Nodular fasciitis
Pseudosarcomatous fasciitis ยท proliferative fasciitis ยท infiltrative fasciitis ยท Konwaler tumour
Nodular fasciitis is a rapidly-growing benign myofibroblastic / fibroblastic proliferation that closely mimics sarcoma clinically and histologically. The characteristic clonal driver โ a USP6 gene rearrangement (most commonly t(17;22) MYH9-USP6) โ supports a neoplastic rather than reactive origin and has revolutionised diagnosis. Lesions are self-limiting, but the alarming clinical / radiological / histological features often prompt aggressive treatment unless recognised. Awareness prevents unnecessary radical surgery.
Epidemiology
- Adults 20-40 years; equal gender distribution.
- Rapid onset (weeks to months); often after recent trauma.
- Sites: upper limbs (commonest โ forearm), trunk, head & neck, lower limbs.
- Less common variants: intravascular fasciitis, cranial fasciitis (paediatric), ossifying fasciitis.
Pathology
- Subcutaneous or fascial nodule; well-circumscribed but lacks true capsule.
- Plump spindle / stellate fibroblasts and myofibroblasts in feathery / storiform / tissue-culture-like arrangement.
- Loose myxoid or collagenous stroma; cleft-like spaces.
- Numerous mitoses (high cellularity) โ alarming but no atypical mitoses.
- Scattered lymphocytes, mast cells, multinucleated giant cells.
- Microcystic / haemorrhagic foci.
- USP6 gene rearrangement (t(17;22) MYH9-USP6 commonest) โ diagnostic when detected.
- IHC: SMA+ (myofibroblastic), calponin+; CD68+ in giant cells; negative for desmin, S100, cytokeratins, ฮฒ-catenin, ALK, MDM2.
Clinical features
- Rapidly-growing painful subcutaneous nodule.
- 1-3 cm typically; up to 5 cm.
- Sites: forearm (commonest), trunk, neck, head & neck.
- Duration prior to presentation: 2 weeks to 3 months.
- History of preceding trauma in ~10-15%.
- Overlying skin normal.
- Often clinically interpreted as soft-tissue sarcoma โ radical excision.
Investigations
- USS: ill-defined hypoechoic mass.
- MRI: irregular outline; T2-hyperintense; gadolinium enhancement; can resemble sarcoma.
- Core biopsy: confirms diagnosis; specialist soft-tissue pathologist review.
- USP6 break-apart FISH: definitive diagnosis when histology is equivocal.
- Avoid radical excision before pathology.
Differentials
- Sarcoma: especially fibrosarcoma, myxofibrosarcoma, leiomyosarcoma, UPS, malignant peripheral nerve sheath tumour โ must be excluded.
- Atypical fibroxanthoma / pleomorphic dermal sarcoma.
- Dermatofibrosarcoma protuberans โ chronic; trunk; COL1A1-PDGFB.
- Dermatofibroma โ chronic; dimple sign.
- Inflammatory myofibroblastic tumour โ ALK rearrangement.
- Other benign reactive lesions: proliferative fasciitis, proliferative myositis, myositis ossificans.
Management
- Surgical excision: simple complete local excision is curative.
- Some cases regress spontaneously over months.
- Recurrence rare (<2%) after excision.
- Steroid injection: intralesional triamcinolone has been reported to induce regression in selected cases.
- No metastatic potential.
- Avoid radical / disfiguring surgery โ pathology first.
- Patient education: rapid growth alarming but benign; full recovery expected.
References
- Erickson-Johnson MR et al. Nodular fasciitis: a novel model of transient neoplasia induced by MYH9-USP6 gene fusion. Lab Invest. 2011;91:1427-1433.
- Konwaler BE, Keasbey L, Kaplan L. Subcutaneous pseudosarcomatous fibromatosis (fasciitis). Am J Clin Pathol. 1955;25:241-252.
- Bernstein KE, Lattes R. Nodular (pseudosarcomatous) fasciitis, a non-recurrent lesion: clinicopathologic study of 134 cases. Cancer. 1982;49:1668-1678.
- WHO Classification of Tumours Editorial Board. WHO Classification of Soft Tissue and Bone Tumours, 5th ed. Lyon: IARC; 2020.
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