Radiosurgical techniques and clinical outcomes of gamma knife radiosurgery for brainstem arteriovenous malformations

Abstract

Objective: Brainstem arteriovenous malformation (AVM) is rare and radiosurgical management is complicated by the sensitivity of the adjacent neurological structures. Complete obliteration of the nidus is not always possible. We describe over 20 years of radiosurgical procedures for brainstem AVMs, focusing on clinical outcomes and radiosurgical techniques.

Methods: Between 1992 and 2011, the authors performed gamma knife radiosurgery (GKRS) in 464 cerebral AVMs. Twenty-nine of the 464 patients (6.3%) reviewed had brainstem AVMs. This series included sixteen males and thirteen females with a mean age of 30.7 years (range : 5-71 years). The symptoms that led to diagnoses were as follows : an altered mentality (5 patients, 17.3%), motor weakness (10 patients, 34.5%), cranial nerve symptoms (3 patients, 10.3%), headache (6 patients, 20.7%), dizziness (3 patients, 10.3%), and seizures (2 patients, 6.9%). Two patients had undergone a previous nidus resection, and three patients had undergone a previous embolization. Twenty-four patients underwent only GKRS. With respect to the nidus type and blood flow, the ratio of compact type to diffuse type and high flow to low flow were 17 : 12 and 16 : 13, respectively. In this series, 24 patients (82.8%) had a prior hemorrhage. The mean target volume was 1.7 cm(3) (range 0.1-11.3 cm(3)). The mean maximal and marginal radiation doses were 38.5 Gy (range 28.6-43.6 Gy) and 23.4 Gy (range 18-27 Gy), and the mean isodose profile was 61.3% (range 50-70%).

Results: Twenty-four patients had brainstem AVMs and were followed for more than 3 years. Obliteration of the AVMs was eventually documented in 17 patients (70.8%) over a mean follow-up period of 77.5 months (range 36-216 months). With respect to nidus type and blood flow, the obliteration rate of compact types (75%) was higher than that of diffuse types (66.7%), and the obliteration rate of low flow AVMs (76.9%) was higher than that of high flow AVMs (63.6%) (p<0.05). Two patients (6.9%) with three hemorrhagic events suffered a hemorrhage during the follow-up period. The annual bleeding rate of AVM after GKRS was 1.95% per year. No adverse radiation effects or delayed cystic formations were found.

Conclusion: GKRS has an important clinical role in treatment of brainstem AVMs, which carry excessive surgical risks. Angiographic features and radiosurgical techniques using a lower maximal dose with higher isodose profiles are important for lesion obliteration and the avoidance of complications.

Keywords: Arteriovenous malformation; Brainstem; Gamma knife radiosurgery.

Fig. 1

Radiosurgical dose planning for a pontine AVM. A : Dose planning using a 50% isodose profile. B : Dose planning using a 60% isodose profile. The hot spot (80% isodose profile) in Fig. 1B is larger than in Fig. 1A. On the other hand, the 8 Gy and 12 Gy volumes of Fig. 1B are smaller than those of Fig. 1A. AVM : arteriovenous malformation.

Fig. 2

A : A T1 weighted contrast enhanced magnetic resonance (MR) image of a 21-year-old female before her 1st radiosurgery showing midbrain bleeding. B : A stereotactic vertebral artery angiography showing a nidus. C : A CT image 10 years after the first radiosurgery showing midbrain rebleeding. D : A digital subtraction angiography (DSA) for the second radiosurgery showing a remaining nidus (missed target). E : A T2 weighted MR image 15 years after the 1st radiosurgery showing rebleeding. F : A DSA for the 3rd radiosurgery showing remaining arteriovenous shunting (black arrow).