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Endoscopic Skull Base Surgery
Chapter 7: The Fully Endoscopic Transglabellar Approach

By Hrayr K. Shahinian, M.D., FACS

This chapter discusses the application of the fully endoscopic transglabellar keyhole approach in surgical management of tumors of the anterior cranial base and the suprasellar region. Traditionally, approaches to these tumors have required large frontal craniotomies along with prolonged retraction of the frontal lobes, subjecting patients to undesirable neurological and cosmetic morbidity. In our practice, the endoscopic transglabellar approach has allowed thorough visualization of the anterior fossa, suprasellar region, and all critical structures at the paramedian skull base. Endoscopic imaging thereby facilitates complete tumor resection via a minimally invasive technique that utilizes a small hidden incision that runs in a natural skin crease between the eyebrows. The chapter provides a thorough description of the fully endoscopic transglabellar approach, including indications, operating room setup, patient positioning, operative technique, state-of-the-art illustrative cases, potential complications, and ways to avoid these complications (in the author's experience).

1. Introduction

Surgical management of tumors of the anterior cranial base and the suprasellar region has traditionally required large frontal craniotomies with prolonged retraction of the frontal lobes. These wide surgical exposures often subject patients to undesirable neurological and cosmetic morbidity. However, the ease with which endoscopes and instruments can be maneuvered in the space between the frontal lobes and the base of the skull and the ability of rigid endoscopes to overcome the barriers to visualization that a diminutive craniotomy may pose have allowed minimally invasive surgical access to the anterior cranial fossa and suprasellar region with excellent visualization.

Through a transglabellar keyhole approach, the endoscope is advanced directly to the lesion; thus the effective operating distance is significantly reduced, as is the need for wide skin flaps. The use of 0-degree and angled endoscopes has allowed unprecedented panoramic views of the anterior cranial fossa, as well as the ability to see around anatomical "corners" that normally would obscure gross and microscopic observation. Therefore, through a limited transglabellar keyhole craniotomy, the floor of the anterior cranial fossa, the paranasal sinuses, the anterior clinoids, and the suprasellar region can all be surgically accessed without the need for wide scalp flaps, large frontal craniotomies, or extensive craniofacial approaches.

2. Indications

The fully endoscopic transglabellar approach provides minimally invasive access for surgical resection of midline tumors such as craniopharyngiomas, cystic lesions such as Rathke's cleft and arachnoid cysts, dermoids and epidermoids, aneurysms of the anterior circle of Willis, chiasmatic and hypothalamic gliomas, tumors of the pituitary stalk such as hamartomas and germinomas, olfactory groove and suprasellar meningiomas, intracranial extensions of paranasal sinus neoplasms, suprasellar extensions of pituitary tumors, and other tumors of the anterior skull base and suprasellar region.

3. Instrumentation

The instruments needed to successfully execute this procedure include an endoscopic tower containing a 3-chip high-definition digital camera, a xenon or halogen light source, 0- and 30-degree rigid endoscopes, two endoscope holding arms, endoscope irrigation sheaths, and precision microinstruments.

4. Operating Room Setup (Figure 1)

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 airway circuit is extended with corrugated tubing and the head is turned 180 degrees away from the anesthesiologist. The endoscopic tower is placed above the patient's head. Two separate pneumatically-powered holding arms are affixed to the table, one on each side of the patient, and wrapped in sterile drapes. One holding arm is dedicated to holding the endoscope and the other is used to hold other endoscopic instruments or soft silicone spatulas.

5. Patient Positioning (Figure 2)

The patient is placed supine on the operating room table and the head of the bed is raised 45 degrees to facilitate venous drainage and a subfrontal trajectory. The patient's neck is then slightly flexed and rotated ipsilaterally approximately 15 degrees to face the surgeon. The patient's head is fixed in position using a three-pin Mayfield clamp. Thus positioned-and with mild hyperventilation, cerebrospinal fluid (CSF) drainage, and intravenous mannitol-the frontal lobes will eventually "relax," enhancing a subfrontal path along which the endoscope is advanced.

6. Operative Technique

Once the patient is under general anesthesia, a color marker is used to define the landmarks of the skin incision and the frontal and nasal areas are cleansed with an aqueous antiseptic solution and then draped. A 3 cm incision is made between the medial ends of the eyebrows, crossing the nasion in a natural skin crease. The skin flap is developed in a subcutaneous plane and retracted superiorly. The glabellar periosteum is elevated separately and retracted inferiorly for further use as an inferiorly-based pericranial flap in reconstructing the skull base (Figures 3 (A), (B), and (C)). A small burr hole is placed in the frontal bone and the outer table of the frontal sinus is osteotomized. Once the sinus cavity is exposed, its mucosa is stripped and both nasofrontal ducts are obliterated. A burr hole is then placed in the posterior wall of the sinus and a second bone flap is removed, revealing the underlying dura. The craniotomy can be extended laterally over the orbital roofs as dictated by the pathological anatomy (Figures 4 (A) - (D)). A curved dural incision is then made and reflected superiorly; the falx cerebri is divided at its anterior attachment to the crista galli of the ethmoid bone; and CSF is liberally drained to relax the frontal lobes (Figures 5 (A) and (B)). The endoscope is then slowly advanced posteriorly between both olfactory tracts to the level of the pathology. A preliminary endoscopic survey can then be conducted to reveal the degree of intracranial tumor spread. A combination of a custom designed bipolar electrocautery system, microCUSA, and dissecting instruments are utilized to gradually resect the tumor.

Following tumor removal, strict hemostasis, and copious irrigation of the surgical field, the endoscope is gradually withdrawn. A second survey of the entire region is conducted using a 30-degree endoscope. The dura is then closed in a watertight fashion and the pericranial flap is sutured to its lower margin in a single layer. A collagen dural substitute membrane is then applied to the sutured dura and the entire area is covered with a dural sealant (Figures 6 (A), (B), and (C)). The nasoglabellar bone flap, constituting the outer table of the frontal sinuses, is then repositioned and secured in place by absorbable microplates and screws; a hydroxyapatite bone substitute is also applied to completely fill bone defects (Figures 7 (A) and (B)). The subcutaneous tissues and skin are closed in layers with careful attention to the aesthetic repair, and Steri-strips followed by an adhesive bandage dressing are applied to the suture line. The patient is then monitored in the intensive care unit (ICU) or a step-down unit overnight. The majority of patients undergoing this procedure are discharged home 48 hours postoperatively (Figures 8 (A) - (E)).

7. Illustrative Cases

7.1. Craniopharyngioma and Suprasellar Lesions

7.1.1. Background

Craniopharyngiomas are histologically benign, extraaxial, slow-growing tumors that are more common in children and adolescents and are thought to be derived from squamous cell nests of the hypohyseal stalk. They occur exclusively in the sellar region, starting usually at the junction of the pituitary infundibulum and gland. These tumors can be solid, cystic, or full of debris, and they often show various degrees of calcification or bone formation. Despite their histologic appearance, craniopharyngiomas may rarely behave like malignant tumors and can metastasize. Craniopharyngiomas can be completely asymptomatic or they may enlarge, causing various endocrine, visual, or psychological disorders. They may cause various degrees of hypopituitarism by compression of the adenohypohysis, pituitary stalk, or the hypothalamus, or they may cause obstructive hydrocephalus by invading the third ventricle.

Pituitary macroadenomas may also enlarge and extend upward to occupy the suprasellar cistern and compress the optic nerves and chiasm. Furthermore, they may cause elevation of the third ventricle, occupy the anterior aspect of the third ventricle, or even extend beyond the foramen of Monro. Lateral extension into the cavernous sinus or parasellar extension lateral to the carotid artery into the middle cranial fossa or projection anteriorly onto the planum sphenoidale and anterior skull base are also possible. In our practice, a large suprasellar tumor component is often approached via an endoscopic transglabellar approach.

Suprasellar cystic lesions are another diverse group of entities, which are often indistinguishable on the basis of clinical and radiographic findings. A diagnosis can often be made only by gross and histologic examination. They include cystic craniopharyngiomas, Rathke's cleft cysts, arachnoid cysts, dermoid and epidermoid cysts, and others. The cysts may be completely asymptomatic; alternatively, they can enlarge, causing compression of the pituitary gland, pituitary stalk, optic chiasm, or hypothalamus, producing symptoms that include headaches, visual impairment, and endocrine disorders. In many cases (e.g., Rathke's cysts), the cysts are most commonly treated with transsphenoidal surgery, in which the cyst is partially excised and drained; less commonly, they may be approached through a formal craniotomy. In many cases, simple cyst aspiration is not recommended as the cysts may readily recur. For cysts with a significant suprasellar component, complete cyst removal is achieved by an endoscopic transcranial approach, which can be either transglabellar or supraorbital. The endoscopic endonasal approach is preferred for cysts confined to the sella turcica or with a small suprasellar component

7.1.2. Approach

Following the induction of general anesthesia and after positioning, prepping, draping, initial exposure, and adequate CSF drainage in the previously described manner, the endoscope is advanced posteriorly along the base of the skull between both olfactory tracts toward the optic nerves and chiasm.

For craniopharyngiomas, or other suprasellar tumors or tumor extensions such as in large pituitary macroadenomas extending into the suprasellar cistern, the endoscope is advanced all the way to the suprasellar area and the optic nerves and chiasm are identified. The tumor occupying the suprasellar cistern and typically elevating the optic chiasm is noticed. A small biopsy is then obtained for intraoperative frozen section confirmation of the pathology. Following that and under direct endoscopic visualization and using a combination of the microCUSA, bipolar diathermy, and custom-designed endoscopic instruments, the tumor is gradually debulked. The portion of the tumor adherent to the optic nerves and chiasm is only sharply dissected with straight and angled microscissors. After the tumor is removed a Teflon sponge is left in the suprasellar cistern as a marker of the extent of suprasellar resection; this is beneficial in the rare cases of massive tumors, for which a combination of an endoscopic endonasal with either an endoscopic transglabellar, supraorbital, or subtemporal approach has been planned.

The same essential principles apply for the resection of cystic suprasellar lesions; upon advancing the endoscope to the suprasellar region, the thin-walled cyst and the optic nerves and chiasm are visualized. The cyst is incised and its fluid content is slowly drained; a biopsy of the cyst wall is sent for immediate intraoperative pathology. Following that, the cyst wall is dissected free from the surrounding brain tissue. The part of the cyst adherent to the optic apparatus is dealt with last with sharp dissection from the optic nerves and chiasm.

At the end of the operation, the 0-degree endoscope is slowly withdrawn from the operative field and a second survey using an angled 30- or 70-degree endoscope is performed. Any remaining tumor or residual cyst wall is identified and resected. The entire area is then copiously irrigated and hemostasis is secured. The dura, bone flap, and skin incision are then repaired in layers as described previously.

7.1.3. Cases

7.1.3.1. Craniopharyngioma with a large cystic component: Figures 9 (A) - (T)

7.1.3.2. Craniopharyngioma: Figures 10 (A) - (I)

7.1.3.2. Suprasellar Meningioma: Figures 11 (A) - (Y)

8. Potential Complications

Potential complications of the fully endoscopic transglabellar approach include the following:
  • Bleeding (intracerebral/extradural/subdural), wound infection, meningitis, cerebrovascular accident, CSF leak, and death (These are also potential complications associated with open approaches with more extensive dissection.)..
  • Different approaches have varying degrees of risk for endocrinological morbidity, vascular complications, neuropsychological and behavioral disorders, neurocognitive disorders, and learning disabilities.
  • Direct injury can occur to olfactory nerve(s) (anosmia), optic apparatus (visual deficits), cranial nerves, carotid artery or its branches, or pituitary gland or stalk
  • Postoperative severe headache, lethargy, confusion, or slow mentation may occur due to tension pneumocephalus
  • Frontal lobe edema, contusion, or direct injury
  • Meningocele, encephalocele

9. Avoiding Complications in Author's Experience

The most common complications of an endoscopic transglabellar approach result from the consequences of suboptimal reconstruction of the bone flap with inadequate separation of the cranial cavity from the frontal sinuses and nasal cavity. This may potentially lead to CSF rhinorrhea, ascending infection, meningitis, osteomyelitis, and pneumocephalus. Therefore, reconstruction of the skull base should be carried out carefully to avoid these complications. The dura should always be closed in a watertight fashion and any dural defects or meningeal tears (which may later cause a meningocele or encephalocele) should be sealed with a pericranial graft. The frontal sinus is cranialized to eliminate the dead space and the nasofrontal ducts are bilaterally obliterated. A dural allograft should be used to further ensure a watertight seal if this is felt to be necessary by the surgeon and the pericranial flap is interposed between the dura and the paranasal sinuses to reconstruct the base of the skull; no suction drains are used. The nasoglabellar bone flap must be carefully created during craniotomy so that it can easily "fit in" when repositioned at the end of the operation; it is secured in place with absorbable microplates and screws.

Unexpected postoperative visual deterioration is the result of injury to the optic apparatus or its blood supply; ischemia or traction injury to the hypothalamus may lead to diabetes insipidus (DI) and other metabolic and endocrine problems. Frontal lobe edema, hematoma, or direct injury typically results from overenthusiastic brain retraction, which is virtually never used in the described approach. In our experience, minimizing trauma to the brain and careful attention to wound closure with adequate separation of the intracranial cavity from the frontonasal sinus are surgical strategies that have dramatically reduced the incidence of complications. Careful attention to even minor details during the operation can often prevent the most severe complications. As stated above, patients typically have an average hospital stay of 48 hours, cosmetic results are excellent, and the skin incision is inconspicuous.

Craniopharyngiomas of the suprasellar region with adhesions to the optic chiasm can occasionally be removed endonasally, but this may cause unnecessary traction on the optic nerves as well as an increased incidence of postoperative CSF leak. They are better approached under direct endoscopic visualization thorough the endoscopic transglabellar approach. This minimally invasive approach is ideal for most craniopharyngiomas since they invariably extend to the suprasellar area and also invariably have adhesions to the optic chiasm.

The resection of large suprasellar extensions of pituitary macroadenomas that have a "narrow-waist" at the diaphragma sellae from an endonasal approach is not recommended as this imposes traction or even injury to the optic nerves, and it is accompanied by an increased incidence of postoperative CSF leak. It is recommended that these kinds of tumors undergo a two-stage surgical approach for complete tumor resection that involves a combination of an endoscopic endonasal resection of the intrasellar tumor and either an endoscopic transglabellar, supraorbital, or subtemporal approach. This can be done simultaneously or can be staged as two separate procedures.

Legends

Figure 1: Operating Room Setup
Figure 2: Patient Positioning
Figures 3 (A), (B), and (C): Marking, Draping and Skin Incision
  • Lower Case Figure 3 (C): a. Pericranium Reflected Inferiorly
Figures 4 (A) - (D): Burr hole and Keyhole Craniotomy Lower Case Figure 4 (A): a. Outer Table of Frontal Sinus b. Burr Hole Lower Case Figure 4 (C): a. Inner Table of Frontal Sinus b. Burr Holes Lower Case Figure 4 (D): a. Keyhole Bone Flap Figures 5 (A) and (B): Dural Opening Lower Case Figure 5 (B): a. Superiorly Reflected Dura b. Anterior Attachment of Falx Cerebri Figures 6 (A), (B), and (C): Dural Closure Lower Case Figure 6 (B): a. Collagen Dural Substitute (Only Graft) Lower Case Figure 6 (C): a. Dural Sealant Figures 7 (A) and (B): Cranioplasty Lower Case Figure 7 (A): a. Absorbable Microplates and Screws Lower Case Figure 7 (B): a. Hydroxyapatite Bone Substitute Figures 8 (A) - (E): Skin Closure and Dressing Figures 9: (A) Saggital contrasted T1-weighted MRI showing a craniopharyngioma with a large cystic component (B) Coronal contrasted T1-weighted MRI showing a craniopharyngioma with a large cystic component (C) and (D) Intraoperative endoscopic view showing the initial exposure of a craniopharyngioma Lower Case Figure 9 (C): a. Craniopharyngioma b. Elevated Optic Chiasm c. Right Optic Nerve (II) d. Left Optic Nerve (II) e. Planum Sphenoidale f. Lower Aspect of Right Frontal Lobe g. Lower Aspect of Left Frontal Lobe (E) and (F) Intraoperative endoscopic view showing the gradual evacuation of the cystic component of a craniopharyngioma Lower Case Figure 9 (E): a. Craniopharyngioma fluid (G) - (O) Intraoperative endoscopic view showing the gradual resection of a craniopharyngioma using a combination of blunt and sharp dissection Lower Case Figure 9 (H): a. Craniopharyngioma b. MicroCUSA Tip Lower Case Figure 9 (J): a. Craniopharyngioma Adherent to Optic Chiasm b. Sharp Dissection using a Left Curved Micro Scissors Lower Case Figure 9 (K): a. Craniopharyngioma b. Pituitary Stalk Lower Case Figure 9 (L): a. Craniopharyngioma Being Sharply Dissected from Optic Chiasm Lower Case Figure 9 (M): a. Posterior Capsule of Craniopharyngioma Lower Case Figure 9 (N): a. Posterior Capsule of Craniopharyngioma Adherent to Optic Chiasm b. Sharp Dissection using a right Curved Scissors Lower Case Figure 9 (O): a. Final Portion of Craniopharyngioma Adherent to Optic Chiasm b. Pituitary Stalk (P) - (R) Intraoperative endoscopic view following complete tumor removal and gradual withdrawal of the endoscope Lower Case Figure 9 (P): a. Pituitary Stalk b. Optic Chiasm c. Right Optic Nerve (II) d. Left Optic Nerve (II) Lower Case Figure 9 (R): a. Craniopharyngioma Cavity after Complete Resection b. Optic Chiasm c. Right Optic Nerve (II) d. Left Optic Nerve (II) e. Planum Sphenoidale f. Medial Aspect of Right Frontal Lobe g. Medial Aspect of Left Frontal Lobe h. Right Olfactory Bulb (I) i. Left Olfactory Bulb (I) (S) Postoperative T1-weighted, contrast-enhanced sagittal MRI (T) Postoperative T1-weighted, contrast-enhanced coronal MRI Figures 10: (A) Saggital contrasted T1-weighted MRI showing a craniopharyngioma (B) and (D) Intraoperative endoscopic view showing the initial exposure for a craniopharyngioma Lower Case Figure 10 (B): a. Right Olfactory Bulb (I) b. Left Olfactory Bulb (I) c. Medial Aspect of Right Frontal Lobe d. Planum Sphenoidale Lower Case Figure 10 (C): a. Craniopharyngioma b. Elevated Optic Chiasm (E) and (F) Intraoperative endoscopic view showing the resection of a craniopharyngioma using a combination of blunt and sharp dissection Lower Case Figure 10 (E): a. Craniopharyngioma Partly Decompressed Lower Case Figure 10 (F): a. Craniopharyngioma Adherent to Optic Chiasm b. Sharp Dissection using straight Mircroscissors (G) and (H) Intraoperative endoscopic view following complete tumor removal Lower Case Figure 10 (G): a. Craniopharyngioma Cavity after Complete Tumor Resection Lower Case Figure 10 (H): a. Teflon b. Gelfoam c. Optic Chiasm d. Right Optic Nerve (II) e. Left Optic Nerve (II) f. Planum Sphenoidale g. Medial Aspect of Right Frontal Lobe h. Medial Aspect of Left Frontal Lobe (I) Postoperative T1-weighted, contrast-enhanced saggital MRI Lower Case Figure 10 (I): a. Teflon Figures 11: (A) Saggital contrasted T1-weighted MRI showing a suprasellar meningioma (B) Coronal contrasted T1-weighted MRI showing a suprasellar meningioma (C) Intraoperative endoscopic view showing the initial exposure of a suprasellar meningioma Lower Case Figure 11 (C): a. Meningioma b. Left optic nerve (II) c. Planum Sphenoidale d. Right Lesser Wing of Sphenoid e. Left Lesser Wing of Sphenoid f. Lower Aspect of Frontal Lobes g. Right Olfactory Nerve (I) (D) - (T) Intraoperative endoscopic view showing the resection of a suprasellar meningioma Lower Case Figure 11 (L): a. Right Optic Nerve (II) b. Anterior Communicating Artery Lower Case Figure 11 (M): a. Left Internal Carotid Artery Lower Case Figure 11 (O): a. Meningioma b. MicroCUSA c. Left Internal Carotid Artery (U) - (W) Intraoperative endoscopic view following complete tumor removal and gradual withdrawal of the endoscope Lower Case Figure 11 (V): a. Right Optic Nerve (II) b. Left Optic Nerve (II) c. Optic Chiasm d. Tumor Cavity following Complete Resection Lower Case Figure 11 (W): a. Meningioma Cavity Following Complete Tumor Resection b. Right optic nerve (II) c. Left optic nerve (II) d. Planum Sphenoidale e. Right Lesser Wing of Sphenoid f. Left Lesser Wing of Sphenoid g. Right Anterior Clinoid Process h. Left Anterior Clinoid Process i. Left Internal Carotid Artery j. Lower Aspect of Frontal Lobes (X) Postoperative T1-weighted, contrast-enhanced saggital MRI (Y) Postoperative T1-weighted, contrast-enhanced coronal MRI


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