Fractionated stereotactic radiotherapy in the treatment of vestibular schwannoma (acoustic neuroma): predicting the risk of hydrocephalus.
OBJECTIVE
To determine the incidence and predictive factors for the development of hydrocephalus in patients with acoustic neuromas (AN) treated with fractionated stereotactic radiotherapy.


METHODS
Seventy-two patients with AN were treated with fractionated stereotactic radiotherapy between 1998 and 2007 (45-50 Gy in 25-30 fractions over 5 to 6 weeks). The pretreatment MRI scan was assessed for tumor characteristics and anatomic distortion independently of subsequent outcome and correlated with the risk of hydrocephalus.


RESULTS
At a median follow-up of 49 months (range, 1-120 months), 5-year event-free survival was 95%. Eight patients (11%) developed hydrocephalus within 19 months of radiotherapy, which was successfully treated. On univariate analysis, pretreatment factors predictive of hydrocephalus were maximum diameter (p = 0.005), proximity to midline (p = 0.009), displacement of the fourth ventricle (p = 0.02), partial effacement of the fourth ventricle (p < 0.001), contact with the medulla (p = 0.005), and more brainstem structures (p = 0.004). On multivariate analysis, after adjusting for fourth ventricular effacement, no other variables remained independently associated with hydrocephalus formation.


CONCLUSIONS
Fractionated stereotactic radiotherapy results in excellent tumor control of AN, albeit with a risk of developing hydrocephalus. Patients at high risk, identified as those with larger tumors with partial effacement of the fourth ventricle before treatment, should be monitored more closely during follow-up. It would also be preferable to offer treatment to patients with progressive AN while the risk of hydrocephalus is low, before the development of marked distortion of fourth ventricle before tumor diameter significantly exceeds 2 cm.
Powell
Ceri
C
Neuro-oncology Unit, Royal Marsden NHS Foundation Trust, London, United Kingdom.
Micallef
Caroline
C
Gonsalves
Adam
A
Wharram
Bev
B
Ashley
Sue
S
Brada
Michael
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001933:Brain Stem; D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D020546:Fourth Ventricle / Q000473:pathology; D006801:Humans; D006849:Hydrocephalus / Q000209:etiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008526:Medulla Oblongata; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000473:pathology / Q000601:surgery*; D016634:Radiosurgery / Q000009:adverse effects* / Q000379:methods; D011879:Radiotherapy Dosage; D047368:Tumor Burden; D055815:Young Adult