{'fraction_non_alphanumeric': 0.03187812059915504, 'fraction_numerical': 0.010113941876840353, 'mean_word_length': 4.851685393258427, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Giant cell tumor of soft tissues: A case report of extra-articular diffuse-type giant cell tumor of the quadriceps

Highlights • Report a rare entity of extra-articular Diffuse-type Intramuscular Tenosynovial Giant Cell Tumor of the Quadriceps.• It is a benign but locally aggressive tumor. If surgically treated with wide excision, it is expected t have a benign clinical course.• This case may be instructive for differential diagnoses of primary intramuscular tumors.


Introduction
Tenosynovial giant cell tumors (GCTs), also known as pigmented villonodular synovitis, are benign soft tissue tumors that arise from the synovium of the joints, bursae and tendon sheath [1,2]. These tumors are classified into two forms: localized and diffuse (Fig. 1). Diffuse-type giant cell tumor is an extra-articular form of pigmented villonodular synovitis [3].
Localize-type tenosynovial GCTs are frequent, indolent, and arise from the synovium of the joint, bursa, or tendon sheath. In contrast, the less frequent diffuse-type tenosynovial GCTs are locally aggressive and commonly affect peri-articular soft tissue, but on rare occasion these lesions can be intramuscular [2,4]. The yearly incidence of diffuse −type tenosynovial GCTs is two per 1,000,000 cases. Extra-articular diffuse-type GCTs represent only 5-15% of all diffuse-type tenosynovial GCTs. Despite the rarity of intramuscular diffuse GCTs, it is important to know that they infiltrate surrounding the soft tissue and have a high recurrence rate [2]. Localized versus diffuse forms of tenosynovial GCTs may cause different clinical symptoms.
Here we describe the case of 44-year-old woman who presented with a thigh pain and a mass in the right quadriceps. The final diagnosis was an extra-articular diffuse type intramuscular giant cell tumor treated by a complete surgical resection. It is a rare benign tumor but locally aggressive which must be known as a differential diagnosis of sarcoma.
This case report is in line with the SCARE criteria [5].

Case report
The patient was 44-year-old, a sedentary housewife, with threeyear history of vague pain in the right thigh without any antecedent of trauma or infection. She visited our institution, on June 2015, with a right mass above the knee first noted 10 months prior to presentation. There was no restriction of movement of the right knee, and the patellar compression test was negative.   On examination, it appeared to be a non-tender soft tissue mass measuring about 7.0 * 4.0 cm in size. The mass was fixed to the muscle.
The radiographs of the knee and the femur demonstrated a lobulated soft tissue mass at the anterior and lateral aspect of the right lower thigh. There were no calcification related to the lesion (Fig. 2).
On sonographic examination, the mass was heterogenous echoic mass with a hypoechoic central portion (Fig. 3).
A magnetic resonance imaging (MRI) study was performed which showed a mass confined to the Rectus Femoris muscle. The size of the mass was 7.2 * 5.3 * 2.5 cm. The signal intensity was less than of subcutaneous fat on T1-weighted sequences. On T2-weighted images, the tumor was heterogenous, it was hyper intense with focal areas of low signal intensity within the mass. The major portion of the mass showed enhancement after gadolinium enhancement (Fig. 4).
We provided a differential diagnosis of rhabdomyosarcoma, synovial sarcoma and desmoid tumor based on these MRI features.
A biopsy of the tumor was performed. In histological findings, The tumor was densely cellular and was composed of sheets of mononuclear cells admixed with multinucleated giant cells, the mononuclear cells are round or polygonal «histiocytic» and exhibit little pleomorphism nuclei. Some of these cells contain intracytoplasmic hemosiderin. The cells dysplasia are occasional mitotic figures. Multinucleated giant cells are intermingled scattered throughout the lesion and have a variable number of nuclei, rangin from 3 to 20. Inflammatory cells, particularly lymphocytes, siderophages and xanthoma cells are scattered randomly throughout the tumors but very greatly in number. Pseudogranular spaces are focally seen. The tumor infiltrates the tendon sheath. The stroma was collagenous and inconspicuous. The pronounced cellularity coupled with the polymorphic population of cells is likely to lead to a diagnosis of malignancy.
The histopathological diagnosis was a diffuse-type giant cell tumor (Fig. 5).
After preoperative evaluation and preparation, a carefully complete surgical resection of the tumor was done. Infection prevention, venous thrombosis prevention, analgesia and other conventional medical treatments were given according to standard clinical pathway in perioperative period of soft tissue tumors.
Abundant hemosiderin pigment was seen in macroscopic examination. The diagnosis of diffuse-type GCT was confirmed by the histological findings of the final piece of tumor. The patient remained symptom-free with no local recurrence 1 year after surgery; MRI should have been made, but the patient was lost in follow up.

Discussion
The extra-articular form of diffuse-type tenosynovial GCT was first described by Jaffe et al. [1]. Diffuse-type GCTs are now classified as «fibrohistiocytic tumors» in the World Health Organization system of classification of bone and soft-tissue tumors [7]. Unlike localized types, these tumors are aggressive and recur in 33-50% of the cases, often with multiple recurrences. A long-term following up is needed in our case.
Diffuse-type GCTs have a slight female preponderance [8]. These lesions are seen usually under the age of 40 [7].
Diffuse-type tumors are commonly located in the periarticular soft tissues, but on rare occasions these lesions can be purely intramuscular or subcutaneous and can be challenging to diagnose [6].
Most intramuscular diffuse-type GCTs are located in the lower extremities such as the thigh, buttock, and lower leg, but all the muscles can be affected [6].
In a review of 50 cases of diffuse-type giant cell tumors by Somerhausen and Fletcher [6] there were only three cases (6%) with involvement of the subcutaneous tissues, of which two were in the knee region.
MRI is highly sensitive and specific for the diagnosis of intra-articular PVNS and its extra-articular localized and diffuse forms. Characteristic findings include gradient echo secondary to hemosiderin deposition, and the low signal on T2 [8]. In comparison, our case showed only a few areas of low T2 signal in a mass that was hyperintense to muscle.
Because extra-articular diffuse-type GCTs are rare, the differential diagnosis is challenging. Our pre-operative differential diagnosis included soft-tissue sarcoma and desmoid tumor [9].  Giant cell tumors of soft tissue are slowly grown, painless lesions, and are treated with surgical excision. Although benign, these tumors have a high recurrence rate ranging from 9% to 44%.
There are a few case reports of malignant PVNS [10,11]. The clinical outcomes of diffuse-type GCTs are unclear because of their rarity.
In our case, the tumor may have possibly arisen from the tendon or bursal surface (Fig. 6).

Conclusion
In summary, we reported a case of intramuscular diffuse-type Giant Cell Tumor in a female of 44-year-old. It is a benign but locally aggressive tumor; its local recurrence cannot be predicted. Proper surgical excision and a long period of follow up are essential in these cases. Because of the unusual type and location and the lack of typical T2 shortening seen in extra-articular GCTs, the present case may be instructive for differential diagnoses of primary intramuscular tumors.

Conflict of interest
No potential conflict of interest relevant to this article was reported.

Funding
None.

Ethical approval
Approval has been given by the patient.