Extracranial arteriovenous malformations: from bedside to bench

Ethanol Embolization of Nasal Arteriovenous Malformations: A 10-Year, Single-Institution Experience

PURPOSE

To summarize a 10-year, single-institution experience with ethanol embolization of nasal arteriovenous malformations (NAVMs) in 52 patients.

PATIENTS AND METHODS

The present work was a retrospective study of 52 patients (aged between 1 and 67 years) with NAVMs who were treated with ethanol embolization between August 2009 and August 2019. The diagnosis of NAVMs was established based on clinical and imaging studies including ultrasound, computer tomography angiography, and digital subtract angiography. Embolization techniques used in the current study included transarterial, direct puncture, and a combination of both. The clinical and angiographic features, treatment methods, clinical outcomes, and complications were assessed within the mean period of 55.2 months (range, 1-119 months) after the last embolization.

RESULTS

The total number of embolization sessions (140 embolization procedures in 52 pts) included transarterial approach (1 pt), direct puncture (2 pt), and a combination of transarterial and direct puncture (49 pts). There was a positive correlation between nidus size and treatment sessions (r = 0.780, P = 0.0005) and the amount of ethanol injected (r = 0.840, P = 0.0004). Results of the current study showed that the therapeutic outcomes were complete response in two patients (3.8%) without recurrence throughout the follow-up period (range, 1-119 months; mean, 55.2 months), and partial response in 50 patients (96.2%). A total of seven patients (13.5%) experienced one or more complications, including skin necrosis in one patient (1.9%), transient hemoglobinuria in five patients (9.6%), and skin blister in five patients (9.6%).

CONCLUSION

The reported single-institution experience evidently indicated that ethanol embolotherapy has the potential to successfully devascularize NAVMs and also significantly improve symptoms and signs. Further, it was evident that the use of a combination of transarterial and direct puncture techniques has the potential to increase the rate of therapeutic response in patients with NAVMs.

Stereotactic Body Radiotherapy (SBRT) for an Extracranial Arteriovenous Malformation of the Pelvis

Extracranial arteriovenous malformations (AVMs) are rare pathological, benign conditions that are characterized by aberrantly connected arteries and veins without normal intervening capillary vasculature. Although stereotactic radiosurgery is an established, efficacious, safe treatment for intracranial AVMs, there is no known published data on the use of stereotactic body radiotherapy (SBRT) for the treatment of abdominopelvic AVMs. One patient with an extracranial AVM in the pelvis that was only partially responsive to embolization was treated with SBRT to a dose of 21 Gy, delivered in three fractions over six calendar days. At presentation, the patient was non-ambulatory due to neuropathic pain from a sciatic impingement of the AVM. The patient underwent two prior catheter-based embolization procedures that had achieved partial obliteration, but with the persistence of neuropathic pain and symptoms. After SBRT to the pelvic AVM, the patient had marked improvement in pain over 10 months and was able to ambulate again. Follow-up angiography and CT demonstrated the obliteration of previously visualized AVM. We describe the first known report of pelvic AVM successfully treated with a combination of embolization and SBRT. Three-fraction SBRT to a total dose of 21 Gy appears to be safe and effective for extracranial AVMs arising in the pelvis. This strategy may be considered for patients with pelvic AVMs that are refractory to standard interventional therapies. However, these findings should be validated in larger cohorts.

Oscillatory shear stress promotes angiogenic effects in arteriovenous malformations endothelial cells

Background

Vascular endothelial cells (ECs) are subject to continuous shear stress due to blood circulation. Mechanical stress due to high shear flow can also cause arteriovenous malformation (AVM) when ECs respond hyper-sensitively to shear flow. This study was conducted to test the hypothesis that angiogenesis could be promoted in response to mechanical stress via regulation of pro-angiogenic factors in AVM cells.

Methods

ECs were extracted from the tissue samples from six AVM patients and six normal patients. Shear stress at 7 dynes/cm2 were applied for 24 h. Before and after application of shear stress to each group, RT-PCR was performed to access the expression levels of angiopoietin2(AGP2), aquaporin1(AQP1) and TGFβR1. Immunofluorescences was also performed to evaluate the level of protein expressions.

Results

In both normal and AVM tissues, AGP2 and TGFβR1 under the shear stress showed increased expression in the ECs compared to the non-sheared samples. When AVMs and normal arterial vasculature were compared, the expression levels of both AGP2 and TGFβR1 in AVMs were higher when compared to normal arterial vasculature with or without shear stress. Immunofluorescence-based protein analysis also confirmed shear-induced AGP2 and TGFβR1 in both samples of normal and AVM patients.

Conclusions

AVMs exhibited higher sensitivity to shear stress by producing higher expressions of some marked genes and proteins that regulate the endothelial functions upon exposure to shear stress. While the physiological mechanism for AVMs remain elusive, our study shows the plausibility of physical stress imposed by the shearing flow can cause the occurrence of AVMs.

Clinical Assessment and Lesion-Specific Management of Orbital Vascular Malformations

The systematic classification of vascular disease as proposed and refined by the International Society for the Study of Vascular Anomalies (ISSVA) divides vascular pathology first into tumors and malformations. Malformations are described as simple and complex, where simple malformations contain a single vascular system and complex malformations comprised of multiple vascular systems. Arteriovenous malformations are considered in terms of inflow characteristics which are primarily responsible for the key management challenges. Management utilizing endovascular embolization and/or surgical resection is often employed; however, recurrence can occur, particularly in diffuse cases. There may be an increasing role for systemic antiangiogenic therapy in such cases. Lymphaticovenous malformations are divided into the principle components on the lymphatic and venous sides for clarity of discussion. Lymphatic malformations are described morphologically as macrocystic and microcystic, and physiologically in terms of the processes responsible for growth. In both cases, surgical options are challenging and local therapeutics intended to close large luminal spaces in the case of macrocystic and to slow biological signaling for growth in microcystic. Venous malformations are described physiologically in terms of flow and distensibility, as volume plays a critical role in the limited space of the orbital cavity. Combined embolic-surgical approaches can be effective for management. More complicated, combined lesions can be managed by dividing the lesion into principal components and treating each appropriately.