Clinical Profile:

A 72-year-old woman came with the complaints of gradually increasing breathlessness for one year, associated with weight loss for the last two months. 

• She gave history of swelling in the right thigh region for the last 20 years which became more evident in the last two months due to weight loss. 

Radiological findings:

Plain radiograph: 

Frontal chest radiograph shows multiple well defined fluffy cotton wool spots scattered throughout both the lung fields.

Right femur radiograph shows a well-defined soft tissue opacity in the upper aspect of the right thigh. There is no calcification within. There is no involvement of the underlying bone.

Fig. 2 :  Frontal chest radiograph shows multiple well-defined fluffy cotton wool spots scattered throughout both the lung fields.

CECT Chest: 

• shows multiple variable sized well defined, round, enhancing soft tissue density lesions scattered in both the lung parenchyma, largest measuring 4.9x4.5x4.6cm in the anterior segment of the right upper lobe.

CECT Right thigh:

• shows a well-defined heterogeneously enhancing multiloculated mass in the posterior aspect of the right upper thigh in gluteus maximus muscle causing splaying of its lower insertion fibres.

• The lesion measures 7.8x11x13.6 cm with multiple vascular channels supplying it.

• Anteriorly the lesion is seen displacing adjacent hamstrings and adductor muscles with maintained fat planes.

• Posteriorly the lesion is not extending into skin.

• Adjacent shaft of right femur appears unremarkable.

Fig. 4 : The plain[A] and contrast enhanced[B] computed tomography of the chest shows multiple variable sized well defined, round, enhancing soft tissue density lesions scattered in both the lung parenchyma, largest measuring 4.9x4.5x4.6cm in the anterior segment of the right upper lobe.

Fig. 5  :Plain computed tomography image of the right thigh in axial[A]. Sagittal[B], coronal[C] section shows a well-defined multiloculated mass in the posterior aspect of the right upper thigh in gluteus maximus muscle.

Fig. 6  Contrast enhanced computed tomography image of the right thigh in axial[A]. Sagittal[B], coronal[C] section shows the mass is heterogeneously enhancing and measures 7.8x11x13.6 cm with multiple vascular channels supplying it

MRI right thigh:

• There is a well-defined multilobulated T2 heterogeneous lesion measuring 8.7x10x15cm with multiple hypointense fibrous thin septae, with thick peripheral homogeneous enhancement.

• There are areas of T1 hyperintensities within few of the locules suggestive of haemorrhage.

• It is seen arising from the gluteus maximus extending in the intramuscular plane of the right posterior thigh and extending superficially into the subcutaneous plane posteriorly.

• The adductor magnus is displaced anteriorly.

Fig. 7  MRI of the right thigh in axial section of T2 weighted[A] image shows a well-defined multilobulated T2 heterogeneous lesion measuring 8.7x10x15cm with multiple hypointense fibrous thin septae. The lesion shows thick peripheral homogeneous enhancement in post contrast image[B]T1 weighted coronal[C] section shows areas of hyperintensities within few of the locules suggestive of haemorrhage.

Radiological diagnosis:

Undifferentiated sarcoma

Pathological diagnosis and treatment:

An ultrasound guided biopsy of the right thigh swelling was performed and histopathology showed low grade fibro-myxoid sarcoma

Fig. 8  Histopathological image shows the myxoid areas are moderately cellular and the bland lesion cells are fusiform or spindle.

Timeline

Discussion

Low grade fibromyxoid sarcoma (LGFMS) has been defined as a cytologically bland malignant neoplasm with alternating fibrous and myxoid stroma of low-grade/low malignant potential.[1] This uncommon entity was described first by Evans.

• The tumours vary in size from 1 to 23 cm. [2,3] These tumours are classically situated in the trunk and lower extremities. The most common tumour locations were the shoulder, thigh, and inguinal area. However, some tumours have been rarely noted in other areas like the mesentery and intracranial location. [4,5]

• Radiologically, LGFMS appear as a well-circumscribed single mass at initial diagnosis and as a cluster of masses at local recurrence on CT and MRI. The multiplicity of masses seen at local recurrence could potentially be due to multiple residual tumour foci after incomplete surgical resection, as LGFMS displays variable degrees of infiltration into adjacent soft tissue on histology.[6]

• On CT, the tumours appear iso/hypodense with variable contrast enhancement. The variable contrast enhancement pattern seen on CT probably reflects different amounts and locations of fibrotic and myxoid tissue in different tumours. Calcification is uncommon. On MRI, the myxoid areas shows findings of high signal intensity on T2-weighted images, whereas the hypercellular areas shows low signal intensity on T2-weighted images.  

• These tumours show alternating fibrous and myxoid stroma. Grossly, the tumour appears as a circumscribed mass, but microscopic infiltration may be present. Tumour cells are 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, tumour cells are usually characterised by absent to sparse mitotic figures, nuclear anaplasia, or necrosis.[7]

• On immunohistology, the staining is positive for vimentin and MUC4, and negative with antibodies, such as Desmin, keratin, S-100 protein, EMA, CD34, and CD31.

• Differential diagnosis of LGFMS includes lesions showing spindle cell proliferations with myxoid pattern with or without fibrous component.[8] The entities with predominantly myxoid pattern without significant fibrous component include myxomas, low-grade myxofibrosarcoma, angiomyxomas, myxoid liposarcoma, and a myxoid neurofibroma. Tumours with mixed myxoid and fibrous morphologies include neurofibroma, fibromatosis, perineurioma, malignant peripheral sheath tumour, and fibrous histiocytoma. Additional entities that should be encountered are desmoid tumour, desmoplastic fibrosarcoma, and low-grade differentiated liposarcoma.

• The recommended treatment is wide surgical excision. Margins were called as marginal if the resection included the pseudo capsule or wide if the resection included a cuff of normal tissue.[9] Local recurrences were treated with surgery without adjuvant therapy. However, distant metastases were treated with chemotherapy agents including ifosfamide, doxorubicin, imatinib, trabectedin, gemcitabine, docetaxel, as well as palliative radiotherapy. Trabectedin yielded the best response.

• As these tumours are known to metastasise after a long interval, sometimes after as many as 45 years, a thorough clinical follow-up is recommended. However, no study has till date recommended any protocol for the follow-up. Once a diagnosis of LGFMS has been made a thorough oncological evaluation including observing the chest carefully is advisable as chest metastases are the most common.

References:

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Acknowledgement :

We are grateful to the Department of Pathology  at our institution for providing us with an image from the histological findings as also its description.