**9.2 Meningioma close to optical apparatus and skull base vital structures**

Management of meningioma at anterior skull base close or adhered to optical apparatus is always challenging in radiosurgery considerations (**Figure 5**).

#### **Figure 5.**

*Treatment of anterior cranial fossa meningioma near bilateral optic nerves using LINAC 27.5 Gy in 5 fractions in our centre.*

Tumor control has to be balanced by risk of high-dose radiation exposure leading to optic neuritis and radiation-induced neuropathy. As mentioned, vision preservation can be achieved by confounding the maximum radiation exposure of optic pathway to 8–10 Gy per session. Su et al. in Taiwan treated 4 patients with large tumor volume by volume-staged Gamma Knife Radiosurgery. In stage I, the treatment was focused on the basal part of tumor (mean volume 13.2 cm3 , range 3.9–54.7 cm3 ) with marginal dose of 13.5 Gy (range 12–15 Gy), followed by smaller upper portion of tumor close to the optical apparatus (mean volume 4.3, range 1.5–16.2 cm3 ) with marginal dose of 9 Gy (range 9–10 Gy) in stage II. 34–46% tumor reduction was observed during the median follow-up period of 100.5 months with no new visual deterioration [35]. A study from Williams et al. on parasellar meningiomas treatment with Gamm Knife Radiosurgery had reviewed the tumor control together with any radiation induced neurological deficit. Totally 138 patients were reviewed from 1989 to 2006. The mean radiation volume was 7.5 cm3 (range 0.2–54.8 cm3 ). Radiographic progression free suvivial at 5 and 10 years were 95.4% and 69%. Only 4% of their patients had radiation related optic neuropathy [36].

Starke et al. had also similar promising findings in Gamma Knife Radiosurgery treatment for other skull base meningiomas. Around 10% of their cases had deterioration in neurological symptoms [37]. His group in another review specifically focus on posterior fossa cases in 152 patients. The radiographic progression free survival at 3, 5, and 10 years to b 98%, 96%, and 78% respectively. 9% of study patients showed deterioration in symptom. They concluded the predicative factors of new or worsening symptoms were clival or petrous-based location [38]. In Austria, Kreil et al. had a review of 200 patients with skull base meningimas with a follow up of 5–12 years. The tumor volume ranged from 0.38 to 89.8 cm3 (median 6.5 cm3 ), and the median dose was 12 Gy (7–25 Gy). They achieved actuarial progression free survival rate of 98.5% at 5 years and 97.2% at 10 years with only 1% radiation induced oedema and 4.5% neurological deterioration [39]. The promising tumor control with low new neurological deficit in Gamma Knife Radiosurgery can also be demonstrated in centres using LINAC system. Villavicencio et al. in Brigham and Women's Hospital had reviewed 56 patients with treatment for skull base meningiomas. The minimal peripheral dose ranged from 12 to 18.5 Gy (mean 15 Gy). The actuarial progression free rate was 95% in median follow-up of 26 months (range 6–66 months) [40].

In cases where skull base meningiomas had extension into the internal auditory meatus, the concern will be more towards the facial nerve function and hearing preservation after radiation. Pollock et al. had reviewed 16 patients from 1992 to 2002. The median tumor margin dose was 15 Gy. They achieved 63% tumor reduction in size at medial follow-up period of 36 months. No facial nerve palsy was reported, and 1 patient had worsened facial sensation. The actuarial incidences of hearing preservation was 93% at 1 year, 84% at 2 years and 42% at 5 years [41].

#### **9.3 Cavernous sinus meningioma**

Meningiomas at cavernous sinus are cases always have dilemma with clinical management due to its complex anatomy and its specific location in the antero-lateral skull base (**Figure 6**). Despite the advancement in microscopic and endoscopic surgical technique, still a complete radical excision with minimal anantomo-functional preservation remains very challenging. UCLA De Salles group had proposed a radiosurgery grading system for this specific group of tumor (**Table 5**) [42]. Pittsburgh group reviewed 79 patients with cavernous sinus meningioma between October 1987 and December 1995. The median marginal tumor dose was 15 Gy. The achieved actuarial tumor control rate was 95+/−2.8% at 5 years an 88.2+/−7% at 12 years with 12.7% patients experienced adverse radiation effects [43].

#### **Figure 6.**

*Meningioma involving cavernous sinus and petrosal apex was treated by LINAC stereotactic radiotherapy using 25 Gy in 5 fractions in our centre.*


#### **Table 5.**

*Radiosurgery grading system for cavernous sinus meningiomas by UCLA.*

Takanashi had reviewed 101 skull base meningioma patients with Gamma Knife Radiosurgery performed from 1991 to 2003. Among those cases, 38 cases are cavernous sinus in location with mean dose delivered to the tumor 14.5 to 15.2 Gy. The overall tumor control rate were 95.5% in the mean follow-up of 51.9 months (range 6–144 months) [44]. Fariselli et al. had proposed a multidisciplinary treatment algorithm involving microsurgery and stereotactic radiosurgery [45]:


### **9.4 Large tumor volume**

The consensus of tumor size in consideration of radiosurgery for meningioma is generally around 30–35 mm in diameter. Tumor volume greater than

#### *Overview of Radiosurgery for Intracranial Meningiomas DOI: http://dx.doi.org/10.5772/intechopen.100006*

8 cm3 is believed to have poor outcome compared. Starke et al. retrospectively reviewed the Gamma Knife Radiosurgery outcome of 75 patients with mean follow-up of 6.5 years (range 0.5–21 years) whom had tumor volume more than 8 cm3 . The actuarial rates of progression-free survival were 90.3% at 3 years, 88.6% at 5 years and 77.2% at 10 years. Factors associated with tumor progression included [46]:

