Nodular fasciitis

Nodular fasciitis is a rapidly growing non-neoplastic soft tissue lesion that is frequently located in the deep subcutaneous region or in the fascia. The most common locations for nodular fasciitis are the volar aspect of the forearm, the lower extremity, and the chest and back. It typically manifests as a rapidly growing mass.

Epidemiology

Most often, nodular fasciitis occurs in patients between 20 and 40 years of age, but children also may be affected.

Clinical presentation

In mostmany cases (~45%), it is localised to the upper extremity, particularly the volar aspect of the forearm. Other common sites are:

• trunk (20%)
• head and neck (18%)
• lower extremities (16%)

Symptoms of tenderness and pain are frequently described at presentation.

Pathology

The pathogenesis of nodular fasciitis is poorly understood. Some describe it as a reactive lesion related to trauma, others have described chromosomal abnormalities that are suggestive of a neoplastic origin.

The lesions tend to be small (<4 cm). Three general subtypes of nodular fasciitis may be identified on the basis of the lesion location:

• subcutaneous
• intramuscular
• fascial

Most occurrences of nodular fasciitis are subcutaneous, fascia based, and circumscribed; these lesions may be amenable to biopsy or excision without any need for imaging evaluation. 

HistologyClassification

The entity is included in the WHO classification of soft tissue tumors under "fibroblastic/myofibroblastic tumors."

Microscopic appearance

Benign proliferation of fibroblasts and myofibroblasts, typically mistaken for a sarcomatous lesion because of its rapid growth, abundant spindle-shaped cells, and mitotic activity.

Radiographic features

Ultrasound

Sonography can show one or more well-defined isoechoic to hypoechoic nodules with a mildly increased vascular flow in the deep portion of the subcutaneous fat layer, adjacent to or in the fascia.

MRI

Nodular fasciitis may be categorised as myxoid, cellular, or fibrous. This histologic diversity likely accounts for the variable MR imaging appearance of the lesions:

• hypercellular lesions appear nearly isointense to that in skeletal muscle on T1WI and hyperintense to that in adipose tissue on T2WI
• highly collagenous lesions have hypointense signal on all sequences
• contrast enhancement is typically diffuse but may be peripheral

Treatment and prognosis

The imaging-based diagnosis should be verified with an excisional biopsy.

Treatment typically consists of marginal excision of the lesion(s). Several weeks of observation (after a diagnosis based on the results of percutaneous fine-needle biopsy) also have been advocated given the self-limited course of the disease.

Spontaneous regression and involution of lesions in response to steroid injections have been reported ^{ref required}. 

Differential diagnosis

Imaging differential considerations include:

• Dupuytren's disease (palmar fibromatosis)
• extra-abdominal desmoid tumour
• neurofibroma
• fibrous histiocytoma
• soft tissue sarcoma
• if intramuscular early myositis ossificans may be considered