Pathogenesis of radiosurgery-induced cyst formation in patients with cerebral arteriovenous malformations

Hydrocephalus due to a Cavernoma-Like Lesion of an Obliterated Cerebral Arteriovenous Malformation Treated by Embolization and Radiosurgery

BACKGROUND

Gamma-Knife radiosurgery can be the treatment of choice for small cerebral arteriovenous malformations (AVMs) in eloquent brain areas or, in association with endovascular treatment, for large and complex AVMs. Among the possible delayed complications occurring after radiosurgery of AVMs, de novo formation of a cavernoma has only recently been described. The authors report a unique case of communicating hydrocephalus with highly proteinaceous cerebrospinal fluid due to a cavernoma-like lesion of an obliterated cerebral AVM treated by embolization and radiosurgery.

CASE DESCRIPTION

A 43-year-old female patient with a left parieto-occipital AVM (Spetzler-Martin grade III) underwent a multimodality treatment comprising several endovascular procedures and Gamma-Knife radiosurgery. At the follow-up angiograms, the AVM was completely obliterated. Twelve years later, she came back to our attention for headache and vomit with the radiological evidence of brain edema, severe hydrocephalus, and a chronic encapsulated intracerebral hematoma. At the beginning, the drainage of hydrocephalus proved ineffective to improve symptoms and edema. Therefore, the surgical resection of both the obliterated AVM and the cavernoma-like lesion-histologically confirmed-was necessary. The hydrocephalus resolved as well as the cerebral edema after 3 weeks, without necessity of a ventriculoperitoneal shunt.

CONCLUSIONS

In previous neurosurgical literature, the association of a caveroma-like lesion in an obliterated AVM and communicating hydrocephalus with highly proteinaceous cerebrospinal fluid has not yet been discussed. We believe that only the surgical resection of both the obliterated AVM and the cavernoma-like lesion can lead to complete clinical recovery of the hydrocephalus.

Delayed cyst formation after stereotactic radiosurgery for brain arteriovenous malformations

OBJECTIVE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Cyst formation after stereotactic radiosurgery for brain arteriovenous malformations: a systematic review

OBJECTIVE Cyst formation can occasionally occur after stereotactic radiosurgery (SRS) for brain arteriovenous malformations (AVMs). Given the limited data regarding post-SRS cyst formation in patients with AVM, the time course, natural history, and management of this delayed complication are poorly defined. The aim of this systematic review was to determine the incidence, time course, and optimal management of cyst formation after SRS for AVMs. METHODS A literature review was performed using PubMed to identify studies reporting cyst formation in AVM patients treated with SRS. Baseline and outcomes data, including the incidence and management of post-SRS cysts, were extracted from each study that reported follow-up duration. The mean time to cyst formation was calculated from the subset of studies that reported individual patient data. RESULTS Based on pooled data from 22 studies comprising the incidence analysis, the overall rate of post-SRS cyst formation was 3.0% (78/2619 patients). Among the 26 post-SRS cyst patients with available AVM obliteration data, nidal obliteration was achieved in 20 (76.9%). Of the 64 cyst patients with available symptomatology and management data, 21 (32.8%) were symptomatic; 21 cysts (32.8%) were treated with surgical intervention, whereas the remaining 43 (67.2%) were managed conservatively. Based on a subset of 19 studies reporting individual time-to-cyst-formation data from 63 patients, the mean latency period to post-SRS cyst formation was 78 months (6.5 years). CONCLUSIONS Cyst formation is an uncommon complication after SRS for AVMs, with a relatively long latency period. The majority of post-SRS cysts are asymptomatic and can be managed conservatively, although enlarging or symptomatic cysts may require surgical intervention. Long-term follow-up of AVM patients is crucial to the appropriate diagnosis and management of post-SRS cysts.

Surgical Approaches for Symptomatic Cerebral Cavernous Malformations of the Thalamus and Brainstem

Objective

Surgical resection of thalamic and brainstem cerebral cavernous malformations (CCMs) is associated with significant operative morbidity, but it may be outweighed, in some cases, by the neurological damage from recurrent hemorrhage in these eloquent areas. The goals of this retrospective cohort study are to describe the technical nuances of surgical approaches and determine the postoperative outcomes for CCMs of the thalamus and brainstem.

Materials and Methods

We reviewed an institutional database of patients harboring thalamic or brainstem CCMs, who underwent surgical resection from 2010 to 2014. The baseline and follow-up neuroimaging and clinical findings of each patient and the operative details of each case were evaluated.

Results

A total of eight patients, including two with thalamic and six with brainstem CCMs, were included in the study cohort. All patients had progressive neurological deterioration from recurrent CCM hemorrhage, and the median modified Rankin Scale (mRS) at presentation was 3. The median CCM maximum diameter and volume were 1.7 cm and 1.8 cm³, respectively. The thalamic CCMs were resected using the anterior transcallosal transchoroidal and supracerebellar infratentorial approaches each in one case (13%). The brainstem CCMs were resected using the retrosigmoid and suboccipital trans-cerebellomedullary fissure approaches each in three cases (38%). After a median follow-up of 11.5 months, all patients were neurologically stable or improved, with a median mRS of 2. The rate of functional independence (mRS 0-2) was 63%.

Conclusion

Microneurosurgical techniques and approaches can be safely and effectively employed for the management of thalamic and brainstem CCMs in appropriately selected patients.

Radiosurgery for the management of cerebral arteriovenous malformations

Cerebral arteriovenous malformations (AVMs) are rare, unstable vascular lesions which spontaneously rupture at a rate of approximately 2-4% annually. Stereotactic radiosurgery is a minimally invasive treatment for AVMs, with a favorable risk-to-benefit profile in most patients, with respect to obliteration, hemorrhage, and seizure control. Radiosurgery is ideally suited for small to medium-sized AVMs (diameter <3cm or volume <12cm³) located in deep or eloquent brain regions. Obliteration is ultimately achieved in 70-80% of cases and is directly associated with nidus volume and radiosurgical margin dose. Adverse radiation effects, which appear as T2-weighted hyperintensities on magnetic resonance imaging, develop in 30-40% of patients after AVM radiosurgery, are symptomatic in 10%, and fail to clinically resolve in 2-3%. The risk of AVM hemorrhage may be reduced by radiosurgery, but the hemorrhage risk persists during the latency period between treatment and obliteration. Delayed postradiosurgery cyst formation occurs in 2% of cases and may require surgical treatment. Radiosurgery abolishes or ameliorates seizure activity in the majority of patients with AVM-associated epilepsy and induces de novo seizures in 1-2% of those without preoperative seizures. Strategies for the treatment of large-volume AVMs include neoadjuvant embolization and either dose- or volume-staged radiosurgery.