Unusual Extraskeletal Myxoid Chondrosarcoma _______

C. H. Stuart Cameron, PhD Department of Pathology, School of Clinical Medicine, Queen’s University, Gromenor Road, Belfast BT12 6BA, North Ireland

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Brian D. Kenny, MRCPath Department of Histopathology, Northem Area Laboratory, Waveney Hospital,Cushendall Road, Ballyrnena, North Ireland

W. D. Barry Clements, FRCS Surgical Unit, Waveney Hospital, Cus-11 Road, Ballyrnena, North Ireland

Peter G. Toner, FRCPath

KEY WORDS: cytolysosomes, external lamina, extraskeletal myxoid chondrosarcoma, intracisternal tubular aggregates, nerve sheath differentiation.

Department of Pathology, School of Clinical Medicine, Queen’s University, Grosvenor Road, Belfast BT12 6BA, North Ireland

strands of whitish material. There was no calcification.

CLINICAL HISTORY The patient was a 64-year-old woman who presented with an 8-month history of a painless lump in her left thigh. She was otherwise healthy: At operation a plum-shaped mass was enucleated from within the belly of the rectus femoris muscle. There was no attachment to deep fascia, periosteum, or nerve.

LIGHT MICROSCOPY

PATHOLOGIC FINDINGS The tumor was ovoid and partially encapsulated with a rounded, slightly nodular surface. It weighed 15 g and measured 4.0 x 3.0 x 2.5 cm. On sectioning, the surface was slightly lobulated by bands of firmer grayish tissue. Many of the mucoid areas contained convoluted threads and

Address corresoondence to S. Cameron

We describe an unusual soft tissue tumor occurring within the rectus femoris muscle of a 64-year-old woman. The site, size, macroscopic, and histological appearances were all consistent with an extraskeletal myxoid chondrosarcoma. However, the present case differs significantly from previous reports of this uncommon tumor in that electron microscopy did not show any evidence of chondroblastic differentiation. Furthermore, the cells failed to stain for vimentin while labeling intensely for neuron-specific enolase, contained large numbers of cytolysosomes having a multivesicular appearance, and focally produced an external lamina. Based on the typical histological appearances we conclude that this is an unusual variant of extraskeletal myxoid chondrosarcoma in which there is evidence of nerve sheath differentiation.

On routine hematoxylin and eosin staining, the tumor was seen t o have a lobular pattern with small areas of hemorrhage. For the most part the tumor was encapsulated, but in some areas the cells were seen t o invade between muscle fibers. The cells were spindle shaped with blunt-ended nuclei and eosinophilic cytoplasm. They were arranged in cords or strands and frequently had a lacelike pattern, being separated by variable amounts of mucoid material (Fig. 1). In other areas the cells were more rounded and formed small aggregates or whorls. Mitotic figures were rare. Most of the cells contained material positive for periodic acid-Schiff stain, which was removed by diastase digestion. The ground substance reacted strongly with Alcian blue, and this was absent in hyaluronidase-treated sections.

Ultrastructural Pathology, 16: 17-23, 1992 Copyright

0 1992 by Hemisphere Publishing Corporation

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C. H. S. Cameron et al

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FIG. 1 Characteristic lacelike pattern of the spindle-shaped tumor cells, x 200.

IMMUNOHISTOCHEMISTRY Staining with desmin, vimentin, and cytokeratins LP34 and CAM 5.2 was negative, whereas the tumor cells stained intensely for neuron-specific enolase (NSE) and moderately for muramidase. There was some doubtful focal positivity with S-I00 protein.

ELECTRON MICROSCOPY Despite the various cellular patterns seen in histologic sections, the tumor showed a distinct uniformity in its ultrastructural appearance. Mitochondria were numerous and occupied a great deal of the abundant cytoplasm. Arrays of parallel microtubules were often found in the dilated cisternae of rough endoplasmic reticulum (Fig. 2). In addition, the cells were characterized by frequent large cytolysosomes measuring, on average, 1.00 t o 1.25 p m along their longest axis (Figs. 3 and 4). The lysosomes were present in variable numbers in every cell and were usually the predominant cytoplasmic feature. They displayed a

fine vesicular internal structure, and although they were often of low t o medium density there was an obvious gradation t o denser, more osmiophilic, more maturelooking structures (Fig. 5). These denser lysosomal structures continued t o display an internal multivesicular appearance and in some instances filled almost the entire cell cytoplasm t o the exclusion of all other organelles (Fig. 6). At their stromal interfaces, the cells occasionally displayed focal areas of what appeared t o be an external lamina. Their contact surfaces displayed small, poorly formed adhesion specializations (Fig. 7).

DISCUSSION Extraskeletal myxoid chondrosarcoma (ESMC) is an uncommon tumor of soft tissues usually occurring in patients older than 3 5 years of age, with a predilection for the thigh. The tumor cells display a distinctive histologic pattern, and ultrastructural studies have indicated a chondroblas-

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Myxoid Chondrosarcoma

tic origin.’ In the present case, the site, size, and macroscopic and histologic appearances were all consistent with ESMC, whereas the immunoperoxidase staining and ultrastructural findings were not typical of that diagnosis. Among the differential diagnoses considered were myxoid leiomyosarcoma, myxoid nerve sheath tumor, and a myxoid form of chordoma. The absence of physalipherous cells and cytoplasmic vacuolation or of a close relationship between the rough endoplasmic reticulum and mitochondria would eliminate the possibility of a chordoma, however. There was no immunohistochemical or ultrastructural evidence t o support smooth muscle differentiation. Although the tumor did not display the typical multinodular pattern of a myxoid nerve sheath tumor, an unusual

19 variant could n o t be completely excluded. ESMC has been well d o c ~ m e n t e d . ~ ~ ~ The intracisternal tubular aggregates seen in the present case are regarded as a regular feature, occurring in at least one-third of all such tumors.’ Large numbers of mitochondria are another nonspecific but common finding in ESMC.’ The present case differs significantly from the other reported cases in that the cells did not stain for vimentin, contained large numbers of secondary lysosomes, and focally produced what appeared t o be external lamina. Robertson and Hogg6 described an incomplete basal lamina surrounding nests of cells in a chordoid sarcoma, a lesion reportedly synonymous with ESMC.’ They claimed a synovial origin for the tumor, but

FIG. 2 Parallel arrays of microtubules packed within the dilated cisternae of rough endoplasmic reticulum, x 35,000.

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FIG. 3 Numerous mitochondria and lysosomes (arrows) fill the cytoplasm of adjacent tumor cells. There are few other organelles, x 7,500.

FIG. 4 Several pale-staining lysosomes (L) are seen, at higher magnification, to have a fine internal vesicular appearance, x 30,000.

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Myxoid Chondrosarcoma

this tumor bears little resemblance t o the present case. The occurrence of numerous secondary lysosomes analogous t o the granular cell mytoblastoma may represent some unexplained metabolic disorder. When taken together with the focal expression of an external lamina, however, the presence of such lysosomes might suggest some form of neural differentiation. This was also suggested in some areas by the arrangement of the tumor cells. Some additional support for neural differentiation may perhaps be taken from the strong NSE positivity. Although previous reports of ESMC suggest a chrondroblastic origin, w e have failed t o illustrate such features in this case, although the diagnosis was based on typical histologic appearances. We

FIG. 5

21 conclude that this is an unusual variant of EMSC in which there is some evidence suggestive of nerve sheath differentiation.

REFERENCES 1. Enzinger FM, Weiss SW. Soft Tissue Tumours. ~

2nd ed. St Louis, MO: Mosby; 1988:866-874. 2. De Blois G, Wang S, Kay S. Microtubular aggregates within rough endoplasmic reticulum. Hum Pathol. 1986; 17:469-475. 3. Enzinger FN, Shiraki M . Extraskeletal myxoid chondrosarcoma. An analysis of 34 cases. Hum pathol. 1972;3:421-435. 4. Martinez-Tello FJ, Navas-Palacios JJ. Ultrastructural study of conventional chondrosarcomas and myxoid and mesenchymal chondrosarcomas. Virchows Arch Path01 Anat. 1982; 396: 197-21 1. 5. Dardick I, Lgace R, Carlier MT, Jung RC. Chor-

Within the tumor cells the lysosomes show a graduation from low-medium contrast (arrows) to denser, more compact structures (arrowheads), some of which contain myelin figures, x 15,000.

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FIG. 6 Dense lysosomes fill almost the entire cell cytoplasm. Few other organelles are present, x 6,500.

FIG. 7 A cell is partially bounded by an external lamina (arrows), and small surface adhesion specializations are formed between portions of adjacent cells, x 1 7,500.

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Myxoid Chondrosarcoma

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doid sarcoma (extraskeletal rnyxoid chordosarcoma). Virchows Arch Pathol Anat. 1983;399: 61- 7 8 . 6. Robertson DI, Hogg GR. Chordoid sarcoma. Ultrastructural evidence supporting a synovial origin. Cancer. 1980;45:520-527.

23 7. Weiss SW. Ultrastructure of the so-called 'chordoid sarcoma'. Evidence supporting cartilagenous differentiation. Cancer. 1976;37: 300-306.

Unusual extraskeletal myxoid chondrosarcoma.

We describe an unusual soft tissue tumor occurring within the rectus femoris muscle of a 64-year-old woman. The site, size, macroscopic, and histologi...
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