Immediate and delayed migration of Onyx embolisation into the renal collecting system
- 1 Department of Urology, The School of Medicine and Health Sciences, The George Washington University, Washington, DC, USA
- 2 Department of Radiology, The School of Medicine and Health Sciences, The George Washington University, Washington, DC, USA
- 3 Department of Interventional Radiology, The School of Medicine and Health Sciences, The George Washington University, Washington, DC, USA
- Correspondence to Dr Sarah Azari; saraheazari@gmail.com
Abstract
We present a case of Onyx embolisation of a renal pseudoaneurysm following partial nephrectomy with collecting system involvement with subsequent migration of Onyx into the renal collecting system resulting in renal obstruction. This occurred both immediately after embolisation and again 8 years after embolisation. Both cases required ureteroscopic surgical intervention. In the first instance, the pieces were removed using basket extraction. In the second, laser lithotripsy was used in addition to basket extraction. While there are a few cases of embolisation coils eroding into the renal collecting system, this is the second reported case of Onyx migration and the first where ureteroscopy with laser lithotripsy was used. The patient is doing well and undergoing surveillance ultrasounds to ensure there is no further Onyx migration. This may be a consideration for patients with pseudoaneurysm embolisation especially in the setting of prior collecting system damage.
Background
Pseudoaneurysm of the renal artery occurs when an arterial injury forms a contained yet unstable vascular injury. This can occur following renal trauma, or iatrogenically following surgery, and percutaneous procedures. It can present with flank pain, haematuria or anaemia. The first line of treatment for renal pseudoaneurysm is generally endovascular embolisation.1
There are a variety of embolic materials to choose from for embolisation. These include metal coils, particulate and liquid embolic agents. Metal coils are generally used to occlude larger arteries while liquids and particulates can be used for smaller arteries. Examples of liquid embolics include Onyx (Medtronic, Minneapolis, Minnesota, USA) and glue. Examples of particulates include gelfoam, polyvinyl alcohol particles and embospheres.2
Selective embolisation of renal pseudoaneurysm is considered a successful, safe procedure.3 Potential complications include renal artery dissection, postembolisation syndrome (self-limited flank pain, nausea and vomiting), diminished renal function, groin haematoma and migration of embolisation material.3–5 There are a few examples of embolisation coils eroding into the collecting system and only one reported case of this occurring with Onyx.6–13 We present a case of recurrent Onyx migration into the renal collecting system requiring ureteroscopic removal.
Case presentation
The patient is a man in his 60s with metastatic clear cell renal carcinoma. About 10 years ago, he underwent a left partial nephrectomy for what was at the time an endophytic clinical T1bN0M0 isolated renal mass requiring significant repair of the collecting system following tumour excision.
Approximately 1 week after his operation, he presented to the emergency room with significant gross haematuria. CT angiogram identified a pseudoaneurysm at the surgical bed. Interventional radiology was consulted. The pseudoaneurysm and parent branch of the left renal artery were embolised using Onyx. The patient’s haematuria resolved within 24 hours postembolisation.
He was persistently tachycardic and, 3 days later, was found to have a pulmonary embolism. The CT also showed a urine leak from the left kidney. A left ureteral catheter and Foley catheter were placed. Interventional radiology placed a percutaneous drain into the urinoma, the ureteral catheter was removed, and he was discharged home with the drain.
His drain was capped in clinic several days after discharge. He subsequently developed flank pain. The drain was placed to drainage with high output. The CT demonstrated a small urine leak and a metallic-appearing foreign body in the left ureter with similar imaging characteristics to the Onyx liquid embolic (figure 1). The foreign body measured 3070 Hounsfield units (HU).
First CT scan demonstrating Onyx in the left ureter.
The next day, he was taken to the operating room for ureteroscopy. The object in the ureter was extracted in two pieces using a basket. Pathology reported two fragments of black material consistent with Onyx measuring 1.2 × 0.4 × 0.2 cm and 0.4 × 0.2 × 0.2 cm. His drain was gradually backed out and removed a week later. After his ureteroscopy, he had regular CT scans of the abdomen as part of his oncological surveillance. These showed no hydronephrosis and no objects or stones in the renal collecting system, indicated that the ureteroscopy had successfully cleared his collecting system.
He presented to the emergency room again with left flank pain 8 years after his embolisation. CT scan demonstrated a hyperdensity measuring 15 279 HU obstructing his left proximal ureter (figure 2). The object was hypothesised to be a surgical clip in the radiology report; however, it appeared similar to the Onyx embolisation in his renal artery, both of which created streak artefact on the CT. He was taken to the operating room the next day for ureteroscopy with laser lithotripsy. The foreign body was visualised under ureteroscopy and appeared to be covered in a layer of stone. A holmium laser was used to break the stone. Under the stone was a core of black substance consistent with Onyx. The pieces were removed using basket extraction.
Second CT scan also demonstrating Onyx in the left ureter.
Outcome and follow-up
Final pathology was T1b with negative margins. He was followed for his renal cancer and did well for 5 years until a surveillance CT scan identified lesions in his pancreas, lungs and bone. These were confirmed as metastatic clear cell renal carcinoma by biopsy of his scapula. He underwent excision of his femur mass and was treated with pazopanib. The remainder of his lesions are stable and he is currently doing well from an oncological perspective.
He is currently being followed every 6 months with ultrasounds to ensure his embolisation material does not continue to migrate.
Discussion
Onyx is a polymer of ethylene vinyl alcohol, dimethyl sulfoxide and micronised tantalum powder discovered in 1990. While initially approved for embolisation of brain arteriovenous malformations, it is now widely used for peripheral embolisation.14 15 The name is a reference to the dark colour of the substance, which bears similarity to the Onyx stone. Onyx is initially liquid and slowly solidifies, theoretically reducing trauma to nearby structures.14 Onyx is considered both effective and safe in cases of selective renal artery embolisation.15–17
On CT imaging, Onyx appears as a homogenous hyperdensity that follows the shape of the vessels that were embolised. While Onyx tends to be hyperdense, there is not a defined range of HU used to identify it on imaging. Onyx also generates streak artefacts which can obstruct nearby anatomy.18 These streak artefacts, in addition to patient history, can be used to identify Onyx migration on CT scan. The streak artefact is unlike any biological kidney stone and can be used to differentiate Onyx migration from a kidney stone.
There are a few examples in the literature of embolisation coils eroding into the collecting system. Some passed spontaneously.6 7 Others required ureteroscopy or percutaneous nephrolithotomy for removal.8–12 The only other reported case of Onyx embolisation into the collecting system is described by Ierardi et al. Their patient was a man in his late 60s with a renal pseudoaneurysm secondary to trauma. This was embolised with Onyx. During embolisation, Onyx was seen in the collecting system. Microcoils were then used to complete embolisation. He returned for sheath removal 2 days later, where X-ray confirmed passage of the Onyx into the bladder.13 This is markedly different from the case described in this report, as the Onyx did not cause obstruction, did not require laser lithotripsy for removal and did not recur.
Learning points
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Onyx migration is a possible source of renal obstruction, both in the immediate and delayed period.
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Onyx migration can be identified on CT.
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Laser lithotripsy can treat Onyx obstruction.
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Especially for patients with collecting system damage, screening with ultrasound may help identify migration of Onyx before it becomes a nidus for stone formation.
Ethics statements
Patient consent for publication
Footnotes
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Contributors SA and TJ are responsible for the initial conceptualisation. SA wrote the initial draft. BL is responsible for obtaining and interpreting the images. SA, BL, SS and TJ all contributed to the editing process and creation of the final draft.
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Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
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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.
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Competing interests None declared.
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Provenance and peer review Not commissioned; externally peer reviewed.
- © BMJ Publishing Group Limited 2022. No commercial re-use. See rights and permissions. Published by BMJ.
References
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