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Myogenic tumours

Pathology of Rhabdomyosarcoma          

Dr Sampurna Roy MD

 

 

                                                                                                                      

 

Embryonal Rhabdomyosarcoma :

Age and site: Usually occurs in children  (before the age of 10 years).

Common sites include head and neck region, genitourinary tract and retroperitoneum.

Pathological features:

Alternating cellular and myxoid areas.

Classical form is composed of undifferentiated round or spindle cells together with a few scattered eosinophilic rhabdomyoblasts.

Some elongated rhabdomyoblasts show angulation of muscle fibres (broken straw sign).

Multivacuolated or spider web cells may be present.

Cytoplasmic cross striations are noted in about 20-30% cases.

Intracellular glycogen is more prominent in well-differentiated forms.

Immunohistochemistry plays an important role in establishing the diagnosis. 

Desmin and muscle actin are positive.

MyoD1 and myogenin (myf4) are also useful markers.

Variants: 1) Botryoid  2) Spindle cell  3)Anaplastic

Botryoid Rhabdomyosarcoma:

Located in mucosa lined hollow organs. Example: Nasal cavity, nasopharynx, bile duct, urinary bladder and vagina. 

Grossly, the tumour has a polypoid grape like appearance.

Microscopically the tumour arises in the submucosa and is covered by hyperplastic epithelium. 

Subepithelial cambium layer composed of condensed undifferentiated tumour cells is a characteristic feature.

The rest of the tumor consists of  a relatively sparse population of cells in a backround of mucoid stroma.

Scattered spindle shaped or rounded rhabdomyoblasts may be present.

Spindle Cell Rhabdomyosarcoma:

Located in the paratesticular region (rarely head & neck region).Characterized by eosinophilic spindle cells arranged in a fascicular or storiform pattern. 

Differential diagnosis: Nerve sheath tumour , leiomyosarcoma , fibrosarcoma.

Anaplastic Rhabdomyosarcoma:

Characterized by areas of bizarre cell  with giant nuclei in a collagenous backround, together with foci of identifiable embryonal areas.

Atypical mitotic figures are present.

Alveolar Rhabdomyosarcoma :     
   
     
Age and site:  Usually occurs between 10 and 25 years. Commonly located in the upper and lower extremities.

Pathological features:

Alveolar pattern - The tumour consists of aggregates of undifferentiated tumour cells arranged in a alveolar pattern.

Eosinophilic rhabdomyoblasts and giant cells with peripheral wreath-like nuclei are prominent.

The cellular aggregates are separated by dense hyalinized fibrous septa.

The tumour cells at the periphery are well preserved.

The cells at the centre of the alveolar spaces are loosely arranged and poorly preserved.

Cross striations are noted in only 10% cells.

Solid  pattern -  Solid packed masses of tumour cells resembling  round cell areas of embryonal rhabdomyosarcoma (may resemble carcinoma or malignant melanoma). 

A microalveolar pattern has also been described.

Immunohistochemistry:

Demonstrate strong and widespread myogenin expression compared to embryonal type.

The majority of the alveolar rhabdomyosarcomas are associated with specific  chromosomal translocations (pARMS).

Because alveolar variant is much more aggressive than embryonal variant, RMS subclassification has clinical relevance.

Pleomorphic Rhabdomyosarcoma :                 

Pleomorphic rhabdomyosarcoma is considered rare and controversial.

Age and site - Occurs in adults  (above 45 years). Usually located on the large muscle of the extremities specially on the thigh.

Pathological features - The tumour consists of large polygonal or spinde shaped rhabdomyoblasts. The backround stroma is collagenous.

Storiform areas may be present.  

The tumour cells contain glycogen.

Cells with cross striations are usually absent.

Rare variant:  Sclerosing Rhabdomyosarcoma-

8 Pathology Facts - Sclerosing Rhabdomyosarcoma

It is not clear where this variant belong in the current classification of Rhabdomyosarcoma.

Site: Usually located in the extremities.

Characterised by prominent hyaline sclerosis and a pseudovascular growth pattern.

Microscopic features: Histologically, the neoplasms are composed of round/polygonal and spindle-shaped tumour cells including typical rhabdomyoblasts.

The cells are primitive appearing with scanty eosinophilic cytoplasm and irregular nuclear outline and coarse chromatin.

The stroma divides the tumour mass into lobules and small nests.

Tumour cells stained positively for desmin (focal and sometimes dot-like), strongly positive for smooth muscle actin (HHF35) and also for markers of striated muscle differentiation (myogenin, MyoD1).

This tumour may mimic extraskeletal myxoid chondrosarcoma, mesenchymal chondrosarcoma, osteosarcoma, sclerosing epithelioid fibrosarcoma and even angiosarcoma.

Cytogenetics:

Cytogenetics play an important role in confirming the diagnosis rhabdomyosarcoma.

Alveolar rhabdomyosarcoma is associated with a specific translocation, t(2;13)(q37;q14) or its variant t (1;13)(p36;q14).

Embryonal rhabdomyosarcoma often shows loss of heterozygosity for 11p, but there is  no specific cytogenetic or molecular marker comparable to those for alveolar Rhabdomyosarcoma.

Mimics of Rhabdomyosarcoma:

Fetal rhabdomyoma ; pseudosarcomatous fasciitis; genital rhabdomyoma ; atypical spindle cell lesions of the bladder and atypical cells in nasal polyps.

International Classification of Rhabdomyosarcoma:

Superior prognosis: Botryoid Rhabdomyosarcoma ; Spindle cell Rhabdomyosarcoma

Intermediate prognosis: Embryonal Rhabdomyosarcoma

Poor prognosis: Alveolar Rhabdomyosarcoma ; Undifferentiated sarcoma

The combination of histology, immunohistochemistry, chromosome analysis, and molecular cytogenetics played an important role in the diagnosis of Rhabdomyosarcoma.

 

Further reading:

Subtype and prognostic classification of rhabdomyosarcoma by immuno histochemistry. 

Spindle Cell Rhabdomyosarcoma in Adults.

Immunohistochemical analysis of a muscle ankyrin-repeat protein, Arpp, in paraffin-embedded tumors: Evaluation of Arpp as a tumor marker for rhabdomyosarcoma.

Prognostic Significance of DNA Ploidy and Proliferative Index (MIB-1 Index) in Childhood Rhabdomyosarcoma.

Altered expression and molecular abnormalities of cell-cycle-regulatory proteins in rhabdomyosarcoma.

Embryonal rhabdomyosarcoma presenting in an adult: a case report and discussion of immunohistochemical staining.

Primary cutaneous alveolar rhabdomyosarcoma of the perineum.

Are Myogenin and MyoD1 Expression Specific for Rhabdomyosarcoma? A Study of 150 Cases, With Emphasis on Spindle Cell Mimics.

Rhabdomyosarcoma of the Urinary Bladder and Vagina: A Clinicopathologic Study With Emphasis on Recurrent Disease.

Pleomorphic Rhabdomyosarcoma in Adults: A Clinicopathologic Study of 38 Cases with Emphasis on Morphologic Variants and Recent Skeletal Muscle-Specific Markers .

Pleomorphic rhabdomyosarcoma in children: Four cases in the pediatric age group.

Rhabdomyosarcoma and undifferentiated sarcoma in the first two decades of life: a selective review of intergroup rhabdomyosarcoma study group experience and rationale for Intergroup Rhabdomyosarcoma Study

 

 

 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)

 

 


 

 

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