Lateral Transcranial Approaches
Lateral approaches to craniopharyngiomas include the transpetrosal approach and the subtemporal approach.[1,2,27,38] The transpetrosal (posterior petrosal) approach to retrochiasmatic craniopharyngiomas was originally advocated by Hakuba et al. and further popularized by Al-Mefty et al.[1,2] and Kunihiro et al. The transpetrosal approach offers a less commonly used, but accepted, alternative avenue to the retrochiasmatic region coming from a posterior-to-anterior and inferior-to-superior viewing projection to the inferior and posterior surfaces of the chiasm, floor of the third ventricle, and the hypothalamus. Some potential advantages include the working trajectory and access to the retrosellar and retroclival region for retroinfundibular craniopharyngiomas. This approach allows the surgeon to access the tumor behind the stalk without having to mobilize or transpose the pituitary stalk and gland (pituitary transposition) as used in the EEA. The disadvantages of this approach are prolonged temporal lobe retraction, the risk of venous infarct from potential injury to the vein of Labbé or from ligation of the superior petrosal sinus, prolonged operative time due to temporal bone drilling, and technical difficulty in performing a mastoidectomy in young children with a nonpneumatized mastoid sinus. The other major disadvantage is the narrow surgical corridors between the nerves (e.g., oculomotor nerve) and small perforating vessels (posterior communicating artery and perforators). Although division of the posterior communicating artery can be performed to widen the corridor, this maneuver can certainly carry some risk of ischemic injury. Nevertheless, this represents another potential skull base approach in the armamentarium for the surgical removal of retrochiasmatic craniopharyngiomas.
The subtemporal approach is another variation of the lateral corridor that does not require extensive petrosectomy and mastoid bone drilling and can be performed with a smaller linear or curvilinear incision and relatively smaller bony opening. Therefore, the operative time for the surgical exposure is reduced and the potential complications for CSF leakage may be lower by avoiding entrance into a pneumatized temporal bone. However, the smaller working corridor increases the need for more temporal lobe retraction and can limit the surgical freedom and angles of attack when compared with a transpetrosal approach. The lack of complete transtentorial division also eliminates the advantage of the lateral inferior-to-superior viewing trajectory to the retrochiasmatic space that is inherent to the transpetrosal approach. Due to these limitations, the potential for achieving a gross-total resection is less feasible.
Transpetrosal Approach: Technical Pearls
The patient is positioned supine with the head turned to the contralateral side approximately 60°. A lumbar drain is placed prior to surgery to facilitate intraoperative CSF drainage for temporal lobe relaxation. A large retroauricular C-shaped incision is made approximately 3 finger breadths behind the pinna, curving anteriorly to the frontal region just behind the hairline. Alternatively, a hybrid pre- and postauricular incision can be made as well. After reflection of a galeocutaneous skin flap, a temporal fascial-pericranial flap that is pedicled posteriorly at the sternocleidomastoid muscle is raised and used at the time of closure for skull base reconstruction. The degree of petrosectomy is tailored to the patient's pathology and preoperative hearing status. A retrolabyrinthine mastoidectomy is performed in patients who have intact and serviceable hearing function. If additional exposure is needed, a partial labyrinthectomy petrous apicectomy (transcrusal approach) can be performed by drilling off the superior and posterior semicircular canals with sequential sealing off of the openings of the membranous canals, which can preserve hearing in some cases.[30,55] If preoperative hearing is nonserviceable, a translabyrinthine approach can be performed, providing wider exposure to the petrous apex. If needed, an anterior petrosectomy (Kawase's approach) can also be added to the exposure, depending on the size and extent of the tumor. More recently, Kunihiro et al. have described a more limited retrolabyrinthine petrosectomy where only enough petrous bone is exposed to allow ligation and division of the superior petrosal sinus.
After the mastoidectomy and petrosectomy are performed, an L-shaped temporo-occipito-suboccipital craniotomy is performed to expose the temporal lobe dura, retrosigmoid dura, and transverse and sigmoid sinuses. It is important to expose enough bone over the retrosigmoid dura so that the sigmoid sinus can be mobilized posteriorly to open up the presigmoid surgical corridor, particularly in patients with anterior-riding sigmoid sinuses.
The presigmoid dura is opened along the anterior margin of the sigmoid sinus, and the temporal lobe dura is opened horizontally along the temporal base. The superior petrosal sinus is ligated and divided anteriorly to the drainage point of the superior petrosal vein. The tentorium is then incised toward the tentorial incisura behind the entrance of the trochlear nerve. It is critical to avoid injury to the vein(s) of Labbé and the trochlear nerve during splitting of the tentorium. The tentorium can also be excised by making another cut anteriorly at the level of the porus trigeminus.
The temporal lobe is retracted superiorly and the sigmoid sinus and cerebellum are retracted posteriorly to create the surgical corridor to the retrochiasmatic space. The oculomotor nerve, trochlear nerve, trigeminal nerve, optic tract, internal carotid artery, posterior communicating artery and associated perforating vessels, and posterior cerebral artery are identified. The tumor is exposed behind the optic chiasm, under the hypothalamus in the interpeduncular cistern. The working corridors are mainly between the oculomotor nerve and the posterior communicating artery and perforators and between the oculomotor nerve and the trochlear nerve.[38,52]
The dural defect is closed primarily and augmented with dural grafts as needed. The temporal fascial pericranial flap is rotated to cover the dural repair to prevent CSF leakage. Abdominal fat is used to fill the dead space in the mastoidectomy and petrosectomy defect. Care is taken not to overpack the fat so as to avoid mass effect on the temporal lobe. The lumbar drain is kept open at 5–10 ml per hour postoperatively for about 3–5 days to prevent postoperative CSF leakage.
Subtemporal Approach: Technical Pearls
The patient is positioned supine with the head turned with a gel roll underneath the ipsilateral shoulder. Alternatively, if the patient has limited neck mobility, he or she is placed in the lateral position. The key is to have the head positioned completely lateral so that the temporal surface is parallel to the floor. Lumbar catheter drainage should be performed intraoperatively to facilitate brain relaxation for subtemporal retraction.
We prefer a larger skin incision and craniotomy for the subtemporal approach so that there are more angles of surgical freedom in a wider working corridor. A preauricular curvilinear incision is made behind the hairline and the temporalis muscle is mobilized anteriorly. A temporal craniotomy is performed roughly 50% anterior and 50% posterior to the root of the zygoma. The floor of the middle fossa is drilled down extradurally so that there is flat trajectory along the cranial base without obstruction of line of sight. The dura is opened in a horseshoe fashion and reflected toward the temporal base.
After adequate brain relaxation is achieved with lumbar drainage, the temporal lobe is retracted to provide a subtemporal working corridor to the tentorial incisura. The trochlear nerve is identified in the ambient cistern where it enters the tentorium. Either a tentorial stitch placed posterior to the entrance of the trochlear nerve or a tentorial incision can be used to expand the deeper working corridor. The tumor is accessed between the tentorial incisura and oculomotor nerve and between the oculomotor nerve and posterior communicating artery. Care is taken to preserve the small perforators coming off the posterior communicating artery.
This approach has major disadvantages due to the need for temporal lobe retraction that provides a deep, narrow working corridor between critical arteries and nerves. In our opinion, visualization of the perforators to the optic chiasm is poor. The surgeon also has poor visualization of the critical structures on the contralateral side. Thus, the chance for safe gross-total resection is significantly reduced. In a recent series of 5 cases in which a subtemporal approach was used, gross-total resection was not achieved in any of the cases, and temporal lobe edema was seen on postoperative FLAIR images in 80% of the patients.
Neurosurg Focus. 2016;41(6):e5 © 2016 American Association of Neurological Surgeons