Summary The goals of surgery are to control the tumor, and preserve function of the involved nerves. Preservation of hearing is an important goal for patients who present with functional hearing. Surgery cannot restore hearing already lost. During surgery, intraoperative neurophysiological monitoring of the facial, acoustic and lower cranial nerves can reduce the risk of injury. With massive tumors that compress the brainstem and cerebellum, staged surgical approaches or subtotal surgical resection followed by stereotactic radiosurgery may reduce the risks to life, brain and cranial nerves.
The retrosigmoid approach of this surgery remains a mainstay of posterior fossa surgery and represents a modification of the standard suboccipital craniotomy, which provides exposure to the lateral cerebellum and cerebellopontine angle. The patient’s head is ideally turned parallel to the floor or slightly past parallel. To facilitate adequate venous outflow, the patient is placed into a modified park bench position. The head is then secured using a Mayfield clamp. A curvilinear incision is made approximately three fingerbreadths behind the postauricular sulcus, extending into the neck inferiorly. Once the periosteum has been incised, the sternocleidomastoid muscle can be partially divided and retracted to provide inferior exposure. Following circumferential subperiosteal elevation, the craniotomy begins with a burr hole created over the asterion, which is the intersection of the lambdoid, squamosal, and occipitomastoid sutures. The transverse sinus and sigmoid sinus junction can usually be found beneath this landmark. Once the confluence of these sinuses is identified, a circular craniotomy is developed using a high speed burr that traces the posterior margin of the sigmoid sinus, inferior margin of the transverse sinus, and measures approximately 4 cm in diameter. For larger tumors the craniotomy can be enlarged to incorporate the foramen magnum. Any exposed petrous air cells are meticulously sealed with bone wax to prevent postoperative cerebrospinal fluid leak. An initial dural opening in the vicinity of the cisterna magna is made to allow for controlled egress of cerebrospinal fluid, which provides relaxation of the underlying cerebellum. A dural opening is then fashioned by raising separate superior and lateral leaflets extending all the way to the transverse and sigmoid sinuses, thereby allowing for clear visualization of the tentorium and posterior petrous temporal dura. In the case of larger tumors, a self-retaining retractor blade mounted on a Greenberg clamp can also be utilized to gently elevate the lateral cerebellum posteriorly. Further dissection of the cerebellopontine cistern superiorly will then reveal the tumor capsule and continuing arachnoid lysis toward the tentorium will then allow for optimal conditions to begin tumor dissection. Stimulation of the capsular surface and visualization for an aberrant seventh nerve is important at this stage. For smaller tumors, an initial attempt can be made to identify the root exit zone of CN VII and VIII, whereas for larger tumors, lateral debulking is performed followed by transmeatal drilling to reveal the contents of the internal auditory canal. Once tumor resection is completed, it is critical to irrigate out blood products from the intracranial space. Meticulous hemostasis must be obtained with careful attention paid to the lateral cerebellar surface. Finally, a duraplasty is performed with our preference being to utilize a synthetic dural substitute to provide a watertight dural closure. Any exposed bony air-cells are re-waxed. The craniotomy bone flap is re-plated using a low profile, titanium plating system. The procedure ends with a multilayer, watertight closure of the surgical site.
- Removal of tumors which conserve hearing. - Removal of tumors by ignoring 7th and 8th cranial nerves. (enucleation)
Approach (Indications) - Translabyrinthine Approach (Large, medium-sized, or small cerebellopontine angle tumor) - Retrosigmoid Approach *** (Cerebellopontine angle tumors without extensive internal auditory canal involvement) - Retrolabyrinthine (Biopsy of cerebellopontine angle lesions) - Transcochlear (Extensive lesions of petrous apex and clivus) - Transotic (Smae as for transcochlear) - Middle Cranial Fossa Approach (Intracanalicular tumors with minimal cerevellopontine angle involvement and good hearing) - Extended middle fossa (Petroclival lesions involving posterior and middle fossa with good hearing) - Petrosal (Large petroclival lesions with good residual hearing)
Reference - Alex D. Sweeney, Matthew L. Carlson, Moneeb Ehtesham, Reid C. Thompson, David S. HaynesEmail author, Surgical Approaches for Vestibular Schwannoma, September 2014, Vanderbilt University Medical Center, Nashville, USA