Differential diagnosis
The diagnosis was reconsidered to
be nodular fasciitis based on the cellular morphology and the growth
pattern. The tumor consisted of plump fibroblasts with bland nuclear
features and a low mitotic rate (4 per 10 HPFs, f.d. 0.57 mm) in a
myxoid and collagenous stroma. Intersecting fascicles with a storiform
pattern, high cellular density, pseudocyst formation, and an
inflammatory infiltrate containing giant-cell macrophages suggest
nodular fasciitis and help narrow the differential diagnosis.
While nodular fasciitis can be suspected based on histologic features,
it must be differentiated from
fibrosarcoma, smooth muscle tumors, malignant peripheral nerve sheath
tumor, dermatofibrosarcoma protuberans, melanoma, and solitary fibrous
tumor. Nodular fasciitis has no pathognomonic immunohistochemical
markers. However, SMA and vimentin typically show diffuse intensive
staining [3]. Desmin is only rarely positive; S100 and h-caldesmon
are negative [4-5]. Other positive markers include calponin and CD10
[1,7] (Table 1). Proliferative index Ki67 is highly variable in
nodular fasciitis and does not aid in diagnosis.
Fibrosarcoma and malignant smooth muscle tumors are in the differential,
but the absence of necrosis, frank nuclear atypia, and atypical mitotic
figures support this tumor’s benign nature. Immunohistochemistry can aid
in differentiating these diagnoses by the presence or absence of desmin,
h-caldesmon, and estrogen/progesterone receptor positivity (Table 1).
Leiomyosarcoma is positive for desmin and h-caldesmon, but nodular
fasciitis is negative for these markers. Fibrosarcoma can be CD34
positive in some cases, usually in dermatofibrosarcoma protuberans, but
nodular fasciitis, the positivity is excitingly rare [6].
Malignant peripheral nerve sheath tumor that was initial diagnosis at
the time of recurrence was excluded based on the relatively low mitotic
count, absence of atypia, and invasion in surrounding tissue with
negative S-100 staining on immunohistochemistry. Malignant melanoma was
excluded due to the negative S-100 and melan-A staining in this case.
Solitary fibrous tumors must show perivascular growth patterns and tend
to be positive for CD34 and BCL-2 [8].