title: Fatty rind of intramuscular soft-tissue tumors of the extremity: is it different from the split fat sign?
abstract: OBJECTIVE
  To analyze intramuscular soft-tissue tumors with fatty rind, and to evaluate the difference between fatty rind and split fat sign on magnetic resonance imaging (MRI).
  
  
  METHODS
  We retrospectively analyzed 50 pathologically confirmed intramuscular masses on MRI. We evaluated the distribution and shape of fatty rind and muscle atrophy.
  
  
  RESULTS
  Fatty rind was found more frequently in benign lesions (80% [36 out of 45]) compared with malignant lesions (25% [1 out of 5]; P = 0.013). Thirty-six benign lesions were peripheral nerve sheath tumors (PNSTs; n = 19), hemangiomas (n = 11), myxomas (n = 2), ganglion cysts (n = 2), giant cell tumor (n = 1), and leiomyoma (n = 1). One malignant lesion was a low-grade fibromyxoid sarcoma. In all masses with fatty rind, fat was confined to the proximal and the distal ends. In 12 cases, complete or partial circumferential fatty rind was also noted. Fatty rinds at both ends showed crescent, triangular, or combined shape. The prevalence of crescent-shaped fatty rind was significantly higher in benign PNST (17 out of 38) compared with the other tumors (1 out of 32; P < 0.001). Complete circumferential fat was noted only in hemangioma (n = 5). Triangular fatty rind was related to peripheral location of the mass or muscle atrophy.
  
  
  CONCLUSIONS
  Most intramuscular tumors with fatty rinds were benign, and PNST was the most common tumor type. Fatty rind could be caused by displaced neurovascular bundle fat, fatty atrophy of the muscle involved, or intermuscular or perimysial fat. Crescent-shaped fatty rind was noted more frequently in benign PNSTs.
authors.affiliation: Departments of Radiology, St. Vincent's Hospital, College of Medicine, The Catholic University of Korea, 93, Jungbu-daero, Paldal-gu, Suwon, Gyeonggi-do, 16247, South Korea.
authors.forename: Jinkyeong
authors.initials: J
authors.lastname: Sung
authors.affiliation: Departments of Radiology, St. Vincent's Hospital, College of Medicine, The Catholic University of Korea, 93, Jungbu-daero, Paldal-gu, Suwon, Gyeonggi-do, 16247, South Korea. jeeykim@catholic.ac.kr.
authors.forename: Jee-Young
authors.initials: JY
authors.lastname: Kim
mesh_terms: D000273:Adipose Tissue / Q000000981:diagnostic imaging*; D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D003937:Diagnosis, Differential; D005121:Extremities / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009133:Muscular Atrophy / Q000150:complications / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D012983:Soft Tissue Neoplasms / Q000150:complications / Q000000981:diagnostic imaging*; D055815:Young Adult
keywords: Fatty rind; Intramuscular soft tissue tumor; Magnetic resonance imaging; Peripheral nerve sheath tumors