Keyhole approach surgery for petroclival meningioma

Petroclival meningioma accounts for approximately 3%－10% of all posterior fossa meningiomas. Originating from the clivus and petrous apex, the tumor may involve the medial part of the tentorium, Meckle's cave, cavernous sinus and parasellar region. Petroclival meningioma often wedges in the brain stem, and encases cranial nerves, basilar and carotid arteries and their perforating arteries. Resection of the tumor contributes a great challenge to neurosurgeons. Despite advances in microsurgery have brought out better results, surgical injury or death remains high.^1-3 Less invasive surgery is needed in dealing with such cases. From July 2000 to July 2005, we treated 25 cases of petroclival meningioma by keyhole surgery and developed a combined retrosigmoid and subtemporal keyhole approach to resect the tumor invading the supra and infratentorial regions. The extent of resection and clinical results were satisfactory.

METHODS

Patients
From July 2000 to July 2005, 25 patients with petroclival meningioma were treated with subtemporal (6 patients), retrosigmoid (10) or combined keyhole approaches (9). Of the 25 patients, 4 were men and 21 women, aged 28－67 years (average 47.2 years). The course of the disease ranged from 1 to 244 months. Fourteen of the patients had facial numbness, 13 had headache, 6 diplopia, 5 ataxia, 4 decreased hearing, 3 hemiparesis, 2 decreased gag reflex, and 1 blurred vision with eptosis. Fifteen patients presented with cranial nerve (CN) V deficit, 6 with CN VIII deficit, 5 with CN VI, 5 lower CN, 3 CN III, 3 CN VII, and 2 CN II. Six patients showed ataxia and hemiparesis, and four patients had no deficits. Tumor size varied from 2 to 7 cm (average 4.5 cm) according to magnetic resonance imaging (MRI). The tumor extended to the upper and middle clivus in 13 patients, to entire width of the clivus in 11, and to the middle and lower clivus in 1. The tumor infiltrated into the cavernous sinus in 7 patients. All patients were followed up from 3 to 39 months by neuroradiological and neurological examinations.

Combined retrosigmoid and subtemporal keyhole approaches
The patient is placed in supine position with the ipsilateral shoulder slightly elevated. The head is anteflexed, elevated and rotated contralaterally. Retrosigmoid keyhole approach starts with a 6 cm straight skin incision behind the ipsilateral ear. Retromastoid craniotomy is carried out with a bone window 2－3 cm in diameter. Subtemporal keyhole craniotomy is performed after a 5 cm curvilinear incision is made 10 mm anterior to the ear. Tumor resection is performed initially via the retrosigmoid keyhole approach. The dura is opened towards the transverse and sigmoid sinus followed by drainage of cerebrospinal fluid (CSF) before cerebellar retraction. The tumor is located medially to the cranial nerves in the posterior fossa including V, VII, VIII, and sometimes to the lower cranial nerves. Piecemeal tumor resection is performed through the tentorium-V, V－VII, VII-lower nerves interval respectively after coagulation of the attached dura on the petrol apex and clivus. All cranial nerves are separated from the tumor. The brain stem is dissected from the tumor finally. The tumor involving the middle fossa or other supratentorial region is resected through the subtemporal keyhole approach. The dura is opened curvilinearly with its base towards the middle fossa and petrous bone. The temporal lobe can be retracted easily because CSF is drained through infratentorial tumor resection. Subsequently the tumor located in the middle fossa, parasellar region, lateral wall of the cavernous sinus, and the perimesencephalic region can be visualized. These parts of the tumor could be removed easily after the attached dura is coagulated. The cranial nerves (CN) III, IV, VI should be identified and separated if replaced or encased by the tumor. The tumor in Meckle's cave can also be lifted out after resection of the caudal part of the tumor. The tentorium involved by the tumor could be resected, then the infratentorial region could be approached and the remaining part of the tumor can be removed. The tumor invading the cavernous sinus could not be resected usually. Anterior petrosectomy can be avoided if the tumor involves the upper half of the clivus (Fig. 1).

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Fig. 1. Intraoperative pictures demonstrating surgical steps of tumor resection with combined subtemporal and retrosigmoid keyhole approaches. A: Tumor resection via the retrosigmoid approach. The superior and medial clival region after cerebellar retraction. B: Tumor resection via the cranial nerves interval. C: The tumor in the posterior fossa removed. D: The temporal lobe retracted easily because of CSF evacuated after resection of infratentorial tumor. E: Resected tentorium involved by tumor and infratentorial region. F: Totally removed tumor.

RESULTS

Gross total resection (GTR) was made in 14 patients (56%, Fig. 2). Subtotal resection (STR) was carried out in 8 patients and partial resection in 3. The tumor was confirmed pathologically after operation. No additional neurological deficits occurred in 13 patients after operation, whereas others suffered from CN palsy (VII in 8 patients, VI in 4, III in 3, lower CN in 2), One patient died from the brain stem dysfunction 13 days after operation.

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Fig. 2. Pre- (A, B) and post-operative (C, D) MRI of a large petroclival meningioma resected via combined subtemporal and retrosigmoid keyhole approaches.

Recurrent tumor was not seen in the 14 patients in the follow-up period. Postoperative MRI also showed that residual tumor was unchanged after STR. Patients who had undergone partial removal received additional stereotactic radiosurgery. Great improvement of deficit of CN III and VII, and little improvement of deficit of VI were noted.

DISCUSSION

Petroclival meningioma poses a great technical challenge to neurosurgeons because of its location in the posterior skull base, petrol apex, Meckle's cave and cavernous sinus. In close proximity to the brain stem, the encased cranial nerves and arteries of the posterior circulation make the resection of these tumors formidable.

Several approaches and their modifications have been applied to resect petroclival meningioma. Translabyrinthine, transcochlear, and total petrosal approaches have widely exposed the petroclival region, but could cause damage to VII and VIII nerves. Hence these approaches are suitable for patients with hearing loss or lesions involving the temporal bone.^4,5 Kawase et al⁶ described the anterior transpetrosal-transtentorial approach to the lower basilar artery, which was used for resection of petroclival meningioma. This approach prevented hearing loss and facial nerve damage because only the petrous apex was resected. However, the caudal part of the tumor, which extends to the posterior and inferior level of the internal auditory canal, could not be resected. The posterior transpetrosal approach provides a wide view to this region, but greater retraction of the cerebellum, sigmoid sinus and posterior temporal lobe might cause severe damage to the tissues in order to visualize these areas.^7,8

In this series of cases, combined subtemporal and retrosigmoid approaches were used in keyhole surgery, during which the tentorium might be cut to obtain a wider exposure to the upper part of the clivus. The retrosigmoid approach provides a satisfactory view to the cerebral-pontine angel region. The tumor located medially to the V, VII, VIII nerves and caudal nerves creates required space to the midline of the clivus after its lateral component is resected without retraction of the brainstem. Although small craniotomy with its sector-like view does not allow a complete overview at once, changing the direction of a microscope might help us to visualize the complete posterior fossa. The tumor is usually resected via the tentorium-V, V－VIII, VII-caudal nerves interval. The supra-meatal eminence could be drilled if it is helpful to expose the tumor adhered to the posterior wall of the cavernous sinus. Cranial nerves, branch arteries and perforating arteries of the posterior circulation and the brainstem should be separated meticulously from the tumor in the arachnoidal layer. Outrageous manipulation which might cause any injury or fatal results should be avoided.

The subtemporal approach is usually performed after the tumor in the posterior fossa is resected. CSF evacuation in resection of the posterior fossa tumor is easy and safe to retract the temporal lobe. With this approach, it is not difficult to resect parts of the tumor invading the middle fossa, parasellar region and lateral wall of the cavernous sinus. Meckle's cave also can be visualized and the tumor inside it can be lifted out easily. After the matrix tentorium of the tumor is resected, satisfactory view to the dorsum sellae, peripontine and perimesencephalic region can be obtained. In these regions, the tumor can be removed if it is left after the retrosigmoid approach resection. Additional bone removal is unnecessary since ideal exposure could be achieved and the tumor itself is accessible during the resection. Thus, hearing loss and facial nerve palsy can be reduced, and CSF leakage can be avoided. In this series, subtemporal keyhole approach was used when the tumor was located supratentorially and its caudal part did not reach the region lower than the internal auditory meatus. The retrosigmoid approach was suitable for patients with part of the tumor located infratentorially and did not extend to the parasellar region and middle fossa. If the tumor could not be reached through one of the two single approaches, combined retrosigmoid and sub- temporal keyhole approaches should be carried out.

The major complication of the combined keyhole approach is cranial nerve dysfunction. Postoperative neurological deterioration is due to the onset of new cranial nerve deficits or the aggravation of pre-existing deficits. Cautious dissection in the arachnoid plane is necessary to avoid this kind of injury. The IV nerve is likely encased by the tumor and injured during tumor resection or tentorium cutting. Stupor and coma usually happen in patients with poor clinical and neurological conditions and need constant and meticulous assistance. CSF leakage and sinus thrombosis can be prevented because of avoidance of petrosectomy and sinus ligation.

If radical tumor removal is not feasible owing to its invasive nature, little room is left for complete removal, severe indentation of the brain stem and encasement of the arterial and cranial nerves, or tumor invading into the cavernous sinus.⁹ Reduction of operative injury should be considered. A number of subtotally removed petroclival meningioma remains stationary for a long period, and radiosurgery can control eventual regrowth.^10-12

REFERENCES

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