Low grade fibromyxoid sarcoma (LGFMS) is a distinctive variant of fibrosarcoma . It is characterized by an admixture of collagenized hypocellular zones and more cellular myxoid nodules. Tumour cells are usually small, with scanty eosinophilic cytoplasm, round to ovoid nuclei and absent nucleoli. Although focal cytologically atypical areas of high cellularity, increased mitotic activity, nuclear hyperchromatism, and necrosis may be found in approximately 10% of the cases, tumour cells are usually characterized by absent to sparse mitotic figures, nuclear anaplasia or necrosis . Immunohistochemical staining is positive for vimentin only and negative with a variety of antibodies, such as desmin, keratin, S100 protein, epithelial membrane antigen, CD34, and CD31. Muscle specific actin is positive in the wall of small vessels within the tumor and strongly positive in the peripheral fibrous layer.
Ten years after the first description of LGFMS by Evans , a similar pathologic entity, the hyalinizing spindle cell tumor with giant rosettes (HSTGR) was reported . These tumors are characterized by a proliferation of bland spindle cells with fibromyxoid areas that resemble histologically LGFMS. Giant rosettes which are found in HSTGR is a distinctive pattern that is defined by the presence of hyalinized acellular islands surrounded by oval and spindle cells. In a large series of 77 cases of LGFMS and HSTGR, Folpe et al.  supported that these tumors represent the same neoplastic process and are of the spectrum of low-grade sarcomas. According to the same authors, several cases of LGFMS presented the pattern of miniature rosettes that had been overlooked at the time of the initial diagnoses. On the other hand, HSTGR is typically characterized by large areas that are histologically identical to LGFMS. Based on these finding the authors recommended that both entities should be referred to as "fibrosarcoma, low-grade fibromyxoid type" noting either the presence or absence of rosettes. More recently, the view that these two entities share the same pathologic mechanism was strongly supported by several investigators. More specifically, the presence of a balanced t(7;16)(q34;p11) translocation and a fusion between the FUS and CREB3L2 genes in both LGFMS and HSTGR were confirmed by multiple studies [11–16]. This translocation seems to be specific for the diagnosis of these tumors and particularly useful in cases of limited material for examination or in cases that the typical histopathologic features are not present. Furthermore, the FUS/CREB3L1 fusion transcripts of LGFMS can be reliably detected in paraffin-embedded tissues using RT-PCR .
Differential diagnosis of LGFMS includes lesions showing spindle cell proliferations with myxoid pattern with or without fibrous component . The entities with predominantly myxoid pattern without significant fibrous component include myxomas, low-grade myxofibrosarcoma, angiomyxomas, myxoid liposarcoma, and myxoid neurofibroma. Tumors with mixed myxoid and fibrous morphologies include neurofibroma, fibromatosis, perineurioma, malignant peripheral sheath tumor, and fibrous histiocytoma. Additional entities that should be encountered are desmoid tumor, desmoplastic fibrosarcoma, and low grade dedifferentiated liposarcoma.
The diagnosis of LGFMS or HSTGR is usually not difficult if the tumor has been removed completely and all the characteristic morphologic and immunophenotypic features described above are present. This is not usually feasible when the material derives from fine needle aspiration or needle core biopsy . In such cases, a wider biopsy, as in our case, or even an excisional biopsy should be performed. If a myxoid pattern is present and the diagnosis still remains unclear, cytogenetics should be requested in order to exclude the rare case of LGFMS .
The clinical presentation is usually long-standing and is mainly related to the anatomic location of the mass. LGFMS usually presents as a painless soft-tissue mass with a pre-biopsy duration of over 5 years in 15% of patients . In rare occasions acute presentations of the disease may occur, such as acute respiratory distress and chest pain in case of chest wall LGFMS or seizure activity in a patient with intracranial LGFMS [3, 18].
Although imaging findings of LGFMS are nonspecific, certain CT and MRI findings have been described [3, 19–21]. On noncontrast CT images the fibrous component of these tumors has been described as isodense to muscle tissue and the myxoid component as hypodense. On MR imaging, the fibrous component is characterized as hypointense on T1- and T2-weighted MR images, and slightly enhancing on T1-weighted MR images after gadolinium administration. On the other hand, the myxoid component has been described as hypointense on T1-weighted MR images and hyperintense on T2-weighted MR images, and vividly enhancing on T1-weighted MR images after gadolinium administration. Calcifications may also be found within the tumor .
Evans  and Goodlad et al.  suggested that LGFMS were paradoxically aggressive tumors. In these retrospective early series, local recurrence was noted in 68%, metastasis in 41%, and death from disease in 18% . Almost all these patients in these original studies were initially diagnosed with, and treated for a benign lesion. It is obvious that patient selection has influenced the reported rate of recurrence and metastases, as many of those cases were selected on the base of unexplained metastases. In a more recent and larger series local recurrence, metastasis, and death from disease was observed in 54%, 6%, and 2% of the patients, respectively . In the same study it has been shown that the presence of focal areas of high cellularity, nuclear enlargement, increased mitotic activity, and necrosis are not of prognostic significance for recurrence or metastasis. Given the potential of LGFMS for late metastasis, sometimes 45 years after initial diagnosis, the median follow-up of only 24 months in the previous study should be considered too short in order to ascertain safe conclusions .
Once the diagnosis of LGFMS or HSTGR is made, a full oncological assessment should follow. This should include a CT scan of the chest, since metastasis to the lung is the most common scenario. Because of the high risk of late metastasis, clinical follow-up and chest imaging should be performed for an extended period of time. However, it is still unclear how regularly imaging of the chest should be repeated .