal cavity precludes a true en-bloc resection. The lack of long-term results further cast doubts on the efficacy of extensive en-bloc resection in the long-term control of malignant tumours.,,, In the present series, therefore, a
Banerji et al
piecemeal resection of malignant tumours was performed with the aim of tumour debulking to improve the symptoms of mass effect and facilitate the response to subsequent adjuvant chemo-radiotherapy.
Merits and demerits : The EFB exposure provides an excellent visualisation and decompression of the optic nerve, sphenoid sinus, the medial aspect of the cavernous sinus and the clivus. The exposure is enhanced by adding a maxillotomy or orbitozygomatic osteotomy to access lesions extending laterally along the temporal base and the greater wing of sphenoid. Alaywan and Sindou calculated that the orbitozygomatic removal improves the field view angle (i.e. the angle of exposure of the target with minimal brain retraction) by 75% in the subfrontal approach, 46% in the pterional approach and 86% in the subtemporal approach. In case the cavernous carotid is injured, it can be repaired directly. Using this approach, there is potential for resection of a large part of the midline skull base and reconstruction by a vascularised flap that exteriorizes the potentially infected nasoethmoidal region from the cranial cavity and eliminates dead space.
However, the procedure is technically demanding and requires extensive soft tissue and bony dissection. The prolonged operative time, the potential for CSF leak and the direct communication of the cranial cavity with the paranasal sinuses increases the risk of infection. Bilateral olfactory denervation during the dural dissection from the anterior cranial fossa inevitably eliminates the sensation of smell and flavour. Spetzler et al recommended preserving of olfaction by an en bloc mobilisation of the olfactory bulbs, the surrounding frontobasal dura, the cribriform plate and the underlying mucosa with the final reconstruction by repositioning the olfactory complex to its normal anatomical site. However, the efficacy of the method has not been conclusively established. Laterally, the exposure is limited by the optic nerves, cavernous sinus, petrous apices, and VI nerve, necessitating its combination with other approaches, that require further soft tissue and bony dissection. While traversing from anterior to posterior direction, the inferior obliquity of the approach precludes access to a high dorsum sellae. In the clival region, the field of surgery becomes deep and narrow and vital structures like the basilar artery, basilar venous plexus and the brain stem are difficult to access.,
Alternative approaches : The alternative approaches to the sphenoclival region include the trans-ethmoidal, trans-sphenoidal, transoral, and facial translocation techniques. These have the disadvantage of a narrower exposure, difficulty in accessing the middle and lower clivus, inaccessibility of the optic nerve, lateral limitation by the petrous and cavernous ICA, and difficulty in cranial base reconstruction.,
Cranial nerve paresis : Five patients with tumour extension into the cavernous sinus presented with unilateral ophthalmoplegia. Using the EFB approach, the entry into the medial cavernous sinus and petrous apex can be gained. The III, VI, maxillary and mandibular nerves were preserved between the superficial and deep layers of the lateral wall of the cavernous sinus. Using the combined EFB and ST-IT approach, the cavernous sinus could also be accessed from a lateral aspect. The superficial layer of the lateral wall was separated from the V nerve and the tumour was resected from between its divisions. The VI nerve entering the cavernous sinus from the Dorello's canal had to be meticulously dissected from the tumour. Two of the five patients showed improvement in extraocular movements at follow up. Three patients presenting with IX-X nerve paresis had tumour extension in the vicinity of petrous boneforamen magnum. Two of these patients with consequent pneumonitis required a tracheostomy for tracheal toilet. This lateral extension of the tumour may be accessed during the combined EFB and ST-IT approach by deroofing and mobilizing the petrous ICA and drilling the clivus to expose the dura from the petrous apex to the foramen magnum., A patient with giant cell tumour of the sphenoid reaching upto the foramen magnum had postoperative XII nerve paresis probably due to its injury during tumour excision in the vicinity of the hypoglossal canal.
Orbitofacial oedema : Significant orbitofacial oedema, was observed in two patients in the series within 24 hours of surgery. It lasted for 6 days but was not associated with any sequelae.
Frontal lobe retraction haematoma : This complication was observed during excision of a large nasoethmoidal schwannoma and required evacuation of the haematoma. To preempt this complication in other patients, steroids were started in the perioperative period and intraoperative mannitol was administered.
ICA injury : The patients with ICA encasement or displacement by the tumour were subjected to angiography and balloon occlusion test.,, Two patients did not tolerate a 15 minute balloon occlusion test. In these patients, proximal control of cervical ICA and provisions for superficial temporal-middle cerebral artery anastomosis were kept. One patient sustained ICA injury while it was being traced in the cavernous sinus. Fortunately, the small rent could be sealed by bipolar coagulation of the vessel wall without compromising its lumen and he did not have any added deficit.
CSF leak : After mucosal exenteration and fat packing of the paranasal sinuses, basal repair was performed using galeal-pericranial flap based on the supraorbital -supratrochlear vessels., Back cuts were added to the pericranial flaps on one side along the superior orbital margins preserving the contralateral supraorbital vessels to increase the arc of rotation of the flap. Further posterior reinforcement was provided by a fascia lata graft, and in one patient the temporalis muscle was rotated to obliterate the dead space. An autologous temporal bone was used to reinforce the skull base in one patient. However, it is not recommended because it may be detrimental to healing as it may prevent the coaptation of the flap with the dura, decrease the vascularity of the flap, and predispose to infection being in close proximity to the paranasal sinuses., Musculocutaneous and free flaps based on pectoralis major and trapezius as well as free omental flaps have been recommended for basal repair with the added capability to withstand radionecrosis and to avoid infection. Four patients developed CSF leak and were managed by head elevation, acetazolamide administration and closed lumbar drainage for three to five days.
Conclusions : EFB approach provides an adequate exposure of the midline cranial base upto the sphenoclival region and foramen magnum. The exposure can be further enhanced by combining it with transfacial and ST-IT approaches. However, its demerits include extensive dissection, requirement of facilities for vessel anastomosis and adequate skull base reconstruction.