Clinical and Radiological Safety of Retained Implantable Doppler Devices After Free Flaps
Lucas Kreutz-Rodrigues, MD., Matthew A. Frick, MD., Krzysztof R. Gorny, PhD., Brian T. Carlsen, MD., Samir Mardini, MD., Karim Bakri, M.B.B.S..
Mayo Clinic, Rochester, MN, USA.
Purpose: The implantable Cook Swartz Doppler is a commonly used, reliable technique for free flap monitoring. The device is removed once microvascular monitoring is no longer necessary. Occasionally there is difficulty retrieving the device and the use of further tension is avoided due to concerns about disrupting the anastomosis. In these cases, the metallic filament is cut at the skin level and a portion is retained in the soft tissues. Magnetic resonance imaging (MRI) is often strongly indicated in the postoperative followup of these patients who may be treated for malignancy or osteomyelitis, and the presence of retained probes raises some level of concern for MRI safety.
Outcomes of retained probes, as well as safety when using MRI have not been studied. We present a series of retained Cook Swartz devices examining outcomes, clinical MRI safety and image quality.
Methods: A retrospective chart review was conducted of patients who underwent microvascular free tissue transfer and placement of an implantable Cook Swartz Doppler probe from July 2007 to August 2018. Routine postoperative imaging was reviewed for all patients to identify incidental findings of a retained probe. Demographics, post-operative complications, and follow up period were reviewed. Any subsequent MRIs performed on patients who we positively identified to have a retained probe were reviewed by a radiologist to detect any degradation of image quality.
Results: A total of 323 patients underwent microsurgery followed by Cook Swartz monitoring. Eighteen (5.6%) patients were identified with an incidental radiographic finding of a retained probe and were included in this study. The retained device was detected on various imaging modalities on average 21 months (1-65) following surgery. Mean age was 49 years (25-67) with mean follow-up of 34.4 months (2-122). The indications for free tissue transfer were esophageal reconstruction (n=5), breast reconstruction (n=5) extremity reconstruction (n=5), and facial reconstruction (n=3). Removal of the device was attempted on average 36 days (5-165) following surgery. Device-related complications occurred in only 1 patient who underwent lower extremity reconstruction when the filament caused a draining sinus that resolved after surgical device removal. One other asymptomatic patient underwent elective device removal due to concerns with potential imaging quality for cancer followup. A total of 32 MRIs were performed in 8 patients with retained devices, including 6 patients who underwent MRIs of the surgical site. On independent review of these MRI images and the medical record, there were no complications related to the scans, and we found no significant degradation of image quality.
Conclusion: Retained Cook Swartz Doppler probes were not associated with substantial negative clinic outcomes after free tissue transfer for extremity, breast and esophageal reconstruction. Retained filaments did not affect MRI image quality of the surgical site at followup. Additionally, no patient who underwent MRI with a retained probe experienced any MRI-related complications due to heating or motion. If MRI is to be considered in situations with a known retained probe, we recommend that patients should be awake and communicative for the study due to the potential heating effects.
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