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Skull Base Brain Tumor Research




Application of the Supraorbital Endoscopic Approach to Tumors of the Anterior Cranial Base
By Mohamed S. Kabil, M.D. and Hrayr K. Shahinian, M.D.

Abstract

Access to tumors of the anterior cranial fossa, traditionally, has required wide exposure of the surgical field, along with prolonged retraction of the frontal lobes or potentially disfiguring transfacial approaches. These approaches subject patients to undesirable neurological and cosmetic morbidity. With the introduction of progressively less invasive approaches, intracranial tumors with craniofacial involvement have become amenable to en bloc resection with a minimum of deleterious consequences.

We report our experience with a supraorbital endoscopic approach. This technique is suitable for lesions situated in the region of the anterior cranial fossa, the suprasellar and parasellar regions.

The technique was applied to 24 patients. Pathologies treated were meningiomas, craniopharyngiomas, pituitary adenomas with extrasellar extensions, and other variable supratentorial pathologies. The use of endoscopy allowed thorough visualization of all critical structures at the paramedian skull base without the need for a bicoronal scalp flap, bifrontal osteotomies, or brain retraction.

Most lesions were resected in their entirety with no perioperative complications and with excellent cosmetic results. These cases demonstrate how the application of endoscopy to surgery of the anterior skull base and craniofacial skeleton can eliminate the need for traditonal open techniques without compromising surgical success.

Keywords
Endoscopic, Microsurgery, Supraorbital, Eyebrow

Introduction

The primary goal of surgery is complete microsurgical removal of the tumor, including resection of its dural attachment and diseased bone if bony invasion has occurred; this provides the best outcome and prevents recurrence.1,2 Tumors of the anterior cranial base which were once considered to be "inoperable" due to the challenges associated with surgical access have become amenable to en bloc resection with a minimum of deleterious consequences. Complete resection of tumors of the anterior cranial fossa and the paranasal sinuses with both craniofacial and intracranial components has been made possible by the introduction of transcranial and transfacial approaches that offer access to the involved cavities. Wide exposure, however, often comes at the expense of a significant degree of brain retraction and facial dissection, which in turn may result in undesirable perioperative morbidity.3-6

To minimize the deleterious effects of frontal lobe retraction and to avoid the use of facial incisions, approaches to these tumors have become progressively less invasive. Strategic placement of "keyholes" eliminates the need for excessive surgical manipulation without sacrificing exposure or outcome.

Endoscopes with varying angles of view provide a panoramic perspective of the relevant surgical anatomy and allow for thorough evaluation of the extent of intracranial and extracranial disease. The maneuverability of the endoscope allows the surgeon to position it directly at the level of dissection, effectively reducing the viewing and operating distances. Endoscopic imaging thereby facilitates complete tumor resection via a minimally invasive technique.

We adopted a previously developed frontolateral keyhole approach7,8,9 in our surgical practice to demonstrate the efficacy of this minimally invasive exploration. The use of endoscopy as the sole imaging modality was found to be ideally suited to exploration of the anterior cranial fossa and surrounding sinuses. The adaptation of rigid endoscopy to the supraorbital approach broadens the available surgical exposure without the introduction of additional dissection or retraction. The endoscopic supraorbital approach obviates the need for a bicoronal scalp flap or an extensive bifrontal craniotomy without diminishing visualization of the paramedian skull base.

Patients and Methods

In the period from July, 2002 to October, 2004, 24 fully endoscopic supraorbital operations were performed by surgeons at the Skull Base Institute, in Los Angeles, California; 13 of which were for meningiomas, 4 were for craniopharyngiomas, 3 were for extrasellar extensions of large pituitary adenomas. The other 4 supratentorial pathologies which were treated consisted of: 1 frontal sinus mucopyocele, 1 medial temporal arachnoid cyst, which were both excised in their entirety; an astrocytoma and an esthesioneuroblastoma which were only biopsied for pathological analysis, as planned preoperatively. Patients were identified from a continually updated database of all patients presenting to the Skull Base Institute in Los Angeles, California. These patients' charts were retrospectively reviewed and information from follow-up visits was collected to assess operative success rates and the incidence of complications. Pre-operative information collected included: age, sex, presenting symptom(s) and sign(s), prior surgical procedure(s), as well as the routine pre-operative laboratory results and the required investigations. Tumor grade, type, location and size were assessed and determined from pre-operative magnetic resonance imaging, intraoperative observation and pathological analysis of the tumor. Follow-up data was compiled regarding the length of hospitalization and the incidence of complications including: CSF fistulae, hematoma formation, loss of vision, CNS injury (epidural, subdural, hypothalamic injury, meningitis, or carotid artery injury, and death). Patient outcomes were determined from intra-operative assessment of tumor resection, post-operative hormone levels and MR imaging results.

Tumor removal was considered total if the surgeon was convinced that there had been a complete removal of the tumor under the endoscopic visualization and if postoperative contrast-enhanced MR imaging showed no evidence of residual tumor. Removal was considered subtotal when only a small portion of residual tumor remained because of firm attachment to vascular or neural structures or when postoperative imaging revealed a small contrast-enhanced area. Partial removal was defined as the presence of larger residual portion of the tumor.

Surgical technique

The patient is placed supine on the operating room table and the head of the bed is slightly raised. Following the induction of general anesthesia, the patient's neck is flexed approximately 15°-30° to let the optic chiasm be in line with the surgeons scope of view. Following that, the head is rotated laterally either towards the surgeon or away from him depending on the location of the lesion. The surgical positioning is slightly variable as it is tailored according to the individual case of each patient, his symptomatology, and the location of the tumor; but in all cases the head is placed above the level of the heart to improve venous drainage. Following that the head is secured in place using a three-pin clamp. The frontal area is cleansed with an aqueous antiseptic solution and then draped.

The base of a pneumatically powered endoscope holding arm (Mitaka Kohki Co., Tokyo) is fastened to the operating room table opposite the surgeon; the arm extends over the patient. A 4.0 mm 0° rigid endoscope (Karl Storz of America, Culver City, CA, USA) is attached to the holding arm.

A standard skin incision is placed within the hair of the eyebrow few mm's above the orbital rim; it begins medially lateral to the supraorbital notch and ends laterally before the lateral end of the eyebrow at an imaginary line perpendicular to the lateral end of the superior orbital wall. Subsequent to the skin and soft tissue incision, a 1.5cm craniotomy is performed. The skin flap is developed in a subcutaneous plane and retracted superiorly. The periosteum is elevated separately and retracted inferiorly for further use as a pedicled pericranial flap in reconstruction of the skull base. The dura is incised and cerebrospinal fluid drained. The endoscope is introduced thru the keyhole and advanced between the frontal lobe and the floor of the anterior skull base all the way to the tumor, the monitor becomes the surgeon's eyes.

A panoramic view of the tumor is displayed on a flat screen. Endoscopic survey reveals the degree of intracranial tumor spread. Extrasellar extensions of tumor are then exposed and removed from this approach.

Using a combination of a custom designed bipolar electrocoagulation system and a micro cavitron ultrasonic aspirator the tumor is gradually resected. This allows a complete and total resection of virtually most anterior skull base tumors through minimally invasive techniques with minimal or no brain retraction. This approach allows a panoramic visualization of the ipsilateral anterior fossa and a partial visualization of the contralateral anterior fossa.

The posterior wall of the frontal bone, the sphenoid ridge and/or the superior orbital roof could all be drilled away, to either give a better basal view or better access to the tumor. If the frontal sinus is opened, the mucosa is stripped the nasofrontal duct is obliterated and the sinus is cranialized.

The keyhole bone flap is repositioned using absorbable microplates and screws. The skin incision is closed with careful attention to the aesthetic repair. The patient is monitored in the intensive care unit overnight and thereafter transferred to the ward for 24 hours until discharge from the hospital. More than 90% of the patients undergoing these procedures were discharged from the hospital within 48 hours.

Results

Between July 2002 and October 2004, 24 patients were operated upon via the supraorbital approach (Table 1). The mean age was 51.95 years old (ranged 2874 years). There were nineteen women (79.1%) and five men (20.5%).

There was no perioperative mortality or major neurological complications. Two patients developed postoperative severe headache due to pneumocephalus, which was treated promptly with high flow oxygen, in both cases the headaches resolved in one day. Another patient with a large suprasellar meningioma had a slow course of recovery and was generally obtunded due to frontal edema, this resolved with appropriate medical therapy and an increase of the usual dehydrating measures.

Two patients developed transient anesthesia over the frontal part of the scalp due to stretching of the supraorbital and supratrochlear nerves, one of which also had transient swelling and reddening of the periobital area. Finally, one patient with a left frontparietal anaplastic astrocytoma had right hemiparesis postoperatively which improved gradually with physical rehabilitation.

In each case, the supraorbital eyebrow approach allowed excellent visualization of the tumor, the vascular and the neural structures. A macroscopic complete removal of the tumors was obtained in virtually all cases, except in one case with a suprasellar meningioma in which a small <,5 mm part of the tumor was densely adherent to the right optic nerve and it was seen as wise not to remove it in order to avoid the risk of injury to the optic nerve; and one craniopharyngioma. Two cases, an astrocytoma of the left motor cortex and an esthesioneuroblastoma, were only biopsied pathological analysis, as was planned preoperatively. The results were judged on postoperative MR scans. The skin scar was virtually invisisble in all cases. More than 90% of the patients were discharged to their home within 48 hours (figures 1 and 2).

Discussion

Several approaches have been developed that decrease the size of the craniotomy, minimize brain retraction, and promote adequate exposure of the cranial base. Frazier10 reported the first case in 1913. He resected the supraorbital ridge to operate on a pituitary tumor through the anterior cranial fossa. Jane et al.11described a supraorbital exploration, which they considered to be the approach of choice for orbital tumors and for anterior communicating artery aneurysms, pituitary tumors, craniopharyngiomas, and parasellar or olfactory nerve meningiomas as well.

In our series of patients we have found that the adaptation of rigid endoscopy to the supraorbital approach broadens the available surgical exposure without the introduction of additional dissection or retraction. Endoscopes of varying angles of view provide a panoramic perspective of the relevant surgical anatomy and allow for thorough evaluation of the extent of intracranial and extracranial disease. The maneuverability of the endoscope allows the surgeon to position it directly at the level of dissection, effectively reducing the viewing and operating distances. Endoscopic imaging thereby facilitates complete tumor resection via a minimally invasive technique. This technique obviates the need for a bicoronal scalp flap or an extensive bifrontal craniotomy without diminishing visualization of the paramedian skull base.

In our experience, despite the small size of the craniotomy, the exploration followed by slow CSF drainage proved to be large enough for safe intracranial microsurgical interventions while the integrity of as much normal tissue as possible was preserved; unnecessary manipulation or brain retraction was not needed. The advantages that the described approach offers over the conventional unifrontal or bifrontal craniotomy are: 1) a hidden skin incision completely within the eyebrow with no post operative disfiguring of the patient's face; 2) the superficial temporal artery, the frontal branch of the facial nerve, the supraorbital nerve and artery, are preserved, so the blood supply to the region aswell as the wound healing are excellent; 3) the mini-craniotomy bone flap is usually far enough from the frontal sinus to avoid the risk of rhinorrhea and infection; 4) the lens is at the tip of the endoscope just infront of the pathology and thus minimizing unnecessary brain retaraction and the greater part of the brain remains protected with the dura and bone; 5) faster and more direct way to reach the surgical field and obtain an excellent surgical exposure of the field with elimination of unnecessary steps; 6) and finally a smoother , more pleasant postoperative course and an earlier return to work for the patient. The disadvantages of the approach may be: 1) scalp anesthesia due to section or stretch of the supraorbital and supratrochlear nerves; 4) fistula through an occult frontal sinus opening.

Conclusion

The supraorbital keyhole craniotomy, together with the achievements of modern neuroanesthesia, CSF drainage, and microsurgical methods, is a safe approach for the treatment of tumors of the anterior cranial fossa and the parasellar region.

A precise knowledge of anatomic landmarks is important to avoid unnecessary injury to neural or vascular structures within the anterior skull base. Palsy of the supraorbital and supratrochlear nerves may be a handicap for the patient, therefore the medial limit of the incision should always be kept lateral to the supraorbital notch.

This technique represents an interesting option to the field. Due to the tremendous refinements of diagnostics methods, such as CT an MR, previously undetected lesions are now usually detected at an earlier stage. The significance of this is smaller lesions for which large craniotomies seem to be unnecessary or unadvisable.

We believe that this technique is ideally suited for the treatment of lesions located in the anterior fossa, suprasellar and parasellar region. Care should be taken to forestall skin scar problems or damage to a forementioned nerve. This technique is recommended for neurosurgeons that are well trained and also have experience with endoscopic procedures and also with the conventional craniotomy techniques.

References
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