title: Absence of chromosomal abnormalities in herniated orbital fat.
abstract: OBJECTIVE
  Lipomatous tumours of the orbit are rare, and can sometimes be difficult to characterize. Herniated orbital fat is thought to be a reactive process, but its presentation can mimic a lipomatous tumour such as an atypical lipomatous tumour or spindle cell/pleomorphic lipoma. Genetic studies to determine if it is indeed a reactive process rather than an adipocytic neoplasm have not been performed.
  
  
  RESULTS
  Four samples of herniated orbital fat were reviewed clinically, histopathologically and immunohistochemically. Array comparative genomic hybridization (aCGH) was used to search for genome-wide copy number alterations within the tumours. Histological evaluation revealed that all four tumours contained collections of adipocytes surrounded by fibrous septae. Lochkern cells and floret-like multinucleated giant cells were present, consistent with herniated orbital fat. CD34 was positive in all tumours. Staining for MDM2 and CDK4 was negative. ACGH analysis demonstrated no copy number alterations.
  
  
  CONCLUSIONS
  Herniated orbital fat may share some histopathological features with lipoma and atypical lipomatous tumour, but the absence of copy number gains or losses is consistent with the impression that herniated orbital fat is a reactive process. Genetic analysis may be another method to help differentiate herniated orbital fat from a lipomatous orbital tumour when the diagnosis is in question.
authors.affiliation: Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA, USA; Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Stacy
authors.forename: Lindsay A
authors.initials: LA
authors.lastname: Bernardo
authors.forename: Gunnlauger Petur
authors.initials: GP
authors.lastname: Nielsen
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000368:Aged; D000369:Aged, 80 and over; D055028:Comparative Genomic Hybridization; D003937:Diagnosis, Differential; D018628:Gene Dosage; D006547:Hernia / Q000175:diagnosis* / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D008067:Lipoma / Q000175:diagnosis / Q000235:genetics; D008080:Liposarcoma / Q000175:diagnosis / Q000235:genetics; D008297:Male; D008875:Middle Aged; D018205:Neoplasms, Adipose Tissue / Q000175:diagnosis / Q000235:genetics; D009915:Orbit / Q000473:pathology*; D009918:Orbital Neoplasms / Q000175:diagnosis / Q000235:genetics; D012189:Retrospective Studies
keywords: herniated orbital fat; lipoma; liposarcoma; orbital tumour