Spontaneous Obliteration of Postoperative Residual Arteriovenous Malformation

Sir, Generally, arteriovenous malformations (AVMs) are thought to be congenital and static lesions. However, they may have a dynamic natural history. Though rare, an increase in the size, regression and de-novo formation have been recorded as a spectrum of changes that can occur in patients with AVMs.[1-4] We report a relatively rare event of spontaneous disappearance of a residual postoperative nidus in a patient with a large Sylvian AVM. A 30-year-old female presented with a history of multiple episodes of generalized tonic-clonic convulsions for several years for which she was on anticonvulsant drugs. She had recent onset of moderate to severe headaches, which were troublesome and disturbed her daily routine. Considering the formidable nature of the lesion and potential dangers involved with surgery a conservative observation as a mode of treatment was selected. However, the severity of headache increased over the period and became unbearable. In addition, the frequency of convulsions increased despite the anticonvulsant drugs. The surgical option was then selected. Athree-dimensionalcomputed tomography (CT) angiography was performed in addition to a digital subtraction angiography. The investigations revealed a large high-flowAVM in the right Sylvian fissure [Figure 1]. It was fed by branches of the middle cerebral artery and drained by large tortuous veins into the superior sagittal sinus. The veins were dilated and ectatic with venous aneurysms. After an adequate understanding of the AVM’s architecture, surgery was conducted. A relatively large pterional craniotomy was performed. The Sylvian fissure was opened wide and the feeding vessels were identified. The normal middle cerebral artery branches were safeguarded. Then, the feeding arteries were coagulated. Following which, the nidus was sequentially dissected from the surrounding brain parenchyma. The high-flow nature, size, and AVM’s complex architecture made it a formidable surgery. During surgery, the impression was that a total resection of the AVM was achieved. Postoperatively the patient was well and had no neurological deficits. She was relieved of her headaches. As per the departmental protocol, a post-operative CT angiography performed a few days after the surgery showed a significantly large residual AVM [Figure 2].The residual nidus showed a single arterial feeder from the middle cerebral artery with predominant drainage into the superior sagittal sinus by a large draining vein. There was another small vein seen draining into the vein of Galen. Considering the patient had improvement in her headaches and was asymptomatic, it was decided to observe the AVM with sequential follow-up. Initially, the patient regularly followed up and had no complaints. She then went on with her daily activities and did not follow-up. After 5 years of surgery, she came for a follow-up assessment. A repeat CT angiography at this time showed complete obliteration of the AVM [Figure 3].Figure 1: Preoperative images (a): MRI showing the large Sylvian fissure AVM (b): Sagittal view of CT angiography shows the large Sylvian fissure’s vascular malformation (c): Coronal view of the CT angiography showing the AVM (d): 3-D CT scan showing the large and formidable AVMFigure 2: Postoperative images (a): Sagittal view of postoperative CT angiography showing the residual AVM (b): Coronal view showing the residual AVMFigure 3: CT angiography after 5 years of surgery (a): Delayed postoperative CT scan showing postoperative changes. There is no evidence of vascular malformation (b):Delayed postoperative CT angiography showing no evidence of AVMAVMs are complex vascular malformations. The consensus is that these lesions are related to embryonic dysgenesis of cranial blood vessels and form early in the embryonic development. A number of issues related to pathogenesis, cause of symptoms, risks for bleeding, and the selection of the treatment form are still under intense clinical evaluation. Although most AVMs are best known for their lifetime static size and configuration, they have rarely been identified to regress, grow, obliterate, and recur.[1-4] Spontaneous obliteration of arteriovenous fistulae is far more frequent than the obliteration of AVMs.[5] Spontaneous regression in size and obliteration of AVM has been recorded. From the literature survey, it appears that the incidence of spontaneous obliteration is less than 1% of the total number of AVMs.[1,6-8] Apart from six cases of their own, Abdulrauf identified additional 24 cases from the literature.[1] The exact mechanism of obliteration of AVM can only be speculated. Obliteration of cryptic or small-sized AVMs is more common than the obliteration of a large-sized AVM. Obliteration of AVMs having a single feeding artery and/or a single draining vein is generally considered more likely when compared with those having multiple feeding arteries and veins. Intracerebral bleeding and cerebral edema, which is related to the mass effect of the clot, leading to pressure obliteration of feeding or draining vessels, are speculated to be important mechanisms of spontaneous occlusion.[9-11] The premature atherosclerosis of the AVM vessels and intranidal vascular thrombosis because of high turbulence of vascular flow are important speculations.[12] A vessel wall injury related to excessive and high blood flow has also been identified to be a cause of intranidal thrombosis. The hypercoagulable clinical state could be another possible cause. Other possible mechanism include clot embolization from feeding vessels, causing hemodynamic changes within the vessel.[13-15] Repeated microhemorrhages within the nidus causing clot organization and gliosis have also been proposed as a possible mechanism.[1] A single draining vein has been proposed to be a common finding in patients with spontaneous obliteration of AVMs. It was noted in 86% of cases in the literature and in all the cases reported by Abdulrauf et al. that occlusion of a single vein leads to total venous outflow obstruction and stasis that leads to thrombosis and occlusion of the nidus.[1] Spontaneous obliteration of postoperative residual nidus has also been recorded in two cases of a series of 700 surgically treated cases.[1] The residual nidus in our case was of significantly large size. It seemed that the residual nidus had multiple feeding arteries and a single large draining vein. It was impossible to pinpoint the exact lesional or hemodynamic factor that could be responsible for occlusion of AVM. Considering the rarity of cases, it is not possible to advocate a policy as regards for timing of reoperation in cases where AVM has been partially resected. Despite the rarity, angiography just prior to surgery appears to be necessary, as spontaneous obliteration may be a surprising discovery. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.