Posterior fossa meningioma

Posterior cranial fossa meningiomas constitute ~10 % ^{1) 2)} of all the intracranial meningiomas. ^{3) 4) 5) 6) 7) 8)}.

Thus posterior fossa meningiomas constitute only about 2% of intracranial tumors. Nevertheless, they deserve particular attention as they are adjacent to or involve very critical structures, and there are potentially serious consequences related to their surgical excision.

Posterior fossa meningioma classification.

Petroclival and foramen magnum meningiomas are among the most difficult cranial base lesions to treat. Because of their slow growth, they often have caused considerable distortion of the brain stem at presentation, have involved CNs III-XII in various ways, and have encased the vertebrobasilar arteries in about 25% of patients. Before the modern era of cranial base surgery, the surgical treatment of these lesions was unsuccessful; indeed, the results were so poor that the tumors were considered inoperable.

Only one successful total removal was reported before 1970.

More recently, the advent of new cranial base approaches and specific microsurgical strategies has revolutionized the management of these lesions. A comparison of recently reported series indicates a progressive decline in mortality and an increase in the percentage of gross total resection ^{9) 10) 11) 12) 13) 14) 15) 16)}.

Possible postoperative complications include intracranial hematoma, Cerebrospinal fluid fistula or infection, obtundation or hemiparesis due to brain stem dysfunction, and CN palsies. The most significant CN palsies are those involving CNs III, VII, IX and X. A good intensive care and neurosurgical ward, team work, and post-hospital rehabilitation (if necessary) will promote an optimal outcome for these patients.

This study is a retrospective analysis of a prospectively maintained IRB-approved database. Inclusion criteria were a diagnosis of WHO grade I PFM with subsequent treatment via single-session SRS and a minimum of 3 follow-up MRI studies available. Volumetric analysis was performed on the radiosurgical scan and each subsequently available follow-up scan by using slice-by-slice area calculations of the meningioma and numerical integration with the trapezoid rule. RESULTS The final cohort consisted of 120 patients, 76.6% (92) of whom were female, with a median age of 61 years (12-88 years). Stereotactic radiosurgery was the primary treatment for 65% (78) of the patients, whereas 28.3% (34) had 1 resection before SRS treatment and 6.7% (8) had 2 or more resections before SRS. One patient had prior radiotherapy. Tumor characteristics included a median volume of 4.0 cm3 (0.4-40.9 cm3) at treatment with a median margin dose of 15 Gy (8-20 Gy). The median clinical and imaging follow-ups were 79.5 (15-224) and 72 (6-213) months, respectively. For patients treated with a margin dose ≥ 16 Gy, actuarial progression-free survival rates during the period 2-10 years post-SRS were 100%. In patients treated with a margin dose of 13-15 Gy, the actuarial progression-free survival rates at 2, 4, 6, 8, and 10 years were 97.5%, 97.5%, 93.4%, 93.4%, and 93.4%, respectively. Those who were treated with ≤ 12 Gy had actuarial progression-free survival rates of 95.8%, 82.9%, 73.2%, 56.9%, and 56.9% at 2, 4, 6, 8, and 10 years, respectively. The overall tumor control rate was 89.2% (107 patients). Post-SRS improvement in neurological symptoms occurred in 23.3% (28 patients), whereas symptoms were stable in 70.8% (85 patients) and worsened in 5.8% (7 patients). Volumetric analysis demonstrated that a change in tumor volume at 3 years after SRS reliably predicted a volumetric change and tumor control at 5 years (R2 = 0.756) with a p < 0.001 and at 10 years (R2 = 0.421) with a p = 0.001. The authors also noted that the 1- to 5-year tumor response is predictive of the 5- to 10-year tumor response (R2 = 0.636, p < 0.001). CONCLUSIONS Stereotactic radiosurgery, as an either upfront or adjuvant treatment, is a durable therapeutic option for WHO grade I PFMs, with high tumor control and a low incidence of post-SRS neurological deficits compared with those obtained using alternate treatment modalities. Lesion volumetric response at the short-term follow-up of 3 years is predictive of the long-term response at 5 and 10 years ¹⁷⁾.