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
In some patients intramuscular myxomas are associated with
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.
the tumour is composed of bland spindle or stellate-shaped cells and
abundant myxoid matrix.
Some small cells have hyperchromatic nuclei and
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.
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.
Myxoid Tumours of Soft Tissue
Low grade fibromyxoid sarcoma ;
low -grade malignant peripheral nerve
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
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.