Fig. 12.1
MRI of a 52-year-old man with a visual loss and panhypopituitarism with a typical retrochiasmal craniopharyngioma. He underwent uneventful endonasal endoscopic gross total tumor resection. He is currently doing well more than 2 years after surgery with improved vision and on full pituitary hormone replacement therapy. Top row: Preoperative sagittal (a), and coronal (b, c) postgadolinium MRI scans showing large cystic tumor extending into retrochiasmal and suprasellar space. Circle in a indicates position of the optic chiasm. Bottom row: Images d–f show corresponding 1-year postoperative sagittal and coronal MRIs confirming gross total tumor resection without evidence of recurrence.
Fig. 12.2
Examples of MRIs of three patients who underwent the SO approach: (a): 6-year-old pediatric patient with small nostrils, and extensive cystic and solid craniopharyngioma with suprasellar and suprachiasmatic extension. (b) A 71-year-old woman with coexisting cavernous sinus and sellar aneurysm (asterisk) (c): A 51-year-old man who underwent prior endonasal endoscopic surgery and radiation with residual tumor and growing suprachiasmatic tumor cyst
In patients with prior surgery with or without radiation, the SO approach may offer a more favorable route for recurrent craniopharyngiomas than the endonasal approach (Fig. 12.2) [5]. In addition to providing a trajectory that potentially avoids or minimizes dissection through scar tissue, the SO approach has the advantage of a simplified skull base reconstruction with a lower risk of postoperative CSF leak in the setting of recurrent tumors. The extensive scar tissue from the prior endonasal route or a nasoseptal flap in previously irradiated patients in whom the risk of postoperative CSF leak was thought to be relatively high can weigh favorably toward use of the SO approach (Table 12.1).
Table 12.1
Advantages, disadvantages, and possible indications of the SO approach versus the endonasal route
SO approach | Endonasal | |
|---|---|---|
Advantages | Enhanced exposure of lesions lateral to ICA Simplified skull base repair with reduced postoperative CSF leak | Enhanced exposure of sella and retrochiasmal area No brain retraction Enhanced view of the superior hypophyseal arteries |
Disadvantages | Limited access to the retrochiasmal area compared to endonasal Brain retraction (rarely) | Restricted lateral access beyond ICAs and optic nerves Narrower surgical corridor More demanding skull base repair |
Possible indications | Prechiasmal and suprachiasmal craniopharyngiomas Craniopharyngiomas with prominent lateral extension beyond ICAs Prior history of transsphenoidal surgery, transcranial surgery, and/or radiotherapy in whom there is extensive scar tissue and possibly limited endonasal options for skull base repair Young pediatric patients (<5 years old) with small nostrils and poorly pneumatized paranasal sinuses Cavernous sinus/intrasellar aneurysm | Most retrochiasmal craniopharyngiomas Sellar craniopharyngiomas |
Regarding the side of approach, preoperative visual assessment and tumor location are key factors guiding the side of surgical approach. In general, if the tumor is predominantly located eccentrically to one side, approaching from that ipsilateral side is recommended. However, if the tumor is predominantly medial to an optic nerve in the prechiasmatic space, or under an optic nerve, approaching the lesion from the contralateral eyebrow may be advantageous. This contralateral trajectory may avoid scar tissue from an original craniotomy and gives better access to the inferomedial aspect of the contralateral optic nerve. If there is prior severe or complete loss of vision in one eye, the approach may be optimally performed on this side in order to preserve the remaining eye. As detailed below, the size and extent of frontal sinus pneumatization is also a consideration in choosing the best side of approach with the choice being preferably to avoid entering the frontal sinus.
From 2007, we had 33 operations for 30 patients with craniopharyngiomas. Among the 33 operations, 9 operations were performed by the SO approach for 7 patients (27 % of total operations and 23 % of total patients). The remaining 23 operations were done by endonasal endoscopic approach and 1 operation by temporal craniotomy. Among the seven patients treated by SO approach, two patients had an SO for their first and only operation, and the remaining five patients had a previous endonasal endoscopic approach or a previous craniotomy. Two patients had a repeat SO approach.
12.3 Neuroradiology
Prior to surgery, the preoperative MRI including sellar/pituitary protocol must be carefully studied to determine which approach, endonasal endoscopic, SO, or alternative approach, is most suitable. The key anatomical relationships and structures to ascertain are the locations of the optic chiasm and nerves, the infundibulum, the pituitary gland, the circle of Willis vessels, and whether the tumor reaches the hypothalamus. The location and extent of the tumor will dictate the likelihood of success with an SO approach or the potential need for a larger alternative craniotomy or endonasal route. Axial, coronal, and sagittal MRI sequences should be carefully reviewed to determine the lateral and anterior extent of the lesion. Probably the most important factor in choice of approach is the tumor location in relation to the optic chiasm and optic nerves (Figs. 12.1 and 12.2). This anatomical relationship is typically best appreciated on sagittal sellar images and T2-weighted coronal sellar images, but all sequences should be reviewed to provide the best possible three-dimensional understanding of the tumor. Although a pre-fixed optic chiasm may be a relative contraindication to the SO approach, in such cases, the SO approach still allows access through the lamina terminalis to tumor within the retrochiasmal space and third ventricle. Craniopharyngiomas with lateral extension beyond the supraclinoid carotid arteries or large anterior extensions are often best approached via the SO approach or the pterional route. Extension into the middle cranial fossa may necessitate a traditional pterional or mini-pterional craniotomy; however, in most cases, the SO route allows excellent access to the Sylvian fissure and the medial temporal lobe region.
Coronal and sagittal MRI sequences demonstrate the superior extent of the lesion, as well as involvement of the sella and sphenoid sinus. Craniopharyngiomas with significant sellar expansion are typically best approached via an endonasal endoscopic approach. Likewise, lesions with significant superior extension that extend into the third ventricle typically require the inferior-to-superior trajectory provided by the endonasal corridor; rarely such tumors can also be approached via an interhemispheric transventricular approach. Significant superior midline extension is a relative contraindication to the SO approach, as the flat trajectory along the floor of the frontal fossa may not provide access to the superior extent of the tumor.
Finally, the size and lateral extent of the frontal sinus should be considered in the approach decision. A large lateral extension of the frontal sinus may discourage one from using the SO approach, but in general this is only an issue in a minority of cases. If the planned craniotomy will likely enter the lateral edge of the sinus, then one should plan accordingly by prepping the patient for a possible abdominal fat graft or, less frequently, use of a pericranial flap to rotate over the defect.
12.4 Anatomy of the Approach
12.4.1 Anatomical Studies on SO Approach
By the SO approach, the field of view includes the ipsilateral frontal fossa, including the olfactory groove and planum, a portion of the medial contralateral frontal fossa, ipsilateral basal frontal lobe and frontal pole, the ipsilateral proximal Sylvian fissure, the medial temporal lobe, the lateral wall of cavernous sinus, the ipsilateral third nerve, the optico-carotid cistern, the suprasellar region including the optic chiasm and nerves (but only the medial and superior aspect of the contralateral optic nerve), the suprachiasmatic cistern, the perimesencephalic/interpeduncular cistern, the lamina terminalis, both supraclinoid carotid arteries, both A1 segments, the anterior communicating artery, both A2 segments, and the pituitary stalk (Fig. 12.3).
Fig. 12.3
Artistic drawing showing the extent of exposure of the SO approach: shaded areas including cribriform plate area, inferior space directly under ipsilateral optic nerve, ipsilateral medial middle fossa, and medial temporal lobe are difficult to visualize without endoscopy
Additional dissection through the optico-carotid or carotid-oculomotor windows will expose the ventral brainstem, the basilar artery and ipsilateral posterior cerebral artery, and posterior communicating arteries and perforators. When necessary, the SO approach can be used to reach as far posteriorly and inferiorly to the ventral brainstem and top third of the clivus.
Recent anatomical studies have compared the surgical exposure afforded by the keyhole SO approach to standard transcranial approaches [6, 7]. Results showed that the working space deep within the surgical field obtained with the keyhole SO approach is similar to [7] or greater than [6] that obtained by the standard pterional approach. In contrast, the angular exposure appears to be increased with the orbitozygomatic approach or pterional approach due to the more extensive bony removal obtained [7]. Indeed, the pterional and orbitozygomatic craniotomy were able to offer significantly better angles of work in both the vertical and horizontal planes [7]. Similarly, other authors have shown that removal of the orbital rim in the transorbital keyhole approach increases the inferior projection of the inferior boundary of the craniotomy [6].
However, these measurements were performed using the surgical microscope. The introduction of the rigid endoscope to the SO approach either as an adjunctive visualization technique [1, 8, 9] or as the sole imaging modality [10] appears to broaden the surgical exposure without the need for additional bony removal or brain retraction (Fig. 12.4). The panoramic and multidirectional view obtained with the endoscope appears to lessen the need for the larger external openings afforded by conventional craniotomies [8, 10] (Fig. 12.5). With the use of a 30° or 45° angled endoscope, one can also visualize into areas not well seen with the microscope, including the cribriform plate region, under the ipsilateral optic nerve, along part of the ipsilateral medial sphenoid wing, over the tuberculum sellae into the pituitary fossa, and over the dorsum sellae into the prepontine cistern.
Fig. 12.4
Intraoperative photo showing a two-surgeon team using a rigid endoscope in the SO approach for visualization; the endoscope is being “driven” by an assistant allowing two-handed surgery by the primary surgeon
Fig. 12.5
Operative views of SO approach: (a) Right SO approach with microscope. Arrow indicates the blind spot under the ipsilateral optic nerve. (b) Endoscopic view of the right SO approach. Note the contralateral ICA and the PS though the prechiasmal space. (c, d) Endoscopic view of the left SO approach through the ipsilateral optico-carotid space after subtotal removal of recurrent suprasellar craniopharyngioma. In c, blind area behind the ipsilateral optic nerve by microscope is well visualized by endoscope. In d, deeper endoscopic view is provided through optico-carotid space. Posterior circulation is well visualized. The area under the optic chiasm is also visualized. SHA superior hypophyseal artery, BA basilar artery, ICA internal carotid artery, OC optic chiasm, ON optic nerve, PCoA posterior communicating artery, PS pituitary stalk, P1 P1 segment of posterior cerebral artery, SCA superior cerebellar artery
12.5 Surgical Technique
12.5.1 Overview, Instrumentation, and Monitoring
Several authors, including our group [1, 2, 5], have previously described the technical steps of the SO approach with subtle variations [3, 4, 11–14]. For all cases of craniopharyngiomas, intraoperative neuronavigation and evoked potential monitoring are used. Image guidance is helpful in evaluating the anticipated surgical trajectory and in mapping the frontal sinus. Evoked potential monitoring is helpful for cranial nerve monitoring and to monitor for any potential vascular compromise during surgery. The Doppler probe should also be available for all cases, as many if not most craniopharyngiomas will often abut or encase at least one of the circle of Willis vessels [15]. Low-profile micro-instrumentation is essential to allow maximal maneuverability through the relatively narrow SO corridor. Most instruments should be bayoneted or pistol grip in design. Finally, 0°, 30° and 45° 4 mm rigid endoscopes should be available on all cases.
12.5.2 Positioning and Preparation
Proper positioning is necessary to optimize the reach of the SO approach. As previously described, the patient is placed in the supine position and the head fixated in a Mayfield head holder [3]. The table is placed in mild reverse Trendelenburg, and the head is elevated above the level of the heart to enhance venous drainage. The neck is slightly extended with the head above the heart level, and the head is rotated to the contralateral side between 20° and 30° depending on the location of the tumor and its pattern of extension. Head extension, with the vertex angled back toward the floor, is an important maneuver that allows gravity to work in the surgeon’s favor and obviates the need for fixed retraction in opening the subfrontal corridor through which the surgeon will operate [3].
Once the patient is positioned, neuronavigation is registered and the location of the frontal sinus relative to the eyebrow incision and the planned craniotomy is determined. In planning the eyebrow incision, the lateral aspect of the frontal sinus is marked with a surgical pen and the supraorbital notch is palpated. The incision is then marked within the eyebrow extending from just medial to the supraorbital notch and coursing laterally to the lateral termination of the eyebrow. Note that the exposure must allow access to the area immediately below the superior temporal line since that is where the burr hole will be placed.
12.5.3 Skin Incision and Craniotomy
The skin incision is made within the middle of the eyebrow, and care is taken to identify and preserve the supraorbital nerve at the medial aspect of the opening (Fig. 12.6). In patients with relatively short eyebrows, the lateral extent of the incision may need to extend up to 1 cm beyond the eyebrow in a skinfold along the frontozygomatic process. The incision extension should not extend more than 13 mm lateral to the zygomatic process in order to prevent injury to the frontalis muscle branch of the facial nerve [16]. If the eyebrow is very thin, the skin incision can be made in a crease or a previous scar of the supraorbital area [17]. In general, to maximize preservation of the supraorbital nerve, the supraorbital notch represents the medial extent of the incision. As the medial extent of the incision is taken deeper toward the pericranium, the supraorbital nerve should be anticipated and protected. In some cases, careful drilling of the nerve’s bony encasement can be performed, thus allowing the surgeon to gently mobilize it medially and away from the main operative field.
