• Subcutaneous or fascial proliferation similar to nodular fasciitis, but with large basophilic cells resembling ganglion cells (Cancer 1975;36:1450, Stanford University)
• Histologically the same as proliferative myositis, but not located in muscle

• Usually 3 cm or less, poorly circumscribed subcutaneous mass that may extend horizontally along fascia

Childhood variant:

• Circumscribed, lobulated white firm mass, 1.5 to 3 cm (Am J Surg Pathol 1992;16:364)

• Resembles nodular fasciitis due to zonation effect, tissue culture type growth and plump fibroblastic and myofibroblastic spindle cells, but has large ganglion-like cells with abundant amphophilic to basophilic cytoplasm, round vesicular nuclei (occasionally 2 - 3 nuclei) and prominent nucleoli
• Ill defined margins
• Stroma is collagenous or myxoid, often with focal myxoid cystic degeneration
• Often arborizing vascular pattern
• Variable mitotic figures but no atypical ones

Childhood variant:

• More cellular than adult form with prominent ganglion-like cells and pleomorphism resembling rhabdomyoblasts
• May have many mitotic figures
• May have acute inflammatory cells and focal necrosis (unusual in adult form)
• Often no / minimal fibroblasts
• Pushing border instead of infiltrative like adult form

AFIP images

Fig 1: Prominent hemorrhage and vague centering of cellular proliferation on interlobar septa of subcutaneous fat
Fig 2: Mixture of ganglion-like cells, myofibroblasts and inflammatory cells
Fig 3: Ganglion-like cells have abundant amphophilic cytoplasm and prominent nucleoli
Fig 4: Ganglion-like cells mixed with inflammatory cells within myxohyaline matrix
Fig 5: Condensed around thin walled vascular channel

Contributed by Mark R. Wick, M.D.


Contributed by Dr. Meggen Walsh and Dr. Dana Richards
Childhood variant:


Images hosted on other servers:

• Spindle cells: smooth muscle actin, muscle specific actin
• Ganglion-like cells: vimentin, focal or membranous actin

• Ganglioneuroma: background spindle cell proliferation similar to neurofibroma, ganglion cells and spindle cells are positive for neural markers such as S100
• Nodular fasciitis: no or very few ganglion-like cells
• Proliferative myositis: histologically identical, but intramuscular location
• Rhabdomyosarcoma: background spindle cells appear malignant rather than fasciitis-like; rhabdomyoblasts may have striations; desmin+, myogenin+
• Sarcoma: large mass, nuclear atypia and pleomorphism in background spindle cells, atypical mitotic figures, often tumor necrosis

Childhood variant:

• Rhabdomyosarcoma: rhabdomyoblasts may have cross striations (unlike ganglion-like cells); desmin+, myogenin+