title: Cause of hematic cysts of the orbit: increased fibrinolysis and immunohistologic expression of tissue plasminogen activator.
abstract: OBJECTIVE
  Hematic cysts of the orbit are relatively uncommon. These cysts expand gradually, leading to progressive orbital symptoms. To clarify the cause of hematic cyst, especially the mechanisms leading to its gradual expansion, we investigated the immunohistologic expression of tissue-type plasminogen activator (tPA), a key enzyme of fibrinolysis, in cases of hematic cysts.
  
  
  METHODS
  Retrospective small case series.
  
  
  METHODS
  Three patients with hematic cyst of the orbit were studied.
  
  
  METHODS
  Three surgically removed hematic cysts were studied from a histologic perspective, including immunohistochemistry for tPA. The cyst content was also analyzed chemically.
  
  
  METHODS
  The pathologic features of hematic cyst of the orbit, expression of tPA in the cyst wall, and coagulation-fibrinolytic factors in the content of the cyst.
  
  
  RESULTS
  The cyst wall was composed of dense collagen fibers lacking an epithelial lining and contained many fine capillary- or venule-like vessels. Hemosiderin-laden macrophages were observed among the collagen fibers. Strong immunoreactivity for tPA was revealed in the endothelial cells of the vessels in the cyst wall. Chemical analysis of the cyst content revealed a marked delay in the activated partial thromboplastin time and prothrombin time, a low fibrinogen concentration, and high concentrations of the D-dimer and tPA-plasminogen activator inhibitor-1 complex.
  
  
  CONCLUSIONS
  Our findings indicate that blood coagulation and hemostasis occur first and that fibrinolysis occurs second in hematic cysts. Gradual expansion of the cyst may be due to hyperfibrinolysis resulting from oversecretion of tPA from the endothelial cells in the cyst wall, thus impairing normal hemostasis. Hemorrhage may then recur, resulting in enlargement of the hematic cyst. These mechanisms are similar to those occurring in chronic subdural hematomas.
  
  
  BACKGROUND
  The author(s) have no proprietary or commercial interest in any materials discussed in this article.
authors.affiliation: Department of Neurosurgery, Yamaguchi University School of Medicine, Yamaguchi, Japan. koyoshi@yamaguchi-u.ac.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Yoshikawa
authors.forename: Hirosuke
authors.initials: H
authors.lastname: Fujisawa
authors.forename: Koji
authors.initials: K
authors.lastname: Kajiwara
authors.forename: Masami
authors.initials: M
authors.lastname: Fujii
authors.forename: Shoichi
authors.initials: S
authors.lastname: Kato
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Akimura
authors.forename: Sadahiro
authors.initials: S
authors.lastname: Nomura
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Gondo
authors.forename: Michiyasu
authors.initials: M
authors.lastname: Suzuki
mesh_terms: D000368:Aged; D003560:Cysts / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism; D004730:Endothelium, Vascular / Q000378:metabolism; D005260:Female; D005342:Fibrinolysis; D005343:Fibrinolytic Agents / Q000378:metabolism*; D006406:Hematoma / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism; D006801:Humans; D007124:Immunoenzyme Techniques; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009916:Orbital Diseases / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism; D010314:Partial Thromboplastin Time; D017395:Plasminogen Activator Inhibitor 1 / Q000032:analysis; D011517:Prothrombin Time; D012189:Retrospective Studies; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D014057:Tomography, X-Ray Computed
chemical_list: D005343:Fibrinolytic Agents; D017395:Plasminogen Activator Inhibitor 1; C051321:SERPINE1 protein, human; D010959:Tissue Plasminogen Activator