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Muscular Tumour   

Pathology of Sclerosing Rhabdomyosarcoma

Dr Sampurna Roy MD   





(1) Sclerosing rhabdomyosarcoma is a rare variant of Rhabdomyosarcoma.

(Note: Rhabdomyosarcoma comprises a group of malignant soft tissue tumours with skeletal muscle differentiation.)


(2) It was first described in 2000 by Mentzel and Katenkamp.

They described three cases of rhabdomyosarcoma in adult patients, characterized by prominent hyaline sclerosis and a pseudovascular growth pattern, and called it "sclerosing, pseudovascular rhabdomyosarcoma".


(3) In 2002, Folpe et al. also described four cases of an unusual hyalinizing, matrix-rich variant of RMS. They named it "sclerosing rhabdomyosarcoma".


(4)  Sclerosing rhabdomyosarcoma is an exceedingly rare tumour and it is still debated whether it is a distinct variant of rhabdomyosarcoma or a subtype of embryonal or alveolar rhabdomyosarcoma.


(5) Microscopically, the neoplastic cells are arranged into lobules, small nests, microalveoli and even single-file arrays in an abundant hyalinized, eosinophilic to basophilic matrix that closely resembles primitive osteoid or chondroid material.

The mitotic rate is very high.

In some cases tumor cells focally display the cribriform pattern closely mimicking adenoid cystic carcinoma.


(6) The tumour is strongly positive for Vimentin, Desmin and MyoD1, and weakly, focally positive for Myogenin suggesting its skeletal muscle differentiation, but negative for cytokeratin, S-100, CD34, and CD31. Some cases can also show positive expression of CD99, SMA and CD56.


(7)  Differential diagnosis of Sclerosing rhabdomyosarcoma includes osteosarcoma, extraskeletal myxoid chondrosarcoma, mesenchymal chondrosarcoma, sclerosing epithelioid fibrosarcoma, angiosarcoma, parachordoma and even metastatic carcinoma.

It is important for pathologists to be familiar with Sclerosing rhabdomyosarcoma, because it potentially may be mistaken for other entities.



- The typical osteosarcoma is characterized by the presence of matrix calcification, osteoclasts.


- Extraskeletal myxoid chondrosarcoma typically forms a well circumscribed, multilobulated architecture separated by incomplete fibrous septa. It is composed of round or slightly elongated cells of uniform shape and size usually arranged in short anastomosing strands or cords in myxoid matrix.


-  Mesenchymal chondrosarcoma is characterized by distinct undifferentiated tumour cells admixed with well differentiated cartilagenous components.


- Sclerosing epithelioid fibrosarcoma is composed of epitheloid cells arranged in nests and cords and deposited in a densely hyalinized collagenous matrix. However, in almost all cases the tumor also shows foci of spindle-shaped sarcoma similar to conventional fibrosarcoma.


- Angiosarcoma : Sclerosing rhabdomyosarcoma focally may also form anastomosing vascular and gland-like spaces mimicking angiosarcoma, but angiosarcoma lacks characteristic hyalinizing matrix of sclerosing rhabdomyosarcoma.


- Parachordoma is typically lobulated and contains nests of vacuolated cells deposited in a myxoid matrix, resembling the physaliphorous cells of chordoma. It usually expresses S-100 protein and CK simultaneously.


- Metastatic carcinoma :  Positive expression of Desmin and MyoD1, negative expression of CK can also rule out the possibility of metastatic carcinoma.



(8) The prognosis of Sclerosing rhabdomyosarcoma in adults  is significantly worse than the pediatric population.

The rate of recurrence and metastasis is about 40-50%.

The prognosis of tumors located in the head and neck are poorer than those located in the extremities.





Lin X-Y, Wang Y, Yu J-H, et al. Sclerosing rhabdomyosarcoma presenting in the masseter muscle: a case report. Diagnostic Pathology. 2013;8:18. (open access article distributed under the Creative Commons Attribution License)


Chen Q, Lu W, Li B. Primary sclerosing rhabdomyosarcoma of the scalp and skull: report of a case and review of literature. International Journal of Clinical and Experimental Pathology. 2015;8(2):2205-2207.







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