Desmoplastic fibroblastoma also known as collagenous fibromas are rare benign fibroblastic soft tissue tumors with an abundant collagenous or myxocollagenous stroma seen in adults1-3.
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Epidemiology
Desmoplastic fibroblastomas are rare and usually occur in the adult population with a median age of 50-60 years. There is no known gender predilection 1.
Diagnosis
The diagnosis of desmoplastic fibroblastoma is pathological 1.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
- low cellularity lesion with abundant collagenous and variable myxoid stroma
- stellate-shaped bipolar and spindled cells with small nucleoli
Clinical presentation
Usually desmoplastic fibroblastomas present as slow-growing painless subcutaneous masses 1.
Pathology
Desmoplastic fibroblastomas are hypocellular sparsely vascularized tumors with abundant collagenous and myxocollagenous matrix 1.
Etiology
The etiology of desmoplastic fibroblastomas is unknown 1.
Location
Desmoplastic fibroblastomas usually occur in the subcutaneous tissues but the involvement of skeletal muscle and fascia is common. The extremities and limb-girdle areas are most commonly involved such as the shoulder, upper arm, lower limb, the back, the forearm or the hand and feet. There are also cases occurring in the head and neck region 1-4.
Macroscopic appearance
Macroscopically desmoplastic fibroblastomas are well-defined oval to fusiform or discoid masses some of them feature a lobulated cobblestone appearance. They are of pearl-grey color and feature a firm cartilage-like consistency 1.
Microscopic appearance
Histological features of desmoplastic fibroblastomas include the following 1-3:
- abundant collagenous and myxocollagenous matrix with low vascularity
- low to moderate cellularity with uniformly distributed stellate fibroblasts and myofibroblasts
- subcutaneous fat infiltration
- extension into the skeletal muscle (≈ 25%)
- low mitotic activity
Immunophenotype
Immunohistochemistry stains might express vimentin or desmin and be focally positive for smooth muscle actin (SMA) 1-3.
Genetics
In desmoplastic fibroblastomas, recurrent 11q12 rearrangements with deregulated FOSL1 gene expression have been observed 1,2.
Radiographic features
Desmoplastic fibroblastomas have been described as well-defined soft tissue masses often adjacent to dense connective tissues and associated with muscle, deep muscular fascia, joints and tendons 2-5.
Ultrasound
Ultrasound shows mixed echogenicity 3-5.
CT
On CT desmoplastic fibroblastomas usually, appear as non-specific inhomogeneous soft tissue density mass 4,5.
MRI
Desmoplastic fibroblastomas are ovoid to fusiform well-circumscribed sometimes lobulated-looking lesions adjacent to connective tissue structures 2-5.
Signal characteristics
- T1: low signal to intermediate intensity
- T2: low signal intensity to mixed hyperintensity compared to muscle
- STIR/T2FS/PDFS: heterogeneous hypointense to intermediate with high signal intensity areas
- T1 C+ (Gd): peripheral enhancement and enhancing septae
Radiology report
The radiological report should include a description of the following:
- location and size of the tumors
- relation to muscles and deep fascia
- relation to joints and tendons
- relation to nerves and vessels
- relation to other organs or glands
Treatment and prognosis
Desmoplastic fibroblastomas are benign tumors. There are no reports of recurrences after surgical excision 1.
History and etymology
Desmoplastic fibroblastoma was first described by the American pathologist Harry L Evans in 1995 6.
Differential diagnosis
Conditions that can mimic the appearance of desmoplastic fibroma include 2,4:
- palmar and plantar fibromatosis
- desmoid tumor
- fibroma of the tendon sheath
- peripheral nerve sheath tumor
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