Retrolabyrinthine Transsigmoid and Extreme Lateral Infrajugular Transcondylar-Transtubercular Exposures for Aneurysms

The retrolabyrinthine transsigmoid (RLT) and extreme lateral infrajugular transcondylar-transtubercular exposure (ELITE) are indicated for select aneurysms of the basilar artery—anterior inferior cerebellar artery (AICA) junction, lower basilar trunk, vertebrobasilar junction, the distal vertebral artery, and proximal posterior inferior cerebellar artery (PICA) ( ▶ Fig. 16.1). Aneurysms more distal on the AICA and PICA typically do not require the anterior exposure afforded by these approaches. Additionally, the geometry, orientation, and size of the aneurysm must be considered when planning the surgical approach. These approaches can be particularly useful for aneurysms that project posteriorly into the basilar sulcus because of the more anterior line of approach that can be achieved.

Fig. 16.1 The exposures for both the ELITE and RLT approaches.

The laterality of approach is governed by the geometry of the aneurysm, the anatomical orientation of its neck, the relative sizes of the sigmoid sinuses when using the RLT, the collateral venous outflow pattern, and the presence of an internal jugular vein on the ipsilateral side as assessed by preoperative venous phase angiography or computed tomography venography. Most vertebrobasilar junction aneurysms and basilar artery trunk aneurysms point either ventrally or dorsally, and can be approached on the side of the smaller sigmoid sinus. If the origin of the neck is strongly lateralized to one side or the basilar artery is deviated to one side, the approach should be made ipsilateral to that side. For aneurysms directed superiorly or inferiorly, the approach is made on the side of the smaller sigmoid sinus.

Application of these approaches should be limited to those lesions that reside anterior to the brainstem. Lateralized lesions can typically be approached using retrosigmoid or far lateral exposures that reduce the risk to neurovascular structures. These approaches are also recommended only in conjunction with endovascular therapies or in case no effective endovascular therapy is available.

16.3 Contraindications

The RLT approach is not recommended for patients with a diminutive or absent contralateral sigmoid sinus. The ELITE is relatively contraindicated when there is instability at the craniocervical junction because bony removal of the condyle could further exacerbate instability.

16.4 Preoperative Planning

When planning to ligate the sigmoid sinus for the RLT approach, consideration can be given to preoperative testing. Temporary occlusion of the sinus with measurement of the venous sinus pressure proximal to the occlusion can be used. A rise in sinus pressure of less than 5 cm H₂O likely conveys a reasonable margin of safety for sinus ligature. ² This measurement can also be made intraoperatively. However, in the senior author’s experience, the most important factor is the presence of a satisfactory contralateral sigmoid sinus on imaging. It is no longer our practice to perform preoperative or intraoperative venous pressure measurements.

Careful review of preoperative imaging, in particular the bony anatomy of the occipital condyle and the jugular tubercle, can assist the surgeon in effective and safe performance of the ELITE approach. Measurements of the tubercle as well as relationships to the hypoglossal canal and jugular bulb can help facilitate aneurysm exposure while minimizing the required bony removal.

When managing aneurysmal subarachnoid hemorrhage, routine cerebrospinal fluid (CSF) diversion is planned for both the RLT and ELITE procedures. Elective cases are considered individually for possible CSF diversion based on the location of the lesion and the cisternal space available for dissection. A ventriculostomy is often placed for those patients who experience aneurysmal subarachnoid hemorrhage, while a lumbar drain is typically chosen for patients being treated electively. CSF diversion is used to limit the need for retraction and may be continued postoperatively to facilitate wound healing.

16.5 Operative Procedures

16.5.1 Retrolabyrinthine Transsigmoid

Patients are positioned either supine with the head angled 45 degrees away from the side of entry or in a park bench position. It is our preference to position supine when the procedure is contralateral to the handedness of the surgeon and in park bench when the procedure is ipsilateral to the handedness of the surgeon. Pin headrest fixation is not required; however, it is our practice to use a Mayfield skull clamp in almost all cases. This helps ensure a stable surgical field and supports self-retaining retractors. Facial nerve electromyography, brainstem auditory evoked responses, and motor and sensory evoked responses are monitored routinely.

A curvilinear retroauricular scalp incision is made approximately 3 cm behind the ear crease, extending from the asterion or just above the nuchal line to just below the rim of the foramen magnum ( ▶ Fig. 16.2). The skin and subcutaneous tissue are elevated in a separate layer from the muscle and fascia. Additionally, the fascial incision is offset slightly from the skin incision. This facilitates a multilayer closure with offset suture lines to help prevent postoperative CSF leaks. The musculocutaneous flap is then reflected anterolaterally with fishhooks to expose the posterior lip of the external auditory meatus and the spine of Henle. A modified mastoidectomy with retrolabyrinthine exposure is performed using a cutting or diamond burr on a high-speed drill. The posterior semicircular canal is skeletonized and the posterior fossa dura, anterior to the sigmoid sinus (Trautmann’s triangle), is exposed. The sigmoid sinus, from its junction with the superior petrosal sinus to its junction with the jugular bulb, is egg-shelled and the posterior fossa dura for approximately 3 to 4 cm behind the sigmoid sinus is exposed. The limits of the mastoidectomy include the floor of the middle fossa and superior petrosal sinus superiorly, the jugular bulb inferiorly, the posterior semicircular canal anteriorly, and the retrosigmoid dura posteriorly. If there is preexisting hearing loss on the side of the approach, this enables removal of the labyrinth in order to widen the exposure toward the clivus.

Fig. 16.2 The location of the RLT incision as well as the extent of the craniotomy in relationship to the sigmoid sinus.

The retrosigmoid dura is then opened sharply and reflected up against the posterior margin of the sigmoid sinus ( ▶ Fig. 16.3). It has been our practice to sacrifice the sigmoid sinus if preoperative imaging showed a patent and comparable contralateral sinus. When doubt exists about the size of the contralateral transverse and sigmoid sinus, then a temporary occlusion of the ipsilateral sigmoid can be performed and a small-gauge needle can be used to measure the change in pressure in the ipsilateral transverse sinus. If the sinus pressure rises less than 5 cm H₂O, sinus ligation is reasonably safe. In the case of an elevation in pressure greater than 5 cm H₂O, the presigmoid dura can be opened and surgical corridors are available retro- and presigmoid. Alternatively, the superior petrosal sinus can be divided and the craniotomy can be extended slightly superiorly to create a transpetrosal exposure.

Fig. 16.3 (a) Intraoperative photo showing exposure prior to ligation and division of the sigmoid sinus. (b) RLT exposure in the case of a ruptured basilar trunk aneurysm. Extensive subarachnoid hemorrhage is appreciated over the cerebellar hemisphere.

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