Surgical Pathology Criteria–

Abdominal Desmoid Fibromatosis

Differential Diagnosis

Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic Scar
Uniform Multiple stages of organization
Hemosiderin rare Hemosiderin common
Rare under 3 cm Rare over 3 cm
Inflammation not prominent Inflammation may be prominent
Usually infiltrates muscle Infiltration of muscle uncommon

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Nodular Fasciitis
Usually dense collagenous stroma Collagenous stroma focal or rare
Linear fascicles of cells Undulating bundles of cells
Infrequent mitotic figures Frequent mitotic figures
Usually >3 cm Usually <4 cm
Beta-catenin 80-90% Beta-catenin negative

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Proliferative Myositis
Muscle fibers damaged or obliterated Muscle fibers not damaged
Muscle fibers at edge of lesion Muscle fibers throughout
No ganglion-like cells Ganglion-like cells present
Predominantly collagenous Predominantly myxoid
Usually >3 cm Usually <4 cm
Both involve muscle

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Desmoplastic Fibroblastoma
Mild to moderate cellularity Paucicellular
Moderate vascularity Hypovascular
Extensive infiltration of muscle Only focal muscle infiltration
Spindle cells usually in fascicular pattern Spindle and stellate cells randomly aranged

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Intramuscular Myxoma
Mild to moderate cellularity Markedly hypocellular
Areas with collagen No collagen
Prominent vessels Sparse vessels

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Plexiform Fibrous Histiocytoma
Deep to subcutis, in muscle Superficial
Generally solid mass Plexiform architecture
Rare under 3 cm Rare over 3 cm
Giant cells and histiocytes rare Nodules of giant cells and histiocytes

 

Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic Inflammatory Myofibroblastic Tumor
Rare <12 years of age Age usually <14, rare >30
Inflammation not prominent Prominent inflammation, particularly plasma cells
Alk1 negative Alk1 frequently positive
Beta catenin 80-90% Beta catenin negative

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Adult Fibrosarcoma
Mild to moderate cellularity Usually more cellular
Fine chromatin Usually clumped chromatin
Rarely >5 mitotic figures / hpf Usually >5 mitotic figures / hpf
Rarely necrotic Frequent necrosis
Distinction between grade I fibrosarcoma and fibromatosis may not always be clear

 

Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic Low Grade Myxofibrosarcoma
No pleomorphism Cytologic pleomorphism present
Usually dense stroma but focally may be myxoid No dense stroma
Vessels lack arching pattern Arching vessels

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Desmoplastic Melanoma
Based below subcutis, involves muscle Usually based in dermis
S100 negative S100 positive

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Calcifying Fibrous Pseudotumor
Nearly always has cellular areas Uniformly paucicellular
Infiltrative pattern prominent Microscopically infiltrative at most
No calcification Calcification present
Inflammation uncommon Chronic inflammation present

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