The Role of Transsphenoidal Surgery in the Management of Complex Lesions Involving the Skull Base




Introduction


Since the repopularization of the transsphenoidal approach by Guiot and Hardy, most surgeons have adopted this technique as the primary method for the removal of pituitary adenomas. Following the development of modern microinstrumentation and the use of the operating microscope, the transnasal transsphenoidal approach has become the preferred method for approaching lesions of the sellar and parasellar region. The transsphenoidal approach and its various modifications (the extended and parasellar transsphenoidal approaches) are also versatile approaches in the armamentarium of the cranial base surgeon to remove complex lesions of the skull base. Lesions of the skull base, particularly the anterior skull base, the clivus, and the cavernous sinus and parasphenoid region, can be readily accessed when the exposure of the standard transsphenoidal approach is extended with additional bone removal or combined with other transfacial approaches. Transsphenoidal approaches can be used alone or in combination with other skull base approaches depending on the extent and location of the lesion. The procedure can be performed microsurgically, endoscopically, or both. Knowledge of the anatomical limitations and the indications for using variations on the transsphenoidal approach is important when choosing the appropriate approach. The transsphenoidal approach provides a minimally invasive technique that avoids a craniotomy and prolonged brain retraction. In this chapter, we discuss the applications of the transsphenoidal approach and its variations in the management of complex skull base lesions.




Anatomical Limitations of Variations on the Transsphenoidal Approach


The transsphenoidal approach and its modifications are suitable for midline lesions that occupy locations from the cribriform plate down to the craniocervical junction ( Figure 14-1 ). Excellent visualization of the anterior skull base, suprasellar cistern, clivus, and cavernous sinuses can be achieved. The anterior communicating artery complex and the optic apparatus can also be visualized superiorly. It is critical to recognize the anatomical limits of the extended transsphenoidal approach when selecting the appropriate skull base approach for a given lesion. The anatomical limits are primarily defined anterosuperiorly by the posterior cribriform region, superiorly by the suprasellar cistern and optic apparatus, laterally by the cavernous sinus and carotid arteries, and inferiorly by the inferior clivus and foramen magnum. The inferior limit can vary with each individual patient and can be determined radiographically on a sagittal MRI by drawing an imaginary line from the hard palate toward the clivus (see Figure 14-1 ). This relationship of the hard palate to the clivus determines the extent of inferior visualization, which is based on the maximal inferior mobilization of the nasal retractor. In some patients, the craniocervical junction can be visualized. The extended transsphenoidal approach is best suited for accessing midline structures but is limited for removing tumors that extend laterally into the maxillary sinuses or superolaterally in the intracranial cavity. If the lateral extent of the lesion exceeds that of the transsphenoidal approach, the transmaxillary route can be used to supplement lateral exposure. Visualization beyond the limits of standard microsurgical visualization can be enhanced with adjunctive use of the endoscope, especially in the suprasellar direction or laterally into the cavernous sinus.




Figure 14-1


Diagram illustrating the zones of exposure of the extended transsphenoidal approach (green shading). Note that the horizontal plane of the hard palate determines the limit at which the nasal retractor can be placed inferiorly, and thus determines the inferior extent of exposure.

(Adapted with permission from Liu JK, Decker D, Schaefer SD, et al: Zones of approach for craniofacial resection: minimizing facial incisions for resection of anterior cranial base and paranasal sinus tumors. Neurosurgery 2003; 53:1126-1137.)




Surgical Indications for Variations of the Transsphenoidal Approach


The transsphenoidal approach and its variations can be used for a variety of skull base lesions. The location and extent of the lesion will determine the most appropriate skull base approach. The standard transsphenoidal approach is favorable for midline lesions arising from the pituitary fossa that may extend into the suprasellar region, into the clivus, or into the sphenoid sinus and nasal cavity. The exposure of the transsphenoidal approach can be extended by removing additional bone at the anterior skull base or laterally and inferiorly to access lesions of the parasellar and clival region, respectively.


Lesions of the anterior skull base can be accessed by removing bone from the planum sphenoidale and tuberculum sellae. We have used this approach for removing small midline tuberculum sellae/planum sphenoidale meningiomas that range from 2 to 3 cm in size ( Figure 14-2 ). This approach offers the advantage of early devascularization of the tumor at its base and removal of the tumor beneath the chiasm and optic nerves with no manipulation of the neural structures.




Figure 14-2


A, Preoperative sagittal MRI demonstrating a tuberculum sellae meningioma in a 36-year-old woman, which was completely resected using an extended transsphenoidal approach. B, Postoperative CT scan.

(Adapted with permission from Couldwell WT, Weiss MH, Rabb C, et al: Variations on the standard transsphenoidal approach to the sellar region, with emphasis on the extended approaches and parasellar approaches: surgical experience in 105 cases. Neurosurgery 2004; 55:539-547.)


Craniopharyngiomas that occupy both sellar and suprasellar regions are favorable for transsphenoidal resection, especially if the sella is enlarged ( Figure 14-3 ) . However, if the tumor is purely suprasellar with a normal-sized sella, extended variations such as the transsellar/transdiaphragmatic approach or the transsphenoidal/transtuberculum approach can sometimes be used. In these cases, the additional bony exposure provides improved visualization of the suprasellar portions of the tumor and reduces the amount of blind curettage in this region. Cystic tumors are particularly amenable to drainage and removal by this approach. Excellent results of craniopharyngiomas resected via the transsphenoidal route or an extended variation have been reported by Laws et al, Maira et al, and Couldwell et al. The transsphenoidal approach may not be suitable for cases that have significant lateral extension. In these cases, a frontotemporal or a combined approach may be necessary. We prefer to use a transbasal or frontotemporal pterional approach if the tumor is located entirely suprasellar. We often use an orbitozygomatic approach for craniopharyngiomas that extend superiorly into the third ventricle.




Figure 14-3


Preoperative sagittal ( A ) and coronal ( B ) MRI showing a suprasellar craniopharyngioma. This lesion was removed using an extended transsphenoidal approach with bony removal of the tuberculum sellae. C and D, Postoperative MRI shows complete resection of the tumor.

(Adapted with permission from Couldwell WT, Weiss MH, Rabb C, et al: Variations on the standard transsphenoidal approach to the sellar region, with emphasis on the extended approaches and parasellar approaches: surgical experience in 105 cases. Neurosurgery 2004; 55:539-547.)


Tumors of the clivus, such as chordomas or chondrosarcomas, are readily accessible with extended transsphenoidal approaches because these lesions are primarily extradural and are located in the midline ( Figure 14-4 ). Any extensions into the sphenoid sinus and nasal cavity are easily removed with the transsphenoidal approach. As mentioned previously, the lateral limitations of the approach are the cavernous carotid arteries; larger lesions with significant lateral extension may require combined approaches. Clivus chordomas with a significant lateral component may require a lateral skull base approach (petrosal, transtemporal, far lateral) for their removal, and those with extension below the inferior clivus level are approached via a transoral route.




Figure 14-4


Preoperative MRI ( A and B ) demonstrating an extensive clivus chordoma in a 24-year-old man who had progressive neck pain, diplopia, and nasal obstruction. The lesion was eroding the occipital condyles bilaterally, extending to C2. An initial posterior occipitocervical fusion was performed to stabilize the craniocervical junction ( C ). An extended transsphenoidal approach was used to resect the majority of the tumor. The immediate postoperative MRI ( D ) demonstrates the inferior extent of tumor removal (represented by the dashed line). There is residual tumor below the dashed line that was eventually removed with a transoral approach.

(Adapted with permission from Couldwell WT, Weiss MH, Rabb C, et al: Variations on the standard transsphenoidal approach to the sellar region, with emphasis on the extended approaches and parasellar approaches: surgical experience in 105 cases. Neurosurgery 2004; 55:539-547.)


Lateral exposure of the cavernous sinus to facilitate additional tumor removal may be achieved via the transsphenoidal exposure ( Figure 14-5 ). Additional bone over the carotid grooves can be unroofed, exposing the C3 portion of the internal carotid artery. The cavernous sinus is entered by opening the dura just medial to the carotid artery. The development of this particular technique has enabled more complete resection of adenomas, thereby reducing the need for blind curettage of the tumor, which is performed by reaching into the cavernous sinus via the sella. More recently, the indications for cavernous dissection in the setting of a pituitary tumor have been further reduced with the increased application of stereotactic radiosurgery. In cases where significant residual tumor is left in the cavernous sinus, we use this extended transsphenoidal variation to transpose the pituitary away from the tumor and interpose a fat graft between the cavernous sinus and the gland (hypophysopexy) in preparation for planned adjuvant radiosurgery for the residual tumor in the cavernous sinus. This technique reduces radiation exposure to the pituitary gland to minimize the risk of hypopituitarism. Tumors that extend laterally into the cavernous sinus may be visualized by placing an angled endoscope into the sella.




Figure 14-5


A, Preoperative MRI showing a pituitary tumor with left cavernous sinus invasion. An extended transsphenoidal resection was undertaken with parasellar cavernous sinus exposure of the carotid artery. An endoscope-assisted resection of the lesion was performed. B, Postoperative MRI at 9 months demonstrates a complete resection.

(Adapted with permission from Couldwell WT, Weiss MH, Rabb C, et al: Variations on the standard transsphenoidal approach to the sellar region, with emphasis on the extended approaches and parasellar approaches: surgical experience in 105 cases. Neurosurgery 2004; 55:539-547.)


The spectrum of tumors accessed in a large series of patients in whom variations on the transsphenoidal approach was used is presented in Table 14-1 .



Table 14-1

Location and Histological Characteristics of Lesions Resected Via Variations of the Extended Transsphenoidal Approach








































Location Histological Characteristics Cases
Anterior cranial base Tuberculum/diaphragma sellae meningioma 11
Sellar/parasellar region Pituitary adenoma with cavernous extension 30
Sellar/suprasellar craniopharyngioma 27
Sphenoid mucocele 10
Sphenoid sinus carcinoma 4
Breast adenocarcinoma 2
Clivus Chordoma 18
Monostotic fibrous dysplasia 3

(Reprinted with permission from Couldwell WT, Weiss MH, Rabb C, et al: Variations on the standard transsphenoidal approach to the sellar region, with emphasis on the extended approaches and parasellar approaches: surgical experience in 105 cases. Neurosurgery 2004; 55:539-547.)




Operative Techniques


Patient Positioning and Exposure of the Sella


The patient is placed supine on the operating table with the head elevated approximately 15 degrees on a horseshoe headrest. This positioning is preferred to rigid pin fixation, which limits intraoperative manipulation of the patient’s head to improve visualization. Further flexion allows visualization of lesions that extend inferiorly along the clivus. Extension of the head allows visualization of lesions with suprasellar extension ( Figure 14-6 ). In the standard transsphenoidal transsellar approach, the face is placed parallel to the ceiling. The sella can be exposed with either a sublabial or an endonasal approach as described elsewhere. A bivalve speculum is placed, the sphenoid sinus is exposed in the usual fashion, and all mucosa is exenterated. Specialized microinstruments, such as curved and angled alligator microscissors, a long monopolar coagulator with a malleable tip, and malleable-tip microring curettes, facilitate resection at the lateral extremes of the exposure. In addition, long, narrow bipolar forceps with up- or down-angled fine tips are used.




Figure 14-6


Access to the clivus can be achieved by flexing the patient’s head and directing the dissection inferiorly along the vomer and the roof of the hard palate. Lesions lying over the tuberculum sellae or planum sphenoidale and in the suprasellar region can be approached by extending the head and carrying the dissection anterior to the sella turcica after the rostrum of the sphenoid has been resected.

(Adapted with permission from Couldwell WT, Weiss MH: Transnasal transsphenoidal approach. In Apuzzo MLJ, editor: Surgery of the Third Ventricle, ed 2, Williams & Wilkins, Baltimore, 1998.)

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Jul 8, 2019 | Posted by in NEUROSURGERY | Comments Off on The Role of Transsphenoidal Surgery in the Management of Complex Lesions Involving the Skull Base

Full access? Get Clinical Tree

Get Clinical Tree app for offline access