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Skull Base Brain Tumor Research




Skull Base Surgery
By Hrayr K. Shahinian

Introduction

For decades, the skull base has represented a virtual "no-man's land" in terms of surgical treatment. The area is extremely difficult to navigate due to the numerous vital blood vessels and critical cranial nerves that enter and exit the base of the brain (1, 2, 3).

Perhaps the most distinguishing recent innovation in the field of Skull Base Surgery has been the introduction of Endoscopic Minimally Invasive Techniques in the treatment of complex conditions such as pituitary tumors, microvascular nerve compression syndromes, acoustic neuromas, meningiomas, and a variety of brain and skull base tumors (4, 5).

Endoscopic skull base surgery offers dramatic benefits to patients. Using extremely thin, flexible and precise endoscopic instruments, these minimally invasive approaches eliminate large craniotomies, brain retraction, scarring and nasal packing. They shorten surgery time, dramatically reduce length of stay in the hospital, and result in faster overall recovery, return to work and normal activities (6, 7).

Anatomically the skull base is divided into three subdivisions: the Anterior Skull Base, the Lateral Skull Base, and the Posterior Skull Base.

Anterior Skull Base (Anterior Cranial Fossa)

Midline or Paramedian anterior skull base lesions such as olfactory groove or planum sphenoidale meningiomas, esthesioneuroblastomas or transcranial extensions of orbital or paranasal sinus tumors have traditionally been approached thru "Craniofacial," unifrontal or bifrontal craniotomies with elevation of one or both frontal lobes and significant brain retraction. The introduction of Endoscopic skull base surgery has allowed the resection of these tumors thru two minimally invasive approaches that involve placing a small (2cm) incision either within the skin crease in the bridge of the nose or within the hair of the eyebrow, depending on the exact location of the tumor.

Subsequent to the skin and soft tissue incision, a 1.5cm craniectomy is performed. If necessary the frontal sinus is cranialized and the nasofrontal duct obliterated. 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. A panoramic view of the tumor is displayed on a flat screen. 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. More than 90% of all patients undergoing these procedures are discharged from the hospital within 48 hours.

Lateral Skull Base (Middle Cranial Fossa)

Midline lesion confined to the sella and the suprasellar space such as pituitary tumors, craniopharyngioma's, Rathke's cysts, or chordomas can benefit from the transnasal, transsphenoidal, endoscopic approach to the area. This procedure utilizes a microendoscope 2.7mm wide and 20cm long with an angled tip that is inserted through the right nostril and into the skull base. This technique offers numerous advantages in terms of the surgery and recovery. One of the amazing benefits is the view of the surgical field. Since the camera is "placed" at the tip of the endoscope, surgeons have a vivid panoramic view of the brain. The angled endoscopes allow looking around corners and making a full assessment. This panoramic view provides the surgeon with the ability to remove the entire tumor in most cases. This process is in sharp contrast to the traditional, open translabial, transsphenoidal approach, which requires viewing the tumor site through a microscope outside the skull at a focal distance that limits visibility and working through a nasal speculum that restricts the ability for both viewing and maneuvering instruments laterally. Since the point of entry is through a nostril, no incision is required. Consequently, no more nasal packing is required and the brain is undisturbed. The time required for the actual surgical procedure, the length of hospital stay and overall recovery time are dramatically reduced. Patients return home within twenty-four to thirty-six hours of surgery and enjoy a rapid overall recovery.

Paramedian tumors i.e. sphenoid wing schwannomas or neurofibromas of the trigeminal system or sphenoid wing meningiomas are approached through a preauricular transzygomatic.

1.5cm craniectomy. The dura is incised and CSF is drained from the middle cranial fossa. After adequate relaxation of the temporal lobe, an endoscope is inserted and direct access to the floor of the middle cranial fossa and the entire sphenoid wing is obtained. This technique also provides access to the lateral cavernous sinus and tumors within its lateral triangle. This approach provides access to foramen ovale and the V3 branch of the trigeminal nerve, foramen rotundun and the V2 branch of the trigeminal nerve. It also provides access to the superior orbital fissure and the optic canal. Both the pre-cavernous internal carotid artery segment along the floor of the middle cranial fossa and the post cavernous internal carotid artery segment posterior and medial to the anterior clinoid are accessible.

Posterior Skull Base (Posterior Cranial Fossa)

Posterior skull base lesions such as acoustic neuromas or meningiomas of the cerebellopontine angle and neurovascular compression syndromes such as trigeminal neuralgia or hemifacial spasm can all be approached through a dime size opening behind the ipsilateral ear. This approach is performed by first making a 3cm retrauricular scalp incision, followed by a 1.5cm retrosigmoid craniectomy. The dura is incised and CSF is drained from the posterior fossa. After adequate relaxation of the cerebellum, a 4mm, zero degree endoscope is introduced into the posterior fossa and gradually advanced to the ipsilateral cerebellopontine angle. Tumors such as acoustic neuromas and meningiomas are resected using microsurgical techniques and the use of custom designed microinstruments, a custom designed bipolar electrogoagulation system and a microcaiton ultrasonic aspirator. Neurovascular compression syndromes are similarly managed with the use of custom designed microinstuments which allow the safe dissection of intracranial vessels from cranial nerves and the safe insertion of a teflon pledget between the vessel and the nerve. This alleviates the excruciating facial pain in the case of trigeminal neuralgia and the debilitating facial twitching in the case of hemifacial spasm. More than 95% of these patients spend only one night in the surgical intensive care unit followed by another 24 hours on a regular floor followed by discharge home within 48 hours.

Conclusions

The recent advances in fiberoptic technology, customized micro instrumentation, robotic holding devices, xenon lighting and digital recording equipment have ushered in the era of endoscopic skull base surgery. The principles of minimally invasive approaches, more direct working distances and eliminating brain retraction have guided the skull base surgeon in tackling these challenging problems and removing tumors once thought to be "unresectable." (8,9)

References
  1. Fisch U and Mattox DE (eds) Microsurgery of the Skull Base. New York: Thieme Medical Publishers, 1988.
  2. Sekhar, LN and Janecka IP (eds). Surgery of Cranial Base Tumors. New York: Raven Press, 1993.
  3. Shahinian HK, Dornier C, and Fisch U. Parapharyngeal space tumors: The infratemporal fossa approach. Skull Base Surg. 5:5, 1995.
  4. Jarrahy R, Shahinian HK: Surgical management of pituitary tumors. Pituitary: 3:1, 2000.
  5. Jarrahy R, Cha ST, Berci G, and Shahinian HK: Endoscopic transglabellar approach to the anterior fossa and paranasal sinuses. J Craniofac Surg. 11 (5): 412-7, 2000.
  6. Jarrahy R, Shahinian HK: "Surgical Management of Pituitary Tumors." In: DeGroot LJ, Jameson JL, eds. Endocrinology. 4th ed. Philadelphia: W.B. Saunders Co. Chap 26:343-353, 2000.
  7. Eby J, Cha ST, Shahinian HK: Fully endoscopic vascular decompression of the facial nerve for hemifacial spasm. Skull Base Surgery: 11 (3): 189-196, 2001.
  8. Jarrahy R, Cha ST, and Shahinian HK: Retained foreign body in the orbit and cavernous sinus with delayed presentation of superior orbital fissure syndrome. J Craniofac Surg. 12(1):82-6, 2001.
  9. Jarrahy R, Eby J, Shahinian HK: State of the Art: a new powered endoscope holding arm for endoscopic surgery of the cranial base. Minimally Inv. Neurosurg. 45: 189-192, 2002.