Retroperitoneal and Pelvic Fibromatosis

Definition

• Cytologically bland, at most moderately cellular, deep infiltrative fibroproliferative process primarily involving retroperitoneum or pelvis

Alternate / Historical Names

• Intra-abdominal fibromatosis

Diagnostic Criteria

• Over age 5 years by definition
• Essentially the same as abdominal desmoid fibromatosis except for location and lack of association with pregnancy or polyposis
• Primarily based in retroperitoneum or pelvis by definition
  • Extremely rare outside the pelvic retroperitoneum
  • If retroperitoneum involved by extension from mesentery, lesion should be considered mesenteric fibromatosis
• Low to moderate cellularity
• Bland spindle cells in fascicles or haphazard
• Nuclei small, dark to slightly enlarged and vesicular
• Cytoplasm scant
• Stroma may be densely collagenous or myxoid
• May have keloid like fibers
• Rare metaplastic cartilage and bone
• Mitotic figures infrequent
• Rarely >5 per HPF
• Never atypical
• Inflammation not prominent
• May be seen focally, usually peripherally
• Gross circumscription may be deceptive
• Nearly always over 3 cm
• Usually 3-7 cm
• Focal hemorrhage may be seen
• Hemosiderin rare

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting: October 15, 2007
Updates: January 26, 2008; February 2, 2009; February 8, 2009

Supplemental studies

Immunohistology

Differential diagnosis

• Scar
• Sclerosing mesenteritis
• Retroperitoneal fibrosis
• Gastrointestinal stromal tumor
• Inflammatory myofibroblastic tumor
• Fibrosarcoma
• Low grade myxofibrosarcoma
• The following do not involve the retroperitoneum or pelvis and thus can be excluded:
  • Nodular fasciitis
  • Proliferative myositis
  • Desmoplastic fibroblastoma
  • Intramuscular myxoma
  • Plexiform Fibrohistiocytic Tumor

Clinical

• Over age 5 years by definition
  • Nearly always over age 12
  • Most occur in women 20-30 years old
• Not associated with pregnancy or familial polyposis
• Frequent recurrence
  • 20-30% overall
  • Recurrences may be locally aggressive and destructive
• Deep fibromatoses differ primarily in their clinical association

  	Abdominal	Extra-abdominal	Mesenteric	Pelvic / Retroperitoneal	Infantile
  Pregnancy	+	-	-	-	-
  Familial polyposis	rare	-	10-15%	-	-

Lists

Fibromatoses

• Desmoid type fibromatoses
  • Abdominal desmoid fibromatosis
  • Extra-abdominal desmoid fibromatosis
  • Infantile fibromatosis (subset)
• Fibromatosis colli
• Gingival fibromatosis
• Hyaline fibromatosis
• Inclusion body fibromatosis
• Infantile fibromatosis / lipofibromatosis
• Intra-abdominal fibromatosis
  • Mesenteric fibromatosis
  • Retroperitoneal and pelvic fibromatosis
• Knuckle pads
• Palmar fibromatosis
• Penile fibromatosis (Peyronie disease)
• Plantar fibromatosis

Bibliography

• Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
• Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
• Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 4th edition, 2001
• De Wever I, Dal Cin P, Fletcher CD, Mandahl N, Mertens F, Mitelman F, Rosai J, Rydholm A, Sciot R, Tallini G, Van Den Berghe H, Vanni R, Willen H.  Cytogenetic, clinical, and morphologic correlations in 78 cases of fibromatosis: a report from the CHAMP Study Group. CHromosomes And Morphology.  Mod Pathol 2000 Oct;13(10):1080-5
• Yantiss RK, Spiro IJ, Compton CC, Rosenberg AE. Gastrointestinal stromal tumor versus intra-abdominal fibromatosis of the bowel wall: a clinically important differential diagnosis. Am J Surg Pathol. 2000 Jul;24(7):947-57.
  
• Miettinen M. Are desmoid tumors kit positive? Am J Surg Pathol. 2001 Apr;25(4):549-50.