Delayed cyst formation after stereotactic radiosurgery for brain arteriovenous malformations

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Stereotactic radiosurgery (SRS) is a commonly employed treatment modality for brain arteriovenous malformations (AVMs). However, due to the low frequency of delayed cyst formation after AVM SRS, as well as the prolonged time interval between treatment and its occurrence, the characteristics of post-SRS cyst formation are not well defined. Therefore, the aims of this retrospective cohort study are to determine the rate of cyst formation after SRS for AVMs, identify predictive factors, and evaluate the clinical sequelae of post-SRS cysts.


The authors analyzed an SRS database for AVM patients who underwent SRS at the University of Virginia and identified those who developed post-SRS cysts. Statistical analyses were performed to determine predictors of post-SRS cyst formation and the effect of cyst formation on new or worsening seizures after SRS.


The study cohort comprised 1159 AVM patients treated with SRS; cyst formation occurred in 17 patients (post-SRS cyst rate of 1.5%). Compared with patients who did not develop post-SRS cysts, those with cyst formation were treated with a greater number of radiosurgical isocenters (mean 3.8 vs 2.8, p = 0.047), had a longer follow-up (mean 132 vs 71 months, p < 0.001), were more likely to develop radiological radiation-induced changes (RIC) (64.7% vs 36.1%, p = 0.021), and had a longer duration of RIC (57 vs 21 months, p < 0.001). A higher number of isocenters (p = 0.014), radiological RIC (p = 0.002), and longer follow-up (p = 0.034) were found to be independent predictors of post-SRS cyst formation in the multivariate analysis. There was a trend toward a significant association between cyst formation and new or worsening seizures in univariate analysis (p = 0.054).


Patients with greater nidal complexity appear to be more prone to post-SRS cyst formation. The findings of this study emphasize the importance of long-term follow-up for patients who have undergone AVM SRS, even after nidal obliteration is achieved. Post-SRS cysts may be epileptogenic, although seizure outcomes after AVM SRS are multifactorial.

ABBREVIATIONS AVM = arteriovenous malformation; RBAS = radiosurgery-based AVM score; RIC = radiation-induced changes; SRS = stereotactic radiosurgery; VRAS = Virginia Radiosurgery AVM Scale.

Article Information

Correspondence Jason Sheehan, Department of Neurological Surgery, University of Virginia, Box 800212, Charlottesville, VA 22908. email:

INCLUDE WHEN CITING Published online December 1, 2017; DOI: 10.3171/2017.6.JNS17559.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.



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    Flow diagram showing management of post-SRS cysts. *One patient underwent initial placement of an Ommaya reservoir, which was subsequently converted to a cystoperitoneal shunt, and then eventually underwent craniotomy for resection cyst fenestration. This patient is not included in the craniotomy group in this figure. Overall, 4 patients underwent craniotomy for cyst fenestration and/or resection.

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    Case example. This 39-year-old woman with a history of seizures related to a left posterior frontal AVM subsequently underwent surgical management of a left periodontal cyst that formed following radiosurgery. The cyst was discovered 61 months following radiosurgery and exhibited progressive enlargement over serial MRI. The patient underwent stereotactic placement of the left frontal Ommaya reservoir for cyst aspiration 106 months post-SRS with subsequent reservoir removal and placement of a cystoperitoneal shunt 10 months later. Two months later, the patient underwent shunt removal and left frontotemporal craniotomy and fenestration of the cyst with awake language monitoring. A–D: Pre- and postcontrast T1-weighted MR images obtained before Ommaya reservoir placement. E–H: Pre- and postcontrast T1-weighted MR images obtained immediately following surgery. I–L: Pre- and postcontrast T1-weighted MR images obtained at last follow-up (138 months post-SRS).

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    Case example. This 33-year-old man presented with worsening headaches and blurry vision. Brain MRI at presentation (A–C) showed a left occipital AVM abutting the dura posteriorly and tentorium inferiorly. Cerebral angiography performed at the time (D–F) showed a 2.7 × 1.7 × 2.6 cm lesion fed primarily by temporoparietal and occipital branches of the left posterior cerebral artery, as well as enlarged temporal occipital and angular branches from the left middle cerebral artery and a tiny left posterior meningeal branch from the left vertebral artery. The patient underwent Gamma Knife SRS 1 month later. Approximately 3.5 years after treatment, the patient’s symptoms returned and were managed conservatively. Repeat angiography (G–I) showed no evidence of residual AVM (e.g., successful outcome from SRS procedure). Approximately 5 years after Gamma Knife radiosurgery, MRI (J–L) revealed a new hemorrhage into the cystic cavity, measuring 7 × 4 × 4 cm with associated edema, herniation, and 5 mm of midline shift. The patient subsequently underwent left occipital craniotomy for resection of a vascular radiation-induced malformation and drainage of the associated cyst. He ultimately recovered well with improved edema and mass effect on brain CT (M–O) 1 month after surgery. A–C: Axial T2-weighted (A), T1-weighted precontrast (B), and T1-weighted postcontrast (C) MR images obtained at presentation. D–F: Left internal carotid artery (ICA) injection lateral view (D and E) and left vertebral artery (VA) injection anteroposterior (AP) view (F) cerebral angiograms obtained at presentation. G–I: Left ICA injection lateral view (G and H) and left VA injection AP view (I) cerebral angiograms obtained approximately 3.5 years after treatment. J–L: Axial (J), coronal (K), and sagittal (L) T2-weighted MR images. M–O: Axial (M), coronal (N), and sagittal (O) CT images obtained 1 month after surgery without administration of a contrast agent.

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    Radiation-induced vascular malformation of the left occipital lobe with clinically associated post-SRS cyst in a 38-year-old man (same case as in Fig. 3, approximately 5 years after presentation). A: Section of the resected malformation showing tortuous and disorganized vascular channels of varying diameter and wall thickness, including arterialization of dilated venous structures, with some of the vessels containing fibrin thrombus. There is intervening entrapped gliotic brain parenchyma containing reactive astrocytes, hemosiderin deposition, and hemosiderin-laden macrophages. B: Section of the resected malformation showing vascular structures with thickened vessel walls and hyalinization of vessel walls with degenerative features. H & E, original magnification ×40 (A) and ×100 (B). Figure is available in color online only.



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