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846 radiology.rsna.org n Radiology: Volume 254: Number 3—March 2010

MR Imaging–related Electrical Thermal Injury Complicated by Acute Carpal Tunnel and Compartment Syndrome: Case Report 1

Zvi C. Jacob , MD Matthew F. Tito , MD Alexander B. Dagum , MD

Magnetic resonance (MR) imaging is generally considered a safe procedure. Contraindications include the presence of foreign objects in or on the body, which may be subject to electromagnetic fi elds associated with the MR system. Most of these objects are well known and are routinely screened for prior to the procedure. The authors report an unusual adverse event that appears to have been caused by a unique combination of factors involving an identifi ca-tion bracelet, an item not previously known to present any risks. To the authors’ knowledge, this is the fi rst report in the literature of a severe electrical thermal burn that re-quired surgical intervention. Identifi cation bracelets may need to be removed or padded to prevent direct contact with the patient’s skin during all MR imaging examina-tions for patients unable to communicate, such as those requiring sedation or general anesthesia.

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1 From the Department of Anesthesia and Critical Care (Z.C.J., M.F.T.) and Department of Surgery, Division of Plastic and Hand Surgery (A.B.D.), Stony Brook University Medical Center, Stony Brook, NY 11794-8480. Received April 23, 2009; revision requested June 5; revision received August 12; accepted August 12; fi nal version accepted September 16. Address correspondence to Z.C.J. (e-mail: zvi.jacob@stonybrook.edu ).

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MUSCULOSKELETAL IMAGING: MR-related Electrical Thermal Injury Jacob et al

tunnel syndrome with a wrist burn that if progressed would need urgent decom-pression. The patient was serially evalu-ated overnight and remained stable. At examination the following morning, the carpal tunnel symptoms had worsened, with severely diminished sensation in the anatomic distribution of the median nerve, weakness of the abductor pollicis brevis, and a positive Tinel sign at the carpal tunnel with concomitant develop-ment of a volar forearm compartment syndrome with pain on passive exten-sion and active fl exion of the volar fore-arm musculature and an elevated com-partment pressure in the forearm of 74 mmHg ( Fig 3 ). He underwent an emer-gency carpal tunnel release and a volar fasciotomy of the right forearm.

Intraoperative fi ndings ( Fig 4 ) were signifi cant for a median nerve that over subsequent irrigation and debridement procedures became progressively pale and edematous, and with muscle necro-sis in the pronator quadratus (the deep-est muscle and closest to bone and the postulated entry point). This was char-acteristic of an electrical burn injury, which preferentially damages nerve and muscle tissue because of their lower resistance. Furthermore, the muscle adjacent to the bone likely received a second injury from the increased heat generated by the bone’s high resistance to electricity.

The patient underwent two repeated irrigation and debridement procedures of his forearm wound. There was no

In a supine position, he was placed in the MR imager head fi rst ( Fig 1 ). Pressure points over the face, head, and limbs were inspected and padded with cot-ton blankets or towels as necessary. Monitoring cables were also padded to avoid direct skin contact. The patient was positioned into a standard 1.5-T MR imaging system (Intera, software version 2.6.3.3; Philips Healthcare, Best, the Netherlands). A spinal coil (Spinal CTL sense coil, eight channels; Philips Healthcare) was placed under the patient’s lumbar area. The patient was wearing a cotton hospital gown and sweatpants. The MR imaging study continued for 70 minutes with an un-eventful clinical course ( Table 1 ). After emerging from general anesthesia in the recovery room, the patient complained of severe pain under his identifi cation bracelet (LB2; Laserband, St Louis, Mo) ( Fig 2 ), located on his right wrist, as well as pain over the index, middle, and ring fi ngers ( 2 ). The identifi cation bracelet was immediately removed, and an area of redness under it was noted. In the recovery room the patient was treated with intravenous analgesics (ke-torolac, 30 mg; fentanyl, 50 mg; ket-amine, 20 mg, times three doses) with only a partial response. He was referred to the emergency department for fur-ther evaluation. At repeated examina-tion approximately 2 hours after the conclusion of the MR imaging studies, a blister (2 3 3 cm) was noted in the area under the identifi cation bracelet’s former location, along with pain in the hand and wrist, with numbness in the fi ngers over the median nerve distribu-tion. The right wrist was immobilized in a wrist splint. The patient was ad-mitted for observation under the care of the hand service, as these fi ndings were consistent with an acute carpal

Magnetic resonance (MR) imag-ing is generally considered a safe procedure. Contraindica-

tions include the presence of foreign objects in or on the body, which may be subject to electromagnetic fi elds associ-ated with the MR system. Such objects are routinely screened for prior to the procedure ( 1 ). We report an unusual adverse event that appears to have been caused by a unique combination of fac-tors involving an identifi cation bracelet, an item not previously known to pres-ent any risks.

Identifi cation bracelets may need to be removed or padded to prevent direct contact with the patient’s skin during MR imaging examinations for patients unable to communicate, such those requiring sedation or general anesthesia.

Case Study

A 61-year-old male patient was referred to our facility to undergo a lumbar spine MR imaging study. His past medical his-tory was signifi cant for chronic lower back pain, moderate obesity (body weight, 128 kg; body mass index, 40), hyperlipidemia, coronary artery dis-ease, and obstructive sleep apnea. The patient also had severe claustrophobia for which he required anesthesia dur-ing the MR imaging study. The attend-ing neurosurgeon insisted the study be performed in a cylindrical MR im-ager to achieve the desired quality of images. Previous to this study, the patient had undergone no other MR imaging examinations.

The patient underwent preproce-dural medical evaluation and prepara-tion according to the hospital’s standards. For the MR imaging study, general an-esthesia was induced and maintained by means of an intravenous infusion of propofol (200 m g/kg/min) and sevofl urane (1 MAC [minimum alveolar concentra-tion]). The patient’s airway was secured.

Implication for Patient Care

Identifi cation bracelets may need n

to be removed or padded to pre-vent direct contact with the patient’s skin during MR imaging for patients unable to communi-cate, such those requiring seda-tion or general anesthesia.

Advance in Knowledge

Identifi cation bracelets may con- n

tribute to thermal and electrical burns during MR imaging.

Published online before print 10.1148/radiol.09090637

Radiology 2010; 254:846–850

Abbreviation: RF = radiofrequency

Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of fi nal version of submitted manuscript, all authors; literature research, all authors; clinical studies, Z.C.J., A.B.D.; statistical analysis, Z.C.J.; and manuscript editing, all authors

Authors stated no fi nancial relationship to disclose.

848 radiology.rsna.org n Radiology: Volume 254: Number 3—March 2010

MUSCULOSKELETAL IMAGING: MR-related Electrical Thermal Injury Jacob et al

Heating tends to be problematic pri-marily for conductive objects that have an elongated shape such as electrodes, leads, guidewires, and certain types of catheters ( 4 ). There are also reports of excessive heating or burns caused by iron oxide–based tattoos and transder-mal patches with metal components, such as testosterone (eg, Androderm), nicotine (eg, Habitrol, Nicotrol), sco-polamine (eg, Trasderm Scop), and clo-nidine (Catapress-TTS) patches ( 5–7 ).

Currents may be induced by two oscillating fi elds: the pulsed magnetic-gradient fi eld and the pulsed radiofre-quency (RF) fi eld. These fi elds’ intensities vary with time and may induce an elec-tromotive force in a conductive loop. Heating will result from current fl owing through the loop, and it is proportional to the resistance in the conductive medium ( 3 ). The pulsed magnetic-gradient fi eld is produced by a large gradient coil that encloses the RF coils, which are some-times located in the vicinity of the pa-tient to be imaged. The risk of excessive heating is related to the proximity of the transmit RF coil to the patient’s tissue, as well as to the frequency and the power of the RF used.

In this case, the patient sustained a thermal injury on the volar mid-to-ulnar side of the wrist, which likely represented an entry point for the electrical current. The presence of pro-gressive acute carpal tunnel syndrome with a compartment syndrome is not consistent with a small ulnar thermal burn. For a thermal burn to cause car-pal tunnel syndrome and compartment

other muscle necrosis ( Fig 5 ). The skin under the blister progressed to a deep second- and third-degree burn requiring debridement. Eleven days after the injury, the open forearm wound was again de-brided and was surgically closed with a split thickness skin graft. At the time of discharge, the patient’s condition had improved, but he still experienced severe numbness in the median nerve distribution, weakness in the abductor pollicis brevis muscle, fi nger stiffness, and swelling in the forearm. The patient was discharged and followed up as an outpatient. He underwent a prolonged course of hand therapy. He has had gradual and progressive recovery of his median nerve and hand function.

Discussion

Thermal injuries during MR imaging procedures have been previously de-scribed, mainly linked to monitoring systems including sensors, cables, or other foreign objects placed on the patient. Such injuries may arise from currents induced in the conductive ob-jects by the MR imaging coils, creating heat and eventually burns ( Table 2 ) ( 3 ).

Figure 1

Figure 1: Diagram shows the patient’s position and monitors used during the MR imaging examina-tion. A = blood pressure cuff, B = electrocardi-ography leads, C = SpO

2 probe, D = intravenous

catheter, E = identifi cation bracelet, and F = MR imager.

Table 1

Energy Deposition during the MR Imaging Examination

Step Sequence TR/TE * No. of Images

Specifi c Absorption Rate (W/kg)

Acquisition Time (min:sec)

Localizer Three plane 26/2.5 3 1.3 12:32STIR sagittal TSE 2500/70 8 3 12:33Localizer Three plane 26/2.5 3 1.3 12:41STIR TIR 2500/70 16 3 12:42T2-weighted sagittal FSE-T2 4000/110 16 1.7 12:46STIR sagittal FSE 2500/150 16 2.2 12:50T2-weighted sagittal FSE 4000/110 16 1.7 12:56T1-weighted sagittal FSE 444/10 16 2.0 13:02T2-weighted FSE axial FSE 4000/105 30 1.5 13:07T2-weighted axial block FSE 4000/100 44 1.7 13:13T1-weighted axial block FSE 4000/100 44 1.7 13:19T1-weighted sagittal post FSE 653/10 18 2.6 13:27FS T1-weighted axial C FSE 561/10 44 3 13:33FS T1-weighted sagittal post FSE 653/10 18 2.6 13:42

Note.–Total acquisition time was 70 minutes. FS = fat suppression, FSE = fast spin echo, STIR = short inversion time inversion-recovery, TIR = time inversion recovery, TSE = turbo spin echo .

* TR/TE = repetition time (msec)/echo time (msec).

Figure 2

Figure 2: LB2 (Laserband) identifi cation band used during the MR imaging examination.

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MUSCULOSKELETAL IMAGING: MR-related Electrical Thermal Injury Jacob et al

The exact mechanism causing the injury in this case is unclear. The MR imaging coils, imager, and monitoring system were inspected by the radiol-ogy department and the manufacturer, and no fault was found. A detailed re-port was submitted to the U.S. Food and Drug Administration and to Philips Healthcare ( 8,9 ). Review of the imaging protocol did not show any unexpected energy deposition. The presence of a foreign body in the patient was exclu-ded. Prior to the imaging examina-tion, the patient’s pressure and contact points were padded and isolated from direct contact with the MR imager bore or to different parts of the patient’s body, minimizing the chance of creating a loop as described by Knopp et al ( 10 ). The monitoring equipment did include an oxygen saturation probe and electro-cardiographic electrodes, but they and their associated cables were placed on different parts of the patient and were not in proximity to the injured limb.

At clinical examination immedi-ately following the incident, we found that the blister (or the postulated exit/entrance point of the electrical current) appeared in the area under the barcode print in the identifi cation bracelet (LB2; Laserband) ( 2 ). Further investigation revealed that the toner used to print the identifi cation bracelet barcode contained

tor quadratus muscle was consistent with an electrical burn (injury) to the median nerve. Electrical injury to nerves produces a higher-level nerve injury that recovers more slowly than simple compression neuropathies. The median nerve has been recovering at the appropriate rate of 1 inch a month with both a progressive Tinel sign and level of sensation consistent with an axonotmesis or Sunderland grade 2 nerve injuries. At the patient’s last fol-low-up visit at 6 months, he was hav-ing return of sensation to the tips of his fi ngers (6 inches from the level of injury).

syndrome, it would have had to be a circumferential and deep second- or third-degree burn. The progression of his clinical symptoms, the elevation in compartment pressures, with the development of signs and symptoms of acute carpal tunnel syndrome over an 18-hour period is characteristic of an electrical burn, which shows progres-sive muscle necrosis and nerve injury. The delayed recovery of the patient’s median nerve implies that he sustained a more severe injury than just a neuro-praxia. The intraoperative appearance of a pale swollen nerve together with pro-gressive muscle necrosis of the prona-

Figure 3

Figure 3: Skin blister and redness consistent with the thermal injury. Dressings applied over the proximal forearm at the area of the diagnostic catheter insertion for compartment pressure monitoring.

Figure 4

Figure 4: Intraoperative view of the forearm consistent with a deep electro-thermal injury to the muscular tissue, with signifi cant swelling of the median nerve.

Table 2

Mechanisms Involved in Thermal Injuries

Mechanism Description

Electromagnetic induction

Change of magnetic force line through a closed loop circuit gives rise to an electromotive force and induces an electrical current

Resonant circuit RF energy deposited at the resonance frequency induces heating currentsAntenna effect The cables connected to the patient are serving as an RF antenna; the tip of the wire

will have the most magnetic force density

Note.—Adapted and reprinted, with permission, from reference 1 .

Figure 5

Figure 5: View of the forearm after the fasciotomy and carpal tunnel release.

850 radiology.rsna.org n Radiology: Volume 254: Number 3—March 2010

MUSCULOSKELETAL IMAGING: MR-related Electrical Thermal Injury Jacob et al

40%– 50% iron oxide ( 11 ). We sug-gest that the initial snug placement of the identifi cation bracelet around the wrist at admittance, along with the pa-tient’s wrist anatomy and the addition of sweat, created a conductive loop. We postulate that this in turn caused a fl ow of electrical current into the arm throughout the procedure (electromag-netic induction). Additional risk factors such as long acquisition time and loca-tion of the RF coil in proximity to the wrist may also have played a role.

We recommend having a high index of suspicion during the recovery time because the clinical signs and symp-toms may be initially nonspecifi c dur-ing emergence from sedation or general anesthesia. In this case, prompt clinical attention and close observation with frequent clinical examination, which led to early intervention, prevented a more severe injury to the upper extremity from impending compartment syndrome.

The hospital quality assurance com-mittee recommendations that followed this incident were to remove or pad the

identifi cation bracelets from direct con-tact with the patient’s skin during all future MR imaging examinations for patients requiring sedation and general anesthesia.

References 1 . Shellock FG , Crues JV . MR procedures:

biologic effects, safety, and patient care . Radiology 2004 ; 232 ( 3 ): 635 – 652 .

2 . Laserband Web site. http://www.laserband.com/index.php?pageId=25&mode=mod_laser&action=showProduct&productId=83 . Accessed November 21, 2009.

3 . Dempsey MF , Condon B . Thermal in-juries associated with MRI . Clin Radiol 2001 ; 56 ( 6 ): 457 – 465 .

4 . Haik J , Daniel S , Tessone A , Orenstein A , Winkler E . MRI induced fourth-degree burn in an extremity, leading to amputa-tion . Burns 2009 ; 35 ( 2 ): 294 – 296 .

5 . Tope WD , Shellock FG . Magnetic reso-nance imaging and permanent cosmet-ics (tattoos): survey of complications and adverse events . J Magn Reson Imaging 2002 ; 15 ( 2 ): 180 – 184 .

6 . FDA public health advisory: risk of burns during MRI scans from transdermal drug

patches with metallic backings. U.S. Food and Drug Administration Web site. http://www.fda.gov/bbs/topics/NEWS/2009/NEW01967.html . Accessed November 21, 2009.

7 . FDA medical device reporting fi les. U.S. Food and Drug Administration Web site. http://www.fda.gov/cdrh/mdrfile.html . Accessed November 21, 2009.

8 . Philips MRI systems: Intera 1.5T MRI overview. Philips Healthcare Web site. http://www.healthcare.philips.com/main/products/mri/systems/intera/index.wpd . Accessed November 21, 2009.

9 . MedRad Web site. http://www.medrad.com/en-us/info/products/Pages/VerisMRVitalSignsMonitor.aspx . Accessed November 21, 2009.

10 . Knopp MV , Essig M , Debus J , Zabel HJ , Van Kaick G . Unusual burns of the lower extremities caused by a closed conducting loop in a patient at MR imaging . Radiology 1996 ; 200 ( 2 ): 572 – 575 .

11 . Printer toner specifi cations. Material safety data sheet. Hewlett-Packard Web site. http://www.hp.com/hpinfo/globalcitizenship/environment/productdata/pdf/lj_q1338a-ac-d_gb_eng_v10.pdf . Accessed November 21, 2009.