3. DISCUSSION
IMM is a rare benign soft tissue tumor that probably occurs due to
incomplete differentiation of mesenchymal cells into fibroblasts. Of
course, IMM can be a part of McCune-Albright syndrome and Mazabraud’s
syndrome, which in this case is caused by mutations in the GNAS gene
(8). For the first time, the term myxoma was applied by Virchow to a
soft tissue tumor of mesenchymal cell origin in 1863. Also, Stout in
1948 described the histopathological criteria for the diagnosis of
myxoma and its differentiation from other lesions (9). Capsular mass
with hypocellular tissue in a mucoid background with scattered reticular
fibers in the skeletal muscles, which, if not diagnosed/treated in time,
can cause movement limitation in the joint, interfere with the action of
the involved muscle, and compress the nerves in the area. IMM has a good
prognosis and usually the involved muscle/joint follows its anatomical
function following supportive measures-physiotherapy (3).
This lesion is seen in T1-weighted images as an ovoid-shaped mass with
low signal intensity and in T2-weighted images as high signal intensity.
In the present case, a hyperintense egg-shaped mass was observed in
T2-weighted sections inside the supinator muscle (10). Adamonis et al.
(2019) also reported the presence of IMM in the deltoid muscle in a
34-year-old man, whose tumor lesion was observed in T2-weighted images
with hyperintense appearance. In histopathological evaluation, after
observing spindle-stellate fibroblast cells in mucoid background with
scattered collagen fibers of deltoid IMM was confirmed (5). In the
present case, the mass has a thin capsule around the homogenous
hypocellular mucoid tissue, in which the spindle-shaped cells
(fibroblasts) are located in scattered collagen fibers. The reports of
the upper extremity IMM cases show that the lesions in the muscles are
removed subcutaneously after surgery and cause few complications (11).
Movement limitations caused by IMM are also quickly resolved with
physiotherapy if the nerves of the brachial plexus are not compressed.