Necrotizing fasciitis, recent below-knee amputation Knee: The patient has undergone below knee amputation. Very little soft tissue overlies the distal margin of the remaining tibia and areas of signal void are noted within the surrounding soft tissues and within the medullary cavity of the distal tibia which may represent foci of gas. There is edema within the medullary cavity of the distal tibia noted on series 5 which in conjunction with the suspected gas is concerning for osteomyelitis. There is also increased signal intensity within the medullary cavity of the distal end of the remaining fibula on the fat-suppressed T2 sequences; however there is relatively normal corresponding T1 marrow signal and therefore this may reflect reactive osteitis as opposed to true osteomyelitis. There is superficial ulceration along the distal end of the stump with circumferential thickening of the skin which enhances following contrast administration. There is reticulation of the subcutaneous fat which also enhances reflecting cellulitis. There is mild heterogeneous edema and enhancement of the remaining musculature of the calf indicating inflammation but we see no rim-enhancing inter- or intramuscular collection to suggest abscess. There is a small knee joint effusion with synovial enhancement indicating mild synovitis.The study was not tailored for the evaluation of the internal derangement of the knee. There is mild osteoarthritis of the knee but no findings to suggest ligamentous disruption or an unstable meniscal tear. An additional focus of low signal intensity is identified in the proximal tibia which may reflect a bone infarct. An ossicle distal to the patellar tendon may relate to remote trauma but is not necessarily of any clinical significance.Femur: The cellulitis detailed above extends proximally into the proximal thigh to about the level of the lesser trochanter. Although there is reticular enhancement of the subcutaneous fat and mild enhancement of the posterior crural fascia, the degree of enhancement is less pronounced than that seen more distally suggesting a greater proportion of "cold edema" rather than inflammation. There is mild edema of the vastus medialis, vastus lateralis, hamstring musculature, and adductor musculature on the T2-weighted sequences with very mild enhancement of the medial margin of the distal vastus lateralis and its adjacent fascia indicating inflammation. Intramuscular edema is also noted on the T2-weighted images but does not appear to enhance following gadolinium with the exception of a thin area of intramuscular enhancement between the margin of the vastus lateralis and sartorius distally. We see no rim-enhancing inter or intramuscular fluid collection to suggest abscess and the bone marrow signal of the femur is normal. There is mild edema of the distal fibers of the gluteus maximus muscle with mild enhancement. There are several enlarged inguinal lymph nodes which enhance following gadolinium administration.
1. Surgical changes of below-knee amputation with signal void extending into the medullary canal of the remaining distal tibia that may represent gas, concerning for osteomyelitis. Correlation with radiographs is recommended.2. Soft tissue inflammation as described above indicating cellulitis with additional edema extending into the thigh. We cannot confirm nor exclude necrotizing fasciitis on the basis of these images. Additional findings are described above.