A Collagenous Fibroma (Desmoplastic Fibroblastoma) is a rare, benign, slowly growing, fibroblastic, soft tissue lesion. Here, the case of a 28-year-old woman, who presented with a 1-year history of a slowly growing painless mass in the right anterior aspect of her neck, is described. This type of tumor was first described by Evans in 1995, and named as a Desmoplastic fibroblastoma but was renamed, by Nielsen in 1996 as a Collagenous Fibroma. This type of tumor is frequently reported in men with a mean age at occurance of 50 years. Clinically, a Collagenous fibroma presents as a firm, well-circumscribed subcutaneous, or intramuscular, painless mass of long duration. They are mostly located in the neck and extremities. The tumors range in size from 1 to 20 cm and predominantly occurs within the subcutaneous tissue, but fascial and skeletal muscle involvement is common. The treatment of a Collagenous Fibroma is a total surgical excision. No tumor recurrence has been reported the literature during the follow-up period and no tumor recurrence was observed in our case at the 1-year follow-up.

Desmoplastic fibroblastoma: a light and ultrastructural description of two cases.Ultrastruct Pathol. 2004 May-Jun;28(3):149-57.

The authors report 2 cases of collagenous fibroma in which ultrastructural analysis revealed the presence of fibronexus junctions, markers of myofibroblastic differentiation, never described in this rare lesion before. The tumors occurred in the trapezius muscle and in the right arms of a 41 -year-old and a 25-year-old man. They were both intramuscular and showed sharp edges. Grossly, the excised masses were whitish and firm. Microscopically, they were both composed of stellate or spindle-shaped cells separated by a collagenous hypovascular and focally myxoid stroma. Mitotic figures and necrotic areas were not identified. Immunohistochemistry showed positivity for vimentin and focal positivity for smooth and human muscle actin, and flow cytometry showed the tumoral cells to be diploid.

Superficial collagenous fibroma: immunohistochemical, ultrastructural, and flow cytometric study of three cases, including one pemphigus vulgaris patient with a dermal mass.APMIS. 2002 Apr;110(4):283-9.

Collagenous fibroma (desmoplastic fibroblastoma) is an extremely rare benign soft tissue tumor of fibroblastic origin. The majority of reported cases have been located in the deep subcutis, fascia, aponeurosis, or skeletal muscle of the extremities, limb girdles, or head and neck regions. There has been no mention of underlying diseases in patients who developed this tumor. We here report an additional three cases of superficial collagenous fibroma, one of which was a dermal lesion occurring in the abdomen of a 26-year-old male patient with a 5-year history of pemphigus vulgaris prior to development of the tumor. To the best of our knowledge, an association between collagenous fibroma and pemphigus vulgaris has not previously been reported. The remaining two tumors were located in the superficial subcutaneous tissue of the infrascapular area and right foot, respectively. There was no tumor recurrence or metastasis during follow up of 18, 25, and 47 months, respectively. All three tumors were well-circumscribed and unencapsulated without infiltrating borders. Histologically, the common denominator of all three cases was paucicellular proliferation of spindle or stellate fibroblasts enmeshed within an extensively collagenous background. Immunohistochemically, there was diffuse strong staining for vimentin and intense focal reaction for smooth muscle actin in two tumors tested. Electron microscopy revealed features consistent with a fibroblastic or myofibroblastic lineage. Flow cytometry in two cases demonstrated a diploid DNA content with low S-phase fractions, which correlated with minimal MIB-1 nuclear labeling (less than 1%) and benign behavior of this entity.