By contrast, in all 58 cases in which complete thrombosis of gastric varices was observed on CT 1 to 2 weeks after BRTO, no recurrences developed. In all 5 recurrences, partial thrombosis of the gastric varices was noted on follow-up CT 1 or 2 weeks after BRTO. From our data, including 69 cases monitored over a period of 6 months, recurrence or regrowth of gastric varices was observed in 5 cases (7.2%) on follow-up endoscopy. Some studies with long-term follow-up have shown recurrent gastric varices in 0% to 10% of cases. Reported technical success rates for BRTO procedures have ranged from 90% to 100%, and regression or disappearance of gastric varices on endoscopy was achieved in 80% to 100% of patients after BRTO. Hiro Kiyosue, Hiromu Mori, in Image-Guided Interventions (Third Edition), 2020 Outcomes 68,69 It appears that AVMs with high blood flow and complex geometric shapes have a decreased obliteration after radiosurgery. Other papers have analyzed the blood flow characteristics and other angioarchitectural parameters of AVMs and their relationship to obliteration after radiosurgery. 67 Specifically, the authors noted that patients with a diffuse nidus structure and associated neovascularity were at a higher risk of incomplete nidus obliteration when compared to patients with compact AVMs. A study from the University of Florida suggested that AVM morphology is also an important factor associated with obliteration. 66 They concluded that AVM dose planning without angiography should be limited to patients with smaller AVMs and compact niduses. Yu and colleagues compared AVM dose plans based on a combination of angiography and MRI to those based on MRI alone. 65 They noted significant interobserver variation when outlining the nidus, and concluded that this may contribute to failure in some AVM radiosurgical cases. Buis and coworkers had six independent clinicians contour the niduses of AVM patients based on digital subtraction angiography. Nonetheless, part of the problem in AVM radiosurgery is defining the nidus accurately.
These studies have emphasized the need for complete nidus coverage at the time of radiosurgery. 61-64 Common reasons for incomplete nidus obliteration are targeting errors, recanalization of a portion of the AVM that was previously embolized, reexpansion of nidus after hemorrhage, and low radiation dose. A number of papers have analyzed factors associated with incomplete AVM obliteration after radiosurgery. 60 Analyzing patients having either Gamma Knife or LINAC-based radiosurgery, a relationship was noted between the obliteration prediction index (AVM margin dose ÷ lesion diameter ) and AVM obliteration. Schwartz and colleagues developed the obliteration prediction index as a method to predict success or failure after AVM radiosurgery. Higher average doses also shortened the latency to AVM obliteration. For the group of patients receiving an AVM margin dose of 25 Gy or more, the obliteration rate at 2 years was 80%. The obliteration rate increased linearly with the K index up to a value of approximately 27, and for higher K values, the obliteration rate had a constant value of approximately 80%. 48 Analysis of 945 AVM patients having radiosurgery from 1970 until 1990 showed a logarithmic relationship between minimum dose and AVM obliteration: the product minimum dose × (AVM volume) 1/3 was termed the K index, which increased to a maximum of 87%. Karlsson and associates reported the K index as a method to predict obliteration after AVM radiosurgery. 47,48,57-60 Several models have been developed to predict the chance of AVM cure after radiosurgery. The AVM margin dose is the most important factor associated with obliteration after radiosurgery. 56 The characteristics of the spindle cells were similar to myofibroblasts noted during wound healing, and these cells likely contributed to the occlusive process and obliteration of AVMs after radiosurgery.
55 Electron microscopic studies 10 to 52 months after radiosurgery of seven AVMs resected after bleeding revealed spindle cell proliferation in the connective tissue stroma and in the subendothelial region of irradiated vessels.
The histopathologic changes after AVM radiosurgery include damage to the endothelial cells, progressive thickening of the intimal layer secondary to proliferation of smooth muscle cells that produce an extracellular matrix containing type IV collagen, then cellular degeneration and hyaline transformation. Generally, AVM obliteration requires between 1 and 5 years after radiosurgery. The goal of AVM radiosurgery is complete nidus obliteration to eliminate a patient's risk of future hemorrhage. Richard Winn MD, in Youmans and Winn Neurological Surgery, 2017 Arteriovenous Malformation Obliteration after Radiosurgery
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