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Migration of vascular embolisation material from the intravascular space to surrounding interstitial tissues in arteriovenous malformations
  1. Rohini J Patel1,
  2. Bard C Cosman2,
  3. Erik L Owens3 and
  4. Mahmoud B Malas1
  1. 1Vascular Surgery, University of California San Diego Health System, La Jolla, CA, USA
  2. 2General Surgery, Veterans Affairs San Diego Healthcare System, La Jolla, CA, USA
  3. 3Vascular Surgery, Veterans Affairs San Diego Healthcare System, La Jolla, CA, USA
  1. Correspondence to Dr Rohini J Patel; rjpatel{at}


We present the case of a young man active duty in the military who initially presented with pelvic pain and fullness during sexual activity. Extensive workup showed a large pelvic arteriovenous malformation (AVM). He underwent over 10 interventional radiology procedures to embolise his AVM and suffered multiple postoperative complications resulting in exploratory laparotomies, bowel resections and ultimately a colostomy. Six years after his embolisation procedures, he was found on imaging to have gluteal fluid collections with metallic particles, presumed to be migrated Onyx from his angioembolisations as a result of non-target embolisation. Current literature does not document other instances of Onyx material migrating from an intravascular source to interstitial tissue.

  • Vascular surgery
  • General surgery
  • Radiology
  • Interventional radiology

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Arteriovenous malformations (AVMs) are considered rare disorders and in men are even more unusual and most commonly congenital.1 As of 20 years ago, there were only 17 cases of congenital AVMs in men reported and most describe vague pelvic fullness and urinary symptoms as initial presenting complaints.1 The treatment for pelvic AVMs is based on flow characteristics with sclerotherapy, embolisation and surgical excision as mainstay therapies.2 This case report serves as an example of a potential unusual risk following angioembolisation of a pelvic AVM.

Case presentation

This is a healthy man in his 20s, non-smoker, active individual running 10 miles at a time with no significant family history who started to experience vague pelvic discomfort and back pain during sexual intercourse 10 years ago, which he self-treated with hot water baths. While active duty, he continued to endorse pelvic fullness and worsening pain and began to experience difficulty voiding. He underwent a full workup and was found to have a large high-flow pelvic AVM. Eight years ago, he underwent approximately 12 interventional radiology embolisation procedures with the Medtronic Onyx Liquid Embolic System, which is a radiopaque injectable embolic material (figure 1).3

Figure 1

Kidney-ureter-bladder X-ray depicting the Onyx in the arteriovenous malformation.

He suffered multiple complications in the past 8 years including ischaemic colitis and required an emergent bowel resection and loop ileostomy. He subsequently had his ileostomy reversed, however, was unable to tolerate bowel continuity due to a distal rectal stricture and was treated at a tertiary medical centre, where he had a colostomy. This was then complicated by a small bowel obstruction requiring an extensive lysis of adhesions 4 years ago. On imaging 1 year later, he was found to have a left pelvic AVM with large varix draining into the iliac vein and a dominant arterial feeding branch originating from the aorta with innumerable foci of embolic material (figure 2). Three years ago, he underwent a colonoscopy due to pain and bleeding from his rectum, but there was no evidence of infiltration by the AVM. He then underwent an angiogram with interventional radiology, where he was found to have dense embolic material in his pelvis, diminutive left internal iliac artery, hypertrophied left lumbar artery and collaterals from the right internal iliac artery feeding the AVM and no large draining vein (figure 3). Given his persistent rectal pain and bleeding, he underwent an open rectosigmoidectomy with near total proctectomy, and pathology was consistent with active proctitis and colitis. He tolerated the operation and was doing well for approximately 1 year until he represented to the Emergency Department with gluteal pain 2 years ago.

Figure 2

MRI showing persistent arteriovenous malformation.

Figure 3

Interventional radiology angiography demonstrating arteriovenous malformation (AVM). (A) Light greyed out region represents previously treated AVM. (B) Persistent arteries likely feeding and supplying the AVM.


Considering his symptoms of gluteal pain and discomfort he underwent imaging which showed a gluteal fluid collection involving what was thought to be arterially migrated Onyx embolisation metallic particles. He underwent surgical incision and drainage of the fluid collection with removal of Onyx material due to non-target embolisation, and the wound was primarily closed. However, over the course of the next few months he continued to have drainage from two punctate lesions on his left gluteus (figure 4).

Figure 4

Onyx material expressed from sinus tracts.

Differential diagnosis

There was clear evidence that he was draining Onyx material from his fistulous tracts through the subcutaneous tissues of his buttocks as a result of non-target embolisation. Imaging was able to confirm deep tracts with an unknown connection to his rectum, and full operative exploration was able to fully delineate the anatomy.


Given his slow healing, he underwent additional imaging which did not reveal a residual fluid collection. He was seen in clinic 1 year ago, where he was found to have two chronically draining sinus tracts on his left gluteal buttocks, approximately 6 cm tracking anterior and 11 cm deep secondary to foreign material from his previous embolisation. He underwent a tractogram which showed a fistulous connection between the two tracts and Onyx particulate matter that could be expressed from the wound tracts (figure 5). He was taken to the operating room, where his sinus tracts were laid open approximately 30 cm over an area of 75 cm2 without an obvious deep or intrapelvic source and no evidence of foreign material (figure 6).

Figure 5

Sinus tracts on left buttock tracking to pelvis.

Figure 6

Sinus tracts laid open in operating room.

Outcome and follow-up

The patient has since been seen in clinic, most recently 6 months ago, and at that time was noted to be doing well with substantially decreased pain and previous 20 cm wound down to a 1 cm short well-controlled tract. He continues to have some Onyx material draining from the remaining tract and endorses bloody drainage from his rectum; however, on fluoroscopic images, there is no fistulous connection to the rectum. At this time, he will continue with non-operative management and follow-up in clinic in 3 months.


Migrated Onyx material in the subcutaneous tissue has not been previously described in the literature. Current literature regarding improper Onyx material position is focused on intravascular migration. A case series discussed five patients with dural arteriovenous fistulas who were found to have Onyx migration to both the heart and draining veins.4 Similarly, a case report of an individual following treatment of a bleeding intracranial AVM demonstrated that migrated Onyx material could be successfully retrieved from distal embolisation targets with mechanical retrieval.5 An animal model was created to assess spinal cord ischaemia in pigs that underwent Onyx embolisation of lumbar arteries, which found four cases of paraplegia secondary to Onyx material migration to the anterior spinal artery.6 While the manufacturer does acknowledge the potential risk of Onyx material migration, this is primarily attributed to short-term catheter-related complications and not a long-term risk.7 Overall, the literature supports the notion that complications related to Onyx material migration do exist; however, translocation outside of vessel walls to the subcutaneous tissue and long-term complications have yet to be reported in the literature, aside from our case report.

Non-target embolisation or the embolisation of a vessel that is not the intended target is a complication of endovascular procedures. We believe the efflux of Onyx material seen in this case is likely to be a result of complications related to non-target embolisation. However, there are many ways to reduce the risk of non-target embolisation. This includes reflux-control microcatheters, well-differentiated anatomy, slow infusion of the material or balloon occlusion of particular vessels.8 9

Our patient’s overall management could have been altered by regularly scheduled interval imaging. Current guidelines leave the decision to the provider and most follow with an immediate CT scan in the first 6 months and yearly for several years. We recommend continued surveillance annually of treated AVMs with either CT or MRI to help identify early complications. Additionally, we urge primary care providers who see these patients long term to order imaging for complaints of pelvic symptoms and referral to vascular surgery or interventional radiology for further recommendations.

Learning points

  • Complications from embolisation procedures can manifest years after the initial procedure.

  • Have a high index of suspicion for generalised symptoms and pursue with imaging modalities.

  • A soft-tissue infection secondary to foreign material should be drained widely, and consideration should be given to leave the wound open.

  • Interval imaging can be considered in a case-by-case situation.

Ethics statements

Patient consent for publication



  • Contributors Patient was under direct care of BCC and ELO who oversaw patient care and decision making. RJP and MBM wrote report. Supervised by MBM.

  • Funding Rohini J. Patel is supported through a grant with the National Library of Medicine: T15 Postdoctoral Training Grant Fellowship Program in Biomedical Informatics.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.