Periosteal fasciitis, considered a subtype of nodular fasciitis, is a rare benign soft tissue mass often misdiagnosed as a malignant lesion due to its fast and infiltrative growth pattern and histological features. Nodular fasciitis is usually found in the upper extremities in adults and in the head and neck region in children. Incorrect diagnosis may lead to overtreatment, potentially causing disturbed orofacial development in growing children. A rapidly growing asymptomatic mass, initially suspected to be a malignant bone tumour, was found in the left angle area of the mandible in a healthy 7-year-old girl. Radiographic examination revealed an exophytic, expansile and destructive nodule arising from the periosteal region. A diagnosis of periosteal fasciitis was established based on histological findings in an open biopsy specimen and the lesion was subsequently enucleated. Fluorescence in situ hybridization analysis revealed a USP6 gene rearrangement and confirmed the diagnosis molecularly. Due to the aggressive growth pattern without external trauma and the results of the gene rearrangement test, it is suggested that nodular fasciitis be regarded as a benign neoplasm rather than as a reactive process. The patient remains free of disease at 3 years after surgery.
Nodular fasciitis (NF) is a rare and benign soft tissue mass often misdiagnosed as a malignant neoplasm because of its fast and infiltrative growth pattern. It has been considered a reactive process involving the proliferation of fibroblasts, although its pathogenesis remains unknown. The lesion was first described by Konwaler et al. in 1955 as pseudosarcomatous fasciitis. Periosteal fasciitis is considered a subtype of NF, constituting about 4% of all cases. The literature on periosteal fasciitis is sparse.
In adults, NF occurs most commonly in the upper extremities. It can be found at any age, but most cases are detected in adults in their third to fifth decade of life. NF in children is rare. Only a few articles have been published on periosteal fasciitis in paediatric patients, and these have shown the head and neck area to be the most commonly involved site in children. Boys appear to be more often affected than girls.
NF is usually unilateral and typically presents as a painless mass developing in the subcutaneous or deeper soft tissues over the course of only a few weeks. The mass is generally well circumscribed, but can infiltrate into the surrounding tissues.
Due to its varied clinical and radiological presentation and sometimes worrisome histological features (pseudosarcomatous), the diagnosis of NF can be challenging. The preferred treatment is excision, and the risk of recurrence is considered low. Metastases have not been reported. Establishing the correct diagnosis is important to prevent overly radical treatment.
A fast-growing soft tissue mass developing over the course of 1 month in the mandible of a healthy 7-year-old girl was detected by a paediatrician. An ultrasound examination raised the suspicion of a non-homogeneous bone tumour in the left mandibular angle area (diameter 1.5 cm). The tumour was painless and firm on palpation.
Cone beam computed tomography (CBCT) examination revealed a 1.0 × 1.5 cm exophytic juxtacortical mass eroding the cortical bone ( Fig. 1 A–C). Tiny bony septae were detected inside the lesion (see video of the CBCT examination in the Supplementary Material online). A subsequent magnetic resonance imaging (MRI) examination showed a multilocular space filled with liquid in the inferior part of the mandible. An open biopsy was performed.
Microscopically, the lesion was found to be well-circumscribed with a surrounding fibrous capsule ( Fig. 2 A). Some irregular bone trabeculae were found, especially at the periphery ( Fig. 2 B). The lesion consisted mainly of spindle-shaped fibroblasts without a significant amount of atypia or increased mitosis ( Fig. 2 C). After several external consultations, a diagnosis of periosteal fasciitis was established.