Soft Tissue Tumour of Uncertain Differentiation

         

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Pathology of Intramuscular Myxoma

Dr Sampurna Roy MD

 Path Quiz Case 40: Case history and images:

Diagnosis: Intramuscular Myxoma

  August 2014 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)

 

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Aggressive Angiomyxoma

Ossifying fibromyxoid tumour

Synovial Sarcoma

Alveolar Soft Part Sarcoma

Epithelioid Sarcoma

Clear cell sarcoma & PEComas

Extraskeletal Ewing's Sarcoma / PNET

Desmoplastic small round  cell tumour

Pleomorphic hyalinizing angiectatic tumour

Mixed tumour, myoepithelioma,  parachordoma

Ectopic hamartomatous thymoma

Extra-renal rhabdoid tumour

Malignant mesenchymoma                               

 

Spindle cell  hemangioma

Kaposiform hemangioendothelioma 

Retiform hemangioendothelioma 

Papillary intralymphatic angioendothelioma

Composite hemangioendothelioma 

Polymorphous  hemangioendothelioma

Kaposi's sarcoma

Epithelioid hemangioendothelioma

Angiosarcoma

Glomus tumour

 
Intramuscular myxoma is a relatively uncommon benign tumour that presents as a slow growing deeply seated mass confined to the skeletal muscle. 

Local surgical excision is almost always curative and recurrence is extremely rare even in incompletely excised lesions.

The tumour usually occurs between 40 and 70 years and is slightly more common in females.

It is commonly located in the large muscles of the thigh, shoulder, buttocks and rarely upper arm.

Although most cases are solitary, multiple lesions have been reported in 5% of patients.

Multiple intramuscular myxomas are rare and are usually associated with monostotic or polyostotic fibrous dysplasia and is known as Mazabraud's syndrome.

In some patients intramuscular myxomas are associated with Albright's syndrome.

Macroscopically the tumour is well circumscribed, lobulated and gelatinous in appearance. In some cases small fluid filled spaces may be present.

Most cases measure between 5 to 10 cms in greatest diameter, but sometimes the tumour may be as large as 20 cms.

Histologically the tumour is composed of bland spindle or stellate-shaped cells and abundant myxoid matrix. 

Some small cells have hyperchromatic nuclei and scanty cytoplasm.

In many cases there is almost complete absence of vascular structures in the hypocellular areas.

The mucoid material in the backround stroma stains positively with alcian blue and mucicarmine.

Some loose collagen bundles may be present.

At the periphery the tumour merges with the surrounding muscle.

The surrounding muscle fibres may be edematous and atrophic.

Cellular myxoma (low-grade myxoid tumour with recurrent potential). This lesion has features in between intramuscular myxoma and low-grade myxofibrosarcoma.There are hypercellular areas with increased vascularity. The hypercellular areas are not associated with pleomorphism, necrosis or any mitotic activity. Cellular myxomas do not progress to higher grade lesion and they do not metastasize. There is recurrence in 5-10% cases unless excised with a clear margin.

Pathology report should comment on the following:

Microscopic location - (subcutaneous, intramuscular, intermuscular, juxtaarticular) Margin - (circumscribed or infiltrative ) ;  Degree of cellularity ; Degree of vascularity ; Presence of any pleomorphism or mitotic activity ; Presence or absence of cyst formation ; Myxoid content ; Collagen content ; Presence or absence of muscle atrophy and edema.

Differential diagnosis:   

Visit: Myxoid Tumours of Soft Tissue

Myxoid liposarcoma ; Myxofibrosarcoma;   Low grade fibromyxoid sarcoma ; Myxoid neurofibroma and low -grade malignant peripheral nerve sheath tumour.  

(Classically intramuscular myxoma is hypocellular, hypovascular, shows no evidence of pleomorphism or mitotic activity and the cells are S100 protein negative. Vimentin is usually positive and rarely some cells may be actin positive.)

Juxta-articular myxoma histologically resembles intramuscular myxoma but develops adjacent to large joints and involves periarticular ligaments, tendons, joint capsules and muscles.  Almost 30% cases recur locally.

 

                                                          

Further reading:

Presentation of intramuscular myxoma as an unusual neck lump

Soft-tissue myxomatous lesions: review of salient imaging features with pathologic comparison.

Intramuscular myxoma of the hyoglossus muscle: A case report and literature review.

Intramuscular myxoma of the soleus muscle: A rare tumor in an unusual location.

Myxoma is not a single entity: a review of the concept of myxoma. 

Cellular myxoma of soft tissue: a clinicopathological study of 38 cases confirming indolent clinical behaviour. 

Intramuscular myxoma: a clinicopathologic study of 51 cases with emphasis on hypercellular and hypervascular variants. 

Magnetic resonance imaging of intramuscular myxoma with histological comparison and review of the literature. 

Intramuscular myxoma: a clinicopathologic study of 17 patients.

Mazabraud's syndrome: intramuscular myxoma associated with fibrous dysplasia. 

Intramuscular low-grade myxoid neoplasm with recurrent potential (cellular myxoma) of the lower extremity : case report with cytohistologic correlation and review of the literature.

Intramuscular myxoma. A clinicopathologic, immunohistochemical and electron microscopic study. 


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