October 9, 2018
A 22-month-old girl with a right submandibular region mass enlarging over the past month
Desmoid Fibromatosis
- Background
- Desmoid fibromatosis (DF), also known variously as desmoid tumor, deep fibromatosis, and aggressive fibromatosis, is a rare mesenchymal neoplasm.
- Annual incidence is 0.2-0.4/100,000. Patients are predominantly male, age peaks occur between ages 6-15, and between puberty and age 40, although other case series describe presentations as frequent as in the first 2 years of life.
- DF can involve various sites, including the extremities, abdomen, and head and neck. Head and neck involvement in the tongue, mandible, maxilla, or mastoids is reportedly most common in children.
- Histologically, tumors demonstrate myofibroblastic/fibroblastic differentiation characterized by sweeping bundles of bland spindle cells and collagen fibers. Lesions are poorly circumscribed and tend to infiltrate muscle. Cells lack features of malignancy and have no metastatic potential.
- Tumors are often solitary and arise as a firm mass from skeletal muscle, fascia, aponeurosis, or periosteum.
- DF most often occurs sporadically, but can occur in familiar adenomatous polyposis (FAP), in which patients have germline mutations of the APC tumor suppressor gene, esecially the Gardner’s syndrome phenotype of FAP.
- Imaging
- US findings are non-specific, but lesions are often homogeneous and hypoechoic.
- DF is often of similar attenuation to muscle on CT, and often enhances. CT most accurately characterizes bone involvement, including erosion, invasion, and remodeling. Soft tissue components do not demonstrate calcification or bone matrix.
- DF MR signal intensity characteristics are quite variable, and can be hypo-, iso-, or hyperintense to muscle on T1, although they are usually hyperintense to muscle on T2 images. Various enhancement patterns have been described in the literature, although lesions frequently demonstrate at least some enhancement. The diffusion weighted findings with this patient likely reflect the low cellularity of the mass.
- Part of the imaging goal is to define the extent of infiltration, especially regarding nearby neurovascular structures.
- DDX: Rhabdomyosarcoma, fibrosarcoma, lymphoma
- Treatment
- Complete surgical resection is the first line of treatment. Although there is no metastatic potential, local recurrence is common, especially after incomplete resection.
- Adjuvant radiotherapy after surgery has been used to improve local control rates, but this carries significant morbidity in children.
- Chemotherapy regimens can be used and vary depending on the aggressiveness of the lesion being treated.
- Low-dose options such as methotrexate and vinblastine have been used in slower-growing lesions, although rapidly growing lesions have required more intense chemotherapy.
- Treatment with hormonal therapies (such as tamoxifen) has been used, but with unclear and controversial results.
