title: Encapsulated versus nonencapsulated superficial fatty masses: a proposed MR imaging classification.
abstract: OBJECTIVE
  The purpose of this study was to assess the MR imaging appearance of palpable fatty masses and to propose terminology for palpable subcutaneous fatty masses that are nonencapsulated on MR imaging.
  
  
  METHODS
  We searched the past 7 years of our institution's radiology database for reports of MR images containing the word "lipoma." Medical records were reviewed to identify patients with palpable masses corresponding to fat. Two radiologists retrospectively reviewed the MR images for the presence of an encapsulated or nonencapsulated fatty mass in the region of the palpable abnormality. Pathologic specimens, when available, were also reviewed.
  
  
  RESULTS
  Between 1995 and 2001, 184 palpable subcutaneous fatty masses were evaluated on MR imaging. Of these, 46% (85/184) were encapsulated lipomas and 54% (99/184) were nonencapsulated fatty masses on MR imaging. Four masses (three encapsulated and one nonencapsulated) were surgically resected and had pathology consistent with lipomas.
  
  
  CONCLUSIONS
  Many palpable fatty masses do not have definable capsules on MR imaging. We propose that a palpable mass that corresponds to a nonencapsulated prominence of subcutaneous fat on MR imaging should be reported as a nonencapsulated lipoma. More definitive reporting of this relatively common lesion will assure the referring clinician of the benign nature.
authors.affiliation: Department of Radiology, Mayo Clinic Scottsdale, 13400 E. Shea Blvd., Scottsdale, AZ 85259, USA. roberts.catherine@mayo.edu
authors.forename: Catherine C
authors.initials: CC
authors.lastname: Roberts
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Liu
authors.forename: Thomas V
authors.initials: TV
authors.lastname: Colby
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008067:Lipoma / Q000145:classification* / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies