Definition: Nodular fasciitis is a benign proliferation of fibroblasts in the subcutaneous tissues, commonly associated with the deep fascia.
Reports of nodular fasciitis among adults are common; however, this condition is relatively rare in the pediatric population.
Its clinical and histologic characteristics are similar to malignancies such as sarcoma.
Nodular fasciitis is a benign mesenchymal tumor. Often presenting as a rapidly enlarging soft tissue mass, clinically, it can easily be mistaken as a sarcoma or other malignancy during clinical evaluation.
In addition, the pathologist may recognize its high cellularity, high mitotic index, and infiltrative borders, which, as a result, may lead to erroneous diagnosis as a malignancy.
Synopsis
small and solitary subcutaneous nodule
solid lesion, 5 or 20 mm in diameter
rapid growth (less than a month in 50%)
localization:
- upper extremities (volvar aspect of the forearm), lower extremity, trunk in adults
- head and neck region of infants and children
- any superficial soft tissue of the body, including the breast, mucosal surfaces, bladder, and parotid gland.
benign proliferation of fibroblasts and myofibroblasts in the subcutaneous tissues
haphazardly arranged bundles of fibroblasts (medium cellularity)
myxoid or mucoid background
fine capillary network arranged in a radial pattern around a larger central vessel or vessels
fibroblasts are typically large and plump, similar to those of granulation tissue
pleomorphic fibroblasts
common mitoses
spindle-shaped fibroblasts arranged in long fascicles slightly curved, whorled or S-shaped
- extension along the fibrous septa of submucosal fatty tissues.
variable amount of collagen and acid mucopolysaccharide in intercellular matrix
scattered chronic inflammatory cells
foamy histiocytes and osteoclast-like multinucleated giant cells in long-standing lesions
small slit-like spaces often separate the fibroblasts
extravasation of erythrocytes
occasional microcysts
not often encapsulated but usually well demarcated from surrounding tissues
Ultrastructure
myofibroblasts
- basic fibroblastic appearance with peripherally located bundles of myofilaments with dense patches similar to those of smooth muscle cells
Immunochemistry
vimentin + (VIM+)
smooth muscle actin + (SMA+)
muscle-specific actin +
desmin - (DES-)
Cytogenetics
3q21 rearrangements (9797787)
- t(3;15)(q21;q22) (7923068)
Ch.15 rearrangements (15q22-15q25)
t(16;16)(p13.3;p11.2) (12550774) (16p13.3 and 16p11.2)
Differential diagnosis
fibrous tumors
- proliferative myositis
- proliferative fasciitis
fibroblastic tumors
- fibrosarcoma
others
- liposarcoma
small foci of metaplastic bone or cartilage
- ossifying fasciitis
- fasciitis ossificans15)(q31;q26) (7621414)
- t(15;15)(q13;q25) (12606136)
- parosteal fasciitis
Variants
intravascular nodular fasciitis (in blood vessels)
fascial nodular fasciitis (in deep fascia)
intramuscular nodular fasciitis
- muscle is completely replaced by the fibrovascular proliferation (unlike proliferative myositis, which infiltrates between muscle fibers)
Localization
soft tissues
intraarticular nodular fasciitis (16434899)
Prognosis
These lesions rarely recur, do not develop metastases, and are readily cured by local excision.
Despite its often aggressive microscopic appearance, nodular fasciitis is a self-limiting lesion which is readily treated by simple local excision.
Deeper lesions tend to be somewhat larger and less well demarcated, hence, require a wider local excision.
Recurrence rates vary from 1-6% with this treatment and some lesions have been reported to regress and disappear without treatment.