Clinical research of features of magnetic resonance imaging of high-voltage electrical burns in limbs at early stage

Objective To analyze the features of magnetic resonance imaging (MRI) of patients with high-voltage electrical burns in limbs at early stage. Methods Thirty-eight patients with high-voltage electrical burns, conforming to the study criteria, were hospitalized in our unit from March 2013 to August 2016. T₁ weighted imaging (T₁WI), T₂WI, fat-suppression T₂WI plain scan, and fat-suppression T₁WI enhanced scan of MRI were performed in 78 limbs, including 56 upper limbs and 22 lower limbs at post injury hour 72. The MRI signal characteristics of electrical burns in skin and subcutaneous tissue, skeletal muscle, tendon, joint ligament, and skeleton of limbs were analyzed. " Sandwich-like" necrosis and injury in skeletal muscle, injuries of tendon, joint ligament, and skeleton were observed. MRI signal characteristics of amputated upper limbs and salvaged limbs were also analyzed. All patients underwent surgery within 24 h after MRI examination, and the muscle vitality was judged during operation. Muscle tissue without reaction to electrical stimulation which was completely necrotic as shown by MRI, muscle tissue with weak reaction to electrical stimulation which was injured with blood supply as shown by MRI, and muscle tissue with edema as shown by MRI were collected, and then the pathological characteristics of muscle tissue were observed with HE staining. Results (1) The defect area of patients at entrance of current was bigger than that at exit. The skin and subcutaneous tissue extensively unevenly thickened. T₂WI manifested hyperintensity, and T₁WI manifested isointensity, while fat-suppression enhanced T₁WI manifested uneven enhancement. Zonal effusion was seen in the region of serious subcutaneous edema. (2) For complete necrosis of skeletal muscle, T₂WI manifested hypointense, isointensity, or slight hyperintensity, and T₁WI manifested isointensity, slight hyperintensity, or mixed signal of isointensity and slight hyperintensity, while fat-suppression enhanced T₁WI manifested most no enhancement area with clear boundary. The MRI signals of injured skeletal muscle could be divided into two types. Type Ⅰ signal was for partial necrotic muscle adjacent to the completely necrotic zone. T₂WI manifested uneven hyperintensity or slight hyperintensity, with unclear boundary. T₁WI manifested isointensity or slight hyperintensity. Fat-suppression enhanced T₁WI manifested significant banding or laciness enhancement. Type Ⅱ signal was for deep muscle tissue far from the complete necrotic zone. T₂WI manifested hyperintensity, and T₁WI manifested isointensity or main isointensity mixed with hyperintensity, while fat-suppression enhanced T₁WI manifested uneven moderate or slight enhancement. Normal muscle signal, type Ⅰ signal, and type Ⅱ signal were all mixed with necrotic signal, showing " sandwich-like" change. For skeletal muscle edema, T₂WI manifested slight hyperintensity and unclear boundary, and T₁WI manifested hypointense, while fat-suppression enhanced T₁WI manifested no obvious enhancement. (3) For complete necrosis of tendon, T₂WI manifested isointensity or slight hyperintensity, and T₁WI manifested isointensity, while fat-suppression enhanced T₁WI manifested no enhancement. For tendon injury, T₂WI manifested isointensity, and T₁WI manifested isointensity or hypointense, while fat-suppression enhanced T₁WI manifested slight enhancement. (4) Severe injury of wrist joint were manifested as complete necrosis of soft tissue around joint. T₂WI manifested slight hyperintensity or isointensity, and T₁WI manifested isointensity, while fat-suppression enhanced T₁WI manifested no enhancement or slightly uneven enhancement. For completely destroyed wrist joints, the structures were not clear from outside to inside. T₂WI manifested slight hyperintensity or isointensity, and T₁WI manifested hypointense or isointensity, while fat-suppression enhanced T₁WI manifested no enhancement. For elbow injury, T₂WI manifested hyperintensity, and T₁WI manifested isointensity or hypointense, while fat-suppression enhanced T₁WI manifested uneven enhancement. For knee injury, T₂WI manifested hyperintensity, and T₁WI manifested hypointense, while fat-suppression enhanced T₁WI manifested slight enhancement. (5) For bone edema, T₂WI manifested isointensity, while fat-suppression T₂WI manifested slight hyperintensity. T₁WI manifested isointensity, and fat-suppression enhanced T₁WI manifested patchy enhancement. (6) MRI of amputated upper limbs showed necrosis signals, type Ⅰ signals, type Ⅱ signals, and mixed signals of type Ⅰ and type Ⅱ in skeletal muscle. The necrosis signal and type Ⅰ signal area of the distal end were more than 50% greater than those of the lesion. The scope of the ecological tissue was large and the boundary was not clear. There were diffuse injuries in both anterior and posterior muscles, and the ulnar and radial artery pulsation disappeared in the upper limbs. The MRI of salvaged limbs were type Ⅰ signal, type Ⅱ signal, mixed signals of type Ⅰ and type Ⅱ, and local necrosis signals of skeletal muscle. The type Ⅰ signal was the main type, and the distal end showed type Ⅱ signal. (7) For completely necrotic skeletal muscle as shown by MRI, surgical exploration showed loss of muscle viability, and pathological examination showed complete necrosis of striated muscle tissue. For injury area of skeletal muscle as shown by MRI, surgical exploration showed interecological muscle with activity worse than mormal muscle, and pathological examination showed normal muscle cells and muscle fiber mixed with necrotic striated muscle cells having karyopyknosis, with different degree of injury. For edema area of skeletal muscle as shown by MRI, surgical exploration showed swelling skeletal muscle and normal muscle vitality, and pathological examination showed striated muscle interstitial edema with a large number of inflammatory cells infiltration. The manifestions of MRI were consistent with the results of surgical exploration and pathological examination. Conclusions Skeletal muscle complete necrosis, injury, and edema could be preferably differentiated by MRI, and the definite scope and depth of electrical injury, the injury of skin, tendon, joint ligament, and bone could also be displayed well on MRI. It can provide objective imaging basis for the diagnosis of high-voltage electrical burns in limbs at early stage, the establishment of clinical operation plan, and the judgment of intraoperative tissue vitality.