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| Year : 2009 | Volume
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| Issue : 1 | Page : 100-102 |
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| Myoepithelioma of soft tissue |
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Mukhta R Pai1, Ramadas Naik1, Ramachandra Kamath2, Dilasma Magar1
1 Department of Pathology, Kasturba Medical College, Mangalore - 575 001, Karnataka, India
2 Department of Orthopedics, Kasturba Medical College, Mangalore - 575 001, Karnataka, India
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 Abstract | | |
Myoepitheliomas and mixed tumors involving deep subcutaneous and subfascial soft tissues of limb or limb girdle are rare lesions as against salivary lesions that are well established conditions. Here, we report a 22-year-old female who presented with painful hard swelling in the left gluteal region of 1½ year duration. MRI showed a large ill-defined heterogeneous mass lesion measuring about 7-8 cm. in the left sacral region eroding the left sacroiliac region and left sacroiliac joint. With a clinical diagnosis of chondrosarcoma, the tumor with the surrounding tissue was resected in segments at surgery. Histomorphology revealed nests, sheets and cords of round to spindled cells with extensive squamous metaplasia in a myxoid to fibrous stroma. These cells extensively infiltrated muscle and bone. The tumor cells expressed immunoreactivity for cytokeratin (AE1/AE3) and S-100. Keywords: Mixed tumor, myoepithelioma, soft tissue
How to cite this article:
Pai MR, Naik R, Kamath R, Magar D. Myoepithelioma of soft tissue. Indian J Pathol Microbiol 2009;52:100-2 |
| Introduction | |  |
Although salivary gland myoepitheliomas are well established neoplasms, only rare examples of myoepitheliomas and mixed tumors have been reported involving deep subcutaneous and subfascial soft tissues of limb or limb girdle. These neoplasms are equally common in males and females and they occur in a wide range with a peak in the third to fifth decades. They display the same wide range of histological features as those of salivary gland origin. The tumors from both sites are characterized morphologically as well circumscribed lesions exhibiting epithelial and myoepithelial elements in varying proportions within a hyalinized-to-chondromyxoid stroma. [1],[2],[3] These soft tissue tumors that are composed entirely of myoepithelial cells bearing close resemblance to the myoepithelial cells of salivary gland are also referred as myoepitheliomas. The diagnosis of these tumors is important as these tumors histologically show heterogeneous stromal elements and usually behave in a benign fashion despite their invasive nature. There are very few reports of soft tissue myoepithelial tumors describing extensive squamous metaplasia in the literature. Although majority of these morphologically benign or low-grade tumors behave in a benign fashion, there is approximately 20% risk for local recurrence. Here, we report a case of gluteal soft tissue myoepithelioma with extensive squamous metaplasia and infiltration into the surrounding skeletal muscle and sacral bone.
| Case Report | | |
A 22-year-old female presented with painful swelling in the left gluteal region of 1 year duration. The mass was hard and measured 5 x 4 cm in the sacroiliac region. MRI revealed a large ill-defined heterogeneous mass lesion measuring about 7-8 cm in the left sacral region eroding the left sacroiliac region and left sacroiliac joint [Figure 1]. The mass invaded posteriorly into the gluteal region and anteriorly into the pelvic floor muscles. Diagnosis of chondrosarcoma was offered by the radiologist. Biopsy from the soft tissue revealed small ovoid to spindle cells with squamous metaplasia and myxoid tissue. Tentative rare diagnosis of adamantinoma in the sacroiliac region was made.
Peroperative observations confirmed the imaging diagnosis of chondrosarcoma. At operation, lobulated, partly circumscribed tumor with heterogeneous consistency, measuring 12x10x5 cm, was seen infiltrating into the surrounding fibromuscular tissue and bone of the sacrum. Soft tissue component of the tumor with the affected sacral bone was resected in multiple segments.
Pathologic findings
The tumor mass measured 12x10x5cm and bony bits measured totally 12x5x8 cm. Cut surface of the specimen showed a grey-white partly circumscribed lobulated solid tumor with homogeneous to variegated areas composed of myxoid and bony tissue measured 4x3 cm and a grey-white diffuse tumor infiltrating fibroadipose tissue and muscle measured 8x6 cm.
Microscopic examination revealed nests, sheets and cords of rounded to spindled cells with clear cytoplasm [Figure 2] and minimal atypia, occasional mitosis with extensive squamous metaplasia [Figure 3] in a fibrous hyaline and myxoid stroma [Figure 4]. Tumor cells extensively infiltrated muscle and bone [Figure 5].
Immunohistochemistry
Due to the wide morphologic range of myoepitheliomas, confirmatory immunohistochemistry is mandatory to arrive at a correct diagnosis. As in myoepitheliomas of salivary glands, soft tissue counterparts were generally positive for cytokeratins and S-100 protein. Both the markers were strongly positive in the present case. In the present case, the squamous metaplastic areas were strongly positive for cytokeratin (AE1/AE3) and the tumor cells were positive for S-100.
| Discussion | | |
In 1874, Minssen first used the term mixed tumor to describe tumors of the parotid gland with both epithelial and mesenchymal features. [1],[2] Mixed tumors of salivary gland and skin are well described entities and known as pleomorphic adenoma and chondroid syringoma. [3],[4] They are characterized morphologically as well circumscribed lesions exhibiting epithelial/myoepithelial elements in varying proportions within a hyalinized-to-chondromyxoid stoma. Only a few examples of myoepitheliomas or mixed tumors involving deep subcutaneous and subfascial soft tissues have been documented. [2] The age incidence in these tumors ranged from 2 to 83 years with a mean of 35. Their gender distribution showed male preponderance as against the present case who was a 22-year-old female. While considering the site of these tumors, Kilpatrick et al . [1] documented that these tumors predominantly arose in the upper limb and involved the subcutis. While Hornick et al . [2] in their series described 101 cases where majority arose in the upper and lower limb girdles. In the present case, the tumor arose in the gluteal soft tissue and extended into the sacrum up to the midline causing destruction of the bone. All the tumors reported in the literature were above 5 cm in greatest dimension and were circumscribed and lobulated similar to the present case. [3] Focally infiltrative borders were also noted only in an occasional case in the literature similar to the present one. [1] The tumor cells were arranged in cords, trabeculae with or without definite ductal differentiation as observed by previous studies.[4] Myoepithelial cells were round to ovoid and spindly arranged in solid clusters and strands. In the present case, many sections of the tumor tissue showed cells with clear cytoplasm. In some areas of the tumor, nuclear pleomorphism ranged from mild to moderate but was never severe. In the previous studies of soft tissue myoepitheliomas, majority of the tumors showed ovoid to spindle cells separated by variably prominent chondromyxoid or collagenous/hyalinized stroma. [2],[5],[6] Nevertheless, it was noticed that a subset of tumors contained large epithelioid cells with vacuolated cytoplasm and abundant chondromyxoid stroma. Similarity of these tumors to "parachordoma" an enigmatic tumor described by Dabska et al . [7] The extensive squamous metaplastic areas were striking and occasional foci showed osseous metaplasia seen in the present case, which was seen in rare cases as described in the case series of the previous authors. [1],[2] Focal myxoid areas were unmistakably striking in the present case as described by the other authors. [1],[2],[7] However, chondroid areas that are the common components of myoepitheliomas were not observed in the present case. But the presence of prominent myxoid reticulum-like structures with squamous metaplasia in biopsy specimen presented a mistaken impression of adamantinoma. This feature was corrected when the resected specimen was obtained. The majority of the cases in the previous study showed that extensive chondromyxoid stroma was mistaken for chondrosarcoma. Other histologic features observed by Kilpatrick et al . [1] and Hornick et al . [2] are spindle cell morphology of cells, exclusively of plasmacytoid cells. The clinical behavior of these tumors from morphology alone is not advisable because about 20% showed a tendency for local recurrence. [1] Those with frank malignant features such as nuclear pleomorphism, perineural invasion, tumor necrosis and increased mitosis (mean: 4.8 per 10 HPF) were qualified to be called as malignant myoepithelial tumors and they recurred and metastasized, while those with moderate or without cytologic atypia were difficult to tackle as the morphology did not predict biologic behavior. [2] In the present case, the tumor has extensively invaded and destroyed the muscle and bone despite its benign morphology and occasional mitosis.
Immunohistochemistry
Myoepitheliomas present a wide morphologic range; hence, confirmatory immunohistochemistry is required to arrive at a conclusive diagnosis. As in myoepitheliomas of salivary glands, [6] soft tissue counterparts are generally positive for cytokeratins and S-100 protein as in the present case.
The present case would fulfill morphologic criteria for mixed/myoepithelial tumor if arising in salivary tissue, but which developed in the subcutaneous soft tissue with extensive squamous metaplasia against a fibromyxoid stroma with ossification.
In follow up of one year since the surgery, the present patient did not have any recurrence or metastases.
| References | | |
| 1. | Kilpatrick SE, Hitchkock MG, Kraus MD, Calonji E, Fletcher CD. Mixed tumors and myoepitheliomas of soft tissue. Am J Surg Pathol 1997;21:13-22.  |
| 2. | Hornick JL, Fletcher CD. Myoepithelial tumors of soft tissue: A clinicopathologic and immunohistochemical study of 101 cases with evaluation of prognostic parameters. Am J Surg Pathol 2003;27:1183-96. [PUBMED] [FULLTEXT] |
| 3. | Hirsch P, Helwig EB. Chondroid Syringoma Mixed tumor of skin: Salivary gland type. Arch Dermatol 1961;84:177-89. |
| 4. | Stout AP, Gorman JG. Mixed tumors of the skin of the salivary gland type. Cancer 1959;12:537-43. [PUBMED] |
| 5. | Enzinger FM, Shiraki M. Extraskeletal chondrosarcoma: An analysis of 34 cases. Hum Pathol 1972;3:421-35. [PUBMED] |
| 6. | Fletcher CD, Powell G, McKee PH. Extraskeletal myxoid chondrosarcoma: A histochemical and immunohistochemical study. Histopathology 1986;10:489-99. [PUBMED] |
| 7. | Dabska M, Parachordoma: A new clinicopathologic entity. Cancer 1977;40:1586-92. |
Correspondence Address:
Mukhta R Pai
Department of Pathology, Kasturba Medical College, Mangalore
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0377-4929.44983
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5] |
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