Soft tissue
Fibroblastic / myofibroblastic tumors
Nodular fasciitis

Topic Completed: 1 April 2014

Revised: 15 May 2019

Copyright: 2002-2018,, Inc.

PubMed Search: Nodular fasciitis [title] soft tissue

See also: Intravascular fasciitis, Proliferative funiculitis, Cranial fasciitis
Page views in 2018: 24,348
Page views in 2019 to date: 12,616
Cite this page: Wimmer D. Nodular fasciitis. website. Accessed June 17th, 2019.
Definition / general
  • Reactive appearing proliferation of fibroblasts and myofibroblasts in myxoid stroma with granulation tissue-like vascular proliferation, lymphocytes and extravasated red blood cells, usually in young adults in fascia and subcutis, with rapid growth to 2 - 3 cm (Stanford University)
  • Common lesion that typically presents as a rapidly growing mass on the flexor forearm, chest, back or elsewhere
  • Arises from superficial fascia, occasionally intramuscular or intravascular
  • Similar lesions may also develop within bladder (Hinyokika Kiyo 1994;40:427), breast (Breast 2005;14:384), cervix, intra-articular (Am J Surg Pathol 2006;30:237), prostate, vagina, vulva (Int J Gynecol Path 1997;16:117)
  • Peaks at age 40 years; prior trauma in 10% of cases
  • Benign behavior, but sometimes misdiagnosed as sarcoma based on cellularity, mitotic figures and rapid growth
Case reports
  • Excision (curative even if incomplete resection); recurs in 1% after incomplete excision but recurrence should suggest review of diagnosis; no metastases
Clinical images

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Mammogram, courtesy of Mark R. Wick, M.D.

Gross description
  • Tan-white-gray, myxoid appearance, usually 3 cm or less (reconsider diagnosis if greater than 3 cm)
  • Relatively well circumscribed, no capsule
  • May be centered in subcutis, may grow into skeletal muscle
Gross images

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Courtesy of Mark R. Wick, M.D.

Images hosted on other servers:

Hyperpigmented nodule

Microscopic (histologic) description
  • Zonation effect with hypocellular central region and hypercellular periphery
  • Composed of uniform, plump, immature, spindled to stellate fibroblasts or myofibroblasts without atypia, with a feathery, "tissue-culture" like growth pattern due to abundant ground substance
  • Often with mucoid / myxoid pools (microcysts), a very useful diagnostic finding
  • Uniform elongated nuclei with punctate nucleoli and without significant nuclear atypia
  • Cellular areas may have storiform or fascicular patterns (S or C shaped)
  • Often frequent mitotic figures (but no atypical forms), lymphocytes and macrophages, red blood cell extravasation, bands of keloid-type collagen
  • Vasculature is usually prominent
  • Walls of small to medium sized vessels are involved by reactive process at periphery of lesion
  • May infiltrate adjacent fat
  • May have metaplastic bone, focal cystic areas, ganglion type cells but no cells with large, hyperchromatic, atypical nuclei
  • May rarely involve dermis, particularly in the head and neck
  • No / rare plasma cells and neutrophils
Microscopic (histologic) images

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AFIP images:

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Fig 1: Subcutaneous tumor is partially circumscribed nodule infiltrating focally along fascial planes
Fig 2: Focal infiltration into fat, with evenly distributed granulation tissue-like vessels throughout the lesion
Fig 3: Gently curving C and S shaped fascicles of myofibroblastic cells exhibit a characteristic "torn Kleenex" pattern
Fig 4: Focal storiform pattern is suggestive of fibrous histiocytoma
Fig 5: Plump spindled myofibroblastic cells and extravasated red blood cells

Figure 6

Figure 7

Figure 8

Cystic degeneration

Fig 6: Mitotic figures but no abnormal forms
Fig 7: Focally more collagenous stroma with skeletal muscle involvement
Fig 8: Osteoclastic giant cells are present in less collagenous areas, suggesting a variant of MFH

Figure 9

Figure 10

Figure 11

Fig 9: Hyalinized variant resembles keloid or fibromatosis
Fig 10: Vague zonation pattern with bone formation in lower right
Fig 11: Island of new bone surrounded by myofibroblastic cells

Courtesy of Mark R. Wick, M.D.

Case of the Week #65: tumor of wrist

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Leg lesion

Resembles fibroblast culture

Myofibroblasts and staghorn blood vessels

"Tram track" pattern

Cytology description
  • Markedly hypercellular smear with clusters of overlapping, relatively monomorphic spindle or epithelioid cells sometimes resembling sarcoma (Am J Clin Pathol 2005;123:388); also inflammatory cells, single mesenchymal cells, myxoid stroma (Acta Cytol 2004;48:473)
Positive stains
Electron microscopy description
  • Cells resemble myofibroblasts, are elongated with abundant, often dilated rough endoplasmic reticulum, may have cytoplasmic filaments with dense bodies, pinocytotic vesicles and cell junctions
Molecular / cytogenetics description
  • Originally considered a reactive lesion: diploid, no / few genetic aberrations (Am J Clin Pathol 2009;131:701)
  • Recent research suggests nodular fasciitis is perhaps a "transient neoplasia" with most cases carrying the balanced translocation t(17;22)(p13;q13) resulting in MYH9-USP6 gene fusion (Lab Invest 2011;91:1427)
Differential diagnosis
  • Benign fibrous histiocytoma: based in dermis, storiform pattern, infiltrative borders with collagen trapping, sometimes prominent xanthoma cells and often Touton giant cells, no myxoid microcysts
  • Fibromatosis: usually large tumor that infiltrates surrounding soft tissue, spindled cells are parallel and separated by abundant collagen and arranged in broad sweeping fascicles, no loose tissue culture appearance or myxoid microcysts
  • Inflammatory myofibroblastic tumor: larger tumor size, has mixed inflammatory infiltrate, may have ALK expression; no rapid growth, no zonation, no prominent myxoid stroma
  • Myositis ossificans (early): centered in muscle, calcification
  • Myxofibrosarcoma: large, regularly arborizing vessels, atypia and pleomorphism
  • Other sarcoma: nuclear atypia is prominent, may have necrosis, larger size usually
  • Reactive spindle cell nodules: post-biopsy
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