Extraskeletal myxoid chondrosarcoma: Diagnosis of a rare soft tissue tumor based on fine needle aspiration cytology.

Extraskeletal myxoid chondrosarcoma (EMC) is a rare soft tissue sarcoma with limited literature available on its cytological features. We report here one such case where a diagnosis of EMC was made based on fine needle aspiration cytology (FNAC). A 51 year-old male presented to our FNAC clinic with a slowly growing mass in the left thigh, which was subjected to fine needle aspiration biopsy. Radiological images showed no involvement of the underlying bone. Magnetic resonance imaging was suggestive of a malignant neoplasm. The FNA smears showed cell fragments and cords of monotonous cells embedded in abundant myxoid stroma. A diagnosis of a myxoid sarcoma favoring an EMC was made in this patient. Subsequent excision of the mass for histopathological examination confirmed this diagnosis. EMC has distinctive cytological features that are helpful in confidently making a diagnosis in the appropriate clinical setting.

Introduction

Enzinger et al.[1] described for the first time in 1972 a distinct clinicopathological entity comprising a series of unique myxoid soft tissue tumors called, ‘Extraskeletal Myxoid Chondrosarcoma. Many case reports and studies appeared subsequently in the literature, describing this rare tumor with distinct features. Although now recognized as being unrelated to chondrosarcoma of the bone, EMC was initially believed to be of cartilaginous origin.[2] It is a slowly growing tumor, prone to local recurrences and sometimes, metastases.[3-5]

This tumor behaves differently from other sarcomas as it is associated with a prolonged survival even after metastasis in some cases. However, a high rate of death has been described to occur eventually due to these tumors.[5] This unusual tumor typically presents as an enlarging mass in the extremities of adults and rarely in various other locations.

There have been only a few case reports on the cytological features of EMC.[6-9] We describe here a case which was diagnosed based on fine needle aspiration cytology (FNAC) and was later confirmed by histopathology.

Case Report

A 51 year-old male patient was referred to our FNAC clinic with a gradually increasing swelling of ten years’ duration in the left thigh. The swelling had been painful only for the past six months. Local examination showed the swelling to be about 20 × 10 cm in size over the anterior and anterolateral aspects of the left thigh. Radiography showed no evidence of involvement of the underlying bone. An MRI scan showed the mass to be heterogeneous and most likely malignant. The mass appeared to be intramuscular in location with maintenance of the plane between the neurovascular bundle and the mass. The mass was aspirated using a 22 gauge needle and the smears made were cellular and showed sheets and clusters of cells surrounded by a striking and prominent myxoid stroma [Figure 1]. The individual cells were monotonous and displayed vesicular nuclei and well delineated cell borders. Some of the cells also had nuclear grooves [Figure 2]. At places, the cells formed small anastamosing cords and single-file arrangement pattern [Figure 1]. The cells were more or less uniform with no significant pleomorphism. On the basis of the clinical, radiological, and cytological findings, the diagnosis was made of a myxoid sarcoma favoring extraskeletal myxoid chondrosarcoma. The patient later underwent a marginal en bloc resection of the mass.

Figure 1

FNAC smears showed monotonous cells in small clusters and singlefile pattern with a prominent myxoid stroma (Pap, ×100)

Figure 2

FNAC smears showed cells with vesicular nuclei, some exhibiting grooves (H and E, ×400)

Resection revealed that the tumor was a well circumscribed and partly encapsulated mass measuring 20×5×3 cm . The cut surface was gelatinous and showed glistening areas and multiple small cystic spaces filled with mucoid material. Microscopy revealed a lobulated neoplasm with strands and groups of neoplastic cells embedded in an abundant myxoid and chondromyxoid matrix. The cells exhibited round to oval, mildly pleomorphic nuclei. The stroma stained positively with Alcian blue at a pH of 2.5. At places, the histopathological features were reminiscent of the cytomorphological features with anastamosing cords of cells in a myxoid matrix [Figure 3]. Thus, the diagnosis of an extraskeletal myxoid chondrosarcoma was confirmed on histopathology.

Figure 3

Histopathology showed anastamosing cords of neoplastic cells in a myxoid matrix (H and E, ×40)

Discussion

EMC is a rare soft tissue neoplasm of the extremities that was first delineated as a distinct entity by Enzinger and colleagues.[1] This rare entity is a slowly growing neoplasm with metastatic potential. The distinct cytological features that were seen in the present case include the presence of uniform cells with the morphology of immature chondroblasts set in an abundant stroma that is myxoid. As seen in chondrosarcomas, chondrocyte-like cells embedded within lacunae have been described in some case reports, but not in the present case. The arrangement of cells in cords and columns within a myxoid background is an important clue to diagnosis.[8] If available, FISH analysis can also be performed on cytospin preparations to demonstrate the characteristic 22q12 translocation.[8]

Other myxoid tumors of soft tissue that should be considered in the differential diagnoses on cytology include myxoid liposarcoma, soft tissue chondroma, myxoid variant of malignant fibrous histiocytoma, myxoma, and chondrosarcoma. Thus, fine needle aspiration cytology has proved to be a useful tool in the diagnosis of adult myxoid sarcomas.[10]

Myxoid liposarcomas show characteristic lipoblasts with scalloped nuclei and vacuolated cytoplasm and a delicate, branching capillary network against a myxoid background. The myxoid variant of MFH displays marked pleomorphism of the nuclei with histiocyte-like cells. Chondrosarcomas typically possess a chondroid background and cartilage-like cells embedded within lacunae, rather than chondroblast-like cells lying loose within a myxoid stroma as seen in EMC.

Myxomas are sparsely cellular and show stellate cells within a translucent myxoid stroma. Chondroid lipoma is another rare soft tissue tumor that mimics EMC and myxoid liposarcoma.[11] This tumor shows a mixture of mature lipocytes and lipoblast-like cells embedded in a chondromyxoid matrix. None of these tumors display the distinctive cytological features of the cells of EMC; this aids the pathologist in confidently making a diagnosis of EMC.

The diagnosis may be supported on histopathological investigation by the immunohistochemical profile of the tumor. Studies have shown that the tumor cells usually express vimentin, synaptophysin, S-100 protein, and epithelial membrane antigen.[12] According to one of the studies which involved 23 cases, tumor size ≥ 10 cm, high cellularity, presence of anaplasia, and a mitotic activity of more than two per ten high power fields were all factors associated with decreased survival.[12] Ploidy analysis showed the tumor to be diploid, aneuploid, or tetraploid. Ploidy status had no bearing on the prognosis in this study.[12]

In conclusion, although histopathology confirms the diagnosis of EMC after excision, a preoperative diagnosis of EMC can be arrived at confidently due to its distinctive cytomorphological features.