A 20-year-old female patient presented with a 1-year history of a slowly growing mass located in the inner compartment of the proximal third of the left arm. She had no history of trauma or systemic diseases. She did not experience pain, paresthesia, perfusion changes or other signs of neurovascular compression.
Before admission to our hospital, a left-arm ultrasound had been performed, mentioning a solid hypoechoic mass located deeply to the deep fascia of the arm, with ill-defined margins, heterogeneous echotexture, scarce foci of calcifications and internal flow on power-Doppler assessment. The patient was referred to do a magnetic resonance imaging (MRI) study in our institution. Axial T1-weighted images (WI) through the proximal third of the left arm showed a large infiltrating mass with intermediate signal intensity, arising within the deep muscular compartments, crossing fascial boundaries, closely encircling the medial neurovascular bundle of the arm, and blurring the adjacent fat planes (Fig 1). Axial T2-WI and proton density (PD) images with fat suppression (FS) showed a heterogeneous mass, with central areas of low signal intensity, suggesting fibrotic/calcifying nature, surrounded by a diffuse area of high signal intensity (Fig 2 and Fig 3, respectively). After intravenous injection of gadolinium, there was avid contrast enhancement within the peripheral region of the lesion, without enhancement of the central region (Fig 4). There was also a subtle periosteal reaction in the diaphyseal region of the humerus, with associated subcortical oedema, which could represent reactive changes or extension of the tumour (Fig 3). There was no bony destruction.
The differential diagnoses of the lesion included parosteal or extraskeletal osteosarcomas, pseudosarcomatous lesions of the soft tissue, such as desmoid tumours, and myositis ossificans.
The assistant team decided to perform a core needle biopsy and the histopathological examination of the specimens revealed an infiltrative lesion evolving the skeletal muscle and the adjacent fat planes, with interlacing fascicles of spindle-shaped fibroblasts in a dense collagen stroma, characteristic of fibromatosis. Mitotic activity, nucleic pleomorphism and necrosis were not evident.
Given the location and extension of the lesion, the therapeutic approach was conservative.
The follow-up MRI performed one year later, revealed a slight increase in the dimensions of the lesion, and the accentuation of the central internal areas of very low signal intensity in all pulse sequences, suggestive of calcification/ossification (Fig 5 a,b). A simple radiograph of the left arm was performed to demonstrate the presence of areas of calcic density in the inner compartment of the arm, corresponding to the low signal intensity areas depicted on MRI, confirming their ossifying nature (Fig 6).
The final diagnosis was arm fibromatosis with central ossification.
Fibromatoses are uncommon mesenchymal neoplasms characterized by benign proliferation of fibroblasts and myofibroblasts, marked production of intercellular collagen and variable amounts of extracellular myxoid matrix and vessels [1].
The World Health Organization Committee for Classification of Soft Tissue Tumors categorizes these lesions as superficial ("palmar/plantar-type") or deep ("desmoid-type"), based on their anatomic location [2]. The deep group consists of lesions with intermediate behaviour, that generally do not metastasize, but exhibit aggressive infiltrative growth and a tendency toward local recurrence, hence the term “aggressive fibromatosis” [3,4,5].
The incidence is estimated to be 2-4 cases per million per year, and it tends to have a female predominance. The peak age of onset has been reported to be between 25 and 35 years [1,4].
The location may be intra- or extra-abdominal and may involve the musculature of the trunk, abdominal wall, and the extremities, with a predilection for the upper arm and a tendency to arise from the deep compartment of muscle and aponeurotic tissue [3,4,6]. They commonly insinuate around vital structures, limiting the extent of surgical resection [5].
Although dystrophic or psammomatous calcification is well documented, ossification coincident with fibromatosis is extremely rare, with only four cases described in the literature, related to pelvic, chest, forearm, and breast fibromatosis, respectively [7,8,9,10]. The cause of the ossification is not known, but the periosteal involvement may be a factor since fibroblastic proliferations of the periosteum tend to ossify [9].
Although the definitive diagnosis is histopathological, the main roles of imaging in aggressive fibromatosis are: 1) the evaluation of the exact location of the lesion and its relationships with adjacent soft tissue and bony structures, for preoperative planning; 2) the dimensional measurement to be used in follow-up, helping in the detection of recurrence or disease progression in nonsurgically managed patients [3].
MRI provides the optimum method of tumour evaluation, due to its superior soft-tissue resolution. The relationship of the tumour to important local structures, such as nerves, vessels, deep viscera, and bone, can only be accurately assessed using MRI [3,6].
MR imaging patterns of deep fibromatoses are highly variable. The most common findings of aggressive fibromatosis on MRI are of an ovoid or infiltrative lesion that is lobulated or irregular in outline. Up to 80% of the cases present linear extension along fascial planes (the “fascial tail” sign), or a rim of fat (“split-fat” sign) [5]. Typically, aggressive fibromatosis lesions are homogeneously isointense on T1-WI, with intermediate to low signal intensity on T2-WI, PD and short tau inversion recovery (STIR) images and enhance avidly after intravenous gadolinium administration. The heterogeneous signal intensity pattern in fluid-sensitive sequences may correspond to varying proportions of cellular tissue, myxoid matrix, and collagen in each lesion [3]. Bands of low signal intensity within the lesion are seen in 60-90% of the cases and correspond to dense collagen bundles, which are optimally seen on contrast-enhanced T1-WI or T2-WI [3,4]. Diffusion coefficients of fibromatoses are very low, due to the high proportions of spindle-shaped cells [11]. MR imaging findings of hypointense bands and extension along fascial planes add specificity to the diagnosis [3,4].
Histopathologic confirmation is required for a final diagnosis in all cases [3]. Macroscopically, desmoids have spiculated infiltrative margins and are typically adherent to adjacent structures. Microscopically, they consist of poorly defined fascicles of uniform spindle cells and fibroblasts, interlaced in a dense collagen stroma. Mitotic activity is low, and necrosis is rare [1]. Areas of myxoid degeneration and haemorrhage may be seen. Osseous metaplasia in adult fibromatosis is stated to be rare and never a prominent feature [10].
A multidisciplinary approach tailored to the individual patient is required for the optimum management of aggressive fibromatosis. Stable asymptomatic desmoids can be observed. Treatment is necessary for symptomatic desmoids, especially those with mass effects on critical structures [1]. If feasible, surgical resection with a wide margin is the treatment of choice. Adjuvant radiation therapy following surgery has been shown to decrease the local recurrence rate. Additional therapies with reported positive results include radiofrequency ablation, hormonal therapy, tyrosine kinase inhibitors and cytotoxic chemotherapy [4].
Recurrence is common (up to 77% of the cases) and more frequent with extra-abdominal desmoids (30–50%) than intra-abdominal desmoids (15–30%) [1].
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Arm fibromatosis with central ossification
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1. Location and morphology: A soft tissue mass is noted in the proximal medial intermuscular space of the left upper arm, showing relatively irregular margins with a local infiltrative growth pattern.
2. Signal and density characteristics:
• On MRI T1-weighted images, the lesion mostly presents an isointense signal;
• On T2/STIR sequences, it appears to be of intermediate to low signal, with areas of heterogeneous signal in certain regions;
• There is marked enhancement of the lesion, with low-signal fibrous bands inside (consistent with dense collagen fibers);
3. Relationship to surrounding structures: The lesion is adjacent to the deep muscles and fascia of the upper arm and shows extension along the fascia. Although it is in proximity to the neurovascular bundle, no obvious compression or occlusion of blood vessels or nerves is currently observed.
4. X-ray findings: Small patchy high-density shadows can be seen in the corresponding region of the lesion, suggesting the presence of minor calcification or ossification. The continuity of bone remains largely intact without evident bone destruction.
Based on this patient's clinical presentation (20-year-old female, slow-growing, painless, localized infiltrative lesion) and the characteristic MRI findings (low signals on T2 due to fibrous components, extension along the fascia), the leading consideration is aggressive fibromatosis (Desmoid tumor).
Considering the patient's age, lesion location, imaging characteristics, and pathological findings indicating fibrous proliferative tissue, the most likely diagnosis is
Aggressive Fibromatosis (Desmoid tumor).
If further clarification or exclusion of other soft tissue tumors is needed, a more comprehensive histopathological evaluation or immunohistochemistry is recommended.
1. Treatment Strategy:
• For lesions that are symptomatic, rapidly growing, or involve critical structures, surgical resection with a negative margin is the preferred approach, potentially combined with radiation therapy to lower local recurrence rates.
• In cases where complete resection is not feasible or the recurrence risk is high, hormonal therapy, tyrosine kinase inhibitors, or chemotherapy may be considered.
• For stable lesions with mild symptoms, it is reasonable to adopt a watch-and-wait strategy, monitoring the lesion through regular imaging follow-ups.
2. Rehabilitation / Exercise Prescription Suggestions:
• Basic Principles (FITT-VP): Develop an individualized exercise program based on the patient’s recovery status, specifying the exercise type, intensity, frequency, duration, and progression.
• Postoperative Rehabilitation:
Disclaimer: This report is provided solely as a reference for medical analysis and does not replace an in-person consultation or professional medical advice. If you have any questions or notice changes in your symptoms, please consult a specialist for further individualized evaluation and treatment recommendations.
Arm fibromatosis with central ossification
